A vibration-sink in-situ dynamic test bench for ground soil and a test method thereof

Abstract

The application discloses a kind of in-situ dynamic test bench of ground soil vibration subsidence and test method thereof, including vibration table system and sensor in ground soil, water injection trench around ground soil.In-situ test site is vibrated by vibration table to the underlying ground soil body and applies horizontal vibration load, and the dynamic response of ground soil is measured by sensor buried in different positions, reflecting the vibration subsidence deformation of soil body.At present, soil vibration subsidence test includes dynamic simple shear, dynamic triaxial, dynamic torsional shear indoor test method, but there is no mature method for in-situ vibration subsidence test of ground soil.Through the vibration effect of in-situ soil column by vibrator, a method for testing the dynamic response and vibration subsidence deformation of ground soil is proposed, filling the soil dynamics test method.The acceleration response and vibration subsidence deformation of ground soil under in-situ conditions are determined by the application, which has good practical significance for disaster prevention.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of in-situ loess vibration subsidence test, and particularly relates to a vibration subsidence in-situ dynamic test platform for foundation soil. BACKGROUND

[0002] Loess has a significant dynamic structural damage due to its large pore, high pore ratio, weak cementation and vertical structure micro-crack development. The vibration subsidence is an important dynamic deformation characteristic of loess, and thus the loess is prone to soil structure damage and vibration subsidence disasters under the action of medium-strong earthquakes.

[0003] In the study of loess vibration subsidence, instruments such as dynamic triaxial apparatus, dynamic torsional shear apparatus and dynamic simple shear apparatus are used. The dynamic triaxial apparatus simulates dynamic load through reciprocating shear on the 45-degree inclined surface of a cylindrical sample, but cannot simulate the rotation of the principal stress axis. The dynamic torsional shear apparatus simultaneously applies vertical load and horizontal reciprocating torsional shear to a hollow cylindrical sample, and can be used to study the constitutive relationship of soil under complex stress conditions, but has the shortcomings of difficulty in sample preparation and non-uniform shear strain. The dynamic simple shear apparatus can simultaneously apply vertical load and horizontal shear load to the sample, and the loading conditions are close to the seismic action of the actual engineering site, but cannot achieve the same effect as the in-situ test. In summary, the test sites of the above tests are all in the laboratory, so the instruments cannot completely simulate the conditions of the in-situ test.

[0004] At present, there is no mature method for in-situ vibration subsidence test of foundation soil. A method for testing the dynamic response and vibration subsidence deformation of foundation soil is proposed by subjecting the in-situ soil column to the vibration action of a vibrator, which fills the gap in soil dynamics test methods.

[0005] The acceleration response of foundation soil under seismic action is essentially the result of its deformation displacement response and deformation failure instability. The response spectrum method combines the mode superposition principle and random vibration theory to obtain an approximate solution of the average peak value of the seismic response of the structure. The results of the experiment can be analyzed by the response spectrum method to determine whether the site fortification intensity meets the design requirements. SUMMARY

[0006] The purpose of the present application is to provide a vibration subsidence in-situ dynamic test platform for foundation soil.

[0007] The purpose of the present application is also to provide a vibration subsidence in-situ dynamic test method for foundation soil, which fills the gap in the existing in-situ vibration subsidence test of foundation soil, which cannot completely simulate the conditions of the in-situ test.

[0008] The first technical solution of the present application is: a vibration subsidence in-situ dynamic test bench for foundation soil, two column holes are drilled on the center line of the in-situ test site foundation soil, a plurality of groups of displacement sensors and acceleration sensors are uniformly arranged in the column holes from top to bottom, grooves are further arranged on the two sides of the column holes, and the grooves are filled with water; a plastic waterproof membrane is arranged on the top of the foundation soil, and a vibration table is arranged above the plastic waterproof membrane.

[0009] The present application is characterized in that,

[0010] The vibration table comprises a base, the base is fixedly connected with the vibration table foundation through a bolt assembly, and eccentric wheels are symmetrically arranged on the two sides of the base, and the two eccentric wheels are driven and connected through a motor.

[0011] The displacement sensors and the acceleration sensors are wrapped with remolded soil and cut into soil columns; the remaining space in the column hole is backfilled with backfill soil.

[0012] The plastic waterproof membrane is arranged around the foundation and the groove.

[0013] The diameter of the column hole is 20mm, the depth is 10m, the two column holes are spaced apart by 1m, the groove is 0.5m wide, 3m long and 10m deep, and the height interval between adjacent displacement sensors is 2m.

