A method for testing and evaluating soil liquefaction level

Abstract

The present application discloses a method for testing and evaluating the liquefaction grade of soil layers, which relates to soil layer testing technology. The present application sets the vibration acceleration and frequency of a vibration generator in advance according to the design basic earthquake acceleration value, earthquake grouping and site category, arranges a pore water pressure gauge in the vibration generator, and after drilling to the depth of the soil layer to be tested, lowers the vibration generator, monitors the change of pore water pressure in the soil layer by the pore water pressure gauge, and evaluates the liquefaction grade of the excavated layer according to the ratio of the maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer.

Description

Technical Field

[0001] The present application relates to the technical field of soil layer testing, and in particular to a method for testing and evaluating the liquefaction level of a soil layer. Background Art

[0002] Soil liquefaction is a kind of earthquake effect. Soil liquefaction will cause ground cracking, subsidence, house collapse, and road damage. When there is saturated silt and sand in the foundation that may liquefy, it is necessary to carry out on-site testing to determine the liquefaction level of the excavated layer. According to the seismic design code (GB50011-2011), the current method for testing and evaluating the liquefaction level of the soil layer is: drill to the depth of the soil layer to be tested, conduct a standard penetration test on the soil layer, obtain the standard penetration test hammer number N, calculate the critical value of the standard penetration test hammer number Ncr according to the relevant formula (this critical value is related to the design basic earthquake acceleration value, earthquake grouping, penetration point depth, groundwater depth, and clay content in the soil), and then evaluate the liquefaction level of the excavated layer according to the ratio of N to Ncr.

[0003] The current method has two main problems: (1) The standard penetration test requires a 63.5 kg core hammer to be repeatedly lifted to a height of 76 cm and then allowed to fall freely, which is time-consuming and laborious; (2) The Ncr calculation formula is not derived theoretically but is actually an empirical formula. Summary of the invention

[0004] The embodiment of the present application provides a method for testing and evaluating the liquefaction level of soil layers, which monitors the changes in pore water pressure in the soil layer through a pore water pressure gauge, and evaluates the liquefaction level of the excavated layer based on the ratio of the maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer.

[0005] The present application embodiment provides a method for testing and evaluating the liquefaction level of a soil layer, comprising:

[0006] A cylindrical latex film is pre-arranged at the lower part of the vibration generator, and the lower part of the latex film is fixed on the circumference of the bottom of the vibration generator;

[0007] The maximum acceleration of the vibration generator is set according to the design basic earthquake acceleration value of the area to be tested, and the frequency of the vibration generator is set according to the earthquake grouping and site category of the area to be tested;

[0008] Drilling a hole from the ground downwards until the soil layer to be tested, and digging a test hole in the soil layer to be tested, wherein the depth of the test hole is adapted to the height of the latex membrane set at the bottom of the vibration generator;

[0009] The vibration generator is placed in the drill hole, and the latex membrane arranged at the bottom of the vibration generator is placed in the test hole;

[0010] Inflate the latex film so that the film wall of the latex film is in close contact with the wall of the test hole;

[0011] Start the vibration generator, monitor the pore water pressure value measured by the pore water pressure gauge, and record the maximum pore water pressure Pmax;

[0012] Evaluate the soil liquefaction grade according to the ratio of the recorded maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer.

[0013] Optionally, it further includes pre-drilling a small hole in the middle of the plexiglass plate, installing a pore water pressure gauge in the small hole, and the head of the pore water pressure gauge extends outwards.

[0014] Optionally, setting the frequency of the vibration generator according to the seismic grouping and site category of the area to be measured is completed according to the seismic design code.

[0015] Optionally, drilling a hole from the ground down until the soil layer to be measured, and also includes using a casing to protect the hole wall of the drill hole.

[0016] Optionally, inflating the latex film so that the film wall of the latex film is in close contact with the wall of the test hole includes:

[0017] Determine the inflation pressure according to the estimated earth pressure at rest, where the earth pressure coefficient at rest K0 = 1 - sinφ, and φ is the internal friction angle of the saturated silt.

