Method for inverting state parameters of silt based on CPTU calibrated tank test

Abstract

The application discloses a silt state parameter inversion method based on a CPTU calibration tank test, and belongs to the technical field of indoor test of geotechnical engineering; firstly, the CPTU calibration tank is used to carry out silt CPTU penetration tests under different overburden stresses, and an initial silt state parameter model is constructed; then, the influence of pore water pressure of the soil body on the silt state parameter is considered, a relationship between the overburden effective stress and the silt state parameter is established, and a corrected silt state parameter model is obtained; finally, the initial silt state parameter model and the corrected silt state parameter model are combined to obtain a total soil body state parameter model considering the influence of the pore water pressure of the soil body. The scheme can realize accurate acquisition of the silt state parameter of a sea area, has the advantages of rapidness, simplicity, high reliability of test results and the like, provides a theoretical support for safe construction of related facilities such as a submarine tunnel, a cable laying or an oil pipeline, and has important significance for evaluation of silt seabed liquefaction instability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geotechnical engineering indoor test, and particularly relates to a silt state parameter inversion method based on CPTU calibration tank test. BACKGROUND

[0002] Silt seabed is widely distributed in the sea area where global marine construction is frequent, and seabed instability such as submarine landslide is the main threat to marine engineering construction. The research shows that the deformation characteristics of silt mainly depend on its relative density and the effective stress level. In order to describe the double coupling effect of the relative density and the stress level change on the deformation properties of silt, K. Been and M. G. Jefferies proposed the state parameter concept based on the critical state soil mechanics theory.

[0003] The silt state parameter can effectively evaluate the relative density and liquefaction potential of silt. When the state parameter ψ < 0, the soil body is in a dense state, and stress increase will lead to soil body shear dilation; when the state parameter ψ > 0, the soil body is in a loose state, and stress increase will lead to soil body shear shrinkage, which corresponds to the liquefaction sensitive area. From the perspective of soil mechanics, the state parameter ψ is introduced into the analysis of the constitutive model, so that the double coupling effect of density and stress can be considered, thereby constructing a more unified and scientific silt constitutive model. In addition, in engineering practice, the state parameter ψ can directly evaluate the state of the soil body, which is the key to ensuring the safety of marine engineering facilities and is of great significance to the evaluation of silt seabed liquefaction instability.

[0004] The traditional state parameter evaluation method is mostly based on indoor triaxial test and in-situ test technology of high-quality undisturbed samples. However, the triaxial compression test and in-situ test technology still have some inherent defects: (1) the triaxial compression test is time-consuming and labor-intensive; (2) although the in-situ test technology can better restore the stress state and stress level of the soil body, the factors such as deep-sea high pressure, ocean current, temperature, and corrosion environment have high requirements for equipment and complex operation, which affects the stability of the test; (3) the silt itself has small particles, high water content, and loose structure, and is easily disturbed, and the cost of deep-sea sampling is high.

[0005] At present, foreign scholars H. D. Plewes and K. Been have proposed an in-situ state parameter evaluation method based on the results of CPT calibration tank test. However, this method does not consider the influence of overlying soil effective stress, pore water pressure and other factors on the probe when calculating the slope (λ) of the critical state line (CSL) of the soil body, and the soil body has strong regional characteristics, thereby leading to large calculation error of the state parameter of the soil body. SUMMARY

[0006] In order to solve the problems of high cost, long time, soil state being easily disturbed and unsuitable for use in silt layer in the current evaluation method of state parameters of cohesionless soil, the present application provides a silt state parameter inversion method based on CPTU calibration tank test, considers the influence of soil pore static water pressure on silt state parameters, establishes a modified silt state parameter model, and combines the initial silt state parameter model to obtain a total soil state parameter model, which can realize accurate acquisition of silt state parameters in sea area and provide reliable theoretical support for evaluation of silt seabed liquefaction instability.

