Method for Measuring Coefficient of Earth Pressure at Rest of Soil and Multi-Stage Cone

Abstract

To provide a method for measuring a coefficient of earth pressure at rest of ground capable of measuring a highly-accurate coefficient of earth pressure at rest in a simple and low-cost manner.SOLUTION: A method for measuring a coefficient of earth pressure at rest of ground in a measurement object depth of the ground includes the steps of: preparing a multistage cone provided with columnar measurement units of three or more stages having different diameters so as to be widened from a tip (step S1); pushing the measurement unit in the uppermost tip of the multistage cone into the ground of the measurement object depth (step S3); sequentially pushing the measurement units of the second and following stages into the measurement object depth from the tip (steps S4 and S5); and calculating a coefficient of earth pressure at rest of the measurement object depth on the basis of calculation results obtained when the multistage cone is pushed (step S10).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for measuring the coefficient of earth pressure at rest in a ground and a multi-stage cone, which measure the coefficient of earth pressure at rest at a measurement target depth in the ground.

Background Art

[0002] The in-situ loading test shown in Non-Patent Document 1 is currently a standard method. Water is supplied to a pressure meter inserted into a bored ground to inflate it, and the pressure is measured to measure the earth pressure.

[0003] On the other hand, in the method for measuring the coefficient of earth pressure at rest in the ground disclosed in Patent Document 1, when implementing the same method as in Non-Patent Document 1, by also measuring the change in pore water pressure, the overburden pressure can be calculated simultaneously. The precise calculation of the earth pressure in the ground will greatly contribute to the design of piles in view of the situation at that point and the confirmation of the effect of ground improvement.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the conventional in-situ loading test shown in Non-Patent Document 1, since a pressure meter is inserted after boring, there is a problem that the hole wall is disturbed and accurate measurement cannot be performed. In order to solve this problem, a self-boring type in-situ loading test device has also been developed, but there is a problem in that a large amount of labor and cost are required for the installation of a reaction device, etc., and it is often difficult to carry out at a large number of locations.

[0007] Also, Patent Document 1 applying the method of Non-Patent Document 1 discloses a measuring device for excavating a direct test hole provided with a conical excavation part at the tip, but it is assumed that the device becomes large-scale.

[0008] Therefore, an object of the present invention is to provide a method for measuring the coefficient of earth pressure at rest of the ground and a multi-stage cone that can measure the coefficient of earth pressure at rest of the ground simply and at low cost with high accuracy.

Means for Solving the Problems

[0009] To achieve the above object, a method for measuring the coefficient of earth pressure at rest of the ground according to the present invention is a method for measuring the coefficient of earth pressure at rest of the ground at a measurement target depth of the ground, comprising the steps of preparing a multi-stage cone provided with columnar measurement parts having different diameters in three or more stages so as to widen from the tip, pushing the measurement part at the foremost tip of the multi-stage cone into the ground at the measurement target depth, subsequently pushing in the measurement parts from the second stage and subsequent stages in order at the measurement target depth, and calculating the coefficient of earth pressure at rest at the measurement target depth based on the measurement results obtained when the multi-stage cone is pushed in. When pushing in the measurement parts, the circumferential shear force is measured by sensors provided in each measurement part, and the coefficient of earth pressure at rest at the measurement target depth is calculated based on the effective earth pressure estimated from the measurement results of the three or more measurement parts.

[0010] Here, the effective passive earth pressure among the effective earth pressures can be obtained by dividing the circumferential shear force by a friction coefficient set according to the type of soil at the measurement target depth. Further, the coefficient of earth pressure at rest at the measurement target depth can be calculated by dividing the effective earth pressure when the displacement becomes 0 by the effective overburden pressure.

[0011] Furthermore, at the tip of the multi-stage cone, it is preferable that the tip resistance is measured. Also, in the multi-stage cone, it is preferable that the pore water pressure is measured. On the other hand, after pushing in the measurement part of the multi-stage cone by 3 or more stages, a configuration can also be adopted that includes a step of measuring the circumferential shear force of the measurement target depth by each measurement part while pulling it out.