[0014] The second technical solution of the present application is a vibration subsidence in-situ dynamic test method for foundation soil, and the specific operation steps are as follows:

[0015] Step 1: setting a foundation soil with a width of 3m and a length of 3m in the in-situ test site;

[0016] Step 2: drilling two holes A and B with a diameter of 20mm and a depth of 10m on the center line of the foundation soil using a Luoyang shovel, and the two holes are spaced apart by 1m;

[0017] Step 3: wrapping the sensors with remolded soil and cutting them into soil columns, preparing ten soil columns with sensors in two groups; vertically placing the soil columns into the 10m place of the column hole, backfilling the soil to the 8m place, then vertically placing the second soil column, backfilling to the 6m place, and so on until the last sensor is placed;

[0018] Step 4: laying a plastic waterproof membrane on the top of the foundation soil, arranging a vibration table and a vibration load loading system above the foundation soil, and arranging a waterproof membrane between the vibration table foundation and the foundation soil, which is made of plastic film cloth;

[0019] Step 5: digging a groove with a width of 0.5m, a length of 3m and a depth of 10m in the in-situ test site, forming a 2m*2m foundation soil column, and laying a plastic waterproof membrane around the four sides and the bottom of the foundation soil and the groove wall;

[0020] Step 6: carrying out the test through the above test facilitiesK 0 state loess foundation dynamic test in original state structure;

[0021] K 0 refers to the ratio of lateral effective stress and vertical effective stress, the ratio is the static earth pressure coefficient, K 0 state loess dynamic test is the test corresponding to the lateral strain of 0; the method of gradually increasing the amplitude of seismic wave is adopted, acceleration sensor and displacement sensor are used to record the acceleration response generated in the vibration process; the acceleration time history curves of five points in the foundation are calculated according to the generated acceleration response and displacement;

[0022] Step 7: according to the acceleration response and displacement obtained in step 6, the dynamic equilibrium equation of the ground soil mass point system can be obtained by the Duharmel integral formula of single mass point motion:

[0023]

[0024] In the formula, x(t) is the displacement of the single mass point system at any time, is the velocity of the ground soil mass point system at different positions, is the acceleration of the ground soil mass point system at different positions, and t is any time;

[0025] When the initial acceleration is not 0, the integral expression of the solution of the equation is

[0026]

[0027] In the formula, τ is the instantaneous time, λ is the damping ratio, ω is the natural vibration period of the test, ω0 is the natural vibration frequency with damping, and x(t) is the displacement of the single mass point system at any time.

[0028] By changing the vibration natural frequency, the velocity time history curve and the acceleration time history curve under different frequencies can be obtained; the relationship between acceleration and period is analyzed to obtain the acceleration response spectrum under the action of earthquake.

[0029] The beneficial effects of the present application are that the present application applies horizontal vibration load to the underlying ground soil body through the vibration table in the in-situ test site, measures the dynamic response of the ground soil by the sensors buried in different positions, and reflects the seismic subsidence deformation of the soil body. At present, the soil seismic subsidence test includes dynamic simple shear, dynamic triaxial, dynamic torsional shear indoor test methods, but there is no mature method for the in-situ seismic subsidence test of the ground soil. The soil column in the field is vibrated by the vibrator to fill the soil dynamics test method. The acceleration response and seismic subsidence deformation of the ground soil under in-situ conditions are measured by the present application, which has good practical significance for disaster prevention. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1is a structural schematic diagram of the vibration test table of the present application;

[0031] Figure 2 is a sectional schematic diagram of the test of the present application;

[0032] Figure 3 (a) is the acceleration time history curve at monitoring point A1 when the peak acceleration of the present application is 0.3g;

[0033] Figure 3 (b) is the acceleration time history curve at monitoring point A1 when the peak acceleration of the present application is 0.5g;

[0034] Figure 3 (c) is the acceleration time history curve at monitoring point A2 when the peak acceleration of the present application is 0.3g;

[0035] Figure 3 (d) is the acceleration time history curve at monitoring point A2 when the peak acceleration of the present application is 0.5g;

[0036] Figure 3 (e) is the acceleration time history curve at monitoring point A3 when the peak acceleration of the present application is 0.3g;

[0037] Figure 3 (f) is the acceleration time history curve at monitoring point A3 when the peak acceleration of the present application is 0.5g;

[0038] Figure 3 (g) is the acceleration time history curve at monitoring point A4 when the peak acceleration of the present application is 0.3g;

[0039] Figure 3 (h) is the acceleration time history curve at monitoring point A4 when the peak acceleration of the present application is 0.5g;

[0040] Figure 3 (i) is the acceleration time history curve at monitoring point A5 when the peak acceleration of the present application is 0.3g;

[0041] Figure 3 (j) is the acceleration time history curve at monitoring point A5 when the peak acceleration of the present application is 0.5g;

[0042] Figure 4 (a) is the response spectrum curve of each monitoring point under different periods when the peak acceleration of the present application is 0.3g;

[0043] Figure 4 (b) is the response spectrum curve of each monitoring point under different periods when the peak acceleration of the present application is 0.5g.