[0007] The present application is realized by adopting the following technical scheme: a silt state parameter inversion method based on CPTU calibration tank test, comprising the following steps:

[0008] Step A, using CPTU calibration tank to carry out silt CPTU penetration test under different overburden stresses, and constructing an initial silt state parameter model;

[0009] In the process of penetration test, parameters such as silt cone tip resistance q t , side wall friction f s , pore water pressure u0 under different overburden stress states are obtained; a normalized cone tip resistance and normalized pore pressure parameter function relationship is established through parameters such as cone tip resistance, average total stress and average effective stress; based on the slope λ 10 of silt critical state line CSL and the critical state friction ratio slope, a specific coefficient of soil is solved, a function relationship of normalized friction ratio and λ 10 is constructed, and an initial soil state parameter model is obtained;

[0010] ;

[0011] Among them, represents the initial soil state parameter; Q t represents the normalized cone tip resistance, B q represents the normalized pore pressure parameter, , represents the specific coefficient of soil;

[0012] Step B, constructing a modified silt state parameter model: considering the influence of soil pore static water pressure u1 on silt state parameters, establishing a relationship between overburden effective stress and silt state parameters, and obtaining a modified silt state parameter model;

[0013] ;

[0014] Step C, finally combining the initial silt state parameter model and the modified silt state parameter model to obtain a total soil state parameter model considering the influence of soil pore static water pressure;

[0015] .

[0016] Compared with the prior art, the application has the advantages and positive effects that:

[0017] The scheme considers the influence of the pore static water pressure of the soil body on the state parameter of the silt, modifies the initial silt state parameter model, combines the initial silt state parameter model with the modified model, realizes accurate acquisition of the silt state parameter in the sea area, and more effectively evaluates the relative compactness and liquefaction potential of the silt, and has the advantages of rapidness, simplicity, high reliability of test results and the like; in the analysis of the rock-soil constitutive model, the state parameter ψ can simultaneously consider the double coupling influences of the density and the stress, so that a more unified and scientific silt constitutive model is constructed; in the engineering practice application aspect, the accurate acquisition of the state parameter ψ provides a theoretical support for the safe construction of the related facilities such as the submarine tunnel, the cable laying or the oil pipeline, and has important significance for the evaluation of the silt seabed liquefaction instability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The silt state parameter inversion method flowchart of the embodiment of the application is shown in the figure;

[0019] Figure 2 The silt penetration test result schematic diagram under the 60kPa overburden stress of the embodiment of the application is shown in the figure;

[0020] Figure 3 The silt penetration test result schematic diagram under the 40kPa overburden stress of the embodiment of the application is shown in the figure;

[0021] Figure 4 The silt penetration test result schematic diagram under the 20kPa overburden stress of the embodiment of the application is shown in the figure;

[0022] Figure 5 The traditional method and the triaxial compression test result comparison schematic diagram of the application is shown in the figure;

[0023] Figure 6 The silt state parameter error schematic diagram of the embodiment of the application considering the influence of the pore static water pressure of the soil body is shown in the figure;

[0024] Figure 7 The method and the triaxial compression test result comparison diagram of the embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above purpose, features and advantages of the application, the application is further described below in combination with the drawings and embodiments. In the following description, a large number of specific details are set forth in order to fully understand the application, but the application can also be implemented in other ways different from those described herein, therefore, the application is not limited to the specific embodiments disclosed below

[0026] The embodiment is a silty soil state parameter inversion method based on a CPTU calibration tank test, which comprises the following steps: Figure 1 The method comprises the following steps:

[0027] Step A: using a CPTU calibration tank to carry out a silty soil CPTU penetration test under different overburden stresses, and constructing a silty soil state parameter model;

[0028] Step B: constructing a modified silty soil state parameter model: considering the influence of soil pore water pressure u1 on the silty soil state parameter, establishing a relationship between the overburden effective stress And the silty soil state parameter, and obtaining a modified silty soil state parameter model;

[0029] Step C: finally, the initial silty soil state parameter model and the modified silty soil state parameter model are combined to obtain a total soil state parameter model considering the influence of soil pore water pressure, and the accurate acquisition of the silty soil state parameter is realized.

