| US2779195A | 1957-01-29 | |||
| FR1053759A | 1954-02-04 |
| CLAIMS 1) The invention is a penetrometer which is used to identify physical properties of soil and also take a sample from the soil, being pushed into the soil at the borehole bottom by means of a hydraulic system; and comprises of a thick internal wall (2) which is manufactured from stainless steel, starting with a rod connector (1 ) section screw able into the drill rod, and used to measure tip resistance and expansion resistance with the aid of strain gauges (8) installed onto its external surface, two thin-walled friction sleeves (4 and 5) with two different diameters (4 and 5), which are manufactured from stainless steel, mounted with screws (1 1 ) putting it over the internal wall (2), and used to measure friction resistance and peripheral stress with the aid of strain gauges (8) installed onto its internal surface, an expansion section (3) which is mounted outside the internal wall (2) by screwing into the threads cut in the middle of the internal wall (2), and ensures to measure expansion resistance with the strain gauges (8) installed to the internal wall (2), by expanding the soil and transmitting transition between the diameters of friction sleeves (4 and 5) and resistance of soil against expansion, to the internal wall (2), a tip section (6) which is mounted by screwing into the thread cut at the end of internal wall (2), and ensures soil sample to enter the cavity in the internal wall (2) while penetrometer is plunging into the soil, expansion of soil to the diameter of lower friction sleeve (5), and measurement of tip resistance with the strain gauges (8) installed to the internal wall (2) transmitting the resistance developed by soil to the internal wall (2), strain gauges (8) for measurements which are installed to external surface of internal wall (2) and internal surface of friction sleeves (4 and 5), silicon gaskets (9) for the provision of water tightness, screws (11 ) for fastening friction sleeves (4 and 5) to internal wall (2), internal cables (10) for connecting strain gauges (8) to the main cable, and a main cable (7) for combining internal cables (10) and connecting them to data collection system. 2) The invention is the penetrometer in the Claim 1 , and its feature is having friction sleeves with various diameters; diameters of these friction sleeves increases during insertion into soil, which causes formation of increased peripheral pressure on their outer surfaces, and thus causes an increased peripheral friction force; and the friction sleeves measure the varying values of these peripheral pressures and friction forces. 3) The invention is a technique which identifies stiffness in the sandy soils and silty soils, and characterized with such feature that it has the following process steps; - Connection of the penetrometer in the Claim 1 to data collection system, - Calibration of axial loads with strain gauge (8) bridges measuring tip resistance and expansion resistance exposing the penetrometer to gradually increasing axial loads, - Opening boreholes in the sandy and silty soils, - Attaching the penetrometer in the Claim 1 to the drill rod (12), - Pushing the penetrometer attached to the rod (12) tip into the borehole bottom with the hydraulic system of drilling rig, - Obtaining records continuously while the penetrometer is pushed into the soil, - Determination of tip resistance and expansion resistance values corresponding to a 60 cm expansion of the penetrometer from the records, - Pulling the penetrometer in the Claim 1 off the borehole together with the drill rod, - Obtaining sufficient amount of soil samples from the soil sample in the penetrometer pulled out, - Performing particle size distribution test on the sample obtained, - Determination of soil stiffness from readily-prepared graphics or nomograms based on the correlation between relative soil stiffness and tip resistance or expansion resistance, in accordance with the biggest particle diameter of the soil. 4) The invention is a technique which approximately identifies the angle of internal friction and the soil cohesion characterized with such feature that it has the following process steps; - Connection of the penetrometer in the Claim 1 to data logging system, - Exposing the penetrometer to progressively increasing peripheral pressure, and calibration of the peripheral pressure values which are charged by the change in electrical resistance values forming on the strain gauge bridges (8) which are placed in the friction sleeves (4 and 5) and used to measure peripheral pressure. - Calibration of the axial load values which are charged by the change in electrical resistance values, forming in the strain gauge bridges which measure the axial load, placed in the friction sleeves (4 and 5) by exposition to progressively increasing axial load which is applied axially to the penetrometer friction sleeves (4 and 5). - Opening boreholes in the sandy and silty soils, - Attaching the penetrometer in the Claim 1 to the drill rod (12), - Pushing the penetrometer attached to the rod (12) tip into the borehole bottom with the hydraulic system of drilling