JP2003227786A - Method and apparatus for measuring shear strength in soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and quickly measure the adhesive force of a soil layer and an inner friction angle by directly performing a shear test in the soil layer for a number of portions in a field such as a mountain slope. <P>SOLUTION: In a shear strength-measuring apparatus 1 having a cone tip tool, a rod, a spring scale 4, and a grip 5 that are assembled by each combination, two kinds of cone tip tools, namely a cone tip tool 9 without any blade and a cone tip tool 11 having a blade, are exchanged each other and are mounted freely for pushing each into the soil layer, a specific depth load is applied and at the same time rotation is made for measuring torque, direct stress and shear stress are obtained from each torque difference between the cone tip tool 9 without any blades and the cone tip tool 11 having a blade, and the adhesive force and the inner friction of the soil layer are obtained based on it. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring soil shear strength, and in particular on a slope of a mountain,
The present invention relates to a soil shear strength measuring method and device useful in the field of slope disaster prevention, which measures the soil depth and shear strength of a slope easily and in a short time in order to estimate a place where slope failure is likely to occur.

[0002]

2. Description of the Related Art On a slope of a mountainous area, it is necessary to measure the depth of the soil layer up to a portion of hard soil or rock below the surface layer of soft soil, and to measure and grasp the shear strength of that portion. This is important for estimating the places where collapse such as slopes is likely to occur.

As described above, in order to measure the soil layer depth for the purpose of slope disaster prevention, a simple dynamic cone penetration tester as shown in FIG. 5, for example, has been conventionally used. This simple dynamic cone penetration tester and test method uses a guide rod to guide a hammer (weight) having a mass of 5 kg from a height of 50 cm, and a conical tip cone (tip angle 60 degrees, diameter 25
The hardness and the depth of the soil layer are measured from the number of drops required for the tip cone to penetrate 10 cm by dropping and colliding with a rod knocking head having a diameter of 10 mm.

Generally, the hardness of the soil layer where slope failure is likely to occur is the Nd value of the simple dynamic cone penetration test (the number of drops of the weight required for the tip cone and the rod to penetrate 10 cm).
It is said that about 5 to 10 or less.

In addition, as a soil strength measuring device for conducting a penetration test, the inventions described in JP-A-9-15126 are known.

Conventionally, in the stability analysis of slopes, the adhesive force and the internal friction angle have been required, and generally, a plurality of samples are taken from the ground and determined by a triaxial compression test or a single shear test in a room. ing.

Further, there is a method of measuring the pure shear strength by rotating a blade (vane shear test) as a method of measuring the shear strength at a site such as a slope of a mountain. Since it cannot be applied, the internal friction angle cannot be measured, and the measurement is limited to extremely soft soil, and the strength of a slightly hard soil layer involved in slope failure cannot be measured. Similarly in other penetration tests, there is no method that can easily determine the internal friction angle of soil on site.

[0008]

The present invention has the following two specific problems in the background of the above-mentioned conventional techniques and problems.

(1) Problems related to measurement of soil depth In the simple dynamic cone penetration test, the total weight of the equipment is about 10 kg, not only is it inconvenient to transport on a steep mountain slope, but also the weight of 5 kg is measured. Since it is a method of repeatedly dropping, it is usually necessary for two people to work on one measurement,
In that case, the measurement time is generally 10 minutes to several tens of minutes at one location, and there is a danger that the weight is likely to be caught and a finger is easily injured.

Since the soil depth of the slope greatly differs depending on the location, it is necessary to conduct a large number of tests at as many locations as possible, but due to the above-mentioned drawbacks, it is possible to sufficiently grasp the heterogeneity of the soil depth of the slope. It is a problem in slope disaster prevention that the test cannot be performed. The present invention solves such a problem.

(2) Problems concerning measurement of shear strength The shear strength of the soil layer on the slope is generally expressed by the internal friction angle φ and the internal friction angle C because of the necessity of performing the slope stability analysis. The conventional method for obtaining the internal friction angle φ and the internal friction angle C is
Excavated several tens of cm to several m, diameter 5 cm from the ground, length 1
It is necessary to collect 3 to 4 undisturbed samples of about 0 cm, and it is necessary to transport the samples so as not to break them and test them indoors. The present invention solves such a problem.

[0012]

In order to solve the above problems, the present invention uses a bladed cone attached to the tip of a rod to load in the rod direction and apply a vertical load to the soil around the cone with respect to the shear plane. A method for measuring soil shear strength, characterized in that the shear strength of soil under a predetermined vertical load with respect to the shear plane is obtained by performing torque measurement while rotating around the axis of the rod while applying it. To do.