[0044] In the figure, 1, column hole, 2, displacement sensor, 3, acceleration sensor, 4, base, 5, motor, 6, eccentric wheel, 7, plastic waterproof membrane, 8, vibration table foundation, 9, bolt assembly, 10, groove, 11, foundation soil column, 12, plastic waterproof membrane. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution of the application more clear, the application is further described in detail below in combination with the drawings and examples.

[0046] A vibration subsidence in-situ dynamic test bench for foundation soil of the application has two column holes 1 drilled on the center line of the in-situ test site foundation soil, and multiple groups of displacement sensors 2 and acceleration sensors 3 are uniformly arranged in the column holes 1 from top to bottom; grooves 10 are further arranged on both sides of the column holes 1, and the grooves 10 are filled with water; a plastic waterproof membrane 7 is laid on the top of the foundation soil, and a vibration table is placed above the plastic waterproof membrane 7.

[0047] The vibration table includes a base 4, which is fixedly connected with the vibration table foundation 8 through a bolt assembly 9; eccentric wheels 6 are symmetrically arranged on both sides of the base 4, and the two eccentric wheels 6 are drivenly connected through a motor 5.

[0048] The displacement sensors 2 and the acceleration sensors 3 are wrapped with remolded soil and cut into soil columns; the remaining space in the column holes is backfilled with backfill soil.

[0049] The plastic waterproof membrane is laid around the foundation and the grooves 10.

[0050] The column hole 1 has a diameter of 20 mm and a depth of 10 m; the two column holes are spaced 1 m apart; the groove has a width of 0.5 m, a length of 3 m, and a depth of 10 m, and the height interval between adjacent displacement sensors 2 is 2 m.

[0051] A vibration subsidence in-situ dynamic test method for foundation soil of the application has the following specific operation steps:

[0052] Step 1: setting a foundation soil with a width of 3 m and a length of 3 m in the in-situ test site;

[0053] Step 2: drilling two holes A and B with a diameter of 20 mm and a depth of 10 m on the center line of the foundation soil using a Luoyang shovel, and the two holes are spaced 1 m apart;

[0054] Step 3: wrapping the sensors with remolded soil and cutting them into soil columns, preparing ten soil columns with sensors in two groups; vertically placing the soil columns into the 10 m place of the column hole, backfilling the soil to the 8 m place, then vertically placing the second soil column, backfilling to the 6 m place, and so on until the last sensor is placed;

[0055] Step 4: Laying a plastic waterproof membrane on the top of the foundation soil, arranging a vibration table and a loading system of vibration load above the foundation soil, and laying a waterproof membrane between the vibration table foundation and the foundation soil, which is made of plastic film cloth;

[0056] Step 5: Excavating a trench with a width of 0.5 m, a length of 3 m and a depth of 10 m in the in-situ test site to form a 2 m x 2 m foundation soil column, and laying a plastic waterproof membrane around and at the bottom of the foundation soil and the trench wall;

[0057] Step 6: Performing K a dynamic test of the original structural loess foundation under the state of 0;

[0058] K 0 refers to the ratio of lateral effective stress to vertical effective stress, and the ratio is the static earth pressure coefficient, K the dynamic test of the loess under the state of 0 is a test corresponding to a lateral strain of 0; the method of gradually increasing the amplitude of the seismic wave is adopted, and the acceleration sensor and the displacement sensor are used to record the acceleration response and the displacement generated in the vibration process; the velocity time history curve and the acceleration time history curve of the five points in the foundation are calculated according to the generated acceleration response and the displacement;

[0059] Step 7: According to the acceleration response and the displacement obtained in step 6, the dynamic equilibrium equation of the foundation soil mass point system can be obtained by the Duharmel integral formula of single mass point motion:

[0060]

[0061] In the formula, x(t) is the displacement of the single mass point system at any time, is the velocity of the foundation soil mass point system at different positions, is the acceleration of the foundation soil mass point system at different positions, and t is any time;

[0062] When the initial acceleration is not 0, the integral expression of the solution of the equation is

[0063]

[0064] In the formula, τ is the instantaneous time, λ is the damping ratio, ω is the natural vibration period of the test, ω0 is the natural vibration frequency with damping, and x(t) is the displacement of the single mass point system at any time.

[0065] By changing the vibration natural frequency, the velocity time history curve and the acceleration time history curve under different frequencies can be obtained; the relationship between the acceleration and the period is analyzed to obtain the acceleration response spectrum under the action of the earthquake.

[0066] Embodiment

[0067] According to the above test procedure, the peak acceleration ratio of the foundation soil at different depths to the input platform can reflect the dynamic amplification factor, wherein the peak acceleration of the input platform is the peak acceleration of the shaking table after the experiment starts.