[0012] The invention of the multi-stage cone is a multi-stage cone that is pushed into the ground for a ground investigation, and includes three or more cylindrical measurement parts with different diameters provided so as to widen from the tip, a tip resistance measurement part provided at the conical tip for measuring the tip resistance, and a water pressure measurement part for measuring the pore water pressure. In the measurement part, the circumferential shear force with the surrounding ground is measured.

[0013] Here, strain gauges can be provided at intervals in the vertical direction in the measurement part, and the circumferential shear force can be calculated based on the difference between the upper and lower measurement results.

Advantages of the Invention

[0014] The method for measuring the coefficient of earth pressure at rest of the ground of the present invention configured as described above pushes a multi-stage cone provided with three or more cylindrical measurement parts with different diameters so as to widen from the tip into the ground to the measurement target depth, and calculates the coefficient of earth pressure at rest based on the measurement results of each measurement part.

[0015] In short, since it only involves pushing a multi-stage cone that improves the mechanism of the cone penetration tester into the ground, it can be carried out simply and at low cost. Furthermore, since the hole wall is not disturbed, it becomes possible to measure the coefficient of earth pressure at rest with high accuracy.

[0016] In addition, the invention of the multi-stage cone includes a measuring section having three or more cylindrical sections with different diameters provided so as to widen from the tip, a tip resistance measuring section for measuring the tip resistance, and a water pressure measuring section for measuring the pore water pressure. Therefore, the measuring section can measure the circumferential shear force generated between the measuring section and the surrounding ground, and can measure the tip resistance and the pore water pressure together.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining the processing flow of the method for measuring the coefficient of earth pressure at rest of the ground according to the present embodiment. Further, FIG. 2 is an explanatory diagram showing the configuration of the multi-stage cone 1 according to the present embodiment.

[0019] If the coefficient of earth pressure at rest of the ground can be obtained simply and at low cost, liquefaction judgment based on the ground investigation results can be performed not only at large-scale construction sites but also at medium-scale or small-scale construction sites. Further, if a highly accurate coefficient of earth pressure at rest of the ground is obtained, the accuracy of liquefaction judgment of the ground can also be improved.

[0020] Furthermore, when confirming the improved quality of the "vein ground improvement method" developed by the applicants, it is desirable to confirm the increase in the coefficient of earth pressure at rest K 0 of the ground (see "7 others including Hosoi, Study on on-site test construction and quality confirmation method of vein-improved ground, 70th Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, 2015", "7 others including Araki, Study on sustainability of liquefaction countermeasure effect by vein improvement, 71st Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, 2016", etc.). Also in this case, the value obtained by the method for measuring the coefficient of earth pressure at rest of the ground according to the present embodiment can be used. In addition, when accurate grasping of earth pressure in the ground such as pile design is required, the measurement result of the coefficient of earth pressure at rest with high accuracy can be used.

[0021] The multi-stage cone 1 used in the method for measuring the coefficient of earth pressure at rest of the ground according to the present embodiment is an improved version of the electric cone used in the three-component cone penetration test (CPT: Cone Penetration Test: Standard of the Japan Society of Soil Mechanics and Foundation Engineering JGS 1435-2012 "Electrical Cone Penetration Test Method") as shown in FIG. 3.

[0022] In the electric cone of the three-component cone penetration test, measurement of three components, namely tip resistance, pore water pressure, and side shear force, is performed. The tip resistance is measured when the electric cone is pushed into the ground by the conical portion at the tip of the electric cone. On the other hand, the pore water pressure is measured by a piezometer attached to the electric cone.

[0023] Then, the circumferential shear force of the electric cone can be calculated from the measurement results of strain gauges attached at intervals in the vertical direction. That is, one pair or two pairs of strain gauges are attached in the circumferential direction of the electric cone, and the axial force at that position is calculated from the average value of their measurement results. In Fig. 3, the upper axial force N u and the lower axial force N L are shown as an example of being calculated.

