Field of the invention

The invention relates to the field of soil structure detection. More particularly, the present invention relates to methods and systems for detecting soil structure under a water column and for identifying layers of sand.

Background of the invention

During the last decennia the off shore industry and in particular the dredging industry is growing significantly. This growth is partially driven by a new market for land creation. When creating land, huge amounts of sand are dredged, pumped and displaced on the spot of creation. Therefore, it is crucial to identify in the regional waters of the activity spots where sand can be dredged. Deployment of the equipment and time spent to find and gather sand often takes a big amount of the overall project time and financial budget. Reducing both time and economic cost on this part of the activity can lead to a significant return in efficiency. For example, it is not unrealistic that dredging companies gather sand on distances of more than 500km away from the spot of operation. If by having the right detection equipment, sand might be found in an area of less than 100km a significant increase in efficiency and cost can be obtained.

Different types of soil structure analysis equipment exist, often divided in two categories: non-intrusive equipment and intrusive equipment.

Examples of non-intrusive equipment are radioactive soil evaluation equipment and acoustic soil evaluation equipment such as parametric and standard sonar or seismic systems. Non-intrusive equipment typically may allow identifying regions with identical response rather than allowing identifying the type of material from the obtained data as such. Examples of intrusive equipment are soil probe equipment and soil penetrometer equipment. One often used system for detection and/or analysis of the undersea soil structure is a free fall penetrometer. The penetrometer is often built of a cylindrical body with a conical top. In use, the device reaches a terminal velocity under free fall conditions in water and impacts the soil with this known velocity. Often pressure sensors and accelerometers are introduced on board of the free fall penetrometer. Measurement of the deceleration and pressure allows, upon processing of the signal, to find out the finger print of the soil type detected. An exemplary free fall penetrometer, as known from prior art, is shown in FIG. 1. One of the drawbacks of penetrometers on the market is that they are less suitable for detection of sand layers, amongst others, sand layers covered by e.g. a layer of soft sediment.

Summary of the invention It is an object of the present invention to provide good impact devices and corresponding systems and methods for performing free fall penetrometry. It is an advantage of embodiments of the present invention that methods and systems are provided adapted for detection of sand layers, even when these are covered with a layer of soft sediment. It is an advantage of embodiments according to the present invention that the impact device can intrude sand layers or alternatively can intrude a top layer of soft sediment, e.g. mud, and at least part of a subsequent sand layer. It is an advantage of embodiments according to the present invention that the systems are adapted in mechanical design so as to allow accurate penetration of sand layers and/or covered sand layers. It is an advantage of embodiments according to the present invention that systems and methods are provided for characterizing the geotechnical parameters of surface sediments or mud layers on the soil.

It is an advantage of embodiments according to the present invention that the systems can be adapted in electronics design so as to allow accurate detection of sand layers and/or covered sand layers. It is an advantage of embodiments according to the present invention that the systems are adapted for identifying sand layers and/or covered sand layers. The above objective is accomplished by a method and device according to the present invention. Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. The present invention relates to an impact device for detecting sand positioned under water, the impact device comprising a head adapted for, upon impact with soil under water, substantially penetrating into a layer of sand, and the impact device being adapted for obtaining, upon penetrating in or removal from within a soil structure, information for identifying whether the penetrated soil structure comprises a layer of sand. The head comprises a needle shaped portion having an average diameter between 0.5mm and 5mm and a more broad base portion of the head.

The needle-shaped portion may have a length to width ratio of at least 25 to 1.

The needle-shaped portion may have a length of at least 30cm.

The needle-shaped portion and the base portion each may act separately with respect to each other upon impact with the soil structure.

The needle-shaped portion of the impact device may be disposable and the other part of the impact device may be re-used.

The needle-shaped portion of the impact device may be connected by wire with the remainder part of the impact device so as to be able to remove it from the soil if the needle-shaped portion has been broken from the remainder part of the impact device during impact with the soil.

The head may have a concave shape.

The impact device may comprise a fluid injector for injecting fluid from a fluid reservoir via the head into said soil during impact with said soil. The fluid injector may comprise at least one inner portion moveable in an outer shaft for inducing upon or during said impact pressure on a fluid in the fluid reservoir.

The at least one inner portion may be mounted on a spring in the impact device, the spring being adapted to provide a force on the at least one inner portion upon or during impact of the head of the penetrometer with the soil so as to increase the pressure on the fluid in the fluid reservoir.

The needle-shaped portion of the head may be provided with fluid openings in connection with the fluid reservoir.

The impact device may comprise at least one sensor for obtaining information for identifying whether the penetrated soil structure comprises a layer of sand.

The at least one sensor may comprise an accelerometer having a bandwidth of at least 5G.

The impact device furthermore may be adapted with one or more of chemical sensor equipment, resistive measurement equipment, acoustic backscatter measurement equipment, shock and ultrasonic test equipment, optical backscatter measurement equipment, electromagnetic backscatter measurement equipment, measurement equipment based on a tuning needle system or measurement equipment based on a rotating needle.

The impact device furthermore may comprise a control means for controlling the speed, spin and torque of the penetrometer.

The impact device furthermore may comprise a data memory for receiving data from at least one sensor device and for storing said data.

The impact device furthermore may comprise an interface for connecting to a computing and/or displaying device once the impact device is recovered from under the water surface.

The impact device may be a free fall penetrometer.

The head of the impact device may comprise at least two needle-shaped portions.

The present invention also relates to a data processor for processing data for the detection of sand, the data processor being adapted for receiving information regarding penetration of or removal from within a soil structure obtained with an impact device adapted for penetrating into a sand layer and for processing said received information for determining presence or absence of a sand layer in the penetrated soil structure.

The data processor may comprise a means for deriving deceleration information for the impact of the impact device and the soil structure and deriving based thereon presence or absence of a sand layer.

The data processor may be adapted for detecting, based on the received information, a low amount of deceleration of the impact device stemming from penetration of a needle-shaped portion into a sand layer followed by an abrupt deceleration of the impact device stemming from an impact of a base portion of the head of the impact device, and determining, based thereon, that a sand layer is present in the soil structure.

The data processor may be adapted for taking into account a deceleration behavior due to a mechanical shape of the head of the impact device comprising a needle shaped portion and a base portion and/or for taking into account a deceleration behavior due to injection of fluid from the head into the soil upon impact. The data processor may furthermore comprise a means for coupling position information regarding a position of the impact device impact device to the information regarding the type of soil structure obtained with the impact device. The present invention also relates to a system for detection of sand layers under water, the system comprising at least a first impact device as described above and a data processor as described above.