In order to solve the above-mentioned problems, the present invention pushes a bladeless cone tip attached to the tip of a rod into the soil and rotates it around the axial center of the rod without load in the depth direction. Torque is measured, the winged cone tip tool attached to the tip of the rod is pushed into the soil, and while applying the same depth direction load as the above predetermined depth direction load, the rod is rotated about the axial center of the rod and the second Torque is measured, and the combination of the first torque measurement and the second torque measurement is performed a plurality of times by changing the depth direction load, and each measurement of the torque measurement combination is obtained. Provided is a method for measuring soil shear strength, characterized in that the adhesive force and internal friction coefficient of soil are obtained from the direct stress and shear load on the surface of the cone.

In order to solve the above problems, the present invention slowly pushes a soil shear strength measuring device having a bladeless cone tip, a rod, a spring scale and a handle into the soil from the bladeless cone tip, The pushing force is stopped, the shear strength measuring device is rotated about the axial center of the rod in the absence of a load in the depth direction, and the first torque, which is the friction on the peripheral surface of the rod, is measured. At the location where the measurement was performed or at a location displaced therefrom, a shear strength measuring device for soil having a bladed cone tip, a rod, a spring scale and a handle was slowly pushed into the soil from the bladed cone tip, Stop the pushing, rotate the shear strength measuring device around the axial center of the rod while applying a predetermined depth direction load, perform the second torque measurement, and obtain the second torque measurement. The torque obtained in the first torque measurement is subtracted from the obtained torque to obtain the shear torque acting on the surface of the cone sheared by the blades, and the surface of the cone is determined by the predetermined depth load and the shear torque. The combination of the first torque measurement and the second torque measurement, which is combined with the above-mentioned first torque measurement and the second torque measurement, is used for the combined torque measurement by shifting the measurement points and changing the magnitude of the predetermined depth load. The shear strength of soil, which is characterized in that the direct stress and shear stress obtained based on the measurement results of the combined torque measurement performed each time are plotted on the graph to obtain the adhesive force and internal friction angle of the soil layer. Provide a measurement method.

The soil shear strength measuring device having the bladed cone tip, rod, spring scale, and handle is the blade in the soilless shear strength measuring device having the bladeless cone tip, rod, spring scale, and handle. None The cone tip may be replaced with the bladed cone tip described above.

In order to solve the above problems, the present invention is a shear strength measuring device having a cone tip, a rod, a spring scale and a handle, wherein the cone tip, the rod, the spring scale and the handle are screwed together when used. It is assembled and disassembled when not in use, and it can be disassembled when not in use. There are two types of cone tips, a bladeless cone tip and a bladed cone tip, and these two types of cone tips are interchangeable with each other. Provided is a soil shear strength measuring device which is used by being connected to a rod.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method and apparatus for measuring shear strength of soil according to the present invention will be described below based on Examples with reference to the drawings. The present invention can easily measure the depth of a soil layer up to a portion consisting of hard soil or rock under a soft soil layer where slope failure easily occurs, such as in a mountain slope, by a penetration test. The shear strength of the soil layer is measured.

(Measurement Apparatus) FIG. 1 is a diagram showing a shear strength measurement apparatus for carrying out the soil shear strength measurement method of the present invention, and an embodiment of the soil shear strength measurement apparatus of the present invention. FIG. In FIG. 1 (a), this shear strength measuring device 1 comprises a cone tip, a rod 3, a spring scale 4 (cylindrical tension gauge) and a handle 5.

The cone tip 2 is formed by annealing a steel material, and is formed integrally with a cone-shaped cone 6, a neck portion 7 and a shaft portion 8. The cone tip 2 according to the present invention is characterized in that the cone is a cone tip having a normal cone as shown in FIG. 1A (this is referred to as a “bladeless cone tip”) 9. As shown in FIG. 1 (b), the cone is composed of two types, a cone tip tool (this is a “blade cone tip tool”) 11 having a blade 10 attached thereto.

The bladed cone tip unit 11 is constructed by integrally mounting a plurality of blades 10, four blades 10 in a radial manner on the outer surface of a normal cone 6 at equal angular intervals. Two types of cone tips, such as the bladeless cone tip 9 and the bladed cone tip 11, are interchangeably screwed to the rod 3 and can be used in each torque measurement described later.