[0018] Optionally, evaluating the soil liquefaction grade according to the ratio of the recorded maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer includes:

[0019] In the case of Pmax / Pc ≤ 0.33, it is a slight liquefaction grade;

[0020] In the case of 0.33 < Pmax / Pc ≤ 0.66, it is a medium liquefaction grade;

[0021] In the case of 0.66 < Pmax / Pc, it is a severe liquefaction grade.

[0022] The method of the embodiment of the present application pre-sets the vibration acceleration and frequency of the vibration generator according to the design basic seismic acceleration value, seismic grouping and site category. A pore water pressure gauge is arranged in the vibration generator. After drilling to the depth of the soil layer to be measured, lower the vibration generator, monitor the change of the pore water pressure in the soil layer through the pore water pressure gauge, and evaluate the soil liquefaction grade according to the ratio of the maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer.

[0023] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0025] Figure 1 The basic process diagram of the method for testing and evaluating the liquefaction level of soil layers in this embodiment is shown;

[0026] Figure 2 A schematic diagram of drilling a hole downward from the ground for the method of testing and evaluating the liquefaction level of a soil layer in this embodiment;

[0027] Figure 3 For the method of testing and evaluating the liquefaction level of soil layers in this embodiment, a test hole is dug in the soil layer to be tested;

[0028] Figure 4 The diagram shows the arrangement of the vibration generators for the method of testing and evaluating the liquefaction level of soil layers in this embodiment. DETAILED DESCRIPTION

[0029] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0030] The present application embodiment provides a method for testing and evaluating the liquefaction level of soil layers, such as Figure 1 As shown, the following steps are included:

[0031] In step S101, a cylindrical latex membrane is pre-arranged at the bottom of the vibration generator, and the lower part of the latex membrane is fixed on the circumference of the bottom of the vibration generator. In some examples, the bottom of the vibration generator is a circular organic glass plate, and the lower part of the latex membrane can be fixed on the circumference of the organic glass plate. In some embodiments, a small hole is pre-opened in the middle of the organic glass plate, and a pore water pressure gauge is installed in the small hole, and the head of the pore water pressure gauge extends outward.

[0032] In step 102, the maximum acceleration of the vibration generator is set according to the design basic earthquake acceleration value of the area to be tested, and the frequency of the vibration generator is set according to the earthquake grouping and site category of the area to be tested. This step can also be set in advance based on the basic information of the area to be tested.

[0033] like Figure 2 , Figure 3 As shown, in step 103, a hole is drilled downward from the ground until the soil layer to be tested is reached, and a test hole is dug in the soil layer to be tested, wherein the depth of the test hole is adapted to the height of the latex film provided at the bottom of the vibration generator. In some exemplary embodiments, drilling a hole downward from the ground until the soil layer to be tested also includes protecting the borehole wall with a casing.

[0034] like Figure 4 As shown, in step 104, the vibration generator is placed in the drill hole, and the latex membrane provided at the lower part of the vibration generator is placed in the test hole.

[0035] In step 105, the latex membrane is inflated so that the membrane wall of the latex membrane is in close contact with the wall of the test hole.

[0036] In step 106, the vibration generator is started, the pore water pressure value tested by the pore water pressure gauge is monitored, and the maximum pore water pressure Pmax is recorded.

[0037] In step 107, the liquefaction level of the excavated layer is evaluated based on the ratio of the recorded maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer.

[0038] In some exemplary embodiments, the frequency of the vibration generator is set according to the earthquake grouping and site category of the area to be tested according to the seismic design code. For example, for a soil layer with the earthquake grouping being the first group and the site category being I1, according to Table 5.1.4-2 of the seismic design code (GB50011-2011), the frequency of the vibration generator is set to 1 / 0.25 = 4 Hz.

