Method for determining displacement-dependent earth pressure of pile wall type foundation pit retaining structure in sandy soil layer

Abstract

The application provides a method for determining displacement-related earth pressure of a pile wall type foundation pit support structure in a sandy soil layer. The method can determine the pore ratio and relative density of each layer of soil in the foundation pit support by sampling, carry out a plane strain loading / unloading test, draw a stress-strain curve, calculate the internal friction angle, initial modulus and failure ratio of the soil, and finally obtain the active and passive earth pressure at any depth of the support structure. The method can calculate the active and passive earth pressure of the pile wall type foundation pit support structure in the sandy soil layer under any displacement, and can consider the influence of the layering of the soil, is more in line with the actual situation, has clear technical scheme steps, and has a simple calculation method. The method can be used in actual engineering to reduce the manpower and material resources, reduce the waste of support materials, and has good popularization and application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of civil engineering, and particularly relates to a method for determining displacement-related soil pressure of a pile wall type foundation pit retaining structure in a sandy soil layer. BACKGROUND

[0002] Underground space as a valuable natural resource has been valued by many countries in the world. At present, the development and utilization of underground space in various cities of China has entered a new stage of higher quality, higher level and higher level, so a large number of foundation pit excavations close to existing buildings and structures have inevitably appeared. During the construction process of such engineering construction, the key factor to ensure the safety of the foundation pit is the calculation and determination of the soil pressure of the foundation pit retaining structure. For deep foundation pit engineering close to existing buildings and structures, the soil on both sides of the retaining structure generally cannot reach the limit state under the strict deformation control requirement of the retaining structure, and the size of the soil pressure actually acting on the retaining structure is related to the actual deformation size of the retaining structure. The traditional Rankine and Coulomb soil pressure theory can only calculate the size of the soil pressure under the limit state, and the calculation method of the size of the soil pressure of the foundation pit retaining structure under the non-limit state in the existing specification, such as the m value method and the equivalent beam method, has the shortcomings that the calculation parameters of different regions and different soil qualities are difficult to determine and human interference factors are large. SUMMARY

[0003] The purpose of the present application is to provide a method for determining displacement-related soil pressure of a pile wall type foundation pit retaining structure in a sandy soil layer to solve the problems involved in the background art.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] The present application provides a method for determining displacement-related soil pressure of a pile wall type foundation pit retaining structure in a sandy soil layer, which comprises the following steps:

[0006] (1) sampling each layer of soil in the design depth range of the foundation pit retaining structure;

[0007] (2) measuring the void ratio e of each layer of soil i and the relative density RD i ;

[0008] (3) using the sampled soil, preparing a unit body soil sample with a void ratio of e in the laboratory by using the K0 consolidation method, the initial stress state of the soil sample is: K i σ 0i = σ z = σ y = σ x , and loading / unloading test under plane strain state is carried out; three or more different σ z are selected for each layer of soil, and loading and unloading tests are carried out respectively;

[0009] (4) According to the results of the plane strain element test, draw the stress-strain curve of the soil in the loading / unloading test;

[0010] (5) According to the stress-strain curve, calculate the internal friction angle of each layer of soil The initial modulus E ci and failure ratio R ci of the soil in the loading test ei , and the initial modulus E ei and failure ratio R z of the soil in the unloading test y ;

[0011] (6) Calculate the active earth pressure and passive earth pressure at any depth z of the pile-wall type foundation pit retaining structure according to the following formula.

[0012] Active earth pressure:

[0013] Passive earth pressure:

[0014] Further, the loading / unloading test in step (3) under the plane strain state keeps the size of the Z-direction stress σ x unchanged, the size of the y-direction strain ε x unchanged, and loading and unloading are performed in the x-direction.

[0015] Further, in step (4), the soil stress-strain curve is drawn, the vertical coordinate is the change amount △σ ci of the x-direction principal stress, and the horizontal coordinate is the x-direction strain ε ci ; in the loading or unloading test curve, the strain is positive for compressive strain and negative for tensile strain.