The rod 3 is made of a material such as high-strength stainless steel, and it is advisable to prepare rods of several different lengths that can be applied to the soil layer environment of the place to be measured. The handle 5 has a size that can be gripped by the user's hand, and is formed with left and right hollow portions 12 open at both left and right ends.
A torque wrench is attached and used when the shear strength measurement described below is performed.

The cone tip, rod 3, spring scale 4 and handle 5 can be disassembled and carried when not in use. When used, they can be screwed together and assembled as shown in FIG. That is, the upper end of the cone tip 2 can be screwed to the lower end of the rod 3, the upper end of the rod 3 can be screwed to the lower shaft of the spring scale 4, and the upper shaft of the spring scale 4 can be screwed. The handle 5 can be screwed onto the handle 5.

Here, a method for measuring the shear strength of soil according to the present invention will be described using the shear strength measuring apparatus 1 for soil according to the present invention. Specifically, it is a method of measuring the soil layer depth using the shear strength measuring device 1 and measuring the adhesive force and the internal frictional force.

(Measurement of soil layer depth) A method for measuring the soil layer depth by performing a penetration test using the shear strength measuring device 1 will be described. The cone tip 2 may be without blades or with blades, but in any case, the cone tip 2 (with or without blades) has a diameter of 15 mm and an end angle of 60 mm.
It is a cone of degree. The diameter of the shaft portion 8 and the rod of the cone tip 2 is 10 mm.

This shear strength measuring device 1 is put into the layer from the cone tip tool 2 by a human power at a maximum of 500 N (about 50 kg).
Depressed gently with the force of the force, depthwise load W (load applied when pushing in, load measured by spring scale 4)
And the amount of penetration of the rod into the soil at that time is measured. The depth direction load W increases rapidly when it is near a soil layer composed of hard soil or rock under a soft soil layer. Therefore, measure the depth with the depth direction load W and the penetration amount of the rod at that time. You can

[0026] With such a measuring method, actual measurement experiments were carried out for Utsukuba (granite weathered soil), Kochi (Shimanto layer weathered soil) and Ehime (former riverbed gravel layer). The experimental data is shown in FIG. As can be understood from the results of this experiment, according to this measurement method, when pushed with a force of 500 N, the hardness of the soil layer where slope failure easily occurs is 5
It can penetrate to a hardness equivalent to Nd value 15 which is slightly harder than -10.

This soil depth measuring method differs from the conventional soil cone depth measuring method using a dynamic cone penetration tester in that the rod is gently pushed into the soil layer of the slope from the cone tip tool. It is characterized by determining the depth of the soil layer. The total weight of the device is about 4 kg, about 1/3 of the conventional simple dynamic cone penetration tester, and it can be disassembled and assembled freely, so it is sharp. Even in the mountains, it is easy to carry and handle, and the test method is simple, so one person can easily perform the measurement work.

Further, the method for measuring the soil layer depth is as follows:
The measurement time at the location is about 1 to 2 minutes, which is about 1/5 or less of the efficiency of the simple dynamic cone penetration test, so that it can be grasped in a short time even at a location where the soil depth on the slope is inhomogeneous. Furthermore, unlike the conventional penetration test, it is safe because it does not use a falling weight.

(Measurement of Adhesive Force and Internal Friction Force) Next, a method for measuring the adhesive force and internal friction force of the soil layer will be described. In this method of measuring the adhesive force and the internal frictional force, the following combined torque measurement is performed by changing the depth load W conditions. Torque measurement by shear strength measuring device 1 having vaneless cone tip 9 (this is referred to as "first torque measurement", see FIG. 3 (a).) Shear strength measuring device 1 having vane cone tip 11 Torque measurement (this is referred to as “second torque measurement”; refer to FIG. 3B). Hereinafter, the first torque measurement and the second torque measurement will be specifically described.

First, the first torque measurement (see FIG. 3A) is performed. The bladeless cone tip tool 9 is attached to the tip of the rod 3, and the depth is grasped by the above-mentioned soil layer depth measuring method, and the adhesive force and the internal friction angle are measured at a predetermined depth (for a soft soil layer). Push it to the depth near the boundary of the hard soil layer). Then, it penetrates to a predetermined depth, stops pushing, and in this state with no load in the depth direction, a wrench with a torque meter is appropriately attached to the handle 5 to attach the shear strength measuring device 1 to the shaft of the rod 3. Slowly rotate around the center of the screw so that the screws do not loosen.