[0024] The circumferential shear force f s of the electric cone is u the difference between this upper axial force N L and the lower axial force N s divided by the outer peripheral area 2πdL of the electric cone with respect to the vertical interval L between the strain gauges. That is, the circumferential shear force f

[0025] is obtained from the measurement results of the strain gauges. s Here, assuming that the friction coefficient between the outer peripheral surface of the electric cone and the surrounding ground is μ, the circumferential shear force f h is related to the effective earth pressure σ’ s acting horizontally around the electric cone by f h = μσ’ s and can be expressed as such. In the multi-stage cone 1 of the present embodiment, by utilizing this relationship, the effective earth pressure σ’ h is obtained from the circumferential shear force f

[0026] As shown in Fig. 2, the multi-stage cone 1 of the present embodiment includes cylindrical measurement parts with different diameters in three or more stages provided so as to widen from the tip. In the present embodiment, the multi-stage cone 1 provided with three measurement parts will be described, and from the tip side, they are the first measurement part 11, the second measurement part 12, and the third measurement part 13.

[0027] The first measurement part 11, the second measurement part 12, and the third measurement part 13 are all formed in a cylindrical shape such as a cylinder or a circular tube with a constant thickness in the vertical direction. Here, the radius of the first measurement part 11 is d 1Let the radius of the second measurement unit 12 be d 2 Let the radius of the third measurement unit 13 be d 3 Let it be so. The size relationship of the radii is d 1 < d 2 < d 3 That is. For example, d 1 is set to about 15 mm.

[0028] Strain gauges 2 are attached to the first measurement unit 11, the second measurement unit 12, and the third measurement unit 13 at intervals in the vertical direction, respectively. The number of strain gauges in the vertical direction for each measurement unit (11, 12, 13) is not limited to two upper and lower stages, and three or more stages can also be provided. Further, in FIG. 2, a form in which a pair of strain gauges 2, 2 are attached to opposing positions spaced in the circumferential direction is illustrated, but it is not limited to this, and any number of strain gauges 2 can be provided at equal intervals in the circumferential direction.

[0029] Here, let the vertical interval between the strain gauges 2, 2 of the first measurement unit 11 be L 1 Let the vertical interval between the strain gauges 2, 2 of the second measurement unit 12 be L 2 Let the vertical interval between the strain gauges 2, 2 of the third measurement unit 13 be L 3 Let it be so.

[0030] The vertical interval L 1 , L 2 , L 3 between the strain gauges 2, 2 of each measurement unit (11, 12, 13) may be constant, or may be set to different intervals for each measurement unit (11, 12, 13). For example, the intervals L 1 , L 2 , L 3 can be set to about 500 mm.

[0031] Further, the tip 14 of the multi-stage cone 1 is formed in a conical shape, and a tip resistance measurement unit for measuring the tip resistance is provided. This tip 14 and the tip resistance measurement unit can have the same configuration as the tip of the electric cone in the above-described triaxial cone penetration test.

[0032] Based on the tip resistance measured by the tip resistance measurement unit provided at the tip portion 14, it is possible to determine the type of soil of the ground into which the tip portion 14 is pushed. For example, in a three-component cone penetration test, the tip resistance and the shaft resistance measured with an electric cone are plotted on a soil classification discrimination diagram (Robertson, P.K.: Soil classification using the cone penetration test Canadian Geotechnical Journal, Vol.27, No.1, pp.151-158, 1990) to perform soil discrimination such as organic soil, clay, silty clay, sandy silt, sand, gravelly sand, and hard fine-grained soil.

[0033] Also in the multi-stage cone 1 of the present embodiment, by measuring the tip resistance at the tip portion 14, soil discrimination can be performed. Further, above the tip portion 14 of the multi-stage cone 1, a water pressure measurement unit 15 for measuring the pore water pressure is provided.

[0034] The tip resistance measured by the tip resistance measurement unit can also be corrected by the value of the pore water pressure measured by the water pressure measurement unit 15 and used for soil discrimination. That is, when penetrating the tip portion 14, a value affected by the water pressure is measured as the tip resistance, so in order to improve the accuracy of soil discrimination, the measured tip resistance value can also be corrected and used. Further, the water pressure measurement unit 15 can be provided not only above the tip portion 14 (the lower end of the first measurement unit 11) but also at the lower end of the second measurement unit 12 and the lower end of the third measurement unit 13.

[0035] Generally, the tip resistance when penetrating sandy soil or gravelly soil tends to be larger compared to when penetrating cohesive soil. Also, the shaft resistance is larger when penetrating sandy soil or gravelly soil.

