Silt state parameter inversion method based on CPTU calibration tank test

Abstract

The invention 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. The method comprises the steps that firstly, a CPTU calibration tank is used for carrying out silt CPTU penetration tests under different overlying stresses, and an initial silt state parameter model is constructed; then considering the influence of the soil pore hydrostatic pressure on the silt state parameters, establishing a relational expression between the overlying effective stress and the silt state parameters, and obtaining a corrected silt state parameter model; and finally, simultaneously establishing the initial silt state parameter model and the corrected silt state parameter model to obtain a total soil state parameter model considering the influence of the hydrostatic pressure of the pores of the soil. According to the scheme, the sea area silt state parameters can be accurately obtained, the method has the advantages of being rapid, simple, high in test result reliability and the like, theoretical support is provided for safety construction of related facilities such as subsea tunnels, cable laying or oil conveying pipelines, and the method has great significance in assessment of silt seabed liquefaction instability.

Description

Technical Field

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

[0002] Silt seabeds are widely distributed in areas of the world where offshore engineering construction is frequent. Seabed instability, such as submarine landslides, poses a major threat to marine engineering construction. Seabed liquefaction and instability under extreme sea conditions are the primary triggering factor for offshore landslides. Previous studies have shown that the deformation properties of silt depend primarily on its relative density and the effective stress level. To simultaneously describe the dual coupled effects of relative density and stress level on silt deformation, K. Been and MG Jefferies proposed the concept of state parameters based on critical state soil mechanics theory.

[0003] Silt state parameters can effectively evaluate the relative density and liquefaction potential of silt. When the state parameter ψ is less than 0, the soil is dense, and increased stress will lead to shear dilation. When the state parameter ψ is greater than 0, the soil is loose, and increased stress will lead to shear contraction, corresponding to the liquefaction-sensitive zone. From a soil mechanics perspective, incorporating the state parameter ψ into the constitutive model allows for the simultaneous consideration of the coupled effects of density and stress, thereby constructing a more unified and scientific silt constitutive model. Furthermore, in engineering practice, the state parameter ψ can directly assess the soil state, which is key to ensuring the safety of marine engineering facilities and is of great significance for assessing liquefaction instability in silt seabeds.

[0004] Most traditional state parameter assessment methods are based on indoor triaxial tests and in-situ testing technologies of high-quality original specimens. However, triaxial compression tests and in-situ testing technologies still have several inherent defects: (1) Triaxial compression tests are time-consuming and labor-intensive; (2) Although on-site in-situ testing technology can better restore the stress state and stress level of the soil, factors such as deep-sea high pressure, ocean currents, temperature, and corrosive environment place high demands on equipment and make the operation complex, thus affecting the stability of the test; (3) Silt itself has fine particles, high water content, and a relatively loose structure, making it easily disturbed, and the cost of deep-sea sampling is high.

[0005] At present, foreign scholars HD Plewes et al. and K. Been et al. have proposed an in-situ state parameter assessment method based on the results of the CPT calibration tank test. However, this method does not consider the influence of factors such as the effective stress and pore water pressure of the overlying soil on the probe when calculating the slope (λ) of the critical state line (CSL) of the soil. In addition, the soil has a strong regional characteristic, which leads to large errors in the calculation of soil state parameters. Summary of the Invention

[0006] In order to solve the problems of high cost, long time, easy interference of soil state, and inapplicability of current cohesionless soil state parameter assessment methods in silt strata, the present invention provides a silt state parameter inversion method based on the CPTU calibration tank test. Considering the influence of soil pore hydrostatic pressure on silt state parameters, a modified silt state parameter model is established. Combined with the initial silt state parameter model, a total soil state parameter model is obtained. This method can accurately obtain the state parameters of silt in marine areas and provide reliable theoretical support for the assessment of liquefaction instability of silt seabeds.