The maximum torque T ₀ during this rotation is measured with a torque meter. The maximum torque T ₀ is a torque generated by the intrinsic friction of the measuring system such as the rod 3. After the torque measurement is completed, the shear strength measuring device 1 is pulled out from the soil.

Next, the second torque measurement (see FIG. 3B) is performed. Remove the bladeless cone tip 9,
Replace with the bladed cone tip tool 11 shown in FIG. Then, the blade tip cone end tool 11 and the rod of the shear strength measuring apparatus 1 are gently pushed into the soil layer at the location where the shear strength measuring apparatus 1 is pulled out or at a location slightly displaced from the location.

When the soil layer depth is grasped while being pushed in this way and the predetermined depth which is the same as the soil layer depth at the time of the first torque measurement is reached, the torque meter is applied while applying the depth direction load W _1. The shear strength measuring device 1 is slowly rotated with a wrench.

The maximum torque T ₁ during this rotation is measured with a torque meter. At this time, the rotational torque T applied to the soil along the bladed cone 6 (the soil where the shearing load is applied by the blades) is T = T by subtracting the torque T ₀ generated by the inherent friction of the measurement system such as the rod 3. _1- T ₀
Is.

Under this circumstance, the direct stress σn and the shear stress τ of this shear test are calculated as follows.
However, the stress distribution acting on the surface sheared by the blades is uniform for both the direct stress σn and the shear stress τ. or,
Friction between the cone and soil and shearing of the neck 7 are not considered.

FIG. 3 (c) is a schematic view of the cone. Overall Cone Height: H In FIG. 3C, consider a fan-shaped micro area of the cone shear surface at a point of height h from the cone tip. Cone tip angle (angle with respect to the axis of the inclined surface of the cone):
θ If the height from the cone tip of the minute area part is h, the distance from the cone tip to the minute area part is: l (this l
Is a lower case ell. ) L = h / cos θ A sectoral minute area of the cone shearing surface = ldψ · dl.

Shear stress acting on a minute area: τ Torque due to shear stress acting on a minute area: t The torque t due to shear stress τ acting on this minute area is as follows. Arm length = htan θ t = τ · htan θ · ldφ · dl. By the way, since 2πHtan θ = ψH / cos θ, ψ = 2πsin θ. The total torque T obtained by integrating the torque t related to the small area with respect to the entire shear surface is obtained, and the shear stress τ is expressed by this torque T as shown in the following mathematical formula 1.

[0038]

[Formula 1]

FIG. 3D is a side view of the cone. As shown in this figure, since the sum of the vertical components of the normal stress σn acting on the cone shear surface is equal to the depth direction load W, the normal stress σn is given by the following mathematical formula 2.

[0040]

[Formula 2]

The first torque measurement and the second torque measurement have been described above in the case of the depth direction load W = W ₁ , but the measurement in which the depth direction load W is measured is a combination of such measurements. Are tested under different conditions, and the above calculation is performed based on the test results to obtain the direct stress σn and the shear stress τ.

A plurality of direct stresses σn thus obtained
And shear stress τ, the direct stress σn is the horizontal axis (X axis)
The shear stress τ is plotted on the vertical axis (Y axis) in FIG.
An XY graph as shown in (e) is created. If the Y-intercept c and the slope tanφ of this graph are calculated, τ = σn · tanφ
From the formula + c, the adhesive force c and the internal friction angle φ can be obtained.

Thus, according to the soil shear strength measuring method and apparatus 1 of the present invention, the bladeless cone tip 9
By using the bladed cone tip device 11, the shear test can be performed at the measurement site while generating vertical stress (load in the depth direction), and the adhesive force and the internal friction angle can be measured.

The embodiment of the method and apparatus for measuring the shear strength of soil according to the present invention has been described above with reference to the examples.
The present invention is not particularly limited to such an embodiment,
It goes without saying that there are various embodiments within the scope of the technical matters described in the claims.

For example, in the above embodiment, the cone tip 2 with blade is used as the cone tip 2 of the shear strength measuring device 1.
1 and a bladeless cone tip 9 were prepared and screwed to the rod 3 so as to be interchangeable with each other. However, without doing so, the shear strength measuring device 1 with the bladeless cone tip 9 detachably attached was used. By preparing and using in advance two types of shear strength measuring devices to which the bladed cone tip 11 is detachably attached, it is possible to save the labor of replacing the cone tip.

