DYNAMIC SETTLEMENT IN-SITU DYNAMIC TEST BENCH AND TEST METHOD FOR FOUNDATION SOIL

Abstract

An in-situ dynamic settlement test bench and method for the foundation soil is provided. The in-situ dynamic settlement test bench includes a vibration table system, a sensor embedded in the foundation soil, and a water injection trench around the foundation soil. A horizontal vibration load is applied to the lower foundation soil at an in-situ testing site by means of a vibration table, and the dynamic response of the foundation soil is measured through the sensors embedded in different positions, to reflect the seismic settlement deformation of the soil body. Dynamic settlement tests on soils include indoor dynamic simple shear, triaxial and torsional shear tests. A method is proposed for measuring the dynamic response and settlement deformation of the foundation soil by using a vibrator's vibration action on an in-situ soil column. Measurements of the acceleration response and seismic settlement deformation are taken for the foundation soil under in-situ condition.

Claims

1. A dynamic settlement in-situ dynamic test bench for foundation soil, wherein two column holes are drilled on a center line of foundation soil of an in-situ test site, a plurality of sets of displacement sensors and acceleration sensors are uniformly distributed in each of the two column holes in sequence from top to bottom, trenches are arranged on two sides of the two column holes separately, and the trenches are filled with water; and a first plastic waterproof film is laid on a top of the foundation soil, and a vibration table is arranged on the first plastic waterproof film.

2. The dynamic settlement in-situ dynamic test bench for the foundation soil according to claim 1, wherein the vibration table comprises a base, and the base is fixedly connected to a vibration table foundation by a bolt assembly; and two eccentric wheels are symmetrically arranged on two sides of the base, and the two eccentric wheels are in driving connection by an electric motor.

3. The dynamic settlement in-situ dynamic test bench for the foundation soil according to claim 1, wherein the displacement sensors and the acceleration sensors are each wrapped in remolded soil and cut into soil columns; and a remaining space in each of the two column holes is backfilled with backfill soil.

4. The dynamic settlement in-situ dynamic test bench for the foundation soil according to claim 1, wherein a second plastic waterproof film is laid around a foundation and the trenches.

5. The dynamic settlement in-situ dynamic test bench for the foundation soil according to claim 1, wherein each of the two column holes has a diameter of 20 mm and a depth of 10 m; a distance between the two column holes is 1 m; and each of the trenches has a width of 0.5 m, a length of 3 m and a depth of 10 m, and a height distance between adjacent displacement sensors is 2 m.

6. A dynamic settlement in-situ dynamic test method for foundation soil, comprising: step 1: setting the foundation soil with a width of 3 m and a length of 3 m in an in-situ test site; step 2: drilling a first column hole and a second column hole with a diameter of 20 mm and a depth of 10 m on a center line of foundation soil with a Luoyang shovel, wherein a distance between the first column hole and the second column hole is 1 m; step 3: wrapping sensors in remolded soil, cutting the sensors into soil columns, and preparing ten soil columns with the sensors in two groups; and placing a first soil column vertically at 10 m of each of the first column hole and the second column hole, backfilling soil to 8 m, then placing a second soil column vertically, backfilling soil to 6 m, and so on until the last sensor is placed; step 4: laying a first plastic waterproof film on a top of the foundation soil, arranging a vibration table and a loading system of a vibration load on the foundation soil, and arranging a waterproof film made of plastic film cloth between the vibration table foundation and the foundation soil; step 5: digging 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, forming a foundation soil column with a size of 2 m*2 m, and laying a second plastic waterproof film on peripheries and bottoms of the foundation soil and a trench wall; step 6: performing a dynamic test for an undisturbed structural loess foundation under a state K.sub.0 by the above test facility, wherein the state K.sub.0 is: K.sub.0 is a static earth pressure coefficient K.sub.0 being a ratio of a lateral effective stress state to a vertical effective stress state, and a loess dynamic experiment under the state K.sub.0 is a test corresponding to a condition that a lateral strain is 0; recording an acceleration response generated in a dynamic settlement process through a method of increasing an seismic wave amplitude step by step and by acceleration sensors and displacement sensors; and computing time history curves of accelerations of five points in a foundation according to the acceleration response and a displacement; and step 7: changing a natural vibration frequency of vibration to obtain time history curves of velocities and time history curves of accelerations under different frequencies; and analyzing a relation between the accelerations and a period to obtain an acceleration response spectrum under an earthquake.