rig, - Obtaining records continuously while the penetrometer is pushed into the soil, - Pulling the penetrometer in the Claim 1 off the borehole together with the drill rod, - Obtaining sufficient number of soil samples from the soil core developed in the penetrometer pulled out, - Examination of the obtained sample by the drilling expert, estimation of the cohesion value, and/or determination of the internal friction and the cohesion of at least one sample by performing shear box test on it if possible/necessary, - Surveying the sample, estimating approximately the angle of internal friction and the soil cohesion, and performing at least direct shear box test on the sample obtained, - By using the obtained data records, determination of values of change in electrical resistance formed on the strain gauge (8) bridges which are placed in the lower friction sleeve corresponding to 25-30cm penetration of the penetrometer, which measures the axial load and the peripheral pressure, and determination of values of change in electrical resistance formed on the strain gauge (8) bridges which are placed in the upper friction sleeve (4) corresponding to 55-60cm penetration of the penetrometer, which measures the axial load and the peripheral pressure, and calculation of the arithmetic mean of data for each value group obtained along a length of 5cm. - Carrying out the conversion to peripheral pressure and friction force values forming around the friction sleeves (4 and 5), by using the calibration graphs of the arithmetic means of data for each value group, - Determination of average shear stress values separately, by dividing the average friction force values formed around the friction sleeves (4 and 5) with outer surface area of the friction sleeves, - Conversion of the average shear stress values into the shear stress value which is created by the soil-soil internal interaction, by dividing them with a value between 0.4-0.9 depending on the roughness level of the friction sleeves (0.9 for completely roughened friction sleeve (4 and 5), and 0.4 for smooth friction sleeve (4 and 5)), - Determination of converted shear stress values for friction sleeves (4 and 5) separately, - Determination of peripheral pressure values for friction sleeves (4 and 5) separately, - Preparation of a graph representing the shear stress on its vertical axis, and the peripheral pressure on the horizontal axis, - Determination of shear stress and peripheral pressure values for the upper friction sleeve (4) and for the lower friction sleeve (5) on the graph, and marking their intersection point, - Joining the two points marked on the graph with a line - Extension of the line joining the point until the vertical axis of shear stress, and determination of the axial interception point as cohesion - Calculation of the angle of the line, joining the points, with respect to the vertical axis, and determining this value as the angle of internal friction. |
SAMPLING
Technical field
The present invention relates to a penetrometer, consisting of double-walled two parts which have different outer diameters, for investigating soil properties during sampling, and two new soil investigation methods which are performed by using this penetrometer.
Background art
There are many penetrometers in the world, but in-situ tests are usually performed by using one of two types of penetrometers which are the most widely recognized ones. The most commonly used one of these experiments is the Standard Penetration Test (SPT). A standard sampler (penetrometer) is used for the Standard Penetration Test. The test is applied by using repeated blows of a 63.5-kg hammer, falling through 76 cm for dynamically driving a standard sampler into soil. The total number of blows corresponding to the last 30 cm penetration of the sampler into the ground is described as the penetration resistance (SPT- N) of the ground. Cone Penetration Test (CPT) is becoming progressively common in the world, and becoming more useful by being developed constantly. Except SPT, penetrometers are not able to take samples. SPT is widely used and able to take samples, but only indirect measurements are done mechanically from the ground surface, not at the level of the penetrometer, and it is dynamically driven into soil; therefore, the values obtained may be incorrect. On the other hand, due to the fact that the existing penetrometers are single scale, measurement of the friction forces which occur at different pressures around the penetrometer cannot be taken. Also, taking samples and carrying out at least one type of in-situ test during the drilling soil investigations is mandatory in Turkey because of regulations. Withdrawing the drilling equipment and pushing down the sampler in order to obtain samples during the drilling, and withdrawing the rod (12) and pushing down the testing equipment (SPT or pressuremeter) to perform in-situ tests after taking the samples, or performing another test at a second point (CPT, etc.) in addition to the drilling takes too much time. A second in-situ test, in addition to sampling by drilling, results in prolonged periods of soil survey, and causes an increase of costs.