[0007] The present invention is implemented by adopting the following technical solution: a method for inverting silt state parameters based on CPTU calibration tank test, comprising 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; During the penetration test, the cone tip resistance q of the silt under different overburden stress states was obtained. t , side wall friction f s , pore water pressure u0 and other parameter information; establish the normalized cone tip resistance and normalized pore pressure parameter function relationship through parameters such as cone tip resistance, average total stress, average effective stress; based on the slope λ of the silt critical state line CSL 10 The soil specific coefficient is solved by the slope of the critical friction ratio, and the normalized friction ratio and λ are constructed. 10 The functional relationship of is obtained to obtain the initial soil state parameter model; ; in, represents the initial soil state parameter; Q t represents the normalized cone tip resistance, B q represents the normalized pore pressure parameter, 、 represents the soil specific coefficient; Step B: Construct a modified silt state parameter model: Consider the influence of soil pore hydrostatic pressure u1 on silt state parameters and establish the overlying effective stress The relationship between the silt state parameters and the modified silt state parameter model is obtained; ; Step C: Finally, the initial silt state parameter model and the modified silt state parameter model are combined to obtain the total soil state parameter model considering the influence of soil pore hydrostatic pressure; .

[0008] Compared with the prior art, the advantages and positive effects of the present invention are: This scheme considers the influence of soil pore hydrostatic pressure on silt state parameters and modifies the initial silt state parameter model. The initial silt state parameter model is combined with the modified model to accurately obtain the state parameters of marine silt, and more effectively evaluate the relative density and liquefaction potential of silt. It has the advantages of being fast, simple, and having high reliability of test results. In the analysis of geotechnical constitutive models, the state parameter ψ can simultaneously consider the dual coupling effects of density and stress, thereby constructing a more unified and scientific silt constitutive model. In terms of engineering practice applications, the accurate acquisition of the state parameter ψ provides theoretical support for the safe construction of related facilities such as submarine tunnels, cable laying or oil pipelines, and is of great significance for the assessment of liquefaction instability of silt seabeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the process of the silt state parameter inversion method according to an embodiment of the present invention; Figure 2 Schematic diagram of silt penetration test results under 60 kPa overburden stress according to an embodiment of the present invention; Figure 3 Schematic diagram of silt penetration test results under 40 kPa overburden stress according to an embodiment of the present invention; Figure 4 Schematic diagram of silt penetration test results under 20 kPa overburden stress according to an embodiment of the present invention; Figure 5 Schematic diagram comparing the results of the conventional method of the present invention and the triaxial compression test; Figure 6 This is a schematic diagram of silt state parameter errors considering the influence of soil pore hydrostatic pressure according to an embodiment of the present invention; Figure 7 1 is a comparison chart of the method according to an embodiment of the present invention and the triaxial compression test results. DETAILED DESCRIPTION

[0010] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below. Example, a silt state parameter inversion method based on CPTU calibration tank test, such as Figure 1 Said method comprises the following steps: Step A: Conduct CPTU penetration tests on silt under different overburden stresses using a CPTU calibration tank to construct a silt state parameter model; Step B: Construct a modified silt state parameter model: Consider the influence of soil pore hydrostatic pressure u1 on silt state parameters and establish the overlying effective stress The relationship between the silt state parameters and the modified silt state parameter model is obtained; Step C: Finally, the initial silt state parameter model and the modified silt state parameter model are combined to obtain the total soil state parameter model considering the influence of soil pore hydrostatic pressure, thereby achieving accurate acquisition of silt state parameters.

