EP0606433B1 - Method of determining the consistency of sub-soil - Google Patents

Abstract

In order to determine the consistency or nature of soil or sub-soil, or to be able to classify the soil or sub-soil, the permeability of the soil or sub-soil layers under examination is measured. This is done by measuring, as the key parameter, the degree of consolidation or so-called pore-water over pressure. To this end, the invention calls for the use of a penetrator (1) with a measurement probe which has a flattened tip (16, 21).

Description

The present invention relates to a method for determining the consistency or the nature of a substrate or soil or for classifying the same, and to a penetration device for determining the consistency or nature of a substrate or soil or for classifying the same.

Methods for classifying substrates or soil and for determining the quality or consistency, such as strength, density, compactness, resistance, viscosity, etc., are known. For example, Swiss Patent 466 154 describes a penetration or drilling or probing device and a method for measuring and determining the above-mentioned factors from a subsoil or a soil. A further development of the device mentioned is described in Swiss Patent 679 887.

The methods known according to these patents as well as penetration devices and measuring probes work on the principle that the material to be assessed or the corresponding layer is penetrated by means of a conically shaped probe tip, the resistance on the probe tip being measured on the one hand, and the friction or the resistance on the other Resistance at an edge or jacket area surrounding the probe tip, and ultimately the friction or resistance at the probe behind the tip enveloping casing pipe. The friction or resistance at the edge area of the tip and on the casing tube arises primarily through lateral displacement of the material to be penetrated, which results in a strongly compressed zone in the layer to be assessed, both in the edge area of the tip and immediately behind it.

On the basis of these three measured values, the nature or consistency of the subsoil can be inferred, the accuracy of the determined values being limited, in particular because the latter two resistance or friction measured values are relatively imprecise, since the material is hardly displaced evenly and is also strong is influenced by the moisture present in the underground. In addition, it is a variable that is influenced by artificially briefly created tension in the soil. In addition, the measurement of the latter resistances or the friction on the probe ring or on the jacket tube is complex and complicated, since the probe must be constructed in such a way that independent measurement of at least two or three measured values is possible.

No. 4,554,819 proposes a method and a device for classifying the substrate, the classifying being carried out by measuring the so-called pore water pressure. A penetration device is driven into the ground, stopped and pulled back until the measured pore pressure is equal to the hydrostatic pressure at this level. The suggested measurement method is Particularly suitable for the determination of the consistency on the basis of a pre-drilled borehole and less for the classification of the underground exclusively by means of a penetration device.

It is therefore an object of the present invention to propose a measurement method by means of which it is possible in a simple manner to enable the consistency or the nature of a substrate or a soil to be as accurate as possible.

According to the invention, this object is achieved by means of a method according to the wording according to claim 1.

According to the invention, it is proposed to determine the nature or consistency of the substrate by measuring the so-called consolidation (also called consolidation) of the substrate material. For this purpose, not only is a tip-shaped measuring probe used, as is generally customary, but preferably a measuring probe with a blunt "tip", or the probe tip is cylindrical with a flat tip or front surface. As a result, when the probe penetrates, the material to be classified is no longer displaced laterally through the tip, but rather the flat tip "pushes" the material in front of it. However, when measuring the back pressure on the tip, it is no longer the cohesion of the material that is measured, but the permeability of the material. An essential factor for the permeability or the consolidation of the subsoil is the so-called pore water overpressure, i.e. the hydrostatic pressure prevailing in the pores of the material, which arises due to the effective or imaginary moisture in the subsoil when the probe penetrates. Due to the capillary effect in the subsurface, there is practically always a certain water saturation in our latitudes, with which the associated so-called pore water overpressure represents a representative measure of the permeability or consolidation and, associated with this, of the consistency of the subsurface material.

It goes without saying that, for example, a soil whose voids are filled with water can only be compressed if the pore water can escape. In the case of clays, for example, the pores are very narrow and therefore offer great resistance to the flow of water. The pore water can therefore only escape slowly when subjected to a load, the resulting pressure in the water being referred to as the pore water overpressure.

This apparently essential size for the classification of the subsurface or for the determination of the consistency or nature of the subsurface is achieved according to the invention by using a flat probe tip in addition to a conical one. Measuring this characteristic degree of consolidation or excess pore water pressure is difficult with the conventional measuring methods, such as, for example, with the conical probe tips commonly used.

