CN102607965A - Double-cross detector and testing method for testing shearing strength values of soil mass in situ - Google Patents

Abstract

The invention relates to an instrument for in-situ testing of the shear strength value of soil, and belongs to the technical field of geotechnical engineering. One-way bearings include upper one-way bearings and lower one-way bearings, and the connectors include upper connectors and lower connectors; the longitudinal sections of the upper connector and the lower connector are funnel-shaped, and the wider ends of the upper connector and the lower connector They are respectively fixed with the upper one-way bearing and the lower one-way bearing, and the upper connecting piece is set on the outside of the lower connecting piece; The shear plate is respectively fixed with the upper connector and the lower connector. The invention can separately measure the shear strength values in the horizontal direction and the vertical direction of the excavated soil, and overcomes the deficiency that the conventional cross-plate shearing instrument cannot separate the two. By separating the shear strength values in the horizontal and vertical directions of the soil, the test accuracy of the in-situ shear strength of the soil is improved.

Description

Double-cross detector and test method for in-situ testing of soil shear strength

technical field

The invention is an instrument for in-situ testing of the shear strength of soil, and relates to a double cross shear plate composed of two identical cross plates with opposite shear directions. The instrument can test the horizontal direction of the soil respectively. and shear strength values in the vertical direction. It belongs to the technical field of geotechnical engineering.

Background technique

At present, the shear strength tests of soil mainly include direct shear test, triaxial test, torsional shear test, unconfined compressive strength test and cross plate shear test, etc. The first four tests are all indoor tests, which need to take soil samples, which will inevitably disturb the soil samples and affect the test accuracy. The cross-plate shear test is an in-situ test method, which can avoid the influence of soil disturbance and is suitable for on-site determination of the in-situ undrained shear strength of saturated cohesive soil. It has the advantages of simple instrument structure and convenient operation. Widely used in construction. However, for soil, due to the different degrees of consolidation or the influence of anisotropy, the shear strength values in the horizontal and vertical directions are generally not equal, and the cross-plate shear test is During the calculation of the strength value, the shear strength values in the horizontal direction and the vertical direction of the soil are regarded as the same value, so the calculation method is not strict, which is a shortcoming of the cross plate shear instrument.

Contents of the invention

The present invention provides a double-cross detector and a testing method for in-situ testing of soil shear strength values aimed at the deficiencies of the above-mentioned instruments and testing methods.

The present invention adopts following technical scheme:

A double-cross detector for in-situ testing of soil shear strength values according to the present invention includes a gear torque device, a torque measuring device, a rotating shaft, a one-way bearing, a connector, and a shear plate; the gear The torsion device drives the rotating shaft. One-way bearings are fixedly sleeved on the shaft near the bottom of the rotating shaft. The shear plate is connected to the rotating shaft through the one-way bearings and connecting pieces. The one-way bearings include upper one-way bearings and lower one-way bearings. The connecting pieces It includes an upper connector and a lower connector; the longitudinal sections of the upper connector and the lower connector are funnel-shaped, and the wider ends of the upper connector and the lower connector are respectively fixed with the upper one-way bearing and the lower one-way bearing, The upper connector is set on the outside of the lower connector; the shear plate is divided into an upper shear plate and a lower shear plate, and the cross section is cross-shaped, and the upper shear plate and the lower shear plate are respectively fixed with the upper connector and the lower connector .

In the double-cross detector for in-situ testing of the shear strength of soil according to the present invention, the relative rotation directions of the upper one-way bearing and the lower one-way bearing are opposite.

In the double-cross detector for in-situ testing of the shear strength of soil according to the present invention, the center of the upper shear plate is in the shape of a circular tube, which is connected to the upper connecting piece and sleeved on the outside of the lower connecting piece.

In the double-cross detector for in-situ testing of the shear strength of soil according to the present invention, the size of the upper shear plate and the lower shear plate are equal.

In the double-cross detector for in-situ testing of the shear strength of soil according to the present invention, the upper shear plate and the lower shear plate are adjacent to each other up and down.

The double-cross detector for in-situ testing of soil shear strength according to the present invention further includes a conical head arranged at the lower center of the lower shear plate.