[0030] In order to more clearly understand the scheme of the present application, the scheme of the present application will be described in detail as follows:

[0031] Step A: constructing a silty soil state parameter model based on a CPTU calibration tank test, specifically:

[0032] Based on a laboratory CPTU calibration tank, a silty soil CPTU penetration test under different overburden stresses is carried out, and any one of the parameters of the silty soil under different overburden stress states, such as the cone tip resistance q t , the side wall friction f s , and the pore water pressure u0, is obtained;

[0033] In this embodiment, the penetration equipment used in the laboratory CPTU penetration test is a micro-pore pressure static cone penetration instrument, the cone tip angle is 60°, the probe rod diameter is 16 mm, the cone bottom area is 200.96 mm 2 , the unequal area ratio is 0.8, the probe can simultaneously measure three kinds of penetration parameters: the cone tip resistance q t , the pore water pressure u0, and the side wall friction f s , the calibration soil sample chamber has a diameter of 500 mm and a height of 600 mm, can realize top and bottom two-way drainage, top free drainage surface, and bottom 30 mm thick sand layer, which can ensure uniform drainage of the soil sample at the bottom of the consolidation chamber, and the earth pressure cells are arranged on the side wall, top and bottom of the calibration tank.

[0034] (1) the cone tip resistance q t , the total overburden soil pressure , and the overburden soil effective stress obtained by the CPTU penetration test are used to establish a normalized cone tip resistance Q t function relationship;

[0035] ;

[0036] where, total overburden pressure Effective stress of overburden soil is measured by soil pressure cell at the bottom of the tank Subtracting pore water pressure u0 measured by CPTU penetration test from total overburden pressure Pore water pressure u1 is obtained by penetration height h x water specific gravity.

[0037] (2) Tip resistance q0 obtained by CPTU penetration test q t Pore water pressure u0 u 0 Pore water pressure u1 u 1 Normalized pore pressure parameter B q Function relationship;

[0038] ;

[0039] (3) Normalized pore pressure parameter B q and soil specific coefficient 、 Introducing soil state parameter relationship, Obtaining initial silt state parameter model:

[0040] ;

[0041] where, Indicates the initial soil state parameter; soil specific coefficient 、 According to the slope of the critical state line of silt CSL λ 10 And the critical state friction ratio slope M Solve; ; ; λ 10 The slope of the critical state line is 10; M The critical state friction ratio slope is generally taken as 1.2 according to existing research M.

[0042] As can be seen from the above, λ 10 Is an unknown parameter, and accurate acquisition λ 10 Is the basis for accurately solving the state parameters of silt. Here, the parameter λ10 To determine the accurate expression of the initial silt state parameter model, specifically:

[0043] The cone tip resistance obtained by the CPTU penetration test q t The total overburden pressure σ v0 The side wall friction resistance f s Establish the function relationship of the normalized friction ratio F r ;

[0044] ;

[0045] Then establish the function relationship of the normalized friction ratio F r and λ 10 , so as to obtain q t The total overburden pressure σ v0 The side wall friction resistance f s : λ 10

[0046] ;

[0047] Further, the λ 10 Normalized cone tip resistance Q t Normalized pore pressure parameter B q are brought into the initial soil state parameter model, and the following is obtained:

[0048] ;

[0049] In this embodiment, based on the CPTU penetration test, by fitting the penetration test results into the existing state parameter calculation formula and comparing with the triaxial test results (see Figure 5 ), it can be found that there is a large error between the existing state parameter calculation formula and the true value. The reason is that when calculating λ 10 , the normalized friction ratio F r is solved, and F r in the normalized friction ratio σ v0 represents the total overburden pressure, and the pore water pressure u 1 ​The influence exists, and further leads to the result being too large.

[0050] In fact, during the CPTU penetration process, the pore water pressure of the overlying soil has a great influence on the tip resistance q t and the side friction f s When calculating λ 10 , the effective stress of the overlying soil should be used to solve it.

[0051] For λ 10 not considering the pore water pressure u 1 , and further leading to the state parameters being too large, the embodiment considers the pore water pressure on the basis of the existing state parameter u 1 calculation formula, establishes the relationship between the effective stress of the overlying soil and the state parameters of silt, and modifies the initial soil state parameter model.