7. The dynamic settlement in-situ dynamic test method for the foundation soil according to claim 6, wherein according to the acceleration response and the displacement obtained in step 6, a dynamic equilibrium equation of a mass point system of the foundation soil is obtained by a Duharmel integral formula, wherein the dynamic equilibrium equation of the mass point system of the foundation soil is:
{umlaut over (x)}(t)+2{dot over (x)}(t)+.sup.2x(t)={umlaut over (x)}(t), wherein, x(t) is displacement of a single mass point system at any time, {dot over (x)}(t) is a velocity of the mass point system of the foundation soil at different positions, {umlaut over (x)}(t) is an acceleration of the mass point system of the foundation soil at different positions, and t is any time; and when an initial acceleration {umlaut over (x)}.sub.0(t) is not 0, an integral expression of a solution of the dynamic equilibrium equation is $x\left(t\right)=-\frac{1}{{}_0}{}_0^1{\stackrel{.Math.}{x}}_0\left(\right)e^{-\left(t-\right)}\sin {}_0\left(t-\right)d;$ wherein is an instantaneous time, is a damping ratio, is a natural vibration period of the test, .sub.0 is a natural vibration frequency with damping, and x(t) is displacement of the single mass point system at any time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a schematic diagram of the structural design of a vibration test table according to the presented invention;

[0030] FIG. 2 is a schematic sectional view of a test according to the presented invention;

[0031] FIG. 3A is a time history curve of acceleration at monitoring point A1 when the peak acceleration is 0.3 g according to the presented invention;

[0032] FIG. 3B is a time history curve of acceleration at monitoring point A1 when the peak acceleration is 0.5 g according to the presented invention:

[0033] FIG. 3C is a time history curve of acceleration at monitoring point A2 when the peak acceleration is 0.3 g according to the presented invention;

[0034] FIG. 3D is a time history curve of acceleration at monitoring point A2 when the peak acceleration is 0.5 g according to the presented invention;

[0035] FIG. 3E is a time history curve of acceleration at monitoring point A3 when the peak acceleration is 0.3 g according to the presented invention;

[0036] FIG. 3F is a time history curve of acceleration at monitoring point A3 when the peak acceleration is 0.5 g according to the presented invention;

[0037] FIG. 3G is a time history curve of acceleration at monitoring point A4 when the peak acceleration is 0.3 g according to the presented invention;

[0038] FIG. 3H is a time history curve of acceleration at monitoring point A4 when the peak acceleration is 0.5 g according to the presented invention;

[0039] FIG. 3I is a time history curve of acceleration at monitoring point A5 when the peak acceleration is 0.3 g according to the presented invention;

[0040] FIG. 3J is a time history curve of acceleration at monitoring point A5 when the peak acceleration is 0.5 g according to the presented invention; and

[0041] FIG. 4A is a response spectrum curve graph of each monitoring point at different periods when the peak acceleration is 0.3 g according to the presented invention, and FIG. 4B is a response spectrum curve graph of each monitoring point at different periods when the peak acceleration is 0.5 g according to the presented invention.

[0042] In the figures, 1. column hole a, 2. sensor, 3. sensor, 4. vibration table, 5. electric motor, 6. eccentric wheel, 7. plastic waterproof film, 8. vibration table foundation, 9. bolt assembly, 10. trench, 11. foundation soil column, and 12. plastic waterproof film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To provide a clearer understanding of the objectives and technical solutions of the invention, detailed descriptions and embodiments will be presented with drawings.

[0044] According to a dynamic settlement in-situ dynamic test bench for foundation soil in the present invention, two column holes 1 are drilled on a center line of foundation soil of an in-situ test site, a plurality of sets of displacement sensors 2 and acceleration sensors 3 are uniformly distributed in each column hole 1 in sequence from top to bottom, trenches 10 are arranged on two sides of the column holes 1 separately, and the trenches 10 are filled with water; and a plastic waterproof film 7 is laid on a top of the foundation soil, and a vibration table is arranged on the plastic waterproof film 7.

[0045] The vibration table includes a base 4, and the base 4 is fixedly connected to a vibration table foundation 8 by means of a bolt assembly 9; and eccentric wheels 6 are symmetrically arranged on two sides of the base 4, and the two eccentric wheels 6 are in driving connection by means of an electric motor 5.

[0046] The displacement sensors 2 and the acceleration sensors 3 are each wrapped in remolded soil and cut into soil columns; and a remaining space in each column hole is backfilled with backfill soil.

[0047] A plastic waterproof film is laid around a foundation and the trenches 10.