[0016] Further, in step (5), the initial modulus and failure ratio of the soil in the loading / unloading test are determined by fitting the soil stress-strain curve obtained by the test using the following formula:

[0017]

[0018] After fitting, the initial modulus and failure ratio of the soil in the loading / unloading test are calculated according to the fitting parameters a ei and b ei :

[0019] Loading test:

[0020] Unloading test:

[0021] Further, the step (6) is the initial modulus of the soil at different depths z in the active / passive earth pressure expression And According to the following formula:

[0022]

[0023] Wherein, p a is the atmospheric pressure, H2 is the pile wall type foundation pit excavation depth, k ci , k ei , n ci , n ei The fitting parameters of the loading / unloading test results in the plane strain state are:

[0024]

[0025] The determination method of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer of the application can not only calculate the active and passive earth pressure of the pile wall type foundation pit support structure in the sandy soil layer for any displacement size, but also consider the influence of soil layering, which is more in line with the actual situation. The calculation parameters of the technical scheme are obtained through the shear test of the actual soil layer, the physical meaning is clear, the steps are clear, the calculation method is simple, and it can be used in practical engineering to reduce the manpower, material resources, reduce the waste of support materials, and has good popularization and application value. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a flowchart of the determination method of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer of the application;

[0027] Figure 2 It is the calculation diagram of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer shown in the figure; Figure 1

[0028] Figure 3 It is a stress schematic diagram of the soil sample in the loading and unloading test of the determination method of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer shown in the figure; Figure 1

[0029] It is a stress-strain curve schematic diagram of the loading test of the determination method of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer shown in the figure; Figure 4 Figure 1 It is a stress-strain curve schematic diagram of the unloading test of the determination method of the displacement-related earth pressure of the pile wall type foundation pit support structure in the sandy soil layer shown in the figure.

[0030] Figure 5 Figure 1 DETAILED DESCRIPTION​​​​

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. The described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0032] Please refer to Figures 1-5 , the present application provides a method for determining displacement-related soil pressure of a pile wall type foundation pit retaining structure in a sandy soil layer, the method comprising the following steps:

[0033] (1) drilling and sampling each layer of soil in the design depth range of the foundation pit retaining structure;

[0034] (2) measuring the void ratio e of each layer of soil i and the relative density RD i , the relative density being determined according to the maximum void ratio e maxi and the minimum void ratio e mini of the soil sample:

[0035]

[0036] (3) using the sampled soil, preparing a unit soil sample with a void ratio of e i in the laboratory by K0 consolidation method, the initial stress state of the soil sample being: K0σ z = σ y = σ x , and performing loading / unloading test under plane strain state; for each layer of soil, selecting three or more different σ z to perform loading and unloading tests, respectively;

[0037] (4) according to the results of the plane strain unit test, drawing the stress-strain curve of the loading / unloading test of the soil;

[0038] (5) according to the stress-strain curve, calculating the internal friction angle φ of each layer of soil , the initial modulus E ci and the failure ratio R ci of the soil in the loading test, and the initial modulus E ei and the failure ratio R ei of the soil in the unloading test;

[0039] (6) as shown in the expression of the active soil pressure at any depth z of the pile wall type foundation pit retaining structure: Figure 2

[0040] ​

[0041] The passive earth pressure expression is:

[0042]

[0043] where H1 is the height of the pile wall type foundation pit support structure; S z is the lateral displacement of the pile wall type foundation pit support structure at depth z, with displacement in the direction towards the soil being positive and displacement in the direction away from the soil being negative; γ i is the natural unit weight of the soil layer at depth z; K 0i is the static earth pressure coefficient of the soil layer at depth z; and are the initial moduli E ei and E ci of the soil at depth z, respectively; ψ is the average value of the internal friction angles of all soil layers within the height range of the foundation pit support structure.

[0044] As shown in Figure 3 , the plane strain state loading / unloading test in step (3) keeps the z-direction stress σ z unchanged, the y-direction strain ε y unchanged, and loading is performed in the x-direction.

[0045] As shown in Figure 4 and Figure 5 , the soil stress-strain curve is plotted in step (4), with the vertical coordinate being the change amount △σ x of the x-direction principal stress and the horizontal coordinate being the x-direction strain ε x ; in the loading / unloading test curve, the strain is positive for compressive strain and negative for tensile strain.

[0046] The determination method of the initial modulus and failure ratio of the soil in the loading / unloading test in step (5) is to fit the stress-strain curve in the loading / unloading test according to the following formula: Figure 4

[0047]

[0048] where a ci and a ei are the reciprocals of the tangent slope at the 0 point on the stress-strain curve, b ci and b ei are the reciprocals of the size of the vertical coordinate corresponding to the asymptote of the stress-strain curve. According to the fitting parameters a ci and b ci , a ei and b ei可 , the initial modulus E ci and E ei of the soil in the loading / unloading test, and the failure ratios R ci and R​ei Calculation:

[0049] Loading test:

[0050] Unloading test:

[0051] In actual foundation pit engineering, the stress state of soil at different depths is different, that is, the confining pressure is different, so the initial modulus of soil at different depths and are also different. The initial modulus of soil at different depths z in the active / passive earth pressure expression of step (6) and need to be calculated according to the following formula:

[0052]

