Method for testing the effect of gravel soil liquefaction foundation treatment by dynamic penetration

Abstract

The invention discloses a method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration test, which relates to the technical field of water conservancy and hydropower engineering. Dynamic penetration test and relative density measurement are carried out in parallel at adjacent points of representative on-site parts, and a functional relationship between the number of dynamic penetration hammer blows and the relative density is established; according to the provisions of the critical relative density of liquefaction in regulations and specifications, the critical number of liquefaction penetration hammer blows corresponding to the critical relative density of liquefaction is obtained through the functional relationship between the number of penetration hammer blows and the relative density; then, dynamic penetration test is carried out on the treated liquefied foundation according to the regulations and specifications, and the treatment effect of the liquefied foundation is judged according to the number of penetration hammer blows; the method can greatly reduce the time, workload and detection cost of gravel soil liquefaction foundation treatment effect detection, and overcome the difficulty of underwater detection.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy and hydropower engineering, and in particular to a method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic probing. Background Art

[0002] At present, the existing regulations and specifications for the identification and detection of liquefied foundations are mainly aimed at sandy soil and silt, and the identification method is mainly based on the standard penetration hammer number method, and its identification results are also the most reliable; but for gravel soil, the soil particle size is relatively coarse, which exceeds the applicable range of the standard penetration hammer number method; the identification and detection of gravel soil liquefaction foundation is mainly based on the relative density method, and its identification results are also relatively reliable.

[0003] However, it is necessary to excavate and take samples on site to determine the relative density. In order to complete the detection of the entire liquefied soil layer, it is necessary to take samples at a certain depth (generally 0.5m) in the depth direction. Before each sampling, it is necessary to determine the natural dry density by water injection or sand injection at the bottom of the well, and it is necessary to excavate multiple shafts for repeated testing. In short, the relative density method is complicated to operate, the detection time is long, the workload is large, and the cost is also high. The excavated shafts have certain damage to the foundation and need to be backfilled. When the groundwater level is high and the liquefied soil layer is below the groundwater level, drainage measures need to be taken, and the relative density detection is more difficult and the cost is higher. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic probing, which solves the problems raised in the above-mentioned background technology.

[0005] To achieve the above purpose, the present invention is implemented by the following technical scheme: a method for detecting the effect of gravel soil liquefaction foundation treatment by dynamic probing, comprising the following steps:

[0006] Step 1: Select a representative location in the site to dig a shaft and measure the natural dry density of the gravel soil d , the number of excavated shafts can be controlled at 1 to 3, and the number of shafts can be increased according to the site area;

[0007] Step 2: Using the gravel soil excavated from the shaft, determine the maximum ρ of the gravel soil according to the requirements of the Geotechnical Test Method Standard GB / T50123 dmax and minimum dry density ρ dmin ;

[0008] Step 3: Calculate the relative density of gravel soil;

[0009] Step 4: Dynamic penetration points are evenly arranged around the shaft, with a distance of 2 to 3 m between the penetration points and the center of the shaft, and the number is not less than 3; determine whether there is an overlying soil layer on the top of the liquefied soil layer. If there is no overlying soil layer, perform dynamic penetration at multiple locations and depths of the liquefied soil layer according to the requirements of the Technical Specification for Building Foundation Testing JGJ340, and obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ';

[0010] Step 5: Calculate the arithmetic mean N of the number of dynamic penetration hammer strikes at the same depth at multiple penetration points around the same shaft. i ;

[0011] Step 6: Use the number of dynamic penetration hammer blows as the vertical coordinate Ni and the relative density as the horizontal coordinate Dr i , N at the same depth i and Dr. i The data set was formed and the least squares method was used to fit Dr i ~N i The least squares fitting is completed using one of Matlab, Mathcad, and Excel software;