Technical problems which are aimed to be solved by the invention
A limited amount of data about the soil can be obtained from experiments which are carried out with non-sampling penetrometers (CPT, PMT, DT, etc.), and this data is interpreted to obtain information about the soil. Since the SPT is a dynamic experiment, the samples are usually spoiled, and thus it becomes impossible to deduce conclusions due to reception of incorrect data. In case of using samplers to take samples, it is not possible to gather information about the conditions of the soil in-situ. Physical conditions of soil are determined and, at the same time, soil sample can be taken (by pushing it like soil sampler) with the new penetrometer invented in a study carried out as a doctoral thesis in the Geotechnical Department of Civil Engineering. Tip resistance built-up against tip progress and expansion resistance built-up against penetration of bigger diameter by soil are measured. In addition, two distinct stresses exist around it by virtue of its structure having two different outside diameters. Two different peripheral frictions are measured around two friction sleeves advancing under two different stresses built-up around it. Capability to take measurements which will identify the physical properties of soil, during a soil sampling process, increases the speed of drilling operation for soil survey.
Description of drawings
Figure 1 : Elevation view of the penetrometer
Figure 2 : Elongation section of the penetrometer
Figure 3 : Elongation section of parts of the penetrometer
Figure 4 : Elongation section of rod connector sections of the penetrometer Figure 5 : Elongation section of the middle expansion connector section of the penetrometer
Figure 6 : Elongation section of tip section of the penetrometer Figure 7 : Elevation view of inner wall section of the penetrometer
Figure 8 : Elongation section of inner wall section of the penetrometer
Figure 9 : Cross section of rod connector section of penetrometer
Figure 10 : Elevation view of upper large friction sleeve of the penetrometer Figure 11 : Elongation section of upper large friction sleeve of the penetrometer Figure 12 : Elevation view of tip section of the penetrometer
Figure 13 : Elongation section of tip section of the penetrometer
Figure 14 : Elevation view of lower slim friction sleeve of the penetrometer Figure 15 : Elongation section of lower slim friction sleeve of the penetrometer Figure 16 : Elevation view of expansion connector section of the penetrometer Figure 17 : Elongation section of expansion connector section of the
penetrometer
Figure 18 : Plan of the strain gauge of the inner wall of the penetrometer Figure 19 : Plan of the strain gauge of the friction sleeves of the penetrometer Figure 20 : The chart for tip and expansion resistance to relative density relationship
Figure 21 : Wheatstone bridge circuit diagram
Description of the references in the drawings
1 : Rod connector
2: Bearing internal wall
3: Expansion section
4: Upper friction sleeve
5: Bottom friction sleeve
6: Tip section
7: Main Cable
8: Strain gauge
9: Silicon gasket
10: Internal cable
11 : Screw
12: Rod
13: Metal plate Disclosure of Invention
Penetrometer comprises of a thick wall (2) used to measure tip resistance and expansion resistance on the inner side, and two thin-walled friction sleeves with two different diameters (4 and 5) used to measure peripheral stress built-up on the outer surface and friction resistance on the outer side. Appearance of penetrometer is given in the Figure 1 , and longitudinal cross sections are shown in the Figure 2 and Figure 3. Detail drawing of the connector (1) facilitating connection of penetrometer to a drilling rod, detail drawing of expansion section and detail drawing of tip section are given in Figure 4, Figure 5 and Figure 6 respectively. Measurements are performed by means of strain gauges (8) installed to the outer surface of internal wall (2) and the inner surface of friction sleeves (4 and 5) (Figure 18 and Figure 19).
Measurement circuits of the penetrometer is calibrated before putting it into use. Penetrometer is connected to the rod (12) of drilling rig with rod connector (1) by screwing into it. It is lowered to the bottom of borehole together with the drill rod (12). It is pushed towards the bottom of borehole at a speed of 0,2 cm/sec with a thrust exerted by the hydraulic system of drilling rig. Calculation is performed by taking into consideration the values of the upper friction sleeve (4) and lower friction sleeve (5), which are measured while crossing through the same point in soil during the time when penetrometer is pushed into the soil. Values taken at an interval of one second, are recorded along a length of 5 cm after it is pushed 25cm and 60cm into the bottom of borehole without taking notice of the first 10 cm since there may be disturbed soil at the bottom of borehole. Physical soil properties are determined with the methods described below, utilizing averages of such recorded values as tip resistance, lower section peripheral stress, lower section peripheral friction force, expansion resistance, upper section peripheral stress and upper section peripheral friction force.