[0036] When the tip 14 of the multi-stage cone 1 is penetrated into the ground, the soil particles and pore water in the original position are pushed out to the surroundings by the tip while advancing, so an excess pore water pressure greater than the hydrostatic pressure in the original position acts. At this time, if the soil has high water retention, the excess pore water pressure will be measured as it is, and if the soil has high drainage, the pore water pressure similar to the hydrostatic pressure will be measured. Thus, the pore water pressure measured by the water pressure measurement unit 15 can be used for estimating the groundwater level when performing liquefaction judgment, estimating soil type discrimination, etc.

[0037] Figure 4 is an explanatory diagram schematically showing the outline of the relationship between ground displacement and horizontal earth pressure (at-rest earth pressure, passive earth pressure, active earth pressure). Also, Figure 5 is an explanatory diagram showing the relationship between the effective at-rest earth pressure, effective passive earth pressure, and effective active earth pressure, with the relational expressions added. As described above, in the in-situ loading test that has been conventionally performed, this relationship is obtained by inflating the pressure meter to measure the at-rest earth pressure coefficient K 0 thereof.

[0038] In the method for measuring the at-rest earth pressure coefficient of the present embodiment, by pushing the multi-stage cone 1 into the ground, the at-rest earth pressure coefficient K 0 can be measured without performing an in-situ loading test that inflates the pressure meter.

[0039] Furthermore, when pushing in the multi-stage cone 1, the ground is compressed (consolidated) in the horizontal direction, so the measurement on the passive earth pressure side can be performed. In addition, when pulling out the multi-stage cone 1, the ground expands (relaxes) in the horizontal direction, so the measurement on the active earth pressure side can also be performed. The details of this point will be described later, but if the calculations on both the passive earth pressure side and the active earth pressure side can be performed, more precise measurement of the at-rest earth pressure coefficient becomes possible.

[0040] Hereinafter, a specific example of the method for measuring the at-rest earth pressure coefficient of the present embodiment will be described according to the procedure shown in the flowchart of FIG. 1. First, in step S1, a multi-stage cone 1 having a configuration as shown in FIG. 2 is prepared.

[0041] As shown in Fig. 6, the multi-stage cone 1 is inserted from the ground surface of the ground at a construction site or the like toward the measurement target depth (step S2). In Fig. 6, the case of measuring the coefficient of earth pressure at rest of the ground located at one depth shown as the measurement target depth will be described. However, there may be multiple measurement target depths in the depth direction. For example, the measurement target depths can be provided at intervals of 50 cm from the ground surface.

[0042] In step S3, for the ground at the corresponding measurement target depth, the tip portion 14 and the first measurement portion 11 of the multi-stage cone 1 are pushed in, and the tip resistance, pore water pressure, and circumferential shear force are measured. The tip resistance is measured by the tip resistance measurement portion of the tip portion 14, and the pore water pressure is measured by the water pressure measurement portion 15.

[0043] In the first measurement portion 11, as shown in Fig. 6(a), the ground at the measurement target depth is spread by a cylinder with a diameter of 2d 1 , and when the strain gauges 2, 2 arranged at the vertical interval L 1 pass through, the circumferential shear force f sp1 is measured. This circumferential shear force f sp1 is the product of the friction coefficient μ obtained according to the type of soil at the measurement target depth and the effective passive earth pressure σ'. hp1

[0044] Subsequently, in step S4, for the ground at the corresponding measurement target depth, the second measurement portion 12 of the multi-stage cone 1 is pushed in, and the circumferential shear force is measured. In the second measurement portion 12, as shown in Fig. 6(b), the ground at the measurement target depth is spread by a cylinder with a diameter of 2d 2 , and when the strain gauges 2, 2 arranged at the vertical interval L 2 pass through, the circumferential shear force f sp2 is measured. This circumferential shear force f sp2 is the product of the friction coefficient μ obtained according to the type of soil at the measurement target depth and the effective passive earth pressure σ'. hp2

[0045] Then, in step S5, the third measurement unit 13 of the multi-stage cone 1 is pushed into the ground at the corresponding measured depth to measure the circumferential shear force. In the third measurement unit 13, as shown in FIG. 6(c), the ground at the measured depth is spread by a cylinder with a diameter of 2d 3 and when the strain gauges 2, 2 arranged at the vertical interval L 3 pass through, the circumferential shear force f sp3 is measured. This circumferential shear force f sp3 is the product of the friction coefficient μ obtained according to the type of soil at the measured depth and the effective passive earth pressure σ’ hp3 .