[0011] In order to more clearly understand the solution of the present invention, the solution of the present invention is described in detail below: Step A: Construct a silt state parameter model based on the CPTU calibration tank test. Specifically: Based on the indoor CPTU calibration tank, CPTU penetration tests of silt under different overburden stresses were carried out to obtain the cone tip resistance q of silt under different overburden stress states. t , side wall friction f s , any parameter information of pore water pressure u0; In this embodiment, the penetration equipment used in the indoor CPTU penetration test is a micro-pore pressure static penetration instrument with a cone tip angle of 60°, a probe rod diameter of 16 mm, and a cone base area of ​​200.96 mm. 2 , the unequal area ratio is 0.8, the probe can simultaneously measure three penetration parameters: cone tip resistance q t , pore water pressure u0, side wall friction f s The diameter of the calibration soil sample chamber is 500 mm, and the height of the consolidated soil sample is 600 mm. It can achieve two-way drainage at the top and bottom. The top has a free drainage surface and the bottom is covered with a 30 mm thick sand layer, which can ensure uniform drainage of the soil sample at the bottom of the consolidation chamber. At the same time, soil pressure boxes are arranged on the side walls, top and bottom of the calibration tank respectively.

[0012] (1) Cone tip resistance q obtained through CPTU penetration test t , total overburden pressure , effective stress of overlying soil Establish normalized cone tip resistance Q t Functional relationship; ; The total overburden pressure The effective stress of the overlying soil is measured by the earth pressure box at the bottom of the calibration tank. Total overburden pressure It is obtained by subtracting the pore water pressure u1. The pore water pressure u0 is measured by the CPTU penetration test, and the pore water pressure u1 is obtained by the penetration height h×water density.

[0013] (2) Cone tip resistance obtained through CPTU penetration test q t , pore water pressure u0 , pore hydrostatic pressure u 1 Get the normalized pore pressure parameter B q Functional relationship; ; (3) Normalized pore pressure parameter B q and soil specific coefficient 、 Introducing the soil state parameter relationship, The initial silt state parameter model is obtained: ; in, Represents the initial soil state parameters; soil specific coefficient 、 According to the slope of the critical state line CSL of silt λ 10 and the slope of the critical friction ratio M Solve; ; ; λ 10 is the slope of the critical state line with base 10; M M is the slope of the critical friction ratio. According to existing research, M is generally taken as 1.2.

[0014] In summary, λ 10 For unknown parameters, accurately obtain λ 10 It is the basis for accurately solving the state parameters of silt. Here, we need to solve the parameters λ 10 To determine the accurate expression of the initial silt state parameter model, specifically: Cone tip resistance obtained through CPTU penetration test q t , total overburden pressure σ v0 , side wall friction f s Establishing normalized friction ratio F r Functional relationship; ; Then establish the normalized friction ratio F r and λ 10 The functional relationship of the cone tip resistance is qt , total overburden pressure σ v0 , side wall friction f s Obtain λ 10 : ; Furthermore, λ 10 , normalized cone tip resistance Q t , normalized pore pressure parameter B q Substitute the initial soil state parameter model and obtain: ; In this embodiment, based on the CPTU penetration test, by inserting the penetration test results into the existing state parameter calculation formula and comparing them with the triaxial test results (see Figure 5 ), there is a large error between the existing state parameter calculation formula and the true value. The reason is that the formula is λ 10 When the friction ratio is normalized F r Solve and normalize the friction ratio F r in σ v0 Represents the total overburden pressure, without considering the pore hydrostatic pressure u 1 The influence of existence leads to the results being biased upwards.

[0015] In fact, during the penetration of the CPTU probe, the pore water pressure of the overlying soil affects the cone tip resistance. q t , side wall friction f s There is a significant impact on the calculation λ 10 When appropriate, the effective stress of the overlying soil should be used Solve it.

[0016] against λ 10 Failure to consider pore hydrostatic pressure u 1 , which leads to the state parameter The problem of too large, this embodiment through CPTU penetration test, in the existing state parameters The calculation formula takes into account the pore hydrostatic pressure u 1 , establish the effective stress of the overlying soil The relationship between the soil state parameters and the silt state parameters is used to modify the initial soil state parameter model.