[0046]

According to the soil shear strength measuring method and apparatus of the present invention having the above-described structure, the following effects are obtained.
That is, on a mountain slope or the like, the work environment for the penetration test is bad, and the soil layer depth greatly differs depending on the position of the slope, so it is necessary to perform the test at many places.

Even under such severe conditions, the method and apparatus for measuring soil shear strength according to the present invention is compact in size, and by using a cone with blades, vertical stress is generated. However, by performing the shear test in-situ, it is possible to measure the internal friction angles at many places directly and relatively easily in a short time. Therefore, there is no need to bring back the sample, and it is extremely useful for promptly and accurately estimating a place where slope failure is likely to occur on a mountain slope or the like.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a shear strength measuring device for soil according to the present invention, (a) shows a shear strength measuring device with a bladeless cone tip, and (b) shows a bladed cone tip. FIG.

FIG. 2 is a diagram for explaining an experimental example of soil layer depth using the soil shear strength measuring device according to the present invention.

FIG. 3 is a diagram illustrating a method for measuring an adhesive force and an internal frictional force of a soil layer using the soil shear strength measuring method and device according to the present invention.

FIG. 4 is a diagram illustrating a conventional simple dynamic cone penetration tester.

[Explanation of symbols]

1 Shear strength measuring device 2 cone tip 3 rod 4 Spring balance (cylindrical tension gauge) 5 handles 6 cones 7 neck 8 shafts 9 Bladeless cone tip 10 feathers 11 Cone tip with blade 12 Hollow part of handle

Claims (5)

[Claims] 1. A torque measurement is performed by using a cone with blades attached to the tip of a rod, rotating the rod around the axis of the rod while loading in the rod direction and applying a vertical load to the soil around the cone with respect to the shear plane. A method for measuring the shear strength of soil, characterized in that the shear strength of the soil under a predetermined vertical load with respect to the shear plane is obtained by carrying out. 2. The bladeless cone tip attached to the tip of the rod is pushed into the soil, and the first torque is measured by rotating the rod about the shaft center with no load in the depth direction. Push the bladed cone tip attached to the tip into the soil and rotate the rod about the axial center of the rod while applying the same depth direction load as the above predetermined depth direction load to measure the second torque. The combination of the torque measurement of 1 and the measurement of the second torque is performed a plurality of times by changing the depth direction load, and the direct stress on the surface of the cone is obtained for each measurement of the combination of the torque measurement. A method for measuring the shear strength of soil, which comprises obtaining the adhesive force and the internal friction coefficient of the soil from the shear load. 3. A soil shear strength measuring device having a bladeless cone tip, a rod, a spring scale, and a handle is slowly pushed into the soil from the bladeless cone tip, the pushing is stopped, and a depth direction load is applied. In the state where there is no pressure, the above-mentioned shear strength measuring device is rotated around the axial center of the rod to measure the first torque which is the friction of the peripheral surface of the rod, and then the position where the first torque measurement is performed or the displacement from that position. The cone tip with a blade, rod,
Slowly push the soil shear strength measuring device with a spring scale and handle into the soil from the bladed cone tip tool, stop the pushing, and shear around the rod axial center while applying a predetermined depth direction load. The strength measuring device is rotated to perform the second torque measurement, and the torque obtained in the first torque measurement is subtracted from the torque obtained in the second torque measurement to obtain the surface of the cone sheared by the blades. The shear torque acting on the cone is obtained, the direct stress and the shear stress acting on the surface of the cone are obtained by the predetermined depth load and the shear torque, and the combination of the first torque measurement and the second torque measurement is combined. Torque measurement is performed multiple times by shifting the measurement points and changing the size of the above-mentioned depth load, and is obtained based on the measurement result of the combined torque measurement of each time. The normal stress and shear stress which, shear strength measuring method of soil and obtaining the adhesion and internal friction angle of the soil layer is plotted on a graph. 4. A cone tip tool with a blade, a rod,
The soil shear strength measuring device having a spring scale and a handle has the bladeless cone tip in the bladeless cone tip, the rod, the soil shearing strength measuring device having a spring scale and a handle as the bladed cone tip. The soil shear strength measuring method according to claim 3, wherein the soil is replaced. 5. A shear strength measuring device having a cone tip, a rod, a spring scale and a handle, wherein the cone tip, the rod, the spring scale and the handle are assembled by being screwed together when in use, and not used. There are two types of cone tips, a bladeless cone tip and a bladed cone tip, and these two types of cone tips are interchangeably connected to the rod for use. Shear strength measuring device characterized by.