Remodeling sample preparation method for reducing in-situ mechanical properties of sandy soil based on static sounding test
By combining static cone penetration tests with indoor geotechnical tests, in-situ dry and wet densities were calculated, and remolded samples that could truly reflect the in-situ mechanical properties of sand were prepared. This solved the problem of inaccurate test results in traditional methods and achieved a highly representative and low-cost sample preparation method.
Patent Information
- Application Number
- CN202511645083.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-11
- Publication Date
- 2026-02-17
AI Technical Summary
Existing technologies make it difficult to accurately prepare remolded samples that reflect the in-situ mechanical properties of sand through indoor tests. Traditional methods rely on empirical parameters and are disconnected from the in-situ conditions, resulting in inaccurate test results.
Data were obtained by static cone penetration test, and the in-situ relative density was calculated by empirical formula. Dry and wet densities were obtained by combining indoor geotechnical tests. The remolded sample preparation process was controlled to simulate the in-situ state, and the remolded sample was prepared by layered compaction method.
It achieves high representativeness and experimental reliability in the mechanical properties of reconstructed samples, simplifies the preparation process, reduces costs, and is suitable for various engineering survey environments.
Smart Images
Figure BDA0005681686550000031 
Figure BDA0005681686550000041 
Figure BDA0005681686550000061
Abstract
Description
Technical Field
[0001] This application relates to the field of geotechnical engineering testing and geotechnical sample preparation technology, and in particular to a method for preparing reconstituted samples based on static cone penetration tests to restore the in-situ mechanical properties of sand. Background Technology
[0002] Sand is one of the most widely distributed soil types in nature, and its mechanical properties have a decisive influence on foundation bearing capacity, slope stability, and foundation settlement. However, due to the lack of cohesion between sand particles and its strong structure, sand is extremely sensitive to disturbance. During conventional sampling, structural damage easily occurs, leading to a significant reduction in strength. For a long time, the geotechnical engineering community both domestically and internationally has generally considered it difficult to directly obtain undisturbed undisturbed sand samples. my country's "Code for Geotechnical Investigation (2009 Edition)" (GB 50021-2001) stipulates that only Grade I (undisturbed) soil samples can be used for mechanical tests such as strength and consolidation. Since Grade I undisturbed sand samples are difficult to obtain, this seriously affects the accuracy of test results and the reliability of the assessment of sand engineering properties.
[0003] In scientific research, there are methods for obtaining disturbed small sand samples, such as using freezing techniques. However, these methods are costly, complex to operate, and have significant limitations, making them difficult to apply on a large scale in engineering practice. Therefore, using disturbed samples to reconstruct remolded sand samples that can reflect the in-situ mechanical properties, and then conducting related laboratory tests, has become a practical and important technical approach.
[0004] However, traditional methods for preparing reconstituted samples mainly rely on empirical parameters or simple control indicators. For example, they attempt to obtain a small number of "relatively undisturbed" samples from the field, measure their natural density in the laboratory, and use this as the target density for reconstitution. Alternatively, they directly conduct standard compaction tests on disturbed sand in the laboratory, plot the dry density-moisture content curve, and select the maximum dry density and optimum moisture content as the sample preparation standard. Or, based on the qualitative description of the sand layer's compaction in the geological survey report (such as "loose," "slightly dense," "medium dense," "dense," etc.), combined with existing specifications or experience, they assign a relative density value and then calculate the target dry density for sample preparation. These traditional methods generally suffer from several insurmountable problems. The fundamental issue is that the indicators relied upon for sample preparation, including density, dry density, and relative density, are indirectly, vaguely, or even completely disconnected from the in-situ state of the soil. These materials are either difficult to obtain, or they pursue a standardized ideal state, or they rely on subjective human experience and judgment. This leads to a core contradiction: engineers hope to accurately understand the mechanical properties of undisturbed soil through indoor tests, but the standards used to prepare test samples cannot accurately represent the state of undisturbed soil.
[0005] The static cone penetration test (CPT) is an in-situ testing method that requires no sampling, allows for continuous testing, offers high accuracy, and minimizes disturbance. It can simulate the stress state of soil in its in-situ condition. The technology is mature and easy to implement, and it has been widely used for soil layer delineation and parameter estimation. However, currently, there is no technology that directly uses CPT test results to guide the preparation of remolded samples.