[0046] In step S6, it is determined whether to continue the measurement during pulling out. If only the measurement during pushing in is performed, the process proceeds to step S9 to determine the type of soil at the measured depth.

[0047] The determination of the soil type can be performed using the soil classification discrimination diagram described above in the explanation of the three-component cone penetration test. Also, penetration tests can be performed on various soils in advance using the multi-stage cone 1 of the present embodiment, and standard values can be set for each soil classification. In short, a database or soil classification discrimination diagram for discriminating the soil type is created in advance from the measurement results of the tip resistance, pore water pressure, and circumferential shear force obtained when the tip portion 14 and the first measurement unit 11 are penetrated.

[0048] Furthermore, a standard value is also set in advance for the friction coefficient μ between the soil type and the outer peripheral surface of the first measurement unit 11. By doing so, if the soil type is discriminated from the measurement results of the tip resistance, pore water pressure, and circumferential shear force, the friction coefficient μ can be set.

[0049] In step S10, the coefficient of earth pressure at rest at the measured depth is calculated. If the circumferential shear forces (f sp1 , f sp2 , f sp3 ) and the friction coefficient μ are known, the effective passive earth pressures (σ’ hp1 , σ’ hp2 , σ’ hp3) can be calculated.

[0050] FIG. 7 is an explanatory diagram showing a method for estimating the effective earth pressure at rest σ’ from the measurement results of the multi-stage cone 1. The displacements that occur when the first measurement unit 11, the second measurement unit 12, and the third measurement unit 13 are each pushed into the ground are d h0 , d 1 , d 2 , d 3 and can be represented respectively.

[0051] On the other hand, from the circumferential shear forces (f sp1 , f sp2 , f sp3 ) measured when the first measurement unit 11, the second measurement unit 12, and the third measurement unit 13 are each pushed into the ground, by setting the friction coefficient μ at the measurement target depth, the effective passive earth pressures (σ’ hp1 , σ’ hp2 , σ’ hp3 ) can be calculated respectively.

[0052] Then, the measurement results of the first measurement unit 11, the second measurement unit 12, and the third measurement unit 13 are plotted on a graph with the horizontal axis as displacement and the vertical axis as effective earth pressure, and an approximation line such as an approximate straight line or an approximate curve obtained from the three-point plot is created. The intercept at which this approximation line intersects displacement 0 is the effective earth pressure at rest σ’ h0 in the earth pressure at rest state.

[0053] Explaining with reference to FIG. 5, since the effective earth pressure at rest σ’ h0 is the product of the earth pressure at rest coefficient K 0 and the effective overburden pressure σ’ v , by dividing the effective earth pressure at rest σ’ h0 by the effective overburden pressure σ’ v , the earth pressure at rest coefficient K 0 can be calculated. Here, the effective overburden pressure σ’ v can be obtained from the measurement target depth and the like. Note that K p is the passive earth pressure coefficient, and K a is the active earth pressure coefficient.

[0054] Here, the reason for using three or more plots to determine the effective at-rest earth pressure will be explained. As shown in Fig. 4, the curve of the passive earth pressure does not increase at a constant rate as the ground displacement increases, but converges towards a certain value when the displacement exceeds a certain level. Therefore, if the number of plots is two or less, it may not be possible to accurately determine the effective at-rest earth pressure. Thus, three or more plots are used to calculate the effective at-rest earth pressure.

[0055] When it is determined in step S6 that the measurement during extraction is also to be performed, the process proceeds to step S7. The ground where the measurement during extraction can be performed is the case of soil with low adhesion and low ground self-supporting ability. Fig. 8 is a diagram for explaining each step during extraction.

[0056] When the multi-stage cone 1 is pushed in up to the third measurement section 13 with respect to the measurement target depth, the ground is spread out to the diameter indicated by the broken line in Fig. 8(a). Here, if the self-supporting ability of the ground at the measurement target depth is low, the hole wall will collapse when the multi-stage cone 1 is pulled up, and the periphery of the second measurement section 12 that has moved to the measurement target depth will be filled with the collapsed ground.