[0068] As shown in Figure 3 (a), (c), (e), (g), (i), respectively, are the acceleration time history curves at different depth monitoring points A1, A2, A3, A4 and A5, and the peak acceleration is 0.3g; as shown in Figure 3 (b), (d), (f), (h), (j), respectively, are the acceleration time history curves at different depth monitoring points A1, A2, A3, A4 and A5, and the peak acceleration is 0.5g.

[0069] Wherein A1, A2, A3, A4 and A5 are the positions of the five groups of acceleration sensors from bottom to top.

[0070] By changing the natural frequency ω0, the acceleration time history curves at different frequencies can be obtained; by analyzing the relationship between acceleration and period, the acceleration response spectrum under seismic action can be obtained (as shown in Figure 4 (a) and Figure 4 (b)). In the formula, the natural frequency is the free vibration frequency of the loess foundation during the test.

Claims

1. An in-situ dynamic test rig for vibration-induced subsidence of foundation soil, characterized in that, Two column holes (1) were drilled along the centerline of the foundation soil at the in-situ test site. Multiple sets of displacement sensors (2) and acceleration sensors (3) were evenly arranged from top to bottom in the column holes (1). Grooves (10) were also set on both sides of the column holes (1) and filled with water. A plastic waterproof membrane (7) was laid on top of the foundation soil. A vibration table was placed on top of the plastic waterproof membrane (7). The vibration table included a base (4), which was fixedly connected to the vibration table foundation (8) by bolt assembly (9). Eccentric wheels (6) were symmetrically arranged on both sides of the base (4), and the two eccentric wheels (6) were connected by a motor (5). The displacement sensors (2) and acceleration sensors (3) were wrapped with remolded soil and shaped into soil columns. The remaining space in the column holes was backfilled with backfill soil. A plastic waterproof membrane was laid around the foundation and the grooves (10).

2. The in-situ dynamic test rig for foundation soil vibration subsidence according to claim 1, characterized in that, The diameter of the column hole (1) is 20mm and the depth is 10m; the two column holes are 1m apart; the groove is 0.5m wide, 3m long and 10m deep, and the height interval between adjacent displacement sensors (2) is 2m.

3. A method for in-situ dynamic testing of foundation soil under vibration, characterized in that, The specific operating steps for using the test bench according to claim 1 or 2 are as follows: Step 1: Set up a foundation soil 3m wide and 3m long at the in-situ test site; Step 2: Use a Luoyang shovel to drill two holes, A and B, with a diameter of 20mm and a depth of 10m, on the centerline of the foundation soil, with a 1m interval between the two holes; Step 3: Wrap the sensor with remolded soil and cut it into a soil column. Prepare ten soil columns with sensors in two groups. Place the soil column vertically at 10m in the column hole, backfill the soil to 8m, then place the second soil column vertically and backfill to 6m, and so on until the last sensor is placed. Step 4: Lay a plastic waterproof membrane on top of the foundation soil, set up a vibrating table and a vibration load loading system above the foundation soil, and lay a waterproof membrane between the foundation of the vibrating table and the foundation soil. The material is plastic membrane cloth. Step 5: Excavate a trench 0.5m wide, 3m long and 10m deep at the in-situ test site to form a 2m×2m foundation soil column, and lay a plastic waterproof membrane around the foundation soil and trench walls and bottom. Step 6: Conduct testing at the testing facility K Dynamic test of original structural loess foundation under 0-state conditions; K 0 refers to the ratio of lateral effective stress to vertical effective stress; this ratio is the coefficient of earth pressure at rest. K The loess dynamic experiment under the 0-state condition corresponds to the test when the lateral strain is 0; the method of gradually increasing the seismic wave amplitude is adopted, and acceleration and displacement sensors are used to record the acceleration response generated during the subsidence process; the acceleration time history curves of five points in the foundation are calculated based on the generated acceleration response and displacement. Step 7: By changing the natural frequency of the vibration, the velocity time history curves and acceleration time history curves at different frequencies can be obtained; by analyzing the relationship between acceleration and period, the acceleration response spectrum under seismic action can be obtained.

4. The in-situ dynamic test method for vibration subsidence of foundation soil according to claim 3, characterized in that, The specific operation steps are as follows: Based on the acceleration response and displacement obtained in step 6, the dynamic equilibrium equation of the foundation soil particle system can be obtained from the Duharmel integral formula for the motion of a single mass point: ； In the formula, Let be the displacement of the single-particle system at any given time. The velocity of the soil particles at different locations. Let t represent the acceleration of the soil particles at different locations, where t is any time. When the initial acceleration When the constant is not 0, the integral expression for the solution of the equation is: ； In the formula: At any instant, λ is the damping ratio, and ω is the natural period of the test. Let be the natural frequency under damping, and let x(t) be the displacement of the single-mass system at any given time. This represents the acceleration of the soil particles at different locations.

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