[0053] Where, p a is the atmospheric pressure, H2 is the excavation depth of the pile wall type foundation pit, k ci , k ei , n ci , n ei are fitting parameters according to the unloading test results of different confining pressures σ z under the plane strain state. For any soil, according to the test curve under different confining pressures, the corresponding initial modulus E ci and E ei of the soil are obtained according to the method in step (5), the curve with the horizontal coordinate σ z and the vertical coordinate E ci or E ei is drawn, and then the curve is fitted according to the following formula, so as to obtain the corresponding fitting parameters:

[0054]

[0055] The method for determining the displacement-related earth pressure of the pile wall type foundation pit support structure in sandy soil layer of the application can not only calculate the active and passive earth pressure of the pile wall type foundation pit support structure in sandy soil layer for any displacement size, but also consider the influence of soil layering, which is more in line with the actual situation. The technical scheme calculation parameters are obtained through the shear test of the actual soil layer on site, have clear physical meaning, clear steps, and simple calculation method, and can be used in actual engineering to reduce manpower and material resources, reduce the waste of support materials, and have good popularization and application value.

[0056] Finally, it should be noted that the above only describes the preferred embodiments of the present application, and is not limited to the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it can still be modified to the technical solutions described in the foregoing embodiments, or some technical features are replaced, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A method for determining the displacement-dependent earth pressure of a pile wall type foundation pit support structure in a sandy soil layer, characterized by, The method comprises the following steps: (1) sampling each layer of soil in the design depth range of the foundation pit support structure; (2) Determining the void ratio e of each layer of soil i and the relative density RD i ; (3) Using the sampled soil, a unit soil sample with a void ratio of e i = 0. 6 is prepared in the laboratory by K0 consolidation method, and the initial stress state of the soil sample is: 0i σ z = σ y = σ x , and loading / unloading tests under a plane strain state are performed; three or more different σ z are selected for each layer of soil, and loading and unloading tests are performed, respectively; (4) according to the results of the plane strain unit test, drawing the stress-strain curve of the soil in the loading / unloading test; (5) According to the stress-strain curve, the internal friction angle φ of each layer of soil is calculated i , the initial modulus E of the soil in the loading test ci and the failure ratio R ci , and the initial modulus E of the soil in the unloading test ei and the failure ratio R ei ; (6) calculating the active earth pressure and passive earth pressure at any depth z of the pile-wall type foundation pit support structure according to the following formula: Active earth pressure: Passive earth pressure: wherein H1 is the height of the pile wall type foundation pit support structure; S z is the lateral displacement of the pile wall type foundation pit support structure at depth z, with displacement in the direction towards the soil being positive and displacement in the direction away from the soil being negative; γ i is the natural unit weight of the soil layer at depth z; K 0i is the static earth pressure coefficient of the soil layer at depth z; and are the initial moduli E ci and E ei of the soil at depth z, respectively; and ψ is the average value of the internal friction angles of all soil layers within the height range of the foundation pit support structure.

2. The method for determining the displacement-dependent earth pressure of a pile wall type foundation pit support structure in a sandy soil stratum according to Claim 1, wherein The plane strain state loading / unloading test in the step (3) maintains the Z direction stress σ z The size is unchanged, and the y direction strain ε y The size is unchanged, and the x direction is loaded and unloaded.

3. The method for determining the displacement-dependent earth pressure of a pile wall type foundation pit support structure in a sandy soil stratum according to Claim 2, wherein The step (4) draws the stress-strain curve of the soil body, the vertical coordinate is the change amount of the principal stress in the x direction x , and the horizontal coordinate is the strain in the x direction x ; in the loading or unloading test curve, the strain is positive for the compressive strain and negative for the tensile strain.

4. The method for determining the displacement-dependent earth pressure of a pile wall type foundation pit support structure in a sandy soil stratum according to Claim 3, wherein The determination method of the initial modulus and failure ratio of the soil in the loading / unloading test in the step (5) is that the stress-strain curve of the soil obtained through the test is fitted according to the following formula: After fitting, the initial modulus and failure ratio of the soil in the loading / unloading test are calculated according to the fitting parameters a ci and b ci , a ei and b ei . Loading test: Unloading test:

5. The method for determining the displacement-dependent earth pressure of a pile wall type foundation pit support structure in a sandy soil stratum according to Claim 4, wherein The step (6) active / passive earth pressure expression of the initial modulus of the soil at different depths z and The calculation is made according to the following formula: where p a is the atmospheric pressure, H2 is the pile wall foundation pit excavation depth, k ci , k ei , n ci , n ei are fitting parameters of the loading / unloading test results in the plane strain state:

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