The present invention furthermore relates to a system for detection of sand layers under water, the system comprising at least a first and second impact device, wherein at least one of the first and second impact device is an impact device as described above and wherein the first and second impact device are adapted for simultaneous use and are adapted for acting as a sender respectively receiver in a resistive, acoustic or electromagnetic measurement. The present invention also relates to a method for detecting sand positioned under water, the method comprising - bringing an impact device comprising a head with a needle-shaped portion having an average diameter of 0.5mm to 5mm adapted for penetrating into a sand layer in free fall condition under the water surface, thus inducing, upon impact with a soil structure under the water surface, penetration of a needle-shaped portion of a head of the impact device into the soil structure, and

- obtaining, upon penetration in or removal from within the soil structure, information for determining the presence or absence of a sand layer in said soil structure.

The method may comprise inducing penetration of a needle-shaped portion of the head of the impact device into the soil structure.

The method may comprise injecting fluid from a fluid reservoir in the impact device via a head of the impact device into said soil during impact with said soil. The method further may comprise deriving deceleration information for the impact between the impact device and the soil structure and deriving based thereon presence or absence of a sand layer.

The method may comprise detecting, based on the obtained information, a low amount of deceleration of the impact device stemming from penetration of a needle- shaped portion into a sand layer followed by an abrupt deceleration of the impact device stemming from an impact of a base portion of the head of the impact device, and determining, based thereon, that a sand layer is present in the soil structure.

The method may be adapted for taking into account a deceleration behavior due to a mechanical shape of the head of the impact device comprising a needle shaped portion and a base portion and/or for taking into account a deceleration behavior due to injection of fluid from the head into the soil upon impact. The method may comprise capturing one or more of a chemical signal, resistive measurements signal, acoustic backscatter measurement signal, a shock and ultrasonic test signal, an optical backscatter measurement signal and an electromagnetic backscatter measurement signal. The method further may comprise obtaining position coordinates associated with the position of the impact device and coupling the position coordinates with information regarding the soil structure obtained with the impact device.

The method furthermore may comprise simultaneously using a second impact device and using the impact devices as sender and receiver in a resistive, acoustic or electromagnetic measurement.

The present invention also relates to a computer program product adapted for, when run on a computer, receiving information regarding penetration of or removal from within a soil structure obtained with an impact device with a needle shaped portion of a head of the impact device having an average diameter of 0.5mm to 5mm adapted for penetrating into a sand layer and for processing said received information for determining presence or absence of a sand layer in the penetrated soil structure. The computer program product may be adapted for deriving deceleration information for the impact of the impact device and the soil structure and deriving based thereon presence or absence of a sand layer.

The computer program product may be adapted for detecting, based on the received information, a low amount of deceleration of the impact device stemming from penetration of a needle-shaped portion into a sand layer followed by an abrupt deceleration of the impact device stemming from an impact of a base portion of the head of the impact device, and determining, based thereon, that a sand layer is present in the soil structure.

The computer program product may be adapted for taking into account a deceleration behavior due to a mechanical shape of the head of the impact device comprising a needle shaped portion and a base portion and/or for taking into account a deceleration behavior due to injection of fluid from the head into the soil upon impact.

The present invention also relates to a data carrier comprising a computer program product as described above and/or the transmission of such a computer program product over a network. It is an advantage of embodiments of the present invention that the system may allow deep intrusion of soil layers. The latter can enable detection of sand layers on the bottom of water columns.

It is an advantage of embodiments according to the present invention that accurate detection of sand layers can be obtained. The high degree of accuracy can be, according to some embodiments, supported by electronic measurements of intrusion parameters.

It is an advantage of embodiments according to the present invention that advanced data analysis may assist in more accurate identification of sand layers. It is an advantage of embodiments of the present invention that the cost of operation of the system can be low. The system can be made easy to handle, e.g. as it can be made small in size. The system according to some embodiments can be operated from a small vessel or rib.

It is an advantage of embodiments according to the present invention that methods and systems can be provided resulting in an easy, reliable and/or consistent operation. According to some embodiments, the robust design can assist in reliable operation. According to some embodiments, the impact device can be dropped in all directions and will adjust itself to the appropriate direction of impact.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief description of the drawings

FIG. 1 - prior art shows a free fall penetrometer with a conical head as is known from prior art. FIG. 2 shows a schematic drawing of an impact device with head adapted for intrusion in sand layers according to embodiments of the present invention.

FIG. 3 shows a particular example of an impact device with head adapted for intrusion in sand layers according to embodiments of the present invention.

FIG. 4 illustrates a schematic representation of wings as can be used on an impact device according to an embodiment of the present invention. FIG. 5 illustrates an overview and detailed portion of an example of part of an impact device with needle-shaped portion as can be used according to a first particular embodiment of the present invention.

FIG. 6 illustrates different types of needle-shaped portions as can be used in a head of the impact device adapted for intrusion in sand layers according to embodiment of the present invention.

FIG. 7 shows an impact device with head adapted for intrusion in sand layers, the head comprising a concave shape, as can be used in embodiments of the present invention. FIG. 8 shows an impact device comprising a head equipped with a fluid injection system for injecting fluid in the sand layers from a small fluid reservoir according to a particular embodiment of the present invention.

FIG. 9a and FIG. 9b show an impact device comprising a head equipped with a fluid injection system for injecting fluid in the sand layer from a large fluid reservoir respectively without and with separate sensor on the needle-shaped portion, according to a particular embodiment of the present invention.

FIG. 10 shows an impact device as shown in FIG. 8, wherein the needle-shaped portion is adapted with fluid openings so as to allow fluid injection from the needle in the sand layers. In the different drawings, the same reference signs refer to the same or analogous elements.

FIG. 11a illustrates an impact device with a resistivity measurement equipment according to an embodiment of the present invention.

FIG. lib illustrates an impact device with a piezo-electric transducer for evaluating mechanical behavior in situ according to an embodiment of the present invention. FIG. lie illustrates an impact device with a rotatable needle, according to an embodiment of the present invention.