Soil stiffness are determined according to tip resistance and expansion resistance of the penetrometer with the aid of readily-prepared nomograms. An exemplary figure demonstrating the correlation between stiffness of sands, and tip resistance and expansion resistance of the penetrometer, is given in the Figure 20, in the enclosed Pictures.
Peripheral stresses measured at the moment when friction sleeves of differing diameters cross the same point, constituting the horizontal axis and shear stress built-up due to peripheral friction, constituting the vertical axis are plotted on a graph during the time when penetrometer is pushed to the bottom of borehole, and bearing strength parameters of soil are determined with the aid of this graph. A peripheral stress (σ1) exerted to the lower friction sleeve (5) by the soil during the time when thin lower section progresses in the soil after penetrometer is inserted 25 cm into the borehole bottom, and this stress is measured with the aid of two strain gauges (8) mutually installed to the middle section of lower friction sleeve (5) and perpendicular to the axis. Such peripheral stress (σ1) exerted to the lower friction sleeve (5) creates a shear stress (T1) between penetrometer and soil, and this shear stress is measured with the aid of two strain gauges (8) mutually installed to the upper section of lower friction sleeve (5) and parallel to the axis. On the other hand, an peripheral stress (σ2) greater than (σ1) exerted to the thick upper friction sleeve (5) due to increasing indirect thrust force of the soil during the time when thick upper section progresses in the soil after the penetrometer enters 60 cm into the non-disturbed borehole bottom, and this stress is measured with the aid of two strain gauges (8) mutually installed to the middle section of upper friction sleeve (4) and perpendicular to the axis. Such peripheral stress (σ2) exerted to the upper friction sleeve (4) creates a greater shear stress (T2) between penetrometer and soil, and this shear stress is measured with the aid of two strain gauges (8) mutually installed to the top section of upper friction sleeve (4) and parallel to the axis.
Soil internal friction angle and cohesion value can be calculated with the graph plotted utilizing peripheral shear stress value pairs calculated from the lower section peripheral stress and lower section friction force, and peripheral shear stress value pairs calculated from the upper section peripheral stress and upper section friction force. On a graph which has pressure (σ) values on the horizontal axis and sheer stress (T) values on the vertical axis; the peripheral pressure (σ1) measured around the lower thin friction sleeve (5) of the penetrometer and 0.4 times the shear stress (T1) value formed on its surface (0.4 * T1 ) is recorded as the first point; and the peripheral pressure (σ2) measured around the upper thin friction sleeve (4) and 0.4 times the shear stress (T2) formed on its surface (0.4 * T2) is marked as the second point. Instead of multiplying the shear stress (T) values with a coefficient, and marking the result on the vertical axis; calibrations may be made to directly yield cohesion (the soil's own internal interaction) instead of adhesion (interaction between the soil and the metal). In this way, the shear stress value, which is measured directly, can be marked on the graph. Slope of the line intersecting these two points gives the approximate value of the tangent of the soils angle of internal friction. Approximate value of the soil's angle of internal friction is calculated by using this value. The value of the point, where the line intercepts the vertical (T) axis, can be considered as the approximate value of the soil's cohesion.
In the case of roughening the friction sleeves of penetrometer; shear stress (T2) values should be multiplied with some values between 0.4-0.9 depending on the condition of roughness, and should be marked on the graph.
Application alternatives of the invention to the industry
Tip section of penetrometer (6) (Figure 16 and Figure 17), expansion section (3) (Figure 12 and Figure 13) and internal wall (2) (Figure 7, Figure 8 and Figure 9) are manufactured from stainless steel billets of 304 grade, or other grades having greater strength characteristics, with grinding and chip-removal processes performed on a lathe.
Friction sleeves o1 the penetrometer is manufactured from 304 grade stainless steel tubes with thin walls (t=1 mm) (Figure 10, Figure 11 , Figure 14 and Figure 15). Data transmission cables (7 and 10) and strain gauges (8) are used in the electronic equipment. Electronic equipment is manufactured and assembled with a force measurement technology using a strain gauge. Measurements are carried out operating the internal wall (2) and friction sleeve (4 and 5) equipped with a force measurement technology using a strain gauge, as a load cell. Scheme for installing a strain gauge (8) to the outer surface of the internal wall (2) is provided in the Figure 18, and for installing a strain gauge (8) to the friction sleeves (4 and 5) of the Penetrometer is provided in the Figure 19. Silicon gaskets (9) are the gaskets that are made in place during the mounting of parts using a liquid seal. Friction sleeves (4 and 5) are lubricated with grease before the introduction of liquid seal. In this way, adhesion of silicon gaskets (9) to the friction sleeves (4 and 5) are avoided. Penetrometer is utilized to perform in situ tests (in the field) and take soil samples during the test.