[0048] Each column hole 1 has a diameter of 20 mm and a depth of 10 m; a distance between the two column holes is 1 m; and each trench has a width of 0.5 m, a length of 3 m and a depth of 10 m, and a height distance between adjacent displacement sensors 2 is 2 m.

[0049] A dynamic settlement in-situ dynamic test method for foundation soil in the present invention specifically includes: [0050] step 1: set the foundation soil with a width of 3 m and a length of 3 m in an in-situ test site; [0051] step 2: drill a hole A and a hole B with a diameter of 20 mm and a depth of 10 m on a center line of foundation soil with a Luoyang shovel, where a distance between the two holes is 1 m; [0052] step 3: wrap sensors in remolded soil, cut the sensors into soil columns, and prepare ten soil columns with the sensors in two groups; and place one soil column vertically at 10 m of each column hole, backfill soil to 8 m, then place the second soil column vertically, backfill soil to 6 m, and so on until the last sensor is placed; [0053] step 4: lay a plastic waterproof film on a top of the foundation soil, arrange a vibration table and a loading system of a vibration load on the foundation soil, and arrange a waterproof film made of plastic film cloth between the vibration table foundation and the foundation soil; [0054] step 5: dig 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, form a foundation soil column with a size of 2 m*2 m, and lay a plastic waterproof film on peripheries and bottoms of the foundation soil and a trench wall; [0055] step 6: perform a dynamic test for an undisturbed structural loess foundation under a state K.sub.0 by means of the above test facility, where [0056] the state K.sub.0 is: K.sub.0 is a static earth pressure coefficient K.sub.0 being a ratio of a lateral effective stress state to a vertical effective stress state, and a loess dynamic experiment under the state K.sub.0 is a test corresponding to a condition that a lateral strain is 0; record an acceleration response and displacement generated in a dynamic settlement process through a method of increasing an seismic wave amplitude step by step and by means of acceleration sensors and displacement sensors; and compute time history curves of velocities and time history curves of accelerations of five points in a foundation according to the generated acceleration response and the displacement; and [0057] step 7: according to the acceleration response and the displacement obtained in step 6, obtain a dynamic equilibrium equation of a mass point system of the foundation soil by means of a Duharmel integral formula, where the dynamic equilibrium equation of the mass point system of the foundation soil is:

{umlaut over (x)}(t)+2{dot over (x)}(t)+.sup.2x(t)={umlaut over (x)}(t). [0058] where, x(t) is displacement of a single mass point system at any time, {dot over (x)}(t) is a velocity of the mass point system of the foundation soil at different positions, {umlaut over (x)}(t) is an acceleration of the mass point system of the foundation soil at different positions, and t is any time; and [0059] when an initial acceleration {umlaut over (x)}.sub.0(t) is not 0, an integral expression of a solution of the equation is

[00002]$x\left(t\right)=-\frac{1}{{}_0}{}_0^1{\stackrel{.Math.}{x}}_0\left(\right)e^{-\left(t-\right)}\sin {}_0\left(t-\right)d;$ [0060] where is an instantaneous time, is a damping ratio, is a natural vibration period of the test, .sub.0 is a natural vibration frequency with damping, and x(t) is displacement of the single mass point system at any time, and {dot over (x)}(t) is a velocity of the mass point system of the foundation soil at different positions; [0061] change a natural vibration frequency of vibration, to obtain time history curves of velocities and time history curves of accelerations under different frequencies; and analyze a relation between the accelerations and a period, to obtain an acceleration response spectrum under an earthquake.

Embodiment

[0062] A pretest is performed according to the above test steps. A dynamic amplification factor may be reflected by ratios of peak accelerations at different depths of foundation soil to peak accelerations input to a table, where the peak accelerations input to a table are peak accelerations of a vibration table after the experiment is started.

[0063] FIGS. 3A, 3C, 3E, 3G and 3I show time history curves of accelerations at monitoring points A1, A2, A3, A4 and A5 at different depths respectively when a peak acceleration is 0.3 g.

[0064] FIGS. 3B, 3D, 3F, 3H and 3J show time history curves of the accelerations at the monitoring points A1, A2, A3, A4 and A5 at different depths respectively when the peak acceleration is 0.5 g.

[0065] A1, A2, A3, A4 and A5 are positions of 5 groups of acceleration sensors from bottom to top in sequence.

[0066] A natural vibration frequency wo is changed to obtain time history curves of accelerations under different frequencies. A relation between the accelerations and a period is analyzed to obtain an acceleration response spectrum (as shown in FIGS. 4A and 4B) under an earthquake. In the formula, the natural vibration frequency is a free vibration frequency of a loess foundation during the test.