Detailed description of illustrative embodiments

By way of illustration, the invention will now be described in more detail. Reference will be made to different embodiments of the invention and to drawings indicating different parts of the invention, the invention not being limited thereto. The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Any reference signs in the claims shall not be construed as limiting the scope. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element may fulfill the functions of several items recited in the claims, unless stated otherwise. Variations different from the disclosed embodiments can be understood and effected by persons skilled in the art in practicing the claimed invention, from a study of the disclosure, drawings and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

In a first aspect, the present invention relates to an impact device for detecting sand positioned under water. The device may be particularly adapted for detecting layers of sand or layers of sand covered by a layer of soft sediment, e.g. undrained soft sediment. Such cover layers may for example be layers of mud, the invention not being limited thereto. The device may for example be used to distinguish layers of sand from sand-like layers, such as for example sandstone. The system may for example also be advantageous to distinguish layers of sand from other layers having an acoustic fingerprint similar as that of a sand layer. The impact device according to embodiments of the first aspect of the present invention may be a penetrometer, such as for example a free fall penetrometer. The impact device according to embodiments of the first aspect may comprise a head being adapted for substantially penetrating into a layer of sand upon impact with soil under water. The head thereby comprises a needle-shaped portion having an average diameter between 0.5mm and 5mm and a more broad base portion of the head. Such penetration may for example be over at least 10cm, more advantageously at least 30cm, or over at least 50cm in a sand layer. According to embodiments of the present invention, the impact device is adapted for providing, upon penetration in or removal from within a soil structure, information for identifying whether the penetrated soil structure comprises a layer of sand. It is an advantage of embodiments according to the present invention that systems and methods are provided allowing substantial penetration of sand layers and/or covered sand layers so as to accurately detect the presence of sand layers. Such penetration may be without tools external to the impact device. Sand is a granular medium, acting as a hard and stable layer. According to embodiments of the present invention, the head of the impact device may be adapted in mechanical design so as to allow substantial penetration in a variety of ways, such as for example by providing a particular shape of the head, by providing a fluid injector adapted for injecting fluid via the head upon impact with the soil, in any other suitable way or by combination of these adaptations. It is an advantage of embodiments of the present invention that the systems and methods allow intrusion and detection of sand. It is an advantage of embodiments of the present invention that the systems and methods allow identification of a covered sand layer. It can for example be identified if a layer of sand is present whereon cementation has occurred or whereon a matrix is present. It can be distinguished if a clay matrix is present (sand does not behave inter- granular), if a calcite, aragonite or silica matrix is present as this makes from sand a sandstone (on which e.g. a needle will bend or break), etc. It is an advantage of embodiments of the present invention that sand layers with value can be distinguished from sand layers without value. By way of illustration, the present invention not being limited thereto, standard and optional components of the impact device according to embodiments of the present invention are discussed in more detail, with reference to FIG. 2 and with reference to one exemplary embodiment shown in FIG. 3. FIG. 2 illustrates an impact device 100 for detecting sand positioned under water. The impact device may more particularly be a free fall penetrometer, although the invention is not limited thereto. The impact device 100 comprises a head 104 and optionally a distinguishable body 102. FIG. 3 shows an exemplary embodiment of such an impact device 100. The optional body 102 may have any suitable shape. It may for example be cylindrically or tubular shaped, although the invention is not limited thereto. The body 102 may be made of any suitable material such as composites, any kind of alloy, inox, lead, etc. The body 102 may be adapted for carrying the electronics for operating sensors on board of the impact device 100. The latter is e.g. illustrated schematically in FIG. 2 and in FIG. 3 in the enlarged view of the body 102 comprising optional electronic components 142, 144, 146, 148, 150, 152, as will be discussed further. The mass of the impact device advantageously is selected to induce an appropriate impact. It may for example be in a range between 5kg and 25kg, embodiments of the invention not being limited thereto. The size of the body 102 may be adapted to the components it carries. In some embodiments, the average diameter of the body 102 in a direction perpendicular to the intended direction of impact may be between a couple of centimetre and up to 50cm. The body may be adapted for receiving additional weights, such as for example cylindrical lead blocks, for making the device heavier. The head 104 according to embodiments of the present invention is adapted for allowing substantial penetration into a layer of sand. The impact device 100 furthermore may be adapted for obtaining, upon penetration in or removal from within a soil structure, information for identifying the presence or absence of a layer of sand in the soil structure. The information may be obtained during impact or upon removal of the impact device. The penetration and the fact that information regarding the presence of a sand layer will be obtained by the impact device, can be established in a variety of ways, for example by adjusting the head in mechanical shape so that it comprises a needle-shaped portion, by adjusting the head in mechanical shape so that it comprises a needle-shaped portion 106 on a more broad base portion 108, by adjusting the head in mechanical shape so that it has more generally a concave shape, by adapting the head with a fluid injector 120 system, in other ways or by a combination of any of these. By way of example Fig. 3 illustrates a head 104 with a needle shaped portion 106 and a broader base portion 108, the invention not being limited thereto. A more detailed description of different adaptations will be provided in different particular embodiments described later. In one example, the system may be adapted for obtaining information regarding the presence of a sand layer in the penetrated soil structure in that it comprises at least one sensor 140, which in combination with the possibility for substantial penetration of the sand layer, allows for sensing information adapted for identifying whether a layer of sand is indeed present. Such at least one sensor 140 may be a plurality of sensors. The at least one sensor 140 may comprise at least one shear force sensor (friction sleeve) for allowing measurement of shear forces and/or shear resistance on the head 104 or components thereof or on the body 102 during penetration of the one or more soil layers. Alternatively or in addition thereto, the at least one sensor 140 may comprise at least one accelerometer for measuring deceleration upon impact of the impact device 100. Alternatively or in addition thereto, the at least one sensor 140 may comprise at least one pressure sensor for measuring pressure on the head 104 and/or the body 102 during impact of the impact device 100. As the system is adapted for substantially penetrating sand layers, the at least one sensor advantageously may be adapted to be compatible with a relative slow deceleration of the head 104 in a sand layer. It will be clear that the body of the penetrometer itself will decelerate rapidly. The bandwidth of the at least one sensor therefore may be adapted to such a slow deceleration in a sand layer. For example, if an accelerometer is provided, the bandwidth of the accelerometer provided may be at least 5G, and may range up to 100 G. The latter allows a more reliable measurement. In FIG. 3 the at least one sensor 140 comprises, by way of example, a separate sensor 302 for measuring impact on the needle-shaped portion 106 and separate sensors 304 for measuring impact on the broader base portion 108. Alternatively or in addition to the above types of sensors, in one embodiment, the impact device 100, also may be adapted for providing information for identifying whether or not a layer of sand is present in the penetrated soil, by being adapted for obtaining information regarding the pull up shear stress when the impact device is recovered, i.e. pulled up, from out of the soil. Such adaptation may be with at least one sensor for obtaining pull up shear stress information which may be positioned on board or off board of the impact device 100. The sensor may for example be positioned at that side of the wire or rope for pulling up the impact device that is not connected to the impact device, but e.g. present on a boat. According to some embodiments of the present invention, the number of sensors can be limited, in order to increase robustness and simplicity of the device so as to reduce the number of components that may fail. The at least one sensor 140 furthermore may comprise a sensor for chemical analysis of layers of soil, e.g. of a covering layer of soil covering a sand layer. The at least one sensor 140 furthermore may be adapted for providing additional information such as for example it may comprise one or more of chemical sensor equipment, pressure equipment, resistive measurement equipment, acoustic backscatter measurement equipment, shock and ultrasonic test equipment, optical backscatter measurement equipment, electromagnetic backscatter measurement equipment. Shock and ultrasonic test equipment may comprise piezo-elements. This list of further measurement equipment is not exhaustive, but only provided by way of example. In one example equipment is provided for performing soil resistive measurement from the needle top or close thereto to the body. The latter can assist for identifying the material type. Using e.g. a schlumberger method, a wenner method or dipole-dipole method, different types of soils can be distinguished based on their resistivity. For example, sand has a typical resistivity between 1000 and 10000 ohm.m while clay has a resistivity between 10 and 100 ohm.m. Measurement of the resistivity thus can assist in identifying the material type. The resistivity measurement equipment may for example be obtained by providing an electrically insulating coating on the major part of the needle such that the needle is non- conductive over the major part of the surface and only conductive at the top. In this way a resistivity can be measured between the top of the needle and the base portion, e.g. using a DC voltage source. An example of part of such a set up is illustrated in FIG. 11a, also indicating an enlarged view of the needle top portion. A voltage source 1110 is shown for determining a voltage difference between the needle top 1120 and the surface of the base portion 1130. An electrically insulating coating 1140 also is indicated. In another example, piezoelectric transducers or electrical actuators are applied to evaluate the mechanical behavior in situ. A vibration via a piezo-electrical actuator is induced on e.g. a single needle system, a dual needle tuning fork, etc. and the damping and or frequency shift can be monitored for providing information of the material in between or near the needle(s). An example of such a system is illustrated in FIG. lib, indicating a piezo-electrical transducer 1150 and a double needle structure 1160. In some embodiments, the needle also can be rotated, e.g. using a motor. In one example, the needle is rotated by a small motor on board of the penetrometer and the torque of the motor can be measured and is indicative of the resistance on the surface of the needle by the penetrated material. The resistance can be a measure of the material type and has a particular characteristic for sand. An example of such a system with rotatable needle is illustrated in FIG. lie, indicating a motor 1180 and a rotating needle 1190. Combined measurements may result in complementary information being available. For example, combination of the information obtained allowing identifying sand layers with acoustic measurement information may result in rapid identifying of larger areas of sand. It thereby is an advantage that one or more of these measurements may be performed during the same impact measurement as the gathering of the information for identifying soil as sand or covered sand. The latter results in a more efficient identification tool. The at least one sensor 140 advantageously comprises high speed and high accurate multi-channel sampling electronics. The sensors and the driving electronics thereof advantageously are positioned so that the corresponding electronic circuit board is as narrow as possible. Advantageously, the impact device 100 optionally may comprise on board or off board of the body 102 one or more amplifiers 142 for amplifying the signals sensed by the at least one sensor 140. Optionally, the impact device 100 may comprise separate buffers 144 for buffering the obtained sensor results. Buffering also may be performed in the amplifiers. The latter may be especially suitable when a plurality of sensors are applied and/or when sensor results are at least partly processed on board. Optionally, the impact device 100 may comprise at least one controller 146, for example a microcontroller, for controlling sensing by the sensors and/or for controlling the data flow of the sensed data on board of the body 102 or the head 104. The at least one controller 146 may be adapted for controlling the measurement timing and sampling by the at least one sensor 140. The controller 140 may be adapted to generate a time stamp for measurement results obtained with the at least one sensor. The controller may be adapted for on board processing, although the invention is not limited thereto. In such cases, part or all of the tasks of the data processor as will be described later, also may be performed on board by the controller. Optionally, the impact device 100 may comprise a memory 148 for storing obtained data. The size of the memory 148 may be selected so that a plurality of measurements can be performed without the need for pulling the impact device 100 completely out of water, so that a large area can be sampled with the impact device 100 and the impact device only needs to be pulled up to a level above the soil surface allowing sufficient impact force on the soil surface. The latter thus results in the possibility to keep the body and head of the impact device 100 under water and to only lift it up till the altitude level that guarantees the limit speed, which may in the order of about 10 meter above the seafloor.