Stresses developed at the internal sections of a material under an influence of tensile or compression forces cause changes in the form of material. An elongation ΔΙ_ is observed in a bar with a length of L when subjected to an axial tension force. Strain (ε), a unit deformation, is the ratio of change in the length of an element (ΔΙ_) to its initial length (L) (ε=Δΐ_/Ι_). Particles rigidly installed onto a material that has undergone a deformation due to an exerted load, will also exhibit the same unit deformation accordingly. Changes in electrical resistance are observed because of deformations developed when an external load is applied on conducting materials. Changes in resistance (increase or decrease) are directly proportional to the changes in the unit length of conducting bars undergone a deformation in a single direction (elongation or contraction). Strain gauge (8) is used to make indirect measurements based on the difference in its electrical resistance due to its unit deformation created on it by a unit deformation (elongation or contraction) in a single direction, of the element to which it is installed. Strain gauge (8) comprises of resistance wires placed in a protective material providing a complete electrical insulation. Unit deformations developed by a load in an element to which a strain gauge is installed, will cause the same length changes in the resistance wire available in the strain gauge (8) at the same rate as well, and thereby, changes in the resistance. This change can be determined with the following equation; s=AL L=(AR/R)/K. Where ε- Strain (unit deformation), AR - Change in the resistance of strain gauge (8), R - Resistance of strain gauge (8), K - Gauge factor (given on the package of strain gauge by its manufacturer), in this equation. Resistance of strain gauge (8) and gauge factor are known in this equation. Strain (ε) can be calculated from the equation (2) in case the change in the resistance of strain gauge (8) is measured when a strain is created. Strain is directly proportional to the load applied to an element in the elastic region of the stress-strain diagram belonging to the said element to which Strain gauge (8) is installed. Stress value can be determined for a material the strain of which is determined. Force exerted to the element can be determined inserting stress (σ) and cross- sectional area (S) values in the following formula; (F), o=F/S.
Change in the strain gauge (8) resistance can not be measured with sufficient precision and accuracy, with the dimension and precision settings selected to measure strain gauge (8) resistance because the resistance change to be created in the strain gauge (8) undergone a deformation, develops at small values compared to the strain gauge (8) resistance. Various methods are used in order to measure resistance changes (AR) developing at smaller values compared to the base resistance. The most common method to measure resistance changes in the strain gauge (8) is the method known as Wheatstone Bridge, where an electronic circuit is installed and resistance change is measured. Four resistors in the Wheatstone Bridge are connected as shown in the Figure 21.
Voltage difference between B and D points will be proportional to the difference between the individual resistance sums of the resistances connected to each leg if bridge is supplied with an excitation voltage (Vi) from A and C points. There will be no voltage difference between B and D points when there is no difference in resistance between the legs of circuit (R1=R4 and R2=R3). There will be a voltage difference between B and D points if sum of the resistances belonging to any leg of the circuit is different than sum of the resistances belonging to the other leg. Output voltage to be measured between B and D will be calculated with the following formula; Vg=((RrR3-R2*R4)/((R1 +R2) (R3+R4))) * Vi in case an excitation voltage is applied between A and C. One, two, or four of the resistances are designed as strain gauge (8) in case the Wheatstone Bridge is installed in order to perform unit deformation measurements with strain gauge (8). A circuit is called quarter bridge in cases where one of the resistances in the Wheatstone Bridge circuit is active strain gauge (8) being exposed to unit deformation, and the other three resistances are completed in the measuring device. If a circuit is formed using two strain gauges (8), then this type of circuit is called half bridge. If circuit is totally made of strain gauges (8) then this type of circuit is called full bridge. The designed penetrometer is equipped with half Wheatstone Bridge circuit in order not to be affected by the temperature changes and obtain high precision in the measurements. Two of strain gauges are positioned on the structural element and the other two resistances (these two resistances are also used as strain gauge (8) in the penetrometer) are idly positioned next to the penetrometer in this type of bridge circuit. One of the strain gauges on the element is installed to the element and caused to operate actively, the other is disengaged and becomes non functional. In this manner, resistance changes due to the temperature difference between the legs of circuit is avoided. Temperature compensation is not required for the circuit prepared in this way. Fully symmetric two strain gauges (8) perpendicular to the axis and two strain gauges (8) parallel to the axis are installed mutually to the middle of lower and upper sections of internal wall (2). Electric cables of those mutually positioned out of these strain gauges (8) are connected in series and caused them to act as a single resistance. In this way, strain gauges (8) perpendicular to axis is able to eliminate bending moments developed at the internal