[0006] Therefore, there is an urgent need for existing technologies to leverage the advantages of static cone penetration test (CPT) to apply CPT data systems to determine the target density of remolded samples, thereby achieving closed-loop control from in-situ testing to laboratory sample preparation. This would allow for the preparation of sand remolded samples that truly reflect the mechanical properties of the in-situ state, significantly improving the representativeness and reliability of the remolded samples. Summary of the Invention
[0007] The purpose of this application is to provide a method for preparing remolded sand samples based on static cone penetration test (CPT) to restore the in-situ mechanical properties of sand. This method leverages the advantages of CPT to apply CPT data system to determine the target density of remolded sand samples, achieving closed-loop control from in-situ testing to laboratory sample preparation. This method can prepare sand remolded sand samples that truly reflect the mechanical properties of the in-situ state, significantly improving the representativeness and reliability of the remolded sand samples.
[0008] Specifically, this application discloses a method for preparing reconstituted samples based on static cone penetration tests to restore the in-situ mechanical properties of sand, characterized in that the method includes the following steps:
[0009] S1 Static Penetration Test:
[0010] A static cone penetration test was conducted on the target sand layer to obtain static cone penetration test data, including data such as cone tip resistance.
[0011] S2 calculates the in-situ relative density:
[0012] Based on the static cone penetration test data, the in-situ relative density of the sand was calculated using an empirical formula.
[0013] S3 sampling:
[0014] Drilling and sampling were carried out in the target sand layer to obtain sand samples that meet the quality requirements of Grade II to III and Grade IV disturbance samples.
[0015] S4 Indoor Basic Geotechnical Tests:
[0016] The maximum dry density, minimum dry density, and natural moisture content of the sand were obtained by conducting basic indoor geotechnical tests on the sand sample and the disturbed sample.
[0017] S5 calculation of in-situ dry density:
[0018] Based on the relative density, maximum dry density, and minimum dry density obtained in steps S2 and S4, the dry density of sand in its in-situ state is calculated using the definition of relative density.
[0019] S6 calculates wet density:
[0020] Calculate the wet density of the sand in its in-situ state based on the dry density and the natural moisture content.
[0021] Preparation of S7 remodeled samples:
[0022] Using the wet density as the target control index, remolded samples were prepared from disturbed sand.
[0023] In a preferred embodiment, the empirical formula in step S2 is as follows:
[0024]
[0025] Among them, D r For relative density, q c For the cone tip resistance, σ′ v0 To test the effective vertical stress of the overlying soil at the specified depth.
[0026] In a preferred embodiment, the formula for back-calculating the in-situ dry density is as follows:
[0027]
[0028] Among them, D r For relative density, substitute the values into the calculation as decimals, ρ d To calculate the target in-situ dry density; ρ dmin For the minimum dry density, ρ dmax This represents the maximum dry density.
[0029] In a preferred embodiment, the formula for calculating the in-situ wet density in step S6 is as follows:
[0030] ρ=ρ d (1+ω)
[0031] Where ρ is the wet density in g / cm³ 3 ω is the natural moisture content, ρ d This is the in-situ dry density.
[0032] In a preferred embodiment, step S7 employs a layered compaction method to prepare the reshaped sample and then scrapes off the surface after each layer is compacted.
[0033] In a preferred embodiment, the compaction method controls the compaction work and the quality of the sand during the compaction process so that the deviation between the measured wet density and the target wet density of the prepared remolded soil sample does not exceed ±2%.
[0034] In a preferred embodiment, the implementation locations of step S1 and step S3 are located in the same geological unit, and the test depth of step S1 is consistent with the target sand layer depth of step S3.
[0035] In a preferred embodiment, the empirical formula needs to be calibrated and modified regionally or the regional empirical formula can be used directly before it can be used.
[0036] In a preferred embodiment, the maximum and minimum dry densities are determined by standard compaction method, and the natural moisture content is determined by drying method.
[0037] In a preferred embodiment, the method further includes step S8, which is described as follows:
[0038] S8 parameter verification:
[0039] Indoor mechanical tests were conducted on the remolded sample prepared in step S7 to obtain mechanical parameters such as internal friction angle and compression modulus, thereby verifying the consistency between the mechanical parameters of the remolded sample and the in-situ soil.