Optionally the impact device 100 may comprise a power source 150 for powering different components of the impact device 100. Such a power source 150 may for example be a battery. Alternatively or in addition thereto, on board power also may be induced by a fan being present on the impact device 100.

Advantageously, the impact device 100 optionally may comprise an interface 152 for retrieving the obtained information from the impact device. The interface 152 may be any suitable interface, such as for example a USB interface, an Ethernet interface, a serial bus interface, a wireless interface, etc. The interface 152 may allow transfer of data with a computing device for retrieving information such as sensor data or optionally processed sensor data when processing has already been at least partly performed on board. The information may be transferred to a computing and/or displaying device 210, which may be part of the impact system 200. Such a computing and/or displaying device 210 may be a personal computer such as for example a laptop, desktop, pda, printer or plotter, display or the like, the present invention not being limited thereto. The computing and/or displaying device 210 may comprise a data processor 250 adapted for identifying, based on the obtained information, the type of soil structure. It furthermore may be adapted to determine the thickness of the layers detected, an estimated volume of soil material of a given type, etc. The data processor 250 may be programmed for identifying soil as a sand layer or covered sand layer taking into account penetration of the head 104 of the impact device 100 and the obtained information. The data processor 250 may be programmed so as to take into account a particular mechanical design of the head 104 of the impact device 100 and/or fluid injection, as will be illustrated later. For example, in case an impact device with a needle-shaped portion and with a base portion is used, the data processor 250 may take into account that the deceleration will be based on a dual impact mechanism and may use this to identify a type of soil structure that is probed. An impact effect also can be induced by the inner body movement during fluid injection. The data processor 250 also may be adapted to take into account the change in deceleration stemming there from. When fluid injection is combined with a head having a needle-shaped portion on a broader base portion, a triple impact effect may occur, one from impact of the needle-shaped portion, on from the backlash from the injection and one from the impact of the base portion. The data processor 250 will be described in more detail below. The data processor 250 also may be adapted for receiving positioning information during the time of measurement, e.g. captured on the boat from which the impact measurements are performed, so as to allow coupling of positioning information to the information obtained in the impact device upon impact or upon pulling up of the impact device. Typically, synchronization may be performed. The positioning information may be obtained using a global positioning system, the invention not being limited thereto. Combination of positioning information and obtained information of the impact device or a processed version thereof allows providing geographical information regarding properties of the soil structure for which measurements are performed. The impact device 100 furthermore optionally may be adapted with a winching system 160 for winching up the impact device 100 after impact has been finished. Such a winching system may be any winching system as used in existing free fall penetrometer devices, although the invention is not limited thereto. It may typically be provided partly on a boat assisting for performing impact measurements. It may for example comprise a spool 162 for carrying a cable, wire or rope 164 connected to the body 102 of the impact device 100 and able to release the cable, wire or rope 164 during free fall of the impact device 100 and for winding the cable, wire or rope 164 during pulling up of the impact device 100. Alternatively, the impact device is operated using only a cable, wire or rope, without necessarily requiring a full winching system 164. The impact device 100 or the impact system 200 comprising the impact device 100 may optionally comprise a launching system 170 for launching the body 102 and head 104 of the impact device for impact with a soil structure, although embodiments of the present invention are not limited thereby. Such a launching system 170 may be any suitable system, in some embodiments for example being launching systems as used in prior art.