For the determination of the excess pore water pressure or the permeability, as claimed according to the invention, a penetration device is used which has a probe at its end to be driven into the ground or at its tip, preferably with a flattened surface or in the tip of the probe. The probe is now driven into the ground or underground at a certain propulsion speed in a known manner, as is known, for example, from the two aforementioned Swiss patents. At a certain point, the back pressure on the flat tip or the counter force through the substrate is measured (RpV = peak resistance at speed V = breaking resistance), whereupon the penetration device is stopped immediately after the measurement. When stopping has been carried out, the back pressure on the drill probe tip is measured again (RpO = peak resistance when stopping = ground resistance).

As explained above, when the drilling probe is continuously advanced, the moisture present in the subsurface is displaced into the surroundings, this displacement being dependent on the consistency and permeability of the subsurface material. When the penetration device is stopped, depending on the consistency and permeability of the material to be penetrated, the counterpressure relaxes immediately, since the moisture prevailing in the subsurface is displaced depending on the permeability of the material and pressure is therefore relieved. Due to the very precise measuring devices, it is now possible to choose the staggered time between the two or more staggered measurements in such a way that a certain relaxation of the back pressure due to the moisture in the subsurface can occur and which can be determined based on the degree of consolidation. After measuring the two back pressures mentioned on the drilling probe tip, the penetration device is driven further into the subsurface at the predetermined speed specified above.

The degree of consolidation at the corresponding point can now be determined by the respective measured values at the respective measuring points in the subsurface and by the geometry of the drilling probe tip. The excess pore water pressure is proportional to the difference between the back pressure (breaking resistance) prevailing at the specific speed of the penetration device and the back pressure when the measuring device is stopped (bottom resistance) as well as proportional to the cross section of the probe and inversely proportional to the volume of the probe tip, with reference to the calculation of the probe tip volume the figures attached below are to be discussed in more detail.

A classification of the soil is possible by comparing the determined values for the excess pore water pressure with a calibrated comparison scale. The advantage of this measuring method is that, on the one hand, guiding the penetration device with its probe into the ground becomes easier, since the lateral deflection that occurs with pointed measuring probes, which often occurs with penetration devices, is eliminated. In addition, the measurement method is clear, because when using a flat tip, there is always a tip angle of 180 ° and not, as with the use of a conical tip, once an angle of 60 °, once an angle of 90 ° and ultimately another Angle of 130 °. In addition, it is not possible to compare measured values with different conical peaks, since conversion using the correction factor is not possible. It is therefore not surprising that values of the nature of a substrate determined internationally by means of commonly used penetration devices cannot be compared with one another, since different probe tip angles are used in each case. Also based these values on determining the cohesion of the substrate material.

Ultimately, it has also been shown that the penetration or drilling probes can largely be dispensed with considering the lateral friction. However, this method also makes it possible to use, for example, a casing tube which surrounds the penetration or drilling probes, on which casing pipe the so-called lateral friction when driving the drilling probe into the ground can be measured separately, if desired or necessary.

Accordingly, according to the invention, a penetration device is further proposed according to the wording of claim 6.

Further preferred embodiment variants of the penetration device are characterized in the dependent claims 7 to 11.

The invention will now be explained in more detail with reference to the accompanying figures.

Fig. 1

schematisch im Längsschnitt eine erfindungsgemässe Penetrationsvorrichtung, insbesondere eine erfindungsgemässe Sonde, mit Stange und Mantelrohr für getrennte Messungen,

Fig. 2

schematisch im Längsschnitt dargestellt eine Sondenspitze einer herkömmlichen Penetrationsvorrichtung,

Fig. 3

im Längsschnitt eine bevorzugte universelle Ausführungsvariante einer erfindungsgemässen Penetrationsvorrichtung mit zentraler Sonde, und

Fig. 4

eine oberhalb des Erdreiches angeordnete, schematisch dargestellte Messeinrichtung im Längsschnitt.

Show:

Fig. 1

schematically in longitudinal section a penetration device according to the invention, in particular a probe according to the invention, with rod and jacket tube for separate measurements,

Fig. 2

shown schematically in longitudinal section Probe tip of a conventional penetration device,

Fig. 3

in longitudinal section a preferred universal embodiment variant of a penetration device according to the invention with a central probe, and

Fig. 4

a schematically illustrated measuring device arranged above the ground in longitudinal section.