[0040] The specification of this application contains numerous technical features distributed across various technical solutions. Listing all possible combinations of these technical features (i.e., technical solutions) would make the specification excessively lengthy. To avoid this problem, the various technical features disclosed in the above-described invention, the various technical features disclosed in the following embodiments and examples, and the various technical features disclosed in the accompanying drawings can be freely combined to form various new technical solutions (all of which should be considered as described in this specification), unless such a combination of technical features is technically infeasible. For example, one example discloses feature A+B+C, and another example discloses feature A+B+D+E. Features C and D are equivalent technical means that serve the same function, and technically only one needs to be used; they cannot be used simultaneously. Feature E can technically be combined with feature C. Therefore, the solution A+B+C+D should not be considered as described because it is technically infeasible, while the solution A+B+C+E should be considered as described. Attached Figure Description
[0041] Figure 1 This is an overall flowchart of the method described in this invention. Detailed Implementation
[0042] Through meticulous and in-depth research, the inventors have developed for the first time a method for preparing remolded samples based on static cone penetration tests to reconstruct the in-situ mechanical properties of sand. Compared with existing technologies, this application is the first to combine static cone penetration test data with the remolding sample preparation process system. The target density is directly derived from the in-situ test, scientifically reconstructing the in-situ state and ensuring strong representativeness. Furthermore, this invention uses in-situ wet density as a control index during the remolded sample preparation process, thereby effectively simulating actual compaction and obtaining more realistic mechanical parameters, ensuring the authenticity and accuracy of the entire process.
[0043] Compared with existing technologies, the method adopted in this invention is simple to operate, low in cost, and has a clear principle, standardized process, and strong scalability. Therefore, it does not require complex sampling equipment (such as cryogenic sampling), but only conventional static cone penetration and geotechnical tests. It is suitable for various engineering surveys and scientific research projects and is easy to promote and apply in engineering practice. It is especially suitable for sandy soil environments such as oceans, riverbeds, and loose sedimentary layers where it is difficult to obtain undisturbed samples.
[0044] General Method
[0045] This invention aims to overcome the shortcomings of existing technologies in preparing sand remolded samples, such as uncertain target parameters and disconnection from the in-situ state. It provides a method for preparing high-fidelity remolded samples by accurately inverting in-situ wet density based on static cone penetration test data and using this as a control index.
[0046] Typically, the method of the present invention includes the following steps:
[0047] S1 Static Penetration Test:
[0048] A static cone penetration test was conducted on the target sand layer to obtain static cone penetration test data, including data such as cone tip resistance.
[0049] S2 calculates the in-situ relative density:
[0050] Based on the static cone penetration test data, the in-situ relative density of the sand was calculated using an empirical formula, which is as follows;
[0051]
[0052] Among them, D r For relative density, q c For the cone tip resistance, σ′ v0 To test the effective vertical stress of the overlying soil at the specified depth.
[0053] This formula was proposed by Jamiolkowski et al. (2001) and is recommended by my country's "Technical Specification for Static Penetration Testing of Pore Pressure" (T / CCES1-2017). It is applicable to medium-fine sand to coarse sand soils. When the content of silt or clay particles in the sand is high, regional calibration or correction is required. If there is mature experience in the region, the regional empirical formula can also be used.
[0054] S3 sampling:
[0055] Drilling and sampling were conducted in the target sand layer to obtain sand samples meeting the quality requirements of Grade II to III and Grade IV disturbed samples, wherein:
[0056] The Class II to III sand samples are used for natural moisture content testing and can be collected using sand samplers, thin-walled soil samplers, etc. These samples are soils that have undergone slight to significant disturbance, and whose moisture content and soil structure parameters have changed within an acceptable range compared to their in-situ state. This standard is specified in the Chinese standard "Code for Geotechnical Investigation (2009 Edition)" (GB 50021-2001), which stipulates that Class I to III soil samples can be used for moisture content testing.
[0057] The Class IV disturbed sample refers to a soil sample that has been severely disturbed, whose in-situ structure has been completely destroyed, and whose mechanical properties, water content and other parameters have changed significantly compared to the in-situ state. It can be collected by core tubes and is only used for soil identification, naming and compaction tests, preparation of remolded samples and other purposes.
[0058] S4 Indoor Basic Geotechnical Tests:
[0059] The maximum dry density, minimum dry density, and natural moisture content of the sand were obtained by conducting basic laboratory geotechnical tests on the sand sample and the disturbed sample. Specifically, the natural moisture content of the sand sample was obtained by oven drying, and the maximum and minimum dry densities of the disturbed sample were determined by the standard compaction method specified in the "Standard for Geotechnical Testing Methods" (GB / T 50123).