On the body 102, the impact device 100 may comprise a control means 180 for controlling the speed, orientation and/or spin of the impact device 100. At the end portion, opposite to the head 104, fins 182 for more easily obtaining an appropriate free fall direction of the impact device 100 may be present. Such fins 182 thus may assist in more easily obtaining a direction of the impact device 100 wherein the head 104 is directed towards the soil structure to be studied. In one embodiment, the invention not being limited thereto, the fins may comprise four wings, as shown in FIG. 4 by way of example. The impact device 100 also optionally may comprise flaps 184 for further controlling the speed, torque and/or spin of the impact device 100, although the invention is not limited thereby.

By way of illustration, the invention will now be further described with reference to a number of particular embodiments, the invention not being limited thereto. In a first particular embodiment according to the first aspect, the present invention not being limited thereto, an impact device 100 comprising standard features and optionally also optional features as indicated above is described, whereby the head 104 is adapted for substantially penetrating into a layer of sand by its mechanical design. According to the first particular embodiment, the head comprises a needle- shaped portion 106 and a broader base portion 108. The width of the impact device or portions thereof thereby is defined as sizes in the direction perpendicular to the direction of propagation and impact under free fall conditions of the impact device. An example of part of an impact device according to the first particular embodiment is shown in FIG. 5, the invention not being limited thereto. FIG. 5 illustrates an overview of an example of an impact device according to the first particular embodiment of the present invention, with a detailed view of the base portion and the sensor setup for the particular example. By using a needle-shaped portion 106, embodiments according to the present invention can result in a more efficient and deeper penetration in a sand layer, thus allowing more accurate detection of the sand layers and more accurate estimation of a volume of sand being present, even if covered under a layer of undrained soft sediment, such as for example mud. The needle-shaped portion may be made of any suitable material. The material advantageously is a very strong material, so as to reduce the chance of splintering of the material upon impact as much as possible. Some materials that could be used are composites, inox, steel, titanium, platinum, wood, etc. According to some examples, the needle-shaped portion may have a length within the range lcm to 100cm, advantageously within a range having a lower limit of lcm, or 5cm, or 15cm or 30cm and an upper limit of 35cm or 50cm or 70 cm or 100cm. It is an advantage of embodiments according to the present invention that a length of the needle-shaped portion can be selected as function of the application, e.g. as function of the depth over which one wants to probe the soil. The average diameter of the needle-shaped portion may be of the same order of magnitude as the grain size of sand. Typically, sand grains vary in diameter between 0.05mm and 2mm. Anything with a lower diameter is silt, with a diameter typically between 0.05mm and 0.004mm or clay, with a diameter typically smaller than 0.004mm, while larger diameters relate to gravel, having a diameter typically between 2mm and 64mm. The average diameter of the needle-shaped portion may be within the range of 0.5mm to 5mm, over at least 50%, advantageously at least 75%, more advantageously at least 90% of the length of the needle shaped portion. It is an advantage of embodiments according to the present invention that the needle-shaped portion can be selected to have a diameter in the order of the diameter of the sand grains, so that the sand medium will no longer act as a uniform hard granular body. The sand grains thus may interact on a more individual base with the needle-shaped portion allowing easier penetration of that portion. In some embodiments, the needle-shaped portion may have a length to width ratio of at least 25 to 1, or advantageously at least 50 to 1. The length to width ratio of the needle shaped portion may for example be around 500 to 1. The width of the needle-shaped portion 106 thus may be substantially smaller than the base portion 108 of the head 104. By way of illustration, examples of needle shaped portions 106 as can be used in embodiments according to the present invention are shown in FIG. 6. The examples shown illustrate a hollow needle-shaped portion, a solid needle-shaped portion, or a needle-shaped portion with fluid holes, as will be usable in a fourth particular embodiment of the present invention.