In Fig. 1, a penetration device 1 is shown schematically in longitudinal section, essentially comprising drilling or penetration probe 2 and, arranged on the front, a measuring probe 16 which is connected to the penetration or drilling probe 2 via a dowel pin 17. Both the penetration or drilling probe 2 and the probe 16 are cylindrical. The probe 16 has a flat surface 22 at its front end or at its tip 21. In addition, the front part 21 has a larger diameter than the region of the probe located behind it. The zone with an enlarged diameter has a height h. Finally, both the probe and the penetration and drill rods are encased in a casing tube 9.

During the penetration or penetration process into the subsurface, the flat drill probe tip 22 is driven into the subsurface, whereby the material to be assessed or classified by the probe is pushed in front of the probe in the direction of the arrow or, if necessary, laterally is ousted. It is essential that the real or imaginary moisture in the water, which arises from the groundwater as a result of the capillary action, is displaced downwards and sideways. This water pressure or the excess pore water pressure is a measure of the consistency or composition or the permeability of the material to be assessed.

A conventional penetration device or a drill probe tip is shown in longitudinal section in FIG. 2 for comparison, the same parts being provided with the same reference numbers in comparison to FIG. 1 for better understanding. As can be clearly seen from FIG. 2, the drilling or penetration or measuring probe 16 has a conically shaped tip, as a result of which the material to be assessed is laterally displaced when the penetration device is driven into the ground. However, this does not mean that the permeability or permeability of the material can be measured alone, because the measurement result is furthermore essentially determined by the cohesion or. Friction affects. Furthermore, as shown schematically by means of arrows, it can be seen that the laterally displaced material accumulates laterally behind the drill probe tip on the casing tube, as a result of which compression occurs in this zone. However, in contrast to the penetration of the drilling probe of FIG. 1, the lateral friction on the casing tube becomes essential, which is why this size must also be taken into account when assessing or classifying the material.

In comparison of FIG. 1 to FIG. 2, it can thus be stated that the permeability or permeability of the substrate is measured with the penetration device or the probe from FIG. 1, while essentially the cohesion and Friction of the material to be assessed is measured.

3 shows a preferred universal embodiment variant of a penetration device 1 according to the invention in longitudinal section. Again, a measuring probe 16 is arranged on the front on penetration or drilling probes 2 and 10, connected via a dowel pin 17 to the central probing or penetration rod 10 arranged directly behind the probe.

According to the embodiment variant of FIG. 3, the probe 16 is formed in two parts, comprising two parts arranged coaxially to one another, namely a central probe part 16a and an outer annular part 16b. Analogously to the design of the probe of FIG. 1, both parts have a cylindrical portion 21a or 21b formed on the front, which preferably has a diameter which is widened compared to the portion of the probe lying behind it. The front parts or front surfaces 22a and 22b of the two probe parts 16a and 16b are aligned with one another and thus form a single flat surface 22 in the embodiment shown in FIG. 3.

The central probing or penetration probe 2 or 10 are enveloped by a central probe jacket tube 9, which also envelops the central part 16a of the probe. The outer part 16b of the probe is carried or held by a cladding tube or shaft 11, which in turn envelops the jacket tube 9. Enveloping this shaft 11 and enveloping the annular probe section 16b on the front side, a further shaft or jacket tube 14 is arranged, in which the outer probe section 16b is slidably arranged.

The above-mentioned dowel pin 17 can be broken through after completion of the drilling if it is no longer possible to withdraw the probe 16. By destroying this dowel pin connection, all shells and penetration or boring bars can be pulled back to the surface of the earth.

To carry out the penetration probing or to determine the consistency or nature of the substrate, the penetration device 1 according to FIG. 3 is driven into the substrate by suitable drive means. Such drive means can be omitted and described, since they are already well known from the two Swiss patents mentioned above.

The penetration device 1, comprising the two-part probe tip, is driven into the ground at a certain constant rate of advance, with subsequent measuring points the counter pressure or the counterforce on the flat surface 22 of the probe tip 21 is measured. These counterforces are measured on the surface of the earth and result from the force transmission from the probe via the probe or penetration rods behind it, with which this counterforce can be measured on the surface of the earth.