wall of penetrometer. Surfaces to which strain gauges are to be installed, will be prepared for adhesion before installing all strain gauges (8) to the penetrometer. Surface will be first sanded with 200-grit sandpaper for the preparation, later surface is cleaned with acetone. Place of the strain gauge (8) centerline is marked on the cleaned surface with lead pencil. Strain gauge (8) is prepared by soldering its cable (10) before, and is aligned and affixed to the adhesion surface from the end opposite to one cable (10) with a packaging tape. One drop of cyanoacrylate adhesive is applied to the adhesion surface, and strain gauge (8) is pressed against metal surface for two-three minutes with a Teflon paper placed on it. Resistance between the legs of strain gauge (8) glued to the surface is measured, and checked whether it is equal to the one specified in the brochure. Resistance between legs of strain gauge (8) and metal part is checked if it is greater than 10000 Volts in the second place. Strain gauge (8) satisfying these conditions and installed at the desired position (place and direction), is ready for calibration. Ready strain gauges (8) are coated with a thin layer of (0,1 -0,5mm) transparent silicon. In this way, strain gauge (8) adhesive brittleness as a result of drying, in addition, damage to strain gauge (8) during mounting, are prevented.
Friction sleeves (4 and 5) can be calibrated before the installation, as well as they can be calibrated after installation. Calibration friction sleeves (4 and 5), being axially loaded, are calibrated against peripheral stress applying peripheral stress for peripheral friction force with tri-axial rock stress testing equipment.
One output from each of those strain gauges (8) perpendicular to axis and parallel to axis, which are installed to the lower section of penetrometer is taken outside the penetrometer and connected to the main cable (7), other outputs are combined together, taken outside the penetrometer as a single line and connected to the main cable (7). Thus, three internal cables (10) from the strain gauges (8) installed to the lower section of penetrometer are connected to the main cable (7) and establish a contact with data collection system.
In the same manner, one output from each of those strain gauges (8) perpendicular to axis and parallel to axis, which are installed to the upper section of penetrometer is taken outside the penetrometer and connected to the main cable (7), other outputs are combined together, taken outside the penetrometer as a single line and connected to the main cable (7). Thus, three internal cables (10) from the strain gauges (8) installed to the upper section of penetrometer, are connected to the main cable (7) and establish a contact with data collection system. Strain gauge (8) cables (10) installed to internal wall of the penetrometer are glued to and laid on the wall surfaces. In this way, cables (10) are prevented from damage during installation. At the mid-point of the friction sleeves, two strain gauges (8) for each of them are mutually installed perpendicular to axis. Two more strain gauges (8) for each are also installed inside the friction sleeves (4 and 5), being glued at one side after they are glued onto a thin (approximately 0,1 mm thick) metal plate (13) which is 10% greater than their size, pasting a thermal conductive gel underneath. Required measures are taken and it was made sure that small metal plate (13) must be prevented from being completely glued onto the surface. Because this small plate (13) onto which a strain gauge (8) is glued must be affected by the friction sleeve (4 and 5) temperature, however it must not be affected by its stresses. Two outputs of the strain gauge (8) installed perpendicular to the friction sleeve (4 and 5) axis are connected with each other, so they act as a single resistance. Small differences in peripheral stresses coming to the friction sleeves (4 and 5) from different faces are reduced, this means that average stress value is measured. Two strain gauges (8) which are installed perpendicular to the friction sleeves (4 and 5) axis, and the two outputs of which are connected with each other, so they act as a single resistance, have two outputs as a result. One of these two outputs is connected to main cable (7) in order to establish a contact with data collection system, Other output is combined with one terminal of each idle strain gauges (8) and connected to the main cable (7) as a single line cable (10) so as to establish a contact with data collection system. In the same manner, second output of the idle strain gauge (8) pair is connected to the main cable with a cable ( 0) in order to establish a contact with data collection system. Cable (10) connections of the friction sleeves (4 and 5) progress being glued to the friction sleeve (4 and 5) walls in order to protect them during installation and provide convenience in connection. 10 mm wide two mutual slots are opened for the transition of cables running from lower section of the penetrometer to upper section, through expansion section. Cables (10) are glued to the surface in a planned way before mounting expansion connector (3). Internal cable (10) connections of the friction sleeve (4 and 5) put over the internal wall (2), are made in the first place during installation. Internal cable (10) cores are soldered and isolated with an insulation tape. Later, friction sleeves (4 and 5) are accurately placed and fastened with screws around it (11). Color cables (10) are used for the electric connections of internal wall (2) and friction sleeves (4 and 5). In this way, conveniences are provided in the connection tests and calibrations. These colors are recorded together with their locations also before mounting.