The needle-shaped portion 106 may be positioned in front of the base portion 108, i.e. so that the needle-shaped portion 106 reaches the soil structure before the base portion 108 when in appropriate free fall orientation. It may be positioned discrete from the base portion 108. In other words, upon impact, the needle-shaped portion 106 may behave substantially independent from the base portion 108. An example thereof is shown in FIG. 5. According to such an embodiment, the needle behaves as an extremely thin free fall penetrometer, sitting on a more conventionally sized penetrometer. The pressure or resistance on the needle-shaped portion 106 can be measured providing information for identifying a type of soil layer, e.g. as a sand layer. According to such an embodiment, typically a separate pressure, deceleration or resistance sensor may be provided for the discrete needle-shaped portion 106. In the present example, a sensor result is obtained for the needle-shaped portion 106 being in connection with a piston 502 in a shaft 504 and increasing the pressure in the shaft 504 upon impact of the needle-shaped portion 106 with the soil structure, which can be measured with a pressure sensor 302. Alternatively, the needle-shaped portion 106 may not be mounted as a discrete portion but is fixedly mounted to the base portion 108. The latter will be illustrated later for a different embodiment with reference to FIG. 9a and FIG. 9b. The needle shaped portion may be a disposable that is left in the soil structure, whereas the remaining portion can be re-used. According to some embodiments, the needle-shaped portion 106 may be connected by wire to the body or base portion, so that upon pulling up the impact device 100, the needle- shaped portion is removed from the soil structure. The latter assists in reducing or avoiding waste from being left at the soil structure. The outer surface of the base portion 108 may have a substantially conical shape or any other suitable shape such as a tip with a predetermined angle, a flat head (e.g. suitable for soft mud) and adapted at the position where the needle shaped portion is placed. Sensors for measuring the impact of the base portion, discrete from or in combination with the needle-shaped portion, typically may be provided. The latter also is illustrated in FIG. 5, showing an example wherein for a base portion 108 discrete from the needle-shaped portion, two pressure sensors 304 for measuring the impact of the soil structure with the base portion 108 are provided. In the present example, upon impact of the soil structure with the base portion 108, pistons 512 are moved in shafts 514, inducing a pressure increase in the shafts 514 and allowing obtaining sensor results with pressure sensors 304. It will be obvious to persons skilled in the art that alternative sensor setups also can be provided. In the exemplary sensor setup, furthermore also shear resistance sensors 506, 516 are provided for measuring the shear resistance stemming from the needle-shaped portion 104 and for measuring the shear resistance stemming from the broader base portion. The total length and weight of the body in the present embodiment may be selected as function of the needle length, as the body will have the lead weights in it and as this will determine the kinetic energy available for impact and therefore for penetration in the soil structure. In one embodiment, the head may be provided with at least two needle-shaped portions. The head may comprise a multiple of needle- shaped portions. One of the needle-shaped portions then may act as a sender and the other or others may act as a receiver in for example a resistive, acoustic or electromagnetic measurement. Examples thereof also have been given above. Whereas the above particular embodiment has been described with reference to an in particular needle shaped portion, the present invention also encompasses embodiments wherein the mechanical shape of the head is at least substantially sharper than a cone, i.e. wherein the head of the device has a substantially concave shape. By way of illustration, FIG. 7 illustrates a possible shape of a concave shaped head of the impact device. It will be clear to the person skilled in the art that a head comprising a base portion and a needle-shaped portion positioned in front thereof, fulfil this concave shape requirement.

In a second particular embodiment, the present invention relates to an impact device 100 as described in the first particular embodiment, but wherein the impact device is completely needle-shaped, without broader portion e.g. without other body portion. The body and head are then formed by the same needle-shaped portion. Typically in such embodiment, no sensor may be on board, but the sensor may be positioned at the other side of the pull-back rope or wire, allowing to measure pull back shearing stress of the impact device when removed from the soil structure. The average diameter of the impact device may (for its complete length) be limited to between 0.5mm and 5mm. The needle-shaped impact device may be filled with heavy material in order to make it heavier and in order to assist the impact device in obtaining appropriate orientation under free fall conditions. Such material may for example be lead. The portion closer to the tip of the impact device, intended to have the first impact with the soil structure, may be made heavier than the portion of the impact device at the opposite side. Wings may be provided, as described above. Other features and advantages regarding the use of a needle-shaped device may be as set out for the needle-shaped portion in the first particular embodiment. In a third particular embodiment, the present invention not being limited thereto, an impact device 100 comprising standard features and optionally comprising optional features as described in the general description of the first aspect or in the first particular embodiment as indicated above is described, whereby the impact device 100 comprises a fluid injector 120 for injecting fluid from a fluid reservoir 122 via the head into the soil during impact with the soil. It thereby is an advantage that upon injection of the fluid, the pore pressure in the sand can be increased, thus decreasing the contact pressure of the grains in sand and allowing a more easy penetration than without fluid injection. The head thus is adapted for substantially penetrating in a sand layer, as it will provide fluid channels for injection of fluid into the soil. The fluid used may be any suitable fluid such as for example, compressed gas, compressed air, liquid. The fluid injector 120 can take any suitable form, such as for example a recipient filled with compressed air that may be released with a pressure switch and/or that may be injected directly into the soil or that may press another fluid, e.g. liquid to be injected in the soil. Another example is a system comprising an inner portion, e.g. piston, slideably mounted in an outer shaft and connected with the head 104. Upon impact of the soil with the head, the inner portion slides into the outer shaft and fluid in the outer shaft is injected via the head into the soil. The fluid reservoir than is formed by the space between the inner portion and the outer shaft. Pressurization of the fluid can be increased by providing a spring so that the force by which the inner portion slides into the outer shaft is enlarged. The spring may be mechanically or electronically actuated upon impact. It is an advantage of embodiments according to the present invention that the fluid injector can be mechanically self-activated upon or during impact, thus assisting in additional reliability. Alternatively or in addition thereto, a pressure measurement using a pressure sensor may be used for electronically activating the fluid injector upon or during impact of the penetrometer with the soil. In a fourth particular embodiment, the present invention relates to an impact device 100 as described above, combining the fluid injector 120 with the mechanical shape of the head. The head 104 of the impact device 100 may comprise a needle-shaped portion wherein fluid openings are provided that are in connection with the fluid reservoir. Upon impact, fluid can be injected in the soil from the opening in the needle-shaped portion. Alternatively or in addition thereto, fluid openings also may be present in the base portion 108 of the head 104 of the impact device 100. The latter may be particularly useful to further improve penetration of the impact device. Combining both techniques also may increase the life-time of the needle-shaped portion. The holes in the needle shaped portion may be spread equally over the needle-shaped portion 106, mainly at the end first penetrating the soil or mainly at the end closest to the base portion 108.