[0039] In some exemplary embodiments, inflating the latex membrane so that the membrane wall of the latex membrane is in close contact with the wall of the test hole includes: determining the inflation pressure according to the estimated static soil pressure, wherein the static soil pressure coefficient K0=1-sinφ, φ is the internal friction angle of saturated silt sand. For example, when φ is 20 degrees to 25 degrees, the determined K0 can be 0.6, and the static soil pressure is estimated as 0.6 times the self-weight pressure Pc of the overlying soil layer. After recording the maximum pore water pressure Pmax, turn off the vibration generator;

[0040] In some exemplary embodiments, evaluating the liquefaction level of the excavated layer according to the ratio of the recorded maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer includes:

[0041] When Pmax / Pc ≤ 0.33, it is the slight liquefaction level;

[0042] When 0.33 < Pmax / Pc ≤ 0.66, it is the medium liquefaction level;

[0043] When 0.66 < Pmax / Pc, it is the severe liquefaction level.

[0044] The method of the embodiment of the present application pre-sets the vibration acceleration and frequency of the vibration generator according to the design basic seismic acceleration value, seismic group and site category. A pore water pressure gauge is arranged in the vibration generator. After drilling to the depth of the soil layer to be measured, the vibration generator is lowered, and the change of the pore water pressure in the soil layer is monitored through the pore water pressure gauge. According to the ratio of the maximum pore water pressure Pmax to the self-weight pressure Pc of the overlying soil layer, the liquefaction level of the soil layer is evaluated.

[0045] In addition, although the exemplary embodiments have been described herein, their scope includes any and all embodiments based on the present disclosure with equivalent elements, modifications, omissions, combinations (e.g., schemes that cross various embodiments), adaptations or changes. It is not limited to the examples described in this specification or during the implementation of this application, and the examples will be interpreted as non-exclusive.

[0046] The above description is intended to be illustrative rather than restrictive. For example, the above examples (or one or more of their schemes) can be used in combination with each other. For example, those of ordinary skill in the art can use other embodiments when reading the above description.

[0047] The above embodiments are only exemplary embodiments of the present disclosure. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the essence and protection scope of the present disclosure, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention.

Claims

1. A method for testing and evaluating the liquefaction level of soil layers, characterized in that: Including: A cylindrical latex film is pre - arranged under the vibration generator, and the lower part of the latex film is fixed on the circumference of the bottom of the vibration generator; Set the maximum acceleration of the vibration generator according to the designed basic seismic acceleration value of the area to be measured, and set the frequency of the vibration generator according to the seismic grouping and site category of the area to be measured; Drill a hole from the ground down to the soil layer to be measured, and dig a test hole in the soil layer to be measured, where the depth of the test hole is adapted to the height of the latex film arranged under the vibration generator. Drilling a hole from the ground down to the soil layer to be measured also includes protecting the hole wall of the drill hole with a casing; Put the vibration generator into the drill hole, and place the latex film arranged under the vibration generator into the test hole; Inflate the latex film so that the film wall of the latex film is in close contact with the hole wall of the test hole; Start the vibration generator, monitor the pore water pressure value measured by the pore water pressure gauge, and record the maximum pore water pressure Pmax; Evaluate the soil liquefaction grade according to the ratio of the recorded maximum pore water pressure Pmax to the self - weight pressure Pc of the overlying soil layer; Inflating the latex film so that the film wall of the latex film is in close contact with the hole wall of the test hole includes: Determine the inflation pressure according to the estimated earth pressure at rest, where the coefficient of earth pressure at rest K0 = 1 - sinφ, and φ is the internal friction angle of the saturated silty sand; The bottom of the vibration generator is an organic glass plate. A small hole is pre - drilled in the middle of the organic glass plate, and a pore water pressure gauge is installed in the small hole, and the head of the pore water pressure gauge extends outwards.

2. The method for testing and evaluating the liquefaction level of soil layers according to claim 1, characterized in that: Setting the frequency of the vibration generator according to the seismic grouping and site category of the area to be measured is completed according to the seismic design code.

3. The method for testing and evaluating soil liquefaction level according to claim 1, characterized in that: Evaluating the soil liquefaction grade according to the ratio of the recorded maximum pore water pressure Pmax to the self - weight pressure Pc of the overlying soil layer includes: When Pmax / Pc ≤ 0.33, it is a slight liquefaction grade; When 0.33 < Pmax / Pc ≤ 0.66, it is a medium liquefaction grade; When 0.66 < Pmax / Pc, it is a severe liquefaction grade.

Images