At each of these measuring points, the penetration process is interrupted for a short time, with a further measurement of the counterpressure taking place shortly after the measurement in the moving state immediately when the penetration device is stopped. The condition or consistency of the substrate is now determined by this so-called permeability or permeability measurement, in that the difference between the two back pressure measurements mentioned is formed. The excess pore water pressure results from the following equation: $$\text{(Rpv -Rp0) · Probe cross section: probe tip volume}$$

Rpv is the measurement of the so-called breaking resistance in the moving state, for example at a speed of 2cm / s. Rp0 is the back pressure, the so-called ground resistance, at standstill, and the probe cross-section is the distance x according to FIG. 3. The probe tip volume results from the area 22, multiplied by the height h according to FIG. 3 .

Should be due to the nature of the floor, such as the presence of coarse-grained material or isolated stones, which represent external friction an essential factor, there is the possibility with the construction of the penetration device according to FIG. 3 to measure the resistance or the friction on the outer jacket 14.

If, however, a point is reached where the penetration device 1 can no longer be easily advanced at the certain constant speed, for example as a result of loamy or very compact subsoil, analogous to the penetration device according to CH-PS 679 887, the further propulsion can only be undertaken Use of the central probe 16a continues. This significantly reduces the front probe surface, which naturally also results in a reduced resistance to the front part 22a of the central probe 16a. For this purpose, further penetration takes place only by driving the central probe 16a, possibly together with the jacket tube 9 enveloping the central probe section 16a, which furthermore gives the possibility of measuring the lateral friction on the jacket tube 9 in addition to the resistance on the front section 22a .

Analogous to the equation given above, in turn at subsequent measuring points, both the resistance to the probe 16a when the penetration device is moving and at rest are measured and the excess pore water pressure is determined analogously, in which case the probe cross section = y and the probe tip volume = cross-sectional area 22a · h.

The values for the pore water overpressure determined in the respective measurements are now compared with corresponding calibration curves, in which the pore water overpressure is recorded or listed as a function of different propulsion speeds for certain properties or consistencies of substrates or soil. Based on the values determined by means of the measurement and the rate of advance, the consistency or nature of the substrate can be inferred immediately from the calibration curves.

Thus, the assessment of the nature or consistency of the substrate is not based on the cohesion of the substrate material, but rather on the basis of the permeability or permeability of the material or on the basis of the excess pore water pressure in this material. If the penetration device is blocked due to a layer that is difficult to penetrate, the propulsion can also take place dynamically, instead of statically at a constant speed, as described, for example, in Swiss Patent No. 679,887.

4, ultimately, it is to be recorded how the resistance on the measuring probe 16 is measured, on the one hand, and how, on the other hand, the friction on the jacket tube surrounding the probe is measured independently. The measurement of several values during the penetration of a penetration device independently of one another is already known from the two above-mentioned Swiss patents and is described in detail therein, however At this point, the process will be briefly outlined again with reference to the schematic representation of the measuring device.

According to the schematic representation in FIG. 4, a central total load 31 acts to drive the penetration device into the ground. This total load 31 acts primarily on a crossmember 33, the load being transmitted to the central probe or to the probe 2 and the jacket tube 9 surrounding the central probe by means of longitudinal rods 35 and a further crossmember 37. The transmission takes place via a central head part 39 of the probe. By attaching a measuring box 43 between the mentioned cross member 37 and a further cross member 36, the resistance or counterforce on the probe can be measured in the subsurface.

The load is transferred to a head part 41 and thus to the jacket 14 via a further cross member 43 and longitudinal bars 38. The friction occurring on the outer casing tube 14 is measured by means of a further measuring box 45, which is arranged between the two cross members 33 and 34.

The two measuring boxes 43 and 45 can be connected to electronic measuring and evaluation devices in such a way that two measured values are automatically recorded and registered at certain points in the driving of the penetration device into the ground, just before and precisely when the penetration device is stopped. The values measured in this way are, according to the invention, as described above evaluated.

The penetration device according to the invention shown with reference to FIGS. 1 to 4 and the description of the process of course only relate to an example that can be modified, changed or supplemented in any desired manner. It is essential that the measurement or determination of the consistency of the substrate is carried out by recording the permeability or the degree of consolidation of the substrate material. A flat probe tip is preferably used, but the measurement, although more difficult, can also be carried out with a conventionally conical probe. As a further application, any number of time-graded measurements can be carried out in order to use e.g. the permeability coefficient or similar to determine.