By way of illustration, examples of the third and fourth particular embodiments are shown in FIG. 8, FIG. 9a, FIG. 9b and FIG. 10. FIG. 8 illustrates an impact device with no separate sensor for the needle-shaped portion 106 and with a fluid injector 120 comprising a spring 802 and a piston 804 mounted thereon for boosting up the pressure on the fluid in the fluid reservoir 122 upon impact, as also discussed above. FIG. 9a and FIG. 9b illustrate a similar setup, but the position of the fluid reservoir 122 is different, so as to allow a larger fluid reservoir 122 and consequently a larger amount of fluid for injection in the soil structure. Whereas FIG. 9a illustrates an embodiment whereby no separate pressure sensor is present for measuring the impact on the needle-shaped portion 102, FIG. 9b illustrates an embodiment whereby a separate pressure sensor is provided for measuring the impact on the needle- shaped portion 102. It can be seen that different channels are used for the channel for pressure measurements and the channel for fluid injection and that fluid injection can be introduced in the needle-shaped portion based impact devices without too much interference from the fluid injection system with the other components. FIG. 10 illustrates a similar setup as shown in FIG. 8, but shows an enlarged view of the needle-shaped portion comprising fluid openings 1002 for injecting the fluid into the soil structure through the needle-shaped portion 104. By way of illustration, the present invention not being limited thereto, the systems and methods can be applied for different applications. In one application, the systems and methods can be applied for measurement of density of mud layers for determination of the nautical bottom of waterways. The density can for example be measured based on a differential pressure measurement with two distant pressure sensors on board. Besides density also shear stress and viscosity could be parameters to determine e.g. if a ship can still navigate through a sudden mud layer. Shear stress can be measured on the sleeve of the impact device and viscosity can be derived out of the deceleration and the shear stress . In another application, measurement of additional parameters like strength of the soil, bearing capacity and pore pressure can be determined and may serve other applications. These parameters may be used in off shore engineering projects and research on slope stability and sediment mobilization. Another application, as described further, is the identification of different material layers based on measuring deceleration curves for identification of minerals like sand. In a second aspect, the present invention relates to a data processor for processing data to determine presence or absence of a sand layer in a soil structure, advantageously for use with an impact device 100 as described in the first aspect, although the invention is not limited thereto. The data processor according to embodiments of the present invention is adapted for receiving information regarding penetration of or removal from within a soil structure obtained with an impact device adapted for penetrating into a sand layer and for processing the received information for determining presence or absence of a sand layer in the penetrated soil structure. Embodiments of the present invention may relate to a data processor being on board or being partly on board of the impact device 100, although the data processor also may be located outside the impact device 100. The data processor may comprise a two or more processing components, some being present on board, some being present off board. The data processor may be implemented in hardware as well as software. The data processor may for example include a particular software- processing program implemented on a general purpose processor such as for example CPU or an application specific processor such as an DSP, ASIC, FPGA, etc. The data processor may be provided with an input port for receiving raw data, partly processed data or processed data from a sensor in the impact device 100. The input port may be adapted for receiving the data based on USB-technology, serial bus interface technology, Ethernet technology, wireless technology, etc. As indicated above, the data processor is adapted for processing the received information for deriving the presence or absence of a sand layer. In some embodiments a type of soil structure may be determined. The processor therefore may for example comprise a means for deriving deceleration information, e.g. a deceleration profile, for the impact device 100 and a means for deriving based thereon a fingerprint of the soil structure that has been measured. The fingerprint of the soil structure may be representative for the type of layers present in the soil structure. The processing means may be adapted for taking into account a deceleration behavior due to a mechanical shape of the head 104 of the impact device 100 comprising a needle- shaped portion 106 and a base portion 108, a deceleration behavior due to injection of fluid from the head into the soil upon impact, etc. Detection of sand based on the deceleration profile may for example be established for use of an impact device 100 with needle-shaped portion, when a low amount of deceleration of the impact device is noticed in the initial portion of the deceleration profile, stemming from penetration of a needle-shaped portion 106 into a sand layer, followed by an abrupt deceleration of the impact device 100 stemming from impact of the base portion 108 of the head 104 of the impact device 100. By way of illustration, the present invention not being limited thereto, fingerprints of other types of soil structures are identified in the examples, provided below. The particular deceleration of a needle-shaped portion is based on the fact that in embodiments of the present invention the diameter of the head of the impact device is of the same order of magnitude as the grain size of the medium that is to be investigated. It is also an advantage of embodiments of the present invention that the pressure contact surface between the medium to be studied and the head is limited. If fluid injection is used, the latter may assist in reducing inter-granular tension between grains that are physically - mechanically - interacting, resulting in a reduction of shear forces and pressure resistance. Upon reduction of these forces and resistance, the resistance for penetration of the device lowers. As the surface of the interaction between the head and the medium, e.g. sand, in embodiments of the present invention is small, the number of interacting particles, e.g. grains, from the medium is small. In embodiments where fluid injection is used, due to the small number of particles, it is sufficient to inject a small amount of fluid to induce a large effect. The latter is advantageous as this limits the amount of fluid required, and the volume of the fluid reservoir.

According to embodiments of the present invention, the characteristic size of the head may be of the same order as the diameter of the grains in the medium, e.g. sand, so that the medium does not behave as a static block, but acts as a plurality of individual grains, resulting in a lowered resistance for penetrating. Furthermore, based on the deceleration profile or similar information, the thickness of e.g. a sand layer present in the soil structure may be determined. Information regarding presence of the same type of soil structure or different type of soil structure may be obtained by obtaining different measurement data sets by probing a plurality of times at different positions, or e.g. by combining the information received by probing with an impact device 100 according to the first aspect with other techniques, allowing to detect similar soil structures. The data processor furthermore may be adapted for receiving positioning information regarding the impact device during measurement and for coupling the position information to the information regarding the type of soil structure. By combining geographical soil structure information or by combining different sets of measured and determined soil structure information, a volume of sand being present in the soil structure may be derived. The deceleration profile may be established based on pressure sensor information, accelerometry data and/or shear resistance data. Features and advantages corresponding with features of the impact device 100 also may be obtained. The data processor furthermore may be adapted for combining obtained information from impact measurements with other alternative soil analysis data, such as for example data obtained by acoustic screening.

In a third aspect, the present invention relates to a system for detecting sand positioned under water. The system 200 may comprise at least one impact device 100 as described the first aspect of the present invention and/or embodiments thereof and a data processor as described in embodiments of the second aspect of the present invention. Similar features and advantages as set out in these aspects may be present in embodiments of this third aspect of the present invention. The present invention also relates to a system for detecting sand positioned under water wherein at least two impact devices 100 are provided, at least one thereof being an impact device as described in the first aspect of the invention, the impact devices being adapted for simultaneous use and for acting as a sender respectively receiver in a resistive, acoustic or electromagnetic measurement.