[0057] Therefore, in step S7, the second measurement section 12 that has moved to the ground at the measurement target depth is pulled out upward, and the measurement of the circumferential shear force at that time is performed by the strain gauge 2. In the second measurement section 12, as shown in Fig. 8(a), a cylinder with a diameter of 2d 2 is pulled out from the ground at the measurement target depth, and when it passes through the strain gauges 2, 2 arranged at the vertical interval L 2 , the circumferential shear force f sa2 is measured.

[0058] Furthermore, in step S8, the first measurement section 11 that has moved to the ground at the measurement target depth is pulled out upward, and the measurement of the circumferential shear force at that time is performed by the strain gauge 2. In the first measurement section 11, as shown in Fig. 8(b), a cylinder with a diameter of 2d 1 is pulled out from the ground at the measurement target depth, and when it passes through the strain gauges 2, 2 arranged at the vertical interval L 1 , the circumferential shear force f sa1is measured.

[0059] FIG. 9 is an explanatory diagram showing a method of obtaining the effective passive earth pressure and the effective active earth pressure from the measurement results of the multi-stage cone 1 and estimating the effective earth pressure at rest. Here, regarding the calculation on the effective passive earth pressure side, similar to the explanation with reference to FIG. 7 in step S10 above, from the measurement results of the circumferential shear force, the effective passive earth pressure (σ’ hp1 , σ’ hp2 , σ’ hp3 ) can be obtained (see FIG. 5).

[0060] On the other hand, for the effective active earth pressure side, the same calculation as on the effective passive earth pressure side can be performed. That is, the displacements that occur when the second measurement unit 12 and the first measurement unit 11 are respectively pulled out from the ground at the measurement target depth are d 2 -d 3 , d 1 -d 3 and can be respectively represented by.

[0061] Also, from the measurement results of the circumferential shear force measured when the second measurement unit 12 and the first measurement unit 11 are respectively pulled out, the effective active earth pressure (σ’ ha2 , σ’ ha1 ) can be obtained. Therefore, as shown in FIG. 9, an approximate line obtained from five points of plotting is created, and the intercept intersecting with the displacement 0 is calculated as the effective earth pressure at rest σ’ h0 , and this value is divided by the effective overburden pressure σ’ v to calculate the earth pressure coefficient at rest K 0 (step S10).

[0062] Next, the method for measuring the earth pressure coefficient at rest of the ground and the action of the multi-stage cone 1 in the present embodiment will be described. The method for measuring the earth pressure coefficient at rest in the present embodiment configured as described above presses the multi-stage cone 1 provided with columnar measurement units (11, 12, 13) having different diameters in three or more stages so as to widen from the tip to the measurement target depth of the ground, and calculates the earth pressure coefficient K 0 based on the measurement results of each measurement unit (11, 12, 13).

[0063] In short, since the multi-stage cone 1 with an improved mechanism of the cone penetration tester is simply pushed into the ground, it can be carried out simply and at low cost. Furthermore, since the hole wall is not disturbed during measurement, the coefficient of earth pressure at rest K with high accuracy 0 can be measured. Also, if it is a measurement method that can be carried out simply and at low cost, it can be carried out at a large number of points, enabling a detailed ground investigation.

[0064] Here, the effective passive earth pressure and the effective active earth pressure can be obtained by dividing by the friction coefficient μ set according to the type of soil at the measurement target depth of the circumferential shear force measurement. Regarding the friction coefficient μ, data can be collected for various soil types in advance by a preliminary test using the multi-stage cone 1, so that the friction coefficient μ can be set with high accuracy. And the coefficient of earth pressure at rest K 0 at the measurement target depth can be easily calculated by simply dividing the effective earth pressure when the displacement is 0 by the effective overburden pressure.

[0065] Also, if the tip resistance is measured at the tip portion 14 of the multi-stage cone 1, the type of soil can be determined simply by pushing the multi-stage cone 1 into the ground at the measurement target depth. Furthermore, if the pore water pressure is measured with the multi-stage cone 1, it can be used for determination of soil type, estimation of groundwater level, liquefaction determination, etc.