Friction sleeves (4 and 5) are calibrated for tip resistance and expansion resistance of penetrometer mounted by loading axially, after they are calibrated. Since half Wheatstone bridges are used in the penetrometer, data collection systems to complete a half bridge circuit internally or purpose-made cables to
Penetrometer, after the completion of its calibrations, is lowered to the bottom of drilled borehole in order to explore soil and is pushed into the soil with hydraulic thrust system. Resistance changes created in the strain gauges (8) during the time when it is pushed into soil, are detected with data collection system and evaluated in the computer. At the end of the evaluation, tip resistance created during the time when tip section (6) of penetrometer plunges, expansion resistance created during the time when expansion section (3) plunges, peripheral stress and friction force (shear stress) exerted to the lower friction sleeve (5) during the time when lower friction sleeve (5) plunges, and peripheral stress and friction force (shear stress) exerted to the upper friction sleeve (4) during the time when upper friction sleeve (4) plunges, are measured.
Contraction developed in the peripheral length of lower friction sleeve (5) and upper friction sleeve (4) (with the same diameter as steel pipe) due to peripheral stress, is measured with strain gauges (8). Rises developed in the strain gauge (8) resistances due to this contraction are measured. Peripheral stress corresponding to the rise created in the strain gauge (8) resistance is measured with the aid of values obtained from the calibration (peripheral stress- increase in electrical resistance) of lower friction sleeve (5) and upper friction sleeve (4).
Contraction created in the length of lower friction sleeve (5) and upper friction sleeve (4) (with the same length as steel pipe) due to peripheral friction, is measured with a pair of strain gauges (8) mutually installed to the inner surface of pipe and inline with the pipe. Rises developed in the strain gauge (8) resistances due to this contraction are measured. Peripheral friction corresponding to the rise created in the strain gauge (8) resistance is measured with the aid of values obtained from the calibration (peripheral friction- increase in electrical resistance) of lower friction sleeve (5) and upper friction sleeve (4).
Peripheral stress and peripheral shear stress calculated from the data obtained for peripheral stress and peripheral friction developed during the time when friction sleeves (4 and 5) of the penetrometer cross the same points are plotted on a graph. Two points created by the peripheral stress & shear stress data pair on the graph during the time when friction sleeves (4 and 5) cross the same points, are marked. A line is drawn passing through these two points marked on the graph. Thereafter, number of points is increased to minimum five pairs repeating the same procedure for the lower points at an interval of 0,2cm or 1cm. An average line is selected, which will be able to represent al lines passing through these point pairs. By multiplying slope of the average line by a coefficient (1 ,1-2,5) dependent upon soil type, the angle of internal friction, and by multiplying the value at the point where it intersects the axis by a coefficient (1 ,1-2,5) dependent upon soil types and steel roughness, the soil cohesion are calculated. In addition, soil stiffness (Dr) and void ratio (e) can be determined with tip resistance and expansion resistance values obtained from the measured values utilizing nomograms and formulas prepared according to soil types. Penetrometer is pulled out again after the measurement. Soil sample developed inside the penetrometer while it is pushed into the soil, is taken out and sent to a laboratory. Test applicable to the sample are carried out with the sample delivered to the laboratory.