[0012] Step 7: According to Appendix P Table P.0.4-1 of GB50487 "Specifications for Geological Investigation of Water Conservancy and Hydropower Engineering", obtain the critical relative density of liquefaction Dr0 according to the peak acceleration of seismic motion; according to Dr0, Dr obtained from step 6 i ~N i The relationship curve is used to get the critical liquefaction hammer number N0 corresponding to Dr0;

[0013] Step 8: According to the requirements of "Technical Specifications for Building Foundation Testing" JGJ340, dynamic penetration testing is performed on multiple locations and depths of the treated liquefied soil layer to obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ";

[0014] Step 9: N i "Compared with N0, when Ni">N0, it means that the foundation is no longer liquefied and the foundation treatment effect meets the requirements.

[0015] Optionally, if there is an overlying soil layer on top of the liquefied soil layer in step 1, a drill is used to drill to 1±0.1m from the top of the liquefied soil layer, and a vertical shaft is manually excavated with an excavation diameter of not less than 1m.

[0016] Optionally, a steel sleeve is used to protect the wall during the excavation of the shaft.

[0017] Optionally, the natural dry density of the gravel soil in step 2 is d The measurement is carried out using either the sand filling method or the water filling method.

[0018] Optionally, the location measured in step 1 is located underwater. When excavating a vertical shaft to measure the relative density, a precipitation pipe well needs to be arranged around the vertical shaft to ensure that the relative density measurement is carried out in a waterless state.

[0019] Optionally, the calculation formula for the relative density of the gravel soil in step 3 is as follows:

[0020]

[0021] Optionally, in step nine, when N i If the ground is still liquefied, further ground liquefaction treatment is required for the unsatisfactory area, and the ground is tested again after treatment until N i '>N0.

[0022] The present invention provides a method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic probing, which has the following beneficial effects:

[0023] This method uses dynamic probing to detect the effect of gravel soil liquefaction foundation treatment. When there is an overlying soil layer on the top of the liquefied soil layer, the drill can be used to drill to 1m above the top of the liquefied soil layer, and then a vertical shaft is manually excavated with an excavation diameter of not less than 1m; to prevent the well wall from collapsing, a steel sleeve is used to protect the wall when necessary. After artificial excavation to the top of the liquefied soil layer, the excavation surface is leveled, and the natural dry density of the gravel soil is determined by the sand filling method or water filling method. When excavating manually, the movements should be as light as possible to avoid excessive disturbance of the test soil layer. The relative density of the liquefied soil layer is measured every 0.5m in the depth direction, and the specific frequency is determined based on the actual project and local engineering experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a fitting curve diagram of the dynamic penetration number and relative density of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] Step 1: Select a representative location in the site to dig a shaft and measure the natural dry density of the gravel soil d , the number of excavated shafts can be controlled at 1 to 3, and the number of shafts can be appropriately increased when the site area is particularly large;

[0027] Step 2: Using the gravel soil excavated from the shaft, determine the maximum ρ of the gravel soil according to the requirements of the Geotechnical Test Method Standard GB / T50123 dmax and minimum dry density ρdmin ;

[0028] Step 3: Calculate the relative density of gravel soil;

[0029]

[0030] Step 4: Dynamic penetration points are evenly arranged around the shaft, with a distance of 2 to 3 m between the penetration points and the center of the shaft, and the number is not less than 3; determine whether there is an overlying soil layer on the top of the liquefied soil layer. If there is no overlying soil layer, perform dynamic penetration at multiple locations and depths of the liquefied soil layer according to the requirements of the Technical Specification for Building Foundation Testing JGJ340, and obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ';

[0031] Step 5: Calculate the arithmetic mean N of the number of dynamic penetration hammer strikes at the same depth at multiple penetration points around the same shaft. i ;

[0032] Step 6: Use the number of dynamic penetration hammer strikes as the vertical coordinate N i , relative density is the horizontal axis Dr i , N at the same depth i and Dr. i The data set was formed and the least squares method was used to fit Dr i ~N i The relationship curve of the least squares fitting can be completed using commercial software such as Matlab, Mathcad, Excel, etc.

