Physical model test of bottom friction

The underlying model is a three-dimensional and two-dimensional physical model. Pave the slope model made according to the engineering geological profile on the conveyor belt of the bottom friction model tester. When the belt moves, the model is dragged and restricted by the baffle. The force Fb acting on the baffle is equal to the friction acting on the bottom of the model when the belt is dragged, which is used to simulate the gravity of rock mass. [43]

Under the action of self-weight, the friction dFb of unit dz is:

dFb=μbρtdxdz (4-25)

Where: μ b is the sliding friction coefficient between the bottom of the model and the adhesive tape;

ρ-density of model material;

T—— model thickness;

DXdz- the area of unit dz in the model.

Assuming that the tape is running at a constant speed, the z direction is:

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When the width of the model is w and the length is z, the bottom friction is:

Fb(Z)=μbρtWZ (4-27)

Figure 4-20 Bottom Friction Testing System

The stress distribution at the top of the model is:

σZ =μbρZ； σy = 0； σx=μσz (4-28)

Where: μ-Poisson ratio.

The bottom friction model is a qualitative model, which requires that the model and the prototype are similar in gravity, geometry and structure, and the dominant structural plane should remain similar in mechanics.

Test steps:

① Determine the model size. According to the model frame size and the studied engineering rock mass object, the geological section model of engineering rock mass is established in proportion and the model diagram is drawn;

(2) selecting model materials;

③ molding. Draw the profile of the engineering geological model on the adhesive tape, and then make the model as shown in the figure according to the different engineering properties of the rock stratum and the selected model material, so that it is in the initial state;

According to the occurrence of rock mass, it is placed layer by layer from bottom to top. Should be placed in sequence along the bedding direction to maintain the continuity of the rock stratum; The shearing direction is set according to the rock structure; The weak layer, fault fracture zone and goaf should be placed with corresponding materials.

According to the block size and placement mode of model materials, engineering rock masses with different mechanical properties and structural systems can be qualitatively simulated.

④ coating. Coating the surface of the model with a thickness of about 0.2-0.8 mm;

⑤ Draw marking points and marking lines;

⑥ Install measuring instruments and image recording equipment;

The measuring system is fixed on the model surface and the frame; The camera and the camera are installed on the photo frame above the model frame.

⑦ Tests and tests:

Before testing, the initial state of the model should be recorded. Then the slope is excavated step by step according to the set slope profile from the initial position, and the experiment is carried out in stages. When running, it is required to accelerate steadily and uniformly, and the belt running speed is 20 ~ 80 mm/s.

Deformation measurement and image recording are carried out at the beginning of slope profile operation test at each stage, which requires dynamic description of deformation process and failure phenomenon. After the deformation is stable, the excavation and operation test of the slope profile in the next stage can be carried out until it is destroyed.

According to the data arrangement and video data playback of slope test in each stage, the following are given:

(1) displacement trajectory diagram of marker points;

(2) Map of position changes of marker lines in different periods;

③ Displacement trajectory diagram of slope profile in each stage.

The law of slope deformation and failure and possible landslide mode can be obtained through experimental analysis.