[0017] Step B: Construct a modified silt state parameter model, specifically: ; ; Step C: Combine steps A and B to obtain the soil pore hydrostatic pressure u 1 Total soil state parameter model : ; It can be seen that the total soil state parameter model Including existing soil state parameter models Formula and considering soil pore hydrostatic pressure u 1 Impact Modified State Parameter Model Two parts. Relevant parameters obtained through indoor CPTU penetration test, combined with the results of triaxial compression test and existing soil state parameters Calculation formula, and then correct the soil state parameters The relationship can accurately obtain silt state parameters, effectively evaluating the relative density and liquefaction potential of silt. Ultimately, the total soil state parameter model enables accurate acquisition of marine silt state parameters, providing theoretical support for the safe construction of related facilities such as submarine tunnels, cable laying, and oil pipelines. It is also of great significance for the assessment of liquefaction instability in silt seabeds.

[0018] Experimental verification: In order to prove the effectiveness of this scheme, the sea silt in a certain delta was selected as the research object of the field penetration test, and the silt CPTU penetration test under different overburden stresses was carried out. In order to ensure the accuracy of the model obtained by analyzing the indoor CPTU penetration test results, this embodiment relies on the sea silt near a certain delta to carry out indoor triaxial compression tests, combined with Figure 2-4 As shown in Figure 3, the silt state parameter curves under different overburden stress states are obtained.

[0019] Table 1 Parameters of the test silt under triaxial compression test .

[0020] like Figure 6-Figure 7As shown in the figure, based on the data of CPTU penetration test, the triaxial test results are compared with the correction formula of the present invention. The results show that the silt state parameter inversion method based on the CPTU calibration tank test proposed in the present invention can accurately obtain the silt state parameters under different stress states, and can effectively evaluate the relative density and liquefaction potential of the silt. It has the advantages of being fast, simple, and having high reliability of test results.

[0021] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. The silt state parameter inversion method based on the CPTU calibration tank test is characterized by: The following steps are involved: 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, represents the initial soil state parameter; Q t represents the normalized cone tip resistance, B q represents the normalized pore pressure parameter, 、 represents the soil specific coefficient; Step B: Construct a modified silt state parameter model: Consider the influence of soil pore hydrostatic pressure u1 on silt state parameters, and establish the effective stress of the overlying soil The relationship between the silt state parameters and the modified silt state parameter model is obtained; ； Step C: Finally, the initial silt state parameter model and the modified silt state parameter model are combined to obtain the total soil state parameter model considering the influence of soil pore hydrostatic pressure, thereby achieving accurate acquisition of silt state parameters.

2. The silt state parameter inversion method based on the CPTU calibration tank test according to claim 1 is characterized in that: In step A, the soil specific coefficient 、 According to the slope λ of the critical state line CSL of silt 10 and solve for the critical state friction ratio slope M; ； ； Among them, λ 10 is the slope of the critical state line with a base of 10; M is the slope of the critical state friction ratio.

3. The silt state parameter inversion method based on the CPTU calibration tank test according to claim 1 is characterized in that: In step B, the overlying effective stress It is expressed as follows: ； Where u1 is the soil pore hydrostatic pressure, is the total overburden pressure.

4. The silt state parameter inversion method based on the CPTU calibration tank test according to claim 2 is characterized in that: In the step B, 10 Substitute the initial soil state parameter model and obtain: 。 5. The silt state parameter inversion method based on the CPTU calibration tank test according to claim 4 is characterized in that: In step C, the total soil state parameter model is expressed as follows: ； in, represents the initial soil state parameters, ' represents the modified soil state parameter, q t represents the cone tip resistance, f s Indicates the side wall friction.

6. The silt state parameter inversion method based on the CPTU calibration tank test according to claim 1 is characterized in that: In the step A: (1) Cone tip resistance q obtained through CPTU penetration test t , total overburden pressure , effective stress of overlying soil Establish normalized cone tip resistance Q t Functional relationship; ； (2) Cone tip resistance q obtained through CPTU penetration test t , pore water pressure u0, pore hydrostatic pressure u1 to obtain the normalized pore pressure parameter B q Functional relationship; 。

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