In a fourth aspect, the present invention relates to a method for detecting sand positioned under water. The method may be performed using an impact device (100) as described in the first aspect, although the method is not limited thereto. The method comprises the steps of bringing an impact device 100 comprising a needle- shaped portion having an average diameter between 0.5mm and 5mm and a more broad base portion of the head in free fall condition under the water surface, thus inducing, upon impact with soil under the water surface, penetration into a soil structure using an impact device comprising a head adapted for penetrating a sand layer, and, obtaining information, upon penetration of or upon removal from the soil structure, for identifying whether the penetrated soil comprises a layer of sand. The method is particularly useful as, due to the possibility of penetrating sand layers, the sand layers or covered sand layers can be more accurately detected. Inducing penetration into a soil structure using an impact device comprising a head adapted for penetrating a sand layer may be performed in a plurality of ways. It may comprise inducing penetration using an impact device comprising a head with a needle-shaped portion and a base portion, it may comprise inducing penetration using an impact device comprising a concave shaped head, it may comprise a step of injecting fluid from a fluid reservoir in the impact device via the head of the impact device into the soil, or it may comprise a combination thereof. Such a combination may for example comprise injecting a fluid from a fluid reservoir in the impact device through openings in a needle-shaped portion of the head of the impact device into the soil. The method furthermore may comprise, after said obtaining information for identifying whether the penetrated soil comprises a layer of sand, identifying whether or not a layer of sand was present. The latter may be obtained by processing the obtained information. Such processing may comprise receiving sensor data, partly processed sensor data or processed sensor data from the impact device, deriving a deceleration profile or similar information and determining based on said deceleration profile or similar information whether or not a sand layer was present. The latter may e.g. be performed by comparing the deceleration profile or part thereof with a predetermined profile that is considered a fingerprint for the presence of a sand layer and determining whether or not the profile fits the fingerprint within a predetermined error range. By way of illustration, a predetermined profile for presence of a sand layer, if for example use is made of an impact device with needle- shaped portion, may indicate a low amount of deceleration of the impact device upon initial impact, stemming from penetration of a needle-shaped portion with the sand layer, followed by an abrupt deceleration of the impact device stemming from a base portion of the head of the impact device impacting on the sand layer. As the impact device, e.g. the length of the needle, the shape of the base portion, the injection of fluid or not, will influence the deceleration profile, the above processing of information advantageously takes into account a deceleration behavior due to a mechanical shape of the head 104 of the impact device 100 comprising a needle- shaped portion 106 and a base portion 108, a deceleration behavior due to injection of fluid from the head into the soil upon impact, etc.

The method furthermore can comprise additionally capturing one or more of a chemical signal, a pressure signal, a resistive measurement signal, an acoustic backscatter measurement signal, a shock and ultrasonic test signal, an optical backscatter measurement signal or an electromagnetic backscatter measurement signal. In some embodiments, the method may comprise simultaneously using more than one impact device and using the impact devices as sender and receiver in a resistive, acoustic or electromagnetic measurement. The latter may provide complementary information allowing further improving detection of sand layers. For example, detection of such signals may allow deciding that on positions neighboring the impact position on the soil, a similar soil structure is present. Alternatively or in addition thereto, the method also may comprise repeating the impact probing at different positions, so as to be able to derive information regarding the soil structure of an area. The method furthermore may comprise capturing position information regarding the position of the impact device and coupling the corresponding position information to the soil structure information obtained with the impact device. The latter allows for geographic mapping of the soil structure.

In further aspects, embodiments of the present invention also relate to computer- implemented methods for performing at least part of the methods for detecting sand under water as described above, for processing obtained information for identifying sand under water as described above or to corresponding computing program products. Such methods may be implemented in a computing system, such as for example a general purpose computer. The computing system may comprise an input means for receiving data, partly processed data or processed data from the impact device and a processing means for processing the obtained data in agreement with the above method. The system may be or comprise a data processor as described in the second aspect. The computing system may include a processor, a memory system including for example ROM or RAM, an output system such as for example a CD-rom or DVD drive or means for outputting information over a network. Conventional computer components such as for example a keybord, display, pointing device, input and output ports, etc also may be included. Data transport may be provided based on data busses. The memory of the computing system may comprise a set of instructions, which, when implemented on the computing system, result in implementation of part or all of the standard steps of the methods as set out above and optionally of the optional steps as set out above. Therefore, a computing system including instructions for implementing part or all of a method for detecting sand or processing obtained information is not part of the prior art.

Further aspect of embodiments of the present invention encompass computer program products embodied in a carrier medium carrying machine readable code for execution on a computing device, the computer program products as such as well as the data carrier such as dvd or cd-rom or memory device. Aspects of embodiments furthermore encompass the transmitting of a computer program product over a network, such as for example a local network or a wide area network, as well as the transmission signals corresponding therewith.

By way of illustration, the present invention not limited thereto, an example of how different types of layers can be detected using an impact device comprising a needle- shaped portion 106 and a base portion as described in the first particular embodiment are provided below. In the present example, the obtained information is based on resistance measurement results and/or accelerometry results and sensing of resistance, pressure or deceleration of the needle-shaped portion occurs and is measured discrete from that of the base portion. It is to be noticed that this setup is only selected by way of illustration, the invention not being limited thereto. If for example a layer of mud is probed using an example impact device 100 according to the first particular embodiment of the present invention, the needle-shaped portion 106 penetrates the mud and feels resistance that is gradually increasing when penetrating deeper. When the base portion 108 penetrates the mud, a sensor feels almost no resistance while the sleeve feels a stronger resistance. If a layer of sand covered by a layer of mud is probed using an example impact device 100 according to the first particular embodiment of the present invention, the impact device 100 initially acts as in mud, but when reaching the sand layer, the needle- shaped portion 106 penetrates and will feel a similar resistance as in mud but the origin of it is pressure on the top of the needle. Important is that the needle shaped portion 106 penetrates. When the base portion 108 reaches the sand layer, it will not penetrate but immediately stop. The sand layer thus roughly gets its signature by identification of penetration of the needle-shaped portion 106 whereby the needle- shaped portion 106 itself has no significant increase of contribution to deceleration, whereas the base portion 108 has a sudden and strong contribution to the deceleration of the impact device. If a layer of dense clay is probed, in such dense clay (such as Yperian clay) the impact device 100 will touch the soil structure with the needle-shaped portion 106 and the shear resistance on the needle-shaped portion 106 will significantly increase during penetration. It will be a linear function related to the surface of the needle-shaped portion 106 being subject to friction with the clay. The base portion 108 may or may not reach the clay and will react similar as the needle-shaped portion 106. Depending upon the stiffness of the clay the deceleration curve will change its steepness. If a layer of pure sand is probed, the needle-shaped portion reaches the sand whereby sand has almost no shear resistance. It is to be noticed that if shear resistance would be there, water injection using additional features from the second particular embodiment could reduce it to almost zero. The needle shaped portion 106 contact with the sand makes almost no contribution in the deceleration, and the pressure sensor connected to the needle-shaped portion will sense the contact with the sand and record the contribution to the deceleration. When the base portion reaches the sand, it will abruptly decelerate. The combination of the pressure sensor on the needle shaped portion and the deceleration sensor together with the pressure sensor on the base portion in this example results in obtaining a signature of sand. If a layer of sandstone is probed, the needle shaped portion 106 touches the sandstone and breaks or decelerates or the pressure on the needle shaped portion is at its maximum. The base portion will act as on sand or hard clay: high deceleration, high contact pressure on the base portion.

If a layer is probed that consists out of sandy clay and clay sand mixture, the needle shaped portion penetrates the sandy clay but shows the signature of a clay and similar behavior will be seen when the base portion touches the medium.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.