The detection method of the double cross detector for in-situ testing soil of the present invention, the method is as follows:

1) Assemble the instrument: Align the upper and lower shear plates and press them into the test soil;

2) Start the instrument to conduct an experiment: the gear torque device applies a torque in a certain direction through the rotating shaft to make the rotating shaft rotate in one direction, and drives a cross plate to shear the soil through a set of one-way bearings;

3), measure the absolute value _M of the torque applied to the shear plate when the soil body is sheared through the torque measuring device;

4) Start the instrument for a second experiment: the gear torque device applies a torque in the opposite direction through the shaft to make the shaft rotate in the opposite direction, and another set of one-way bearings drives another cross plate to shear the soil;

5), the absolute value _M2 of the torque applied to the shear plate when the soil body is sheared is measured by the torque measuring device;

6), through the following formula:

ΔM=M ₁ -M ₂

Calculate the resistance moment generated by the shear stress on a horizontal plane when the soil is sheared, and then solve the shear strength value in the horizontal direction;

7) Substitute the resistance moment ΔM in the horizontal direction calculated in step 6 into the following formula:

M ₃ =M ₁ -2ΔM

Calculate the resistance moment generated by the shear stress on the vertical plane when the soil is sheared, and then solve the shear strength value in the vertical direction.

Beneficial effect

The invention can separately measure the shear strength values in the horizontal direction and the vertical direction of the excavated soil, and overcomes the deficiency that the conventional cross-plate shearing instrument cannot separate the two. The invention improves the test accuracy of the in-situ shear strength value of the soil by separating the shear strength values in the horizontal direction and the vertical direction of the soil body. The invention realizes the in-situ test of the anisotropic soil body, and overcomes the disadvantages of complex indoor test operation and soil disturbance. The invention can be used as a new method for the research of anisotropic soil, and fills up the gap in the research on the field characteristics of the anisotropic soil.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a schematic diagram of the double cross shear plate structure of the present invention and its connection with the rotating shaft;

Fig. 3 is a structural schematic diagram of a connector of the present invention;

Fig. 4 is a schematic diagram of a single cross shear plate of the present invention;

Fig. 5 is a cross-sectional view of a cross shear plate of the present invention;

Fig. 6 is the shape figure of the hollow cylindrical soil body that the single shear plate of the present invention is cut;

Fig. 7 is the variation diagram of the soil body undrained shear strength tested with depth in A test area with the present invention;

Fig. 8 is the variation diagram of the undrained shear strength of the soil tested with the depth in the B test area with the present invention;

In the figure: 1 is the gear torque device, 2 is the torque measuring device, 3 is the rotating shaft, 4 is the one-way bearing, 5 is the connecting piece, 6 is the shear plate, 7 is the upper shear plate, 8 is the lower shear plate, 9 is an upper one-way bearing, and 10 is a lower one-way bearing, and 11 is an upper connector, and 12 is a lower connector, and 13 is a conical head.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

As shown in the figure: a double cross detector for in-situ testing of soil, including a gear torque device 1, a torque measuring device 2, a rotating shaft 3, a one-way bearing 4, a connecting piece 5, a shear plate 6, and an upper shear Cutting plate 7, lower shearing plate 8, upper one-way bearing 9, lower one-way bearing 10, upper connector 11, lower connector 12, conical head 13.

The gear torsion device 1 drives the rotating shaft 3, and the shaft body near the bottom of the rotating shaft 3 is fixedly sleeved with a one-way bearing 4. The shear plate 6 is connected with the rotating shaft 3 through the one-way bearing 4 and the connecting piece 5. The one-way bearing 4 includes the upper single One-way bearing 9 and lower one-way bearing 10, connecting piece 5 includes upper connecting piece 11 and lower connecting piece 12. The longitudinal sections of the upper connecting piece 11 and the lower connecting piece 12 are funnel-shaped, and the wider ends of the upper connecting piece 11 and the lower connecting piece 12 are respectively fixed with the upper one-way bearing 9 and the lower one-way bearing 10, and the upper connecting piece 11 is sleeved On the outside of the lower connector 12; the shear plate 6 is divided into an upper shear plate 7 and a lower shear plate 8 and the cross section is cross-shaped, and the upper shear plate 7 and the lower shear plate 8 are respectively connected with the upper connector 11 and the lower Part 12 is fixed. The relative rotation directions of the upper one-way bearing 9 and the lower one-way bearing 10 are opposite. The center of the upper shearing plate 7 is in the shape of a circular tube, connected with the upper connecting piece 11 and sleeved on the outside of the lower connecting piece 12 . The upper shear plate 7 is equal in size to the lower shear plate 8 . The upper shear plate 7 is adjacent to the lower shear plate 8 up and down. The conical head 13 is arranged at the central lower end of the lower shear plate 8 .