[0052] Step B, construct the modified silt state parameter model, specifically:

[0053] ;

[0054] ;

[0055] Step C, combine step A and step B to obtain the total soil state parameter model considering the influence of the pore water pressure of the soil u 1 :

[0056] ;

[0057] It can be seen that the total soil state parameter model includes the existing soil state parameter model and the modified state parameter model considering the influence of the pore water pressure of the soil u 1 : Through the related parameters obtained by the indoor CPTU penetration test, combined with the results of the triaxial compression test and the existing soil state parameter calculation formula, the soil state parameter ​​​The formulas can accurately obtain the state parameters of silt, effectively evaluating its relative density and liquefaction potential. Ultimately, the accurate acquisition of marine silt state parameters is achieved through the overall soil state parameter model, providing theoretical support for the safe construction of related facilities such as submarine tunnels, cable laying, or oil pipelines, and is of great significance for assessing the liquefaction instability of silt seabeds.

[0058] Experimental verification:

[0059] To demonstrate the effectiveness of this scheme, silty soil from a delta was specifically selected as the research object for field penetration tests. CPTU penetration tests were conducted on the silty soil under different overlying stresses. As shown in Table 1, to ensure the accuracy of the model derived from the indoor CPTU penetration test results analysis, this embodiment also utilizes silty soil from a near-delta area for indoor triaxial compression tests. Figures 2-4 As shown, the state parameter curves of silt under different overlying stress states are obtained.

[0060] Table 1. Parameters of the test silt under triaxial compression test

[0061] .

[0062] like Figures 6-7 As shown, based on the data from the CPTU penetration test, the triaxial test results are compared with the modified formula of this invention. The results show that the silt state parameter inversion method based on the CPTU calibration tank test proposed in this invention can accurately obtain the silt state parameters under different stress states, effectively evaluate the relative density and liquefaction potential of silt, and has the advantages of being fast, simple, and having high reliability of test results.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for inverting the state parameters of silty soil based on CPTU calibration tank tests, characterized in that, Includes the following steps: Step A: Conduct CPTU penetration tests on silt under different overburden stresses using a CPTU calibration tank to construct an initial silt state parameter model; ； in, Q represents the initial soil state parameters; t B represents the normalized cone tip resistance. q This represents the normalized pore pressure parameter. , Indicates a specific coefficient for the soil; Step B: Constructing a modified silt state parameter model: Considering the influence of soil pore hydrostatic pressure u1 on the silt state parameters, establish the effective stress of the overlying soil. The relationship between the silt state parameters and the state parameters of silt is used to obtain the modified silt state parameter model. ； in 'Indicates the correction of soil state parameters; Step C: Finally, combine the initial silt state parameter model and the modified silt state parameter model to obtain the overall soil state parameter model that considers the influence of soil pore hydrostatic pressure, thus achieving accurate acquisition of silt state parameters. In step B, the effective stress of the overlying soil It is expressed as follows: ； Where u1 is the pore hydrostatic pressure of the soil. This represents the total overlying soil pressure.

2. The method for inverting the state parameters of silt based on the CPTU calibration tank test according to claim 1, characterized in that: In step A, the soil specific coefficient , Based on the slope λ of the critical state line CSL of silt 10 Solve for the slope M of the friction ratio at the critical state; ； ； Where, λ 10 is the slope of the critical state line with base 10; M is the slope of the critical state friction ratio.

3. The method for inverting the state parameters of silty soil based on the CPTU calibration tank test according to claim 2, characterized in that: In step B, λ 10 Substituting the initial soil state parameter model, we get: ； Where, q t Indicates the cone tip resistance, f s This represents the frictional resistance of the sidewall.

4. The method for inverting the state parameters of silt based on the CPTU calibration tank test according to claim 3, characterized in that: In step C, the overall soil state parameter model is represented as follows: ； in, Indicates the initial soil state parameters. 'Indicates the correction of soil state parameters, q t Indicates the cone tip resistance, f s This represents the frictional resistance of the sidewall.

5. The method for inverting the state parameters of silt based on the CPTU calibration tank test according to claim 1, characterized in that: In step A: (1) The cone tip resistance q obtained by CPTU penetration test t Total overburden pressure Effective stress of overlying soil Establish normalized cone tip resistance Q t Functional relation; ； (2) The cone tip resistance q obtained by CPTU penetration test t The normalized pore pressure parameter B is obtained from the pore water pressure u0 and the pore hydrostatic pressure u1. q Functional relation; 。

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