[0033] Step 7: According to Appendix P Table P.0.4-1 of GB50487 "Specifications for Geological Investigation of Water Conservancy and Hydropower Engineering", obtain the critical relative density of liquefaction Dr0 according to the peak acceleration of seismic motion; according to Dr0, Dr obtained from step 6 i ~N i The relationship curve is used to interpolate the critical liquefaction hammer number N0 corresponding to Dr0, as shown in Figure 1 As shown;

[0034] Step 8: According to the requirements of "Technical Specifications for Building Foundation Testing" JGJ340, dynamic penetration testing is performed on multiple locations and depths of the treated liquefied soil layer to obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ";

[0035] Step 9: When N i If the ground is still liquefied, further ground liquefaction treatment is required for the unsatisfactory area, and the ground is tested again after treatment until N i '>N0.

[0036] Embodiment 2: The present invention provides a technical solution: a method for detecting the effect of gravel soil liquefaction foundation treatment by dynamic probing, comprising the following steps:

[0037] Step 1: There is an overlying soil layer on the top of the liquefied soil layer. Select a representative part of the site, use a drill to drill to 1±0.1m from the top of the liquefied soil layer, and then manually excavate a vertical shaft with an excavation diameter of not less than 1m. During the excavation of the vertical shaft, a steel sleeve is used for wall protection; according to the requirements of the "Standard for Geotechnical Test Methods" GB / T50123, the natural dry density ρ of the gravel soil is determined by the water injection method d ; The number of excavated shafts can be controlled at 1 to 3. If the site area is particularly large, the number of shafts can be appropriately increased;

[0038] Step 2: Using the gravel soil excavated from the shaft, according to the requirements of the Geotechnical Test Method Standard GB / T50123, the maximum ρ of the gravel soil is determined. dmax and minimum dry density ρ dmin ; The measured location is underwater. When measuring relative density during shaft excavation, it is necessary to arrange drainage pipes around the shaft to ensure that the relative density measurement is carried out in a waterless state;

[0039] Step 3: Calculate the relative density of gravel soil;

[0040]

[0041] Step 4: Dynamic penetration points are evenly arranged around the shaft, with a distance of 2 to 3 m between the penetration points and the center of the shaft, and the number is not less than 3; determine whether there is an overlying soil layer on the top of the liquefied soil layer. If there is no overlying soil layer, perform dynamic penetration at multiple locations and depths of the liquefied soil layer according to the requirements of the Technical Specification for Building Foundation Testing JGJ340, and obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ';

[0042] Step 5: Calculate the arithmetic mean N of the number of dynamic penetration hammer strikes at the same depth at multiple penetration points around the same shaft. i ;

[0043] Step 6: Take the number of dynamic penetration hammer blows as the ordinate Ni and the relative density as the abscissa Dri, and the N i and Dr. i The data set was formed and the least squares method was used to fit Dr i ~N i The relationship curve of the least squares fitting can be completed using commercial software such as Matlab, Mathcad, Excel, etc.

[0044] Step 7: According to Appendix P Table P.0.4-1 of GB50487 "Specifications for Geological Investigation of Water Conservancy and Hydropower Engineering", obtain the critical relative density of liquefaction Dr0 according to the peak acceleration of seismic motion; according to Dr0, Dr obtained from step 6 i ~N i The relationship curve is used to interpolate the critical liquefaction hammer number N0 corresponding to Dr0, as shown in Figure 1 As shown;

[0045] Step 8: According to the requirements of "Technical Specifications for Building Foundation Testing" JGJ340, dynamic penetration testing is performed on multiple locations and depths of the treated liquefied soil layer to obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i ";

[0046] Step 9: When N i If the ground is still liquefied, further ground liquefaction treatment is required for the unsatisfactory area, and the ground is tested again after treatment until N i '>N0.