[0060] S5 calculation of in-situ dry density:
[0061] Based on the relative density, maximum dry density, and minimum dry density obtained in steps S2 and S4, the dry density of the sand in its in-situ state is calculated using the definition of relative density. The specific formula is as follows:
[0062]
[0063] Among them, D r For relative density, substitute the values into the calculation as decimals, ρ d To calculate the in-situ dry density of the target; ρ dmin For the minimum dry density, ρ dmax This represents the maximum dry density.
[0064] S6 calculates wet density:
[0065] Calculate the wet density of the sand in its in-situ state based on the dry density and the natural moisture content. The specific formula is as follows:
[0066] ρ=ρ d (1+ω)
[0067] Where ρ is the wet density in g / cm³ 3 ω is the natural moisture content, ρ d This is the in-situ dry density.
[0068] Preparation of S7 remodeled samples:
[0069] Using the wet density as the control index, remolded samples were prepared using an indoor layered compaction method (e.g., three layers, 25 blows per layer). By adjusting the sand quality and compaction energy, and by roughening each layer, the deviation between the measured density and the target value was ensured to be less than ±2%.
[0070] S8 Mechanical Compliance Verification:
[0071] Triaxial compression, direct shear, and consolidation tests were conducted on the reshaped samples to obtain mechanical parameters such as internal friction angle and compression modulus. These parameters were then compared with empirically derived values from static cone penetration tests or field test results to verify their consistency.
[0072] It should be noted that the process of obtaining the cone tip resistance to calculate the in-situ relative density (i.e., steps S1 and S2) and the process of obtaining the maximum dry density, minimum dry density and natural moisture content of the soil sample (i.e., steps S3 and S4) do not have a specific order. They can be arbitrarily interchanged in the actual use. That is, the specific operation process can be any combination of S1, S2, S3 and S4, as long as S1 comes before S2 and S3 comes before S4.
[0073] The main advantages of this invention are:
[0074] (1) This invention is the first to combine static cone penetration test data with remodeling sample preparation process system. The target density is directly derived from in-situ testing, scientifically restoring the in-situ state and having strong representativeness.
[0075] (2) In the process of preparing the remolded sample, the present invention uses in-situ wet density as the control index, thereby effectively simulating the actual density and obtaining more realistic mechanical parameters, ensuring the authenticity and accuracy of the entire process.
[0076] (3) Compared with the prior art, the method adopted in this invention is simple to operate and low in cost: no complex sampling equipment (such as cryogenic sampling) is required, only conventional static cone penetration and geotechnical test are required, which is applicable to various engineering survey and scientific research projects.
[0077] (4) The method of the present invention has a clear principle, standardized process, strong promotion and easy application in engineering practice, especially suitable for sandy soil environments such as ocean, riverbed, and loose sediment layer where it is difficult to obtain original samples.
[0078] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the invention, but do not limit the invention in any way. It should be understood that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These modifications and improvements all fall within the scope of protection of the present invention.
[0079] Example
[0080] Specifically, one embodiment of the present invention is as follows: Figure 1 As shown, this embodiment mainly involves geotechnical engineering investigation in a coastal sandy soil site (stable groundwater level at a depth of 1.0m). The specific methods are as follows:
[0081] S1 Static Penetration Test:
[0082] At the target depth of 10.0m (effective stress σ′ of the overlying soil) v0 A static cone penetration test was conducted at 100 kPa, and the cone tip resistance was measured; q c =8.0MPa =8000kPa.
[0083] S2 calculates the in-situ relative density:
[0084] Substituting into the formula mentioned above, we get:
[0085]
[0086] Calculate D r =61%.
[0087] S3 sampling:
[0088] Sand samples meeting Class II to III quality requirements and Class IV disturbed samples were collected at a target depth of 10.0m through drilling for indoor testing.
[0089] S4 Indoor Basic Geotechnical Tests:
[0090] The maximum dry density ρ of the target sand layer was determined through indoor compaction and moisture content tests. dmax =1.72g / cm 3 and minimum dry density ρ dmin =1.42g / cm 3 The natural moisture content ω = 21% = 0.21.
[0091] S5 calculation of in-situ dry density:
[0092] Substituting into the formula above, we get:
[0093]
[0094] Solving the equation, we get: ρ d =1.59g / cm 3 .