The detection method of the double cross detector used to test the shear strength value of the soil in situ cuts the soil successively through two adjacent shear plates of the same size, so that the soil that has been sheared twice has a common The shear surface of the soil is calculated from the torques of the two shear tests to calculate the shear stress resistance moments in the horizontal and vertical directions of the soil, and then solve the shear strength values in the horizontal and vertical directions respectively. Methods as below:

The first step is to align the upper and lower shear plates, press them into the test soil, apply a torque in a certain direction to make the shaft rotate in one direction, drive a cross plate to shear the soil through a set of one-way bearings, and measure the soil by torque The device measures the absolute value M ₁ of the torque applied to the shear plate when the soil is sheared;

The second step is to apply torque in the opposite direction to make the shaft rotate in the opposite direction, and another set of one-way bearings drives another cross plate to shear the soil, and when the soil is broken through the torque measuring device, it is applied to the shear plate The absolute value of the torque on M ₂ .

The soil that was sheared for the first time and the soil that was sheared for the second time have a common shear plane, and the torque difference between the two shear tests is the shear force on the common shear plane when the soil is sheared. Resisting moment due to stress.

Assume that the shear strength value of the soil in the horizontal direction is τ ₁ , and that in the vertical direction is τ ₂ ; the height of a single shear plate is a, the width is D, and the diameter of the circular tube in the center of the shear plate is d( As shown in Figure 5), the soil body sheared by a single plate is a hollow cylinder (as shown in Figure 6), the inner diameter of the hollow cylindrical soil body is equal to the diameter d of the circular tube at the center of the shear plate, and the outer diameter is equal to the shear diameter d The width D of the plate is equal and the height is equal to the height a of the shear plate.

When the soil is sheared, the resistance moment produced by the shear stress on a horizontal plane is

ΔM=M ₁ -M ₂ (1)

When the soil is sheared, the resistance moment produced by the shear stress on the vertical plane is

M ₃ =M ₁ -2ΔM=2M ₂ -M ₁ (2)

On the vertical plane, the shear strength value of the soil is τ ₂ when the soil is broken, then there is,

M ₃ =πD(D/2)aτ ₂ (3)

Right now,

τ ₂ =2M ₃ /(πD ² a) (4)

On the horizontal plane, assuming that the shear stress distribution function on the soil is τ=f(τ ₁ ) when the soil is sheared, we have,

$\mathrm{<span\; class="notranslate">\; \&Delta;M</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; rdrd\&theta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

mark as,

ΔM=g(τ ₁ ) (6)

Using the inverse function operation, we can get,

τ ₁ = g ^-1 (ΔM) (7)

If d is much smaller than D, the hollow cylinder can be treated as a solid cylinder to simplify the calculation. Assuming that the shear stress on the horizontal plane is linearly distributed when the soil is sheared, the center of the circle is zero and the circumference is the maximum value, that is, the shear strength value τ ₁ in the horizontal direction, then:

ΔM=πD ³ τ ₁ /16 (8)

have to,

τ ₁ =16ΔM/(πD ³ ) (9)

Through the above tests and calculations, the shear strength values τ ₁ and τ ₂ in the horizontal and vertical directions of the soil can be easily calculated.

Example 1

The in-situ shear test of the soil was carried out in the A test area. The specifications of the cross plate are: the height of a single plate is 30mm, the width is 90mm, the aspect ratio is 1:3, and the diameter of the circular tube in the center of the shear plate is 11.5mm. Soil quality is silt, and test point spacing is 1m (every 1m is done a test), τ ₁ is the horizontal shear strength value (assuming in the calculation that the shear stress on the horizontal plane is linearly distributed with the inventive method test, and the center of circle is zero, and the circumference place is the maximum value τ ₁ ), τ ₂ is the vertical shear strength value tested by the inventive method, and τ ₃ is the shear strength value tested next to the aforementioned test site using a conventional cross-plate shearer, and the test results are shown in the table 1. The variation of intensity C _u (KPa) with depth h (m) is shown in Figure 7.

Table 1 Test values of test area A

Example 2

Carry out the in-situ shear test in the B test area, the specification of the cross plate is the same as in Example 1, the soil quality of the test area is silt and silty clay, the test point spacing is 1m, the meaning of τ ₁ , τ ₂ , τ ₃ is the same as in Example 1 The same, the test results are shown in Table 2, and the variation of intensity C _u (KPa) with depth h (m) is shown in Figure 8.

Table 2 Test values of test area B

From the results of the above two tests, it can be seen that the horizontal shear strength value τ ₁ and the vertical shear strength value τ ₂ of the soil tested by the instrument and test method of the present invention are _regularly distributed. The h diagram shows that the τ ₂ -h line roughly coincides with the τ ₃ -h line, which is consistent with the test value of the conventional cross-plate shearer mainly reflecting the shear strength value on the vertical surface of the soil; the τ ₁ -h line On the right side of the τ ₂ -h line, the value of τ ₁ is larger than the value of τ ₂ , because the effective consolidation stress σ _cz before shearing on the horizontal plane of the soil is a large principal stress, and the strength on this plane is a large value, and the vertical The pre-shear effective consolidation stress k ₀ σ _cz on the surface is a small principal stress, and the strength on this surface is a small value. The test results show the anisotropy of the soil. The test proves that the instrument and test method of the present invention can test the shear strength values of the anisotropic soil in the horizontal direction and the vertical direction respectively, which can provide new methods and ideas for the research of the anisotropic soil and fill in the anisotropic soil. Blanks in the study of soil field properties.

Claims (7)

1. a diesis detector that is used for in-situ test soil shear strength value comprises gear torque force device (1), torque-measuring apparatus (2), rotating shaft (3), unilateral bearing (4), web member (5), shear plate (6); Described gear torque force device (1) drives rotating shaft (3); The axle body place near the bottom of rotating shaft (3) fixedly is nested with unilateral bearing (4); Shear plate (6) links to each other with rotating shaft (3) with web member (5) through unilateral bearing (4); It is characterized in that: unilateral bearing (4) comprises unilateral bearing (9) and following unidirectional bearing (10), and web member (5) comprises upper connector (11) and following web member (12); The longitudinal section funneling of described upper connector (11) and following web member (12); One end of upper connector (11) and following web member (12) broad is fixed with last unilateral bearing (9), following unidirectional bearing (10) respectively, and upper connector (11) is nested with the outside at following web member (12); Shear plate (6) is divided into shear plate (7) and down cut plate (8) and xsect across, and last shear plate (7) and down cut plate (8) are fixed with upper connector (11), following web member (12) respectively.

2. the diesis detector that is used for in-situ test soil shear strength value according to claim 1 is characterized in that: relatively rotating of last unilateral bearing (9) and following unidirectional bearing (10) is in the opposite direction.

3. the diesis detector that is used for in-situ test soil shear strength value according to claim 1 is characterized in that: the center of last shear plate (7) is cylindrical, is connected with upper connector (11) and is nested with descending web member (12) outside.

4. the diesis detector that is used for in-situ test soil shear strength value according to claim 1 is characterized in that: the equal and opposite in direction of going up shear plate (7) and down cut plate (8).

5. the diesis detector that is used for in-situ test soil shear strength value according to claim 1 is characterized in that: it is neighbouring with down cut plate (8) to go up shear plate (7).

6. the diesis detector that is used for in-situ test soil shear strength value according to claim 1 is characterized in that: also comprise nose cone (13), described nose cone (13) is arranged in the lower end, center of down cut plate (8).

7. utilize the described detection method that is used for the diesis detector of the in-situ test soil body of claim 1, it is characterized in that: method is following:

1), assembling instrument: two shear plate alignment up and down are pressed in the test soil body;

2), start instrument and once test: gear torque force device (1) applies through rotating shaft (3) and a certainly makes rotating shaft towards one to rotation to moment of torsion, through four-bladed vane of one group of unilateral bearing drive the soil body is sheared;

3), measure the absolute value M that puts on the moment of torsion on the shear plate when soil body is broken through torque-measuring apparatus (2) ₁

4), starting instrument carries out the secondary experiment: gear torque force device (1) applies the opposite direction moment of torsion through rotating shaft (3) rotates rotating shaft in the opposite direction, drives another piece four-bladed vane through another group unilateral bearing the soil body is sheared;

5), measure the absolute value M that puts on the moment of torsion on the shear plate when soil body is broken through torque-measuring apparatus (2) ₂

6), through following formula:

△M=M ₁－M ₂

Calculate soil body moment of resistance that shear stress produced on a surface level when breaking, and then find the solution the shearing strength value on the horizontal direction;

7) the following formula of moment of resistance △ M substitution on the horizontal direction that, step 6 is calculated:

M ₃=M ₁－2△M

Calculate soil body moment of resistance that shear stress produced on vertical plane when breaking, and then find the solution the shearing strength value on the vertical direction.

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