[0047] Dynamic penetration tests and relative density measurements are carried out in parallel at adjacent points of representative on-site locations to establish a functional relationship between the number of dynamic penetration hammer blows and the relative density. According to the provisions of the critical relative density of liquefaction in the regulations and specifications, the critical number of liquefaction penetration hammer blows corresponding to the critical relative density of liquefaction is obtained through the functional relationship between the number of penetration hammer blows and the relative density. Then, dynamic penetration testing is carried out on the treated liquefied foundation in accordance with the regulations and specifications, and the treatment effect of the liquefied foundation is judged based on the number of penetration hammer blows, as shown in the following table.

[0048]

[0049] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration, characterized in that: The following steps are involved: Step 1: Select a representative location in the site to dig a shaft and measure the natural dry density of the gravel soil d , the number of excavated shafts can be controlled at 1 to 3, and the number of shafts can be increased according to the site area; Step 2: Using the gravel soil excavated from the shaft, determine the maximum ρ of the gravel soil according to the requirements of the Geotechnical Test Method Standard GB / T50123 dmax and minimum dry density ρ dmin ; Step 3: Calculate the relative density of gravel soil; Step 4: Dynamic penetration points are evenly arranged around the shaft, with a distance of 2 to 3 m between the penetration points and the center of the shaft, and the number is not less than 3; determine whether there is an overlying soil layer on the top of the liquefied soil layer. If there is no overlying soil layer, perform dynamic penetration at multiple locations and depths of the liquefied soil layer according to the requirements of the Technical Specification for Building Foundation Testing JGJ340, and obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i '; Step 5: Calculate the arithmetic mean N of the number of dynamic penetration hammer strikes at the same depth at multiple penetration points around the same shaft. i ; Step 6: Use the number of dynamic penetration hammer blows as the vertical coordinate Ni and the relative density as the horizontal coordinate Dr i , N at the same depth i and Dr. i The data set was formed and the least squares method was used to fit Dr i ~N i The least squares fitting is completed using one of Matlab, Mathcad, and Excel software; Step 7: According to Appendix P Table P.0.4-1 of GB50487 "Specifications for Geological Investigation of Water Conservancy and Hydropower Engineering", obtain the critical relative density of liquefaction Dr0 according to the peak acceleration of seismic motion; according to Dr0, Dr obtained from step 6 i ~N i The relationship curve is used to get the critical liquefaction hammer number N0 corresponding to Dr0; Step 8: According to the requirements of "Technical Specifications for Building Foundation Testing" JGJ340, dynamic penetration testing is performed on multiple locations and depths of the treated liquefied soil layer to obtain the dynamic penetration hammer number N of the sand layer at the corresponding location and depth. i "; Step 9: N i "Compared with N0, when Ni">N0, it means that the foundation is no longer liquefied and the foundation treatment effect meets the requirements.

2. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 1 is characterized in that: If there is an overlying soil layer on top of the liquefied soil layer in step 1, a drilling tool is used to drill to 1±0.1m from the top of the liquefied soil layer, and a vertical shaft is manually excavated with an excavation diameter of not less than 1m.

3. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 2, characterized in that: During the excavation of the shaft, a steel sleeve is used to protect the wall.

4. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 1, characterized in that: The natural dry density of the gravel soil in step 2 is d The measurement is carried out using either the sand filling method or the water filling method.

5. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 1, characterized in that: The location measured in step 1 is located underwater. When the relative density is measured during shaft excavation, a drainage pipe well needs to be arranged around the shaft to ensure that the relative density measurement is performed in a waterless state.

6. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 1, characterized in that: The calculation formula of the relative density of the gravel soil in step 3 is as follows:

7. The method for detecting the effect of gravel soil liquefaction foundation treatment by using dynamic penetration according to claim 1, characterized in that: In step nine, when N i If the ground is still liquefied, further ground liquefaction treatment is required for the unsatisfactory area, and the ground is tested again after treatment until N i '>N0.

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