In summary, the main advantages compared to conventional measurement methods should be listed again:

By using the flat probe tip according to the invention, the measuring method is largely reduced to measuring a single measured value, namely to the resistance on the probe surface. Lateral friction and resistance forces can often be neglected, as they are often of little importance.

By choosing a flat probe tip and measuring the permeability, it is possible to determine the degree of consolidation.

The volume "shifted" by means of a flat tip is considerably less than that when using a conical or conical tip. This results in particular from the surface of the probe tip, which is much smaller than the surface of a cone shell when a flat tip is selected. This means that any correction factors due to the choice of a different cone tip angle are also eliminated.

For the classification and determination of the consistency of a substrate, only one single value, namely the degree of consolidation, can be used.

Claims (11)

1. A penetration method to determine the consistency or nature of a subsoil or soil or to classify them, characterised in that permeability or interstitial overpressure in the subsoil or soil layers to be evaluated are measured.
2. The penetration method according to claim 1, characterised in that the interstitial overpressure determining classifying of the soil or subsoil is defined by measuring permeability with a sound provided with a flat sound surface.
3. The penetration method according to claim 1 or 2, characterised in that to measure permeability, a substantially cylindrical sound with a flat surface is driven into the subsoil at a defined speed, and at periodically succeeding points, the resisting pressure or the resisting force applied to the sound head is measured ; at the successive measuring points driving is interrupted so that the resisting pressure or the resisting force applied to the sound surface can be measured again directly when penetration stops, and both values measured at one point indicate the consolidation or the relative "relaxation" of the soil which determines interstitial overpressure, after which penetration or sounding goes on at the defined penetration speed up to the following point.
4. The penetration method according to claim 2 or 3, characterised in that the consolidation degree is determined from the relation : (Rpv - Rp0) · q : Vol, wherein Rpv = back pressure or resistance applied to the flat sound surface at a defined penetration speed v ; Rp0 = back pressure or resistance with v = 0 ; q = sound cross section and Vol = volume of the sound end, which has a diameter larger than the sound parts provided directly behind the sound surface or than the penetration shaft driving into the subsoil.
5. The penetration method according to one of claims 2 to 4, characterised in that the sound surface has at least two parts and is made out of at least two coaxial parts and has a central sound surface with a reduced cross section, the sound parts, with both sound surfaces aligned and forming one surface, being simultaneously driven to a penetration depth for carrying out the permeability measuring till driving the sound at the defined speed is made very difficult, and then the central sound part alone is driven further by penetration to continue the measuring.
6. A penetration device to determine the consistency or nature of a subsoil or soil or to classify them, characterised in that measuring sound (16) has a sound surface (22) which is at least approximately flat and sound (16) is cylindrical and has a larger diameter (x, y) in its front zone (21).
7. The penetration device according to claim 6, characterised in that sound (16) and the penetration shafts (2, 10) needed to drive the sound are guided in a tubular casing (9, 14).
8. The penetration device according to claim 6 or 7, characterised in that sound (16) has two parts (16a, 16b) provided substantially coaxially, central sound (16a) being movable so that it can be deviated longitudinally to the penetration device relative to the annular sound envelope (16b) surrounding said central sound (16a), in order to be driven further into the subsoil in case the sound with a reduced cross section (y) is blocked.
9. The penetration device according to claim 8, characterised in that both sound parts or the central sound and sound envelope (16a, 16b) are placed close to each other in the zone of their surface (21a, 21b) and form one surface (22a, 22b, 22), whereas in the zone distant from surface (21a, 21b) they are spaced apart so that central sound (16a) is guided by a tubular casing (9) in the gap formed by the spacing, which tubular casing (9) can be driven further, too, in case the central part (16a) of the sound is deviated or is driven further alone.
10. The penetration device according to one of claims 6 to 9, characterised in that measuring devices (43, 45) are provided over the earth's surface to measure the back pressure acting on the sound surface (22) or the resisting force.
11. The penetration device according to one of claims 6 to 10, characterised in that at least two measuring devices (43, 45) are provided so that lateral friction on the tubular casing (9, 14) can be measured in addition to back pressure or resisting force applied to the sound surface (22).

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