[0095] S6 calculates wet density:
[0096] Substituting into the formula above, we get ρ = ρ d (1+ω)=1.59×(1+0.21)=1.92g / cm 3 .
[0097] Preparation of S7 remodeled samples:
[0098] With a wet density of 1.92 g / cm³ 3 To control the target, a compaction cylinder with a diameter of 50mm and a height of 100mm was used, with three layers compacted, each layer receiving 25 blows. By adjusting the quality of the sand, the measured wet density after each compaction was maintained at 1.92±0.038g / cm³. 3 Within the specified range, ensure uniform density.
[0099] S8 Mechanical Compliance Verification:
[0100] Indoor triaxial consolidated drainage (CD) tests were conducted on the reshaped samples to measure the peak internal friction angle. The empirical relationship for estimating the in-situ internal friction angle using static cone penetration testing (CPT) proposed by Robertson et al. (1983) is as follows: The inverted in-situ internal friction angle is approximately 39.4°, with a relative error of <1%. The two values are in good agreement, verifying the effectiveness of the method in this embodiment.
[0101] Furthermore, it should be noted that in this patent application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this patent application, if it refers to performing an action according to a certain element, it means performing the action at least according to that element, including two cases: performing the action only according to that element, and performing the action according to that element and other elements. Expressions such as "multiple," "repeatedly," and "various" include two, two times, two kinds, and more than two, more than two times, and more than two kinds.
Claims
1. A method for preparing a remolded sample based on static cone penetration test for restoring in-situ mechanical properties of sandy soil, characterized by, The method comprises the following steps: S1 static sounding test: Performing static sounding test on the target sand layer to obtain static sounding test data, wherein the static sounding test data comprises cone tip resistance data; S2 calculating in-situ relative density: Calculating in-situ relative density of the sand based on the static sounding test data through an empirical formula; S3 sampling: Drilling and sampling the target sand layer to obtain sand samples meeting quality requirements of grade II to III and disturbed samples of grade IV; S4 indoor basic soil test: Obtaining the maximum dry density, minimum dry density and natural moisture content of the sand through indoor basic soil test on the sand samples and the disturbed samples; S5 calculating in-situ dry density: According to the relative density, maximum dry density and minimum dry density obtained in steps S2 and S4, inversely calculating the dry density of the sand in the in-situ state by using a relative density definition formula; S6 calculating in-situ wet density: According to the dry density and the natural moisture content, calculating the in-situ wet density of the sand; S7 remolded sample preparation: Preparing remolded samples of the disturbed sand by taking the in-situ wet density as a target control index.
2. The method of claim 1, wherein, The empirical formula in step S2 is as follows: where D r is the relative density, q c is the cone tip resistance, σ' v0 is the effective vertical stress of the overburden soil at the test depth.
3. The method of claim 1, wherein, The formula for inversely calculating the in-situ dry density is as follows: where D r is the relative density, in decimal form, ρ d is the in-situ dry density of the target; ρ dmin is the minimum dry density, ρ dmax is the maximum dry density.
4. The method of claim 3, wherein, The formula for calculating the in-situ wet density in step S6 is as follows: p = p d (1 + ω) where p is the wet density in g / cm 3 , ω is the natural moisture content, and p d is the in-situ dry density.
5. The method of claim 1, wherein, The remolded sample preparation in step S7 is performed by using a layered compaction method, wherein uniform loading is performed in layers, and a shaving treatment is performed after compaction of each layer, so as to ensure uniform density.
6. The method of claim 5, wherein, In the compaction method, by controlling compaction work and mass of the sand, the deviation of the measured wet density of the prepared remolded sample from the target wet density is not more than ±2%.
7. The method of claim 1, wherein, The implementation positions of step S1 and step S3 are located in the same geological unit, and the test depth of step S1 is consistent with the depth of the target sand layer of step S3.
8. The method according to any of claims 1 or 2, characterized in that, The empirical formula needs to be regionally calibrated and corrected before use, or a regional empirical formula is directly used.
9. The method of claim 1, wherein, The maximum dry density and the minimum dry density are measured by a standard compaction method, and the natural moisture content is measured by a drying method.
10. The method of claim 1, wherein, The method further comprises step S8, which is described as follows: S8 mechanical consistency verification: Performing indoor mechanical test on the remolded sample prepared in step S7 to obtain mechanical parameters such as internal friction angle and compression modulus, so as to verify the consistency of the mechanical parameters of the remolded sample with the in-situ soil body.