The invention relates to a cone penetrometer test (CPT) tube with a forward pointing cone equipped to be pushed into a soil at a controlled rate.

Wikipedia mentions that such a cone penetrometer test (CPT) tube is developed in the fifties of the previous century at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history it has also been called the "Dutch cone test". Today, the CPT is one of the most used and accepted tools for soil investigation worldwide.

There is a need to complete the measurements that are possible with a cone penetrometer test (CPT) tube, with other measurements, in particular thermal measurements at relatively low depth of 0.3 m up to 10 m. Thermal measurements in connection with geology measurements are in general useful in oil and gas exploration, the offshore wind energy market, and in connection with gas hydrates, but such measurements are usually conducted at relatively larger depths and at great sea depth. In the known systems that are applied for those purposes, sensor-strings with a plurality of temperature sensors are vibrated into the ground.

It is an object of the invention to provide a method or system which is suitable for executing both a conventional cone penetrometer test measurement of a soil as well as a measurement of the thermal properties or conductivity of such soil. This is in particular desirable for assessment of a soil's suitability for cable burial onshore or in coastal zones with a sandy or clay sediment. The latter option in particular applies to offshore electric power cable burial and pipeline burial. According to the invention a cone penetrometer test ( CPT ) tube is proposed with features according to one or more of the appended claims .

The cone penetrometer test ( CPT ) tube of the invention is provided with the feature that at a fixed distance outside and adj acent to the tube a longitudinally extending measurement probe is provided which is equipped for measuring thermal properties of the soil in which the tube is pushed . Preferably the longitudinally extending measurement probe extends along at least 1 m . of the tube . With such a measurement instrument it is possible to simultaneously measure di f ferent parameters of the soil to be investigated .

Notable advantages of the combined tube and probe of the invention are the relatively quick mobili zation and demobi li zation, the fact that deployment from small vessels is possible , and that the instrument requires minimal operator involvement enabling rapid and accurate testing . Further sediment disturbance is minimal which also contributes to accurate thermal property measurements . Because of the combined testing of the thermal properties with the conventional cone penetrometer test , measurement time is reduced by a factor two or more .

Suitably the longitudinally extending measurement probe is fixed to the tube with two or more outriggers so as to ensure that the measurement probe can be pushed into the soil together with the tube while the tube and the probe maintain their relative position with reference to each other .

In order to conduct the desired measurement of the thermal properties of the soil , desirably the longitudinally extending measurement probe is provided with a heat supply portion and/or a cooling portion . The heat supply portion and the cooling portion can be either passive or active . In the passive mode friction between the tube and probe and the soil can be used for heating . This can also be done active with dedicated heating elements . Active cooling is of course also possible .

It is preferred that the tube and probe are mounted in a driving frame which is further provided with at least one central i zer and guide block for the tube and probe so as to be able to push the tube and probe in a controlled fashion into the soil . The driving frame is for instance provided with a set of driving rolls for driving the tube and probe , although other feasible driving options exi st as well , such as driving chains driven by hydraulic engines . Another possible driving mode is for instance a conventional set of CPT rams as used onshore .

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of a combined cone penetrometer test ( CPT ) tube and thermal measurement probe according to the invention that is not limiting as to the appended claims .

In the drawing : figure 1 shows an instrument of the invention in a side view; figures 2A and 2B show the instrument of the invention in two di f ferent side views prior to entering into a soil to be investigated; figures 3A and 3B show the instrument of the invention in two di f ferent side views after entering into the soil to be investigated; and figure 4 shows a detail of the instrument with a centrali zer and guide block for the tube and probe . Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts .

With particular reference to figure 1 a cone penetrometer test ( CPT ) tube 1 is shown with a forward pointing cone 2 equipped to be pushed into a soil at a controlled rate , wherein at a fixed distance outside and adj acent to the tube 1 a longitudinally extending measurement probe 3 is provided which is equipped for measuring thermal properties of the soil in which the tube 1 is to be pushed . It is clear from figure 1 that the longitudinally extending measurement probe 3 extends along more than 90% of the tube 1 .

Figure 1 further shows that the longitudinally extending measurement probe 3 is fixed to the tube 1 with two or more outriggers 4 so as to ensure that the measurement probe 3 can be pushed into the soil together with the tube 1 while the tube 1 and the probe 3 maintain their relative position with reference to each other .

The longitudinally extending measurement probe 3 is provided with a heat supply portion and/or a cooling portion . The way this can be implemented is known to the skilled person and is therefore not shown . Examples are that the heat supply portion and the cooling portion can be either passive or active . In the passive mode friction between the tube 1 and probe 3 and the soil can be used for heating . This can al so be done active with dedicated heating elements . Active cooling is of course also possible .

Figures 2A and 2B show the instrument of the invention in two di f ferent side views prior to entering into a soil to be investigated, whereas figures 3A and 3B show the instrument of the invention in two di f ferent side views after entering into the soil to be investigated . To enable pushing in or pulling out of the combined tube 1 and probe 3 , the tube 1 and probe 3 are mounted in a driving frame 7 . The figures show hydraulic engines 5 , 6 that are arranged to drive a driving chain with clamping blocks to drive the tube 1 and probe 3 . Other driving options are of course feasible also , such as a piston drive , hydraulic rams etc .

Figure 4 is a detail view showing that the frame 7 is further provided with at least one centrali zer and guide block 8 for the tube 1 and probe 3 .

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the instrument of the invention, the invention is not restricted to thi s particular embodiment which can be varied in many ways without departing from the invention . The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith . On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment . The scope of protection of the invention shall there fore be construed in accordance with the appended claims only, wherein a poss ible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment .