In-situ testing device for shear strength of loess

Abstract

The loess shear strength in-situ testing device comprises two underframe rods which are equal in height and are arranged in parallel at an interval, a mounting frame is arranged at the tops of the two underframe rods, a probe rod is longitudinally mounted on the mounting frame, the probe rod is driven by a driving mechanism to move up and down, ground anchors are arranged on the two sides of the bottom of each underframe rod, and the lower portion of the probe rod is connected with a force measuring steel bar meter. The output end of the force-measuring reinforcement meter is electrically connected with the input end of the shear strength data acquisition instrument, and the lower end of the force-measuring reinforcement meter is connected with an isosceles right triangle-shaped pressure-bearing plate with a flat plate surface. According to the utility model, the bearing plate at the bottom of the feeler lever abuts against a specified detection position of a to-be-detected area and applies a vertical force downwards, the force measuring reinforcement meter transmits stress change to the shear strength data acquisition instrument, and the shear strength data acquisition instrument automatically obtains shear strength parameters of the specified detection position; the test principle is basically the same as that of a direct shear test, and related principles can be directly utilized; the disturbance to the soil body is smaller than that of an indoor test, and the result is more reliable.

Description

Technical Field

[0001] The utility model patent relates to the field of loess shear strength testing, and specifically to an in-situ testing device for loess shear strength. Background Art

[0002] Due to the adverse engineering properties of loess, such as collapsibility and water sensitivity, engineering construction in loess areas needs to pay special attention to the accurate testing of various parameters of the original soil in the early exploration work. The shear strength of loess is a basic parameter for determining the slope parameters and foundation bearing capacity in geotechnical engineering problems. It is a controlling indicator for engineering construction. Obtaining accurate loess shear strength is crucial for engineering construction activities.

[0003] At present, the devices used for in-situ testing of loess shear strength parameters include static penetration testers, lateral pressure testers, flat shovel lateral expansion testers, etc. These devices have been widely used in loess areas, but it is difficult to control boundary conditions, such as drainage and stress conditions, during the testing process of these devices. The relationship between the measured data and the engineering properties of the rock and soil is still based on a large number of statistical empirical relationships, and the loess shear parameters are obtained indirectly. There is no strict theoretical basis, and the shear strength parameters obtained are affected by regional empirical formulas. There is uncertainty, which affects the quality of the project. At present, there is no device on the market that can directly and accurately test the shear strength parameters of loess. Therefore, there is an urgent need for a device that is easy to operate, low cost, and accurate in data to test the shear strength parameters of loess in situ. Utility Model Content

[0004] The utility model aims to solve the problems existing in the prior art in-situ testing device for the shear strength of loess, and provides an in-situ testing device for the shear strength of loess which is convenient to operate, low in cost and has accurate test data.

[0005] In order to achieve the above purpose, the technical solution adopted by this utility model is:

[0006] A loess shear strength in-situ testing device comprises two base rods of equal height and parallel spacing, a mounting frame is provided on the top of the two base rods, a probe rod is longitudinally mounted on the mounting frame, and the probe rod is driven up and down by a driving mechanism, a force measuring steel bar meter is connected to the lower part of the probe rod, the output end of the force measuring steel bar meter is electrically connected to the input end of a shear strength data acquisition instrument, the lower end of the force measuring steel bar meter is connected to an isosceles right triangle pressure plate with a flat plate surface, and ground anchors are provided on both sides of the bottom of the base rod.

[0007] Furthermore, both ends of the base frame rod are connected to a fixing frame, the ground anchor is threadedly connected to the fixing frame, and the top ends of the two ground anchors are connected by a transmission chain and rotate synchronously.

[0008] Furthermore, a sliding sleeve is mounted on the outer side of the mounting frame, and cantilever frames are connected to both sides of the sliding sleeve. The cantilever frame is connected to the ground anchor through a bearing seat, and a sprocket is arranged on the top of the ground anchor. The two sprockets are connected by a transmission chain, and the driving unit drives one of the sprockets to rotate.

[0009] Furthermore, the mounting frame is composed of two channel steels arranged at intervals with grooves opposite to each other, a top plate is installed at the upper end of the mounting frame, a bottom plate is installed at the lower end of the mounting frame, a conveyor chain is arranged between the top plate and the bottom plate, one side of the conveyor chain is clamped and connected to the rod body of the probe rod by a pressure-bearing clamp, and the conveyor chain is driven by a driving mechanism.

[0010] Furthermore, guide sleeves are installed on the top plate and the bottom plate, and the probe rod passes through the guide sleeves.

[0011] Furthermore, the driving mechanism includes a transmission shaft installed on a mounting frame, the transmission shaft is located horizontally and arranged parallel to the axle of the sprocket at the upper end of the conveying chain, the axle and the transmission shaft are matched through gear transmission, a handle frame is provided on the outer side of the mounting frame, a mounting seat is mounted on the handle frame, a gear shaft is rotatably provided on the mounting seat, the transmission gear on the gear shaft is matched with the transmission shaft through a belt or chain transmission, and a hand crank is connected to the outer shaft end of the gear shaft.

[0012] Compared with the prior art, the utility model has the following beneficial technical effects:

[0013] 1. The utility model utilizes the pressure plate at the bottom of the probe rod to counteract the designated detection position of the area to be detected and applies vertical force downward. The force measuring steel bar meter transmits the stress change to the shear strength data acquisition instrument, and the shear strength data acquisition instrument automatically obtains the shear strength parameters of the designated detection position. The operation is convenient and the test principle is the same as that of the direct shear test. The disturbance to the soil body using the utility model is smaller than that of the indoor test, and the result is more reliable.

[0014] 2. The utility model is based on the Mohr-Coulomb theory, which reflects the strength characteristics of rock and soil more comprehensively. The utility model obtains the normal stress and shear stress on the loess shear failure surface through the force measuring steel bar meter and the pressure plate, and uses the least square method to obtain the coefficients of the Coulomb equation, and then obtains the loess cohesion and friction angle parameters, and the test is more accurate.

[0015] 3. The top ends of the ground anchors at both ends of the base frame rod of the utility model are connected by a transmission chain to form a synchronous rotation match. When one of the ground anchors is rotated, the other ground anchor can also be rotated synchronously, realizing the synchronous screwing in and out operation of the ground anchors, which can quickly complete the fixing or releasing of the whole machine, improve the operating efficiency of the ground anchor of the whole machine, and quickly carry out the test operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional appearance schematic diagram of the utility model;

[0017] Figure 2 for Figure 1 A-direction view in the figure;

[0018] Figure 3 for Figure 1 The b-direction view in the figure;

[0019] Figure 4 It is a schematic diagram of the bottom structure of the bottom frame rod;

[0020] Figure 5 for Figure 4 A magnified view of part A in FIG.

[0021] Figure 6 It is a partial structural schematic diagram of the utility model;

[0022] Figure 7 It is a schematic diagram of the transmission coordination between the conveyor chain and the hand crank;

[0023] Figure 8 It is a schematic diagram of the connection between the force measuring steel bar meter and the acquisition instrument;

[0024] Fig. 9 This is a schematic diagram of the test groove plane;

[0025] Fig.10 This is a schematic diagram of the test groove corner;

[0026] Fig.11 Schematic diagram of the failure volume and failure surface in the test area;

[0027] Fig.12 It is the schematic diagram of vertical force loading;

[0028] Fig.13 This is the relationship diagram between normal stress and shear stress on the failure surface.

[0029] The meanings of the reference numerals are as follows: 10, base frame rod; 11, mounting frame; 111, top plate; 112, bottom plate; 20, probe rod; 21, force measuring steel bar meter; 22, pressure plate; 30, fixing frame; 40, ground anchor; 41, sprocket; 42, transmission chain; 50, sliding sleeve; 51, overhang frame; 60, drive unit; 70, conveyor chain; 71, pressure clamp; 72, axle; 80, guide sleeve; 90, handle frame; 91, transmission gear; 92, mounting seat; 93, hand crank; 100, transmission shaft; 101, first large gear; 102, belt or chain; 103, third gear; 110, data acquisition instrument. DETAILED DESCRIPTION

[0030] The following will be combined with the attached Figure 1-13 The embodiments of the technical solution of the present application are described in detail.

[0031] A loess shear strength in-situ testing device comprises two base rods 10 arranged at equal heights and parallel intervals, a vertically arranged mounting frame 11 is welded to the tops of the two base rods 10, a probe rod 20 is longitudinally arranged on the mounting frame 11, and the probe rod 20 is driven up and down by a driving mechanism, ground anchors 40 are arranged at both ends of the base rod 10, an output end of a force measuring steel bar meter 21 connected to the lower part of the probe rod 20 is electrically connected to an input end of a shear strength data acquisition instrument 110, and a pressure plate 22 of an isosceles right triangle with a flat plate surface is connected to the lower end of the force measuring steel bar meter 21.

[0032] The force measuring steel bar meter 21 in the utility model adopts a VWR vibrating wire steel bar meter. The shear strength data acquisition instrument adopts a JY-I intelligent data acquisition instrument V1.0.

[0033] The pressure plate 22 is made of 6-20 mm thick hot-rolled steel plate, and the waist length varies from 10-50 cm.

[0034] When testing the shear strength of loess, the entire device is moved to the area to be tested, and after the ground anchor 40 is screwed into the soil to fix the device, the driving mechanism drives the probe rod 20 downward, so that the pressure plate 22 at the bottom of the probe rod 20 is against the designated test position of the area to be tested and applies a vertical force downward, and the force measuring steel bar meter 21 transmits the stress change to the shear strength data acquisition instrument 110, which automatically obtains the shear strength parameters of the designated test position. This new device can visually view the structural characteristics of loess by digging trenches during the test of loess shear strength; the test principle is basically the same as the direct shear test, and the relevant principles can be directly used; the disturbance to the soil is smaller than that of indoor tests, and the results are more reliable.

[0035] The probe rod 20 transmits the force downward to the force measuring steel bar meter 21, and the force measuring steel bar meter 21 transmits the force to the pressure plate 22; the force measuring steel bar meter 21 transmits the data to the shear strength data acquisition instrument 110 through the acquisition cable. The shear strength data acquisition instrument 110 can display and record the change of force during the loading process, and calculate the maximum loading force during the failure process. At the same time, the failure angle and area, volume, loess weight, etc. are input, and linear fitting analysis is performed on multiple groups of loading tests to automatically obtain the shear strength parameters. The specific principle and structure of the shear strength data acquisition instrument 110 are existing technologies and will not be elaborated on here.

[0036] As a preferred solution, a fixing frame 30 is welded to both ends of the base frame rod 10, and the ground anchor 40 is threadedly matched with the corresponding screw hole on the fixing frame 30. The sliding sleeve 50 sleeved on the outer peripheral surface of the mounting frame 11 forms a sliding match with the mounting frame 11 in the vertical direction. Suspension frames 51 are welded on both sides of the sliding sleeve 50, and the ground anchor 40 is connected to the suspension frame 51 through a bearing seat. The two sprockets 41 located at the top of the two ground anchors 40 and coaxially arranged with the ground anchors 40 are connected through a transmission chain 42. The driving unit 60 drives one of the sprockets 41 to rotate, and the transmission chain 42 is in an avoidance position of the probe rod 20.

[0037] Since the top ends of the ground anchors 40 at both ends of the base frame rod 10 form a synchronous rotation cooperation through the sprocket and the transmission chain 42, when one of the ground anchors 40 is rotated, the other ground anchor 40 can also rotate synchronously. The ground anchors 40 on the entire equipment can be screwed in and out synchronously to complete the fixing or release of the entire machine. There is no need to screw the ground anchors 40 independently in and out, thereby improving the operating efficiency of the ground anchors 40 on the entire machine.

[0038] The top ends of the two ground anchors 40 are arranged as a whole by using the sliding sleeve 50 and the cantilever frame 51, so that the ground anchor 40, the sliding sleeve 50 and the cantilever frame 51 form a conjoined structure. When the ground anchor 40 rotates and rises and falls by cooperating with the thread of the fixing frame 30, the conjoined structure formed by the ground anchor 40, the sliding sleeve 50 and the cantilever frame 51 moves up and down synchronously along the mounting frame 11, without affecting the rotation of the ground anchor 40 relative to the cantilever frame 51, so that the screwing in and screwing out of the ground anchor 40 during the lifting process can be realized, which is more stable. The driving unit 60 can be a motor to realize the automatic operation of the ground anchor 40. The driving unit 60 drives the ground anchor 40 to rotate, so that the ground anchor 40 can move up and down relative to the fixing frame 30.

[0039] As a preferred solution, the mounting frame 11 is composed of two channel steels arranged at intervals with grooves opposite to each other. The upper and lower ends of the mounting frame 11 are respectively connected to a top plate 111 and a bottom plate 112 with flat plate surfaces. A conveyor chain 70 is arranged between the top plate 111 and the bottom plate 112. The conveyor chain 70 is composed of two circles on the left and right. The upper and lower parts of the conveyor chain 70 are both mounted on sprockets. The upper sprocket is mounted on the top of the top plate 111, and the lower sprocket is mounted on the bottom of the bottom plate 112. The axle of the sprocket matching the conveyor chain 70 is located in a horizontal direction perpendicular to the extension direction of the base frame rod 10. One side of the chain body of the conveyor chain 70 is clamped and connected to the rod body of the probe rod 20 through a pressure clamp 71 (the two sides of the pressure clamp 71 and the chain body of the conveyor chain 70 close to the pressure clamp 71 are clamped and fixed, and the middle part of the pressure clamp 71 is clamped and fixed to the rod body of the probe rod 20). The conveying chain 70 drives the probe rod 20 to move up and down through the pressure clamp 71, so that the pressure plate 22 at the bottom of the probe rod 20 applies a vertical force to the soil surface at a designated position.

[0040] Combination Figure 1 , 2As shown in , 7, a transmission shaft 100 is inserted between opposite sides of the mounting frame 11. The transmission shaft 100 is located in the horizontal direction and is arranged parallel to the wheel shaft 72 of the upper sprocket that matches the conveying chain 70. The wheel shaft 72 and the transmission shaft 100 form a transmission match through a gear set. A handle frame 90 is provided on the outer wall surface of the mounting frame 11. A mounting seat 92 is fixed on the handle frame 90. The mounting seat 92 is rotatably equipped with a gear shaft. The transmission gear 91 on the gear shaft and the transmission shaft 100 form a transmission match through a belt or chain 102. The outer shaft end of the gear shaft can be used to connect a hand crank 93.

[0041] In order to ensure that the probe rod 20 stably moves up and down, the probe rod 20 passes through the guide sleeve 80 arranged on the top plate 111 and the bottom plate 112 to form a guide sliding fit. The guide sleeve 80 can guide and limit the rod body of the probe rod 20.

[0042] In this solution, the transmission gear 91 is rotated by turning the hand crank 93, and the transmission shaft 100 can be driven to rotate through the transmission of the belt or chain 102, and further the wheel shaft 72 of the upper sprocket matched with the conveying chain 70 can be indirectly driven to rotate through the gear set, so that the sprocket matched with the conveying chain 70 rotates synchronously, realizing the transmission of the conveying chain 70, and controlling the up and down displacement of the probe rod 20. Here, the shaft end of the transmission shaft 100 is arranged by the first large gear 101 to transmit with the transmission gear 91, and the third gear 103 coaxially arranged with the first large gear 101 meshes with the second large gear 73 at the shaft end of the wheel shaft 72, realizing the transmission between the transmission shaft 100 and the wheel shaft 72.

[0043] When testing the shear strength of loess, the following steps can be followed:

[0044] Step 1: First, level the top of the loess, remove the surface soil and weeds, and level an area larger than 1.0 square meters. Dig multiple L-shaped grooves on the loess (such as Fig. 9 , 10 As shown), the trench side length is greater than 1 meter, the depth is not less than 50cm, and the width is not less than 50cm. The plan view is ABCDEF, and the elevation view is ABCO. The sides are mutually orthogonal, and the trench depth is BO. The test soil is a triangle with protruding inner corners of ABC, and the upper part of the triangle is cut off by 20cm;

[0045] Step 2: Select pressure plates 22 of different sizes according to the triangular surface of the on-site excavation. The pressure plates 22 are connected to the force measuring steel bar gauge 21, which is connected to the probe 20. The right angle of the pressure plate 20 corresponds to the inner angle of the trench. Then, a vertical load P is applied to the inner triangular area of ​​the loess until the soil is destroyed. The measured destroyed triangular pyramid soil is as follows: Fig.11 In BKMN, the failure surface is similar to the triangular surface KMN, and the area is S. The measured failure surface has an angle θ with the horizontal plane (e.g. Fig.12As shown), the weight of the triangular pyramid soil is W. Then replace the larger bearing plate 20 and do the same test at another trench, and record the force value, the area of ​​the damaged surface and the inclination angle at the time of failure. The damaged area is determined by simply measuring the base and the oblique length of the damaged triangular surface with a ruler or an area measuring device, and the inclination angle is estimated by the average angle using a mobile phone smart compass;

[0046] Step 3: Since soil particles are not easy to break, they have a strong ability to resist normal (compressive) stress, and shear failure is the main reason for their destruction. According to the shear strength Coulomb equation: τ=σtanφ+c, the Mohr envelope of soil can be approximately represented by a straight line in most cases, where the τ-axis intercept c is called cohesion, and the inclination of the straight line is the internal friction angle φ of the soil;

[0047] Normal stress: The stress component perpendicular to the cross section is called normal stress (or normal stress), represented by σ. Normal stress represents the effect of tension and compression between two adjacent cross sections inside the part. Shear stress: The stress component tangent to the cross section is called shear stress or shear stress, represented by τ.

[0048] W = (S (bottom area) · H (height) ÷ 3) × ρ (weight);

[0049] Normal stress δ calculation:

[0050] N=(P+W)×cosθ, δ=N / S(damage surface area)

[0051] Calculation of shear stress τ:

[0052] T = (P + W) × sinθ, τ = T / S;

[0053] P is the vertical force loaded, W is the gravity of the destroyed soil, N is the normal pressure on the failure surface, T is the shear stress on the failure surface, and θ is the angle of the failure surface.

[0054] Step 4: Carry out more than 3 destructive tests on the same loess area, and control the vertical load P1﹤P2﹤P3﹤Px. Obtain more than 3 sets of failure stresses (σ, τ) respectively, and fit them through Excel linear regression to obtain the loess cohesion C and internal friction angle φ, as shown in Fig.13 shown.

[0055] Compared with traditional in-situ tests, this new device can visually view the structural characteristics of loess by digging trenches during the shear strength test of loess; the principle of this method is basically the same as that of the direct shear test, and the relevant principles can be directly utilized; the disturbance to the soil is smaller than that in indoor tests, and the results are more reliable.

Claims

1. An in-situ testing device for loess shear strength, comprising two base bars (10) of equal height and arranged in parallel, and a mounting frame (11) is provided on the top of the two base bars (10), characterized in that: A probe rod (20) is longitudinally mounted on the mounting frame (11), and the probe rod (20) is driven by a driving mechanism to move up and down. A force measuring steel bar meter (21) is connected to the lower part of the probe rod (20). The output end of the force measuring steel bar meter (21) is electrically connected to the input end of the shear strength data acquisition instrument (110). The lower end of the force measuring steel bar meter (21) is connected to an isosceles right triangle pressure plate (22) with a flat plate surface. Ground anchors (40) are arranged on both sides of the bottom of the bottom frame rod (10).

2. The in-situ testing device for loess shear strength according to claim 1, characterized in that: Both ends of the base frame rod (10) are connected to a fixing frame (30), and the ground anchor (40) is threadedly connected to the fixing frame (30). The top ends of the two ground anchors (40) are connected via a transmission chain (42) and rotate synchronously.

3. The in-situ testing device for loess shear strength according to claim 2, characterized in that: A sliding sleeve (50) is sleeved on the outer side of the mounting frame (11), and both sides of the sliding sleeve (50) are connected to a suspension frame (51), and the suspension frame (51) is connected to the ground anchor (40) via a bearing seat, and a sprocket (41) is arranged on the top of the ground anchor (40), and the two sprockets (41) are connected via a transmission chain (42), and the driving unit (60) drives one of the sprockets (41) to rotate.

4. The in-situ testing device for loess shear strength according to claim 1, 2 or 3, characterized in that: The mounting frame (11) is composed of two channel steels arranged at intervals with notches facing each other. A top plate (111) is mounted on the upper end of the mounting frame (11), and a bottom plate (112) is mounted on the lower end of the mounting frame (11). A conveyor chain (70) is arranged between the top plate (111) and the bottom plate (112). A chain body on one side of the conveyor chain (70) is clamped and connected to a rod body of the probe rod (20) via a pressure clamp (71). The conveyor chain (70) is driven by a driving mechanism.

5. The in-situ testing device for loess shear strength according to claim 4, characterized in that: The top plate (111) and the bottom plate (112) are both provided with guide sleeves (80), and the probe rod (20) passes through the guide sleeves (80).

6. The in-situ testing device for loess shear strength according to claim 4, characterized in that: The driving mechanism comprises a transmission shaft (100) mounted on a mounting frame (11); the transmission shaft (100) is located in a horizontal direction and is arranged in parallel with a wheel shaft (72) of a sprocket wheel at the upper end of a conveying chain (70); the wheel shaft (72) and the transmission shaft (100) are matched by gear transmission; a handle frame (90) is arranged outside the mounting frame (11); a mounting seat (92) is mounted on the handle frame (90); a gear shaft is rotatably arranged on the mounting seat (92); a transmission gear (91) on the gear shaft is matched with the transmission shaft (100) by a belt or a chain (102); and a hand crank (93) is connected to the outer shaft end of the gear shaft.

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