[0066] In short, for the multi-stage cone 1 of the present embodiment, there are provided columnar measurement parts (11, 12, 13) with different diameters in three or more stages that are provided so as to widen from the tip, a tip resistance measurement part that measures the tip resistance at the tip portion 14, and a water pressure measurement part 15 that measures the pore water pressure. Therefore, the circumferential shear force generated between the multi-stage cone 1 and the surrounding ground can be measured by the measurement parts (11, 12, 13), and the tip resistance and the pore water pressure can be measured together at once simply by pushing the multi-stage cone 1 into the ground.

[0067] Furthermore, if the measuring parts (11, 12, 13) of the multi-stage cone 1 are pushed in by three or more stages and then pulled out while measuring the circumferential shear force of the measured depth by each measuring part (11, 12), the coefficient of earth pressure at rest K 0 can be calculated more precisely.

[0068] The calculation of the circumferential shear force by each of these measuring parts (11, 12, 13) can be easily performed by obtaining the difference between the upper and lower measurement results of the strain gauges 2, 2 provided at intervals in the vertical direction.

[0069] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0070] For example, in the above embodiment, the multi-stage cone 1 provided with three measuring parts (11, 12, 13) has been described, but the present invention is not limited thereto, and a multi-stage cone having four or more measuring parts can also be used.

Explanation of reference numerals

[0071] 1: Multi-stage cone 11: First measuring part (measuring part) 12: Second measuring part (measuring part) 13: Third measuring part (measuring part) 14: Tip 15: Water pressure measuring part 2: Strain gauge

Claims

1. A method for measuring the coefficient of earth pressure at rest of soil, which measures the coefficient of earth pressure at rest at a measurement target depth of the soil, comprising: preparing a multi-stage cone provided with cylindrical measurement parts having different diameters in three or more stages so as to widen from the tip; pushing the measurement part at the foremost tip of the multi-stage cone into the soil at the measurement target depth; subsequently, sequentially pushing the measurement parts from the second stage and subsequent stages from the tip into the measurement target depth; calculating the coefficient of earth pressure at rest at the measurement target depth based on the measurement results obtained when the multi-stage cone is pushed in; and when pushing in the measurement part, the circumferential shear force is measured by sensors provided on each measurement part, and the coefficient of earth pressure at rest at the measurement target depth is calculated based on the effective earth pressure estimated from the measurement results of the three or more measurement parts. A method for measuring the coefficient of earth pressure at rest of soil, characterized in that.

2. The effective passive earth pressure among the effective earth pressures is obtained by dividing the circumferential shear force by a friction coefficient set according to the type of soil at the measurement target depth. The method for measuring the coefficient of earth pressure at rest of soil according to claim 1, characterized in that.

3. The coefficient of earth pressure at rest at the measurement target depth is calculated by dividing the effective earth pressure when the displacement becomes 0 by the effective overburden pressure. The method for measuring the coefficient of earth pressure at rest of soil according to claim 1 or 2, characterized in that.

4. At the tip of the multi-stage cone, the tip resistance is measured. The method for measuring the coefficient of earth pressure at rest of soil according to any one of claims 1 to 3, characterized in that.

5. In the multi-stage cone, the pore water pressure is measured. The method for measuring the coefficient of earth pressure at rest of soil according to any one of claims 1 to 4, characterized in that.

6. After pushing in three or more of the measurement parts of the multi-stage cone, a step of measuring the circumferential shear force at the measurement target depth by each measurement part while pulling out is provided. The method for measuring the coefficient of earth pressure at rest of soil according to any one of claims 1 to 5, characterized in that.

7. A multi-stage cone pushed into the soil for soil investigation, comprising: cylindrical measurement parts having different diameters in three or more stages provided so as to widen from the tip; a tip resistance measurement part provided at the conical tip for measuring the tip resistance; a water pressure measurement part for measuring the pore water pressure; and two or more pairs of strain gauges are attached to the measurement part in the circumferential direction, and The multi-stage cone is characterized in that the circumferential shear force with the surrounding ground is calculated based on the difference between the upper and lower measurement results of the strain gauge provided at intervals also in the vertical direction.

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