Unified disturbance degree evaluation method considering soil stress and structural change

Abstract

The invention discloses a disturbance degree unified evaluation method considering soil stress and structural change, and belongs to the technical field of rock soil and underground engineering. The method comprises the following steps: calculating a soil body average effective stress used for representing a soil body stress state, and a body strain and a shear strain used for representing a soil body initial structure; calculating structural parameters for representing the initial structural property of the soil body; and substituting the calculated average effective stress, the shear strain, the body strain and the structural parameters of the soil body into a soil body disturbance degree evaluation formula, respectively calculating soil body disturbance degrees SDD under an unloading working condition and a loading working condition, and evaluating soil body disturbance caused by underground engineering construction. The method has the beneficial effects that the stress level change and the soil structure change caused by underground engineering construction are comprehensively considered, and the accuracy of disturbance degree evaluation is improved; soil disturbance can be accurately predicted before construction, and the method has important guiding significance on actual engineering deformation prediction, reinforcement scheme optimization and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of rock, soil and underground engineering, and in particular relates to a unified evaluation method for disturbance degree taking soil stress and structural changes into consideration. Background Art

[0002] Soil disturbance will occur during underground construction, such as tunneling and foundation pit excavation. The strength and stiffness characteristics of natural soil will be significantly weakened after being disturbed. The change of soil structure (including fabric and cementation characteristics) is the main factor causing this phenomenon. At the same time, construction disturbance will affect the load transfer and deformation of the stratum, as well as the mechanical response of underground structures near the construction site.

[0003] At present, soil disturbance assessment methods include field tests and indoor tests, mainly through directly measurable soil mechanical parameters, such as cone tip resistance, undrained shear strength, compression index, shear modulus, and structural parameters. However, these mechanical parameters may be affected by additional disturbances during sampling and testing, thus affecting the accuracy of the evaluation. In addition, the above methods cannot predict soil disturbance before construction, which is important for evaluating the response of surrounding strata and underground structures.

[0004] Therefore, a unified disturbance evaluation method that considers soil stress and structural changes is urgently needed to solve the above technical problems. Summary of the invention

[0005] The purpose of the embodiment of the present invention is to provide a unified disturbance evaluation method that takes into account soil stress and structural changes. The method is applicable to cohesive soil and non-cohesive soil, and is applicable to unloading (releasing the in-situ stress of the soil, such as tunneling and foundation pit excavation) and loading (increasing the average effective stress level, such as ground loading and bag grouting) conditions. It can also be used to predict soil disturbance caused by construction disturbance without the need for testing after construction, which is of guiding significance to the project and can solve at least one technical problem involved in the background technology.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows: The embodiment of the present invention provides a unified evaluation method for disturbance degree considering soil stress and structural changes, comprising the following steps: Step S1, calculating the average effective stress of the soil used to characterize the stress state of the soil, and the volume strain and shear strain used to characterize the initial structural properties of the soil; Step S2, calculating structural parameters characterizing the initial structural properties of the soil through a one-dimensional consolidation test; Step S3, substituting the calculated soil average effective stress, shear strain, volume strain and structural parameters into the soil disturbance degree evaluation formula, respectively calculating the soil disturbance degree SDD under unloading conditions and loading conditions, to evaluate the soil disturbance caused by underground engineering construction, wherein: The soil disturbance degree SDD under unloading conditions is calculated by the following formula: ; In the formula, represents the average effective stress of soil after disturbance; represents the average effective stress of soil before disturbance; represents structural parameters; represents the generalized shear strain; represents the failure shear strain; represents body strain; An empirical coefficient that represents the contribution of body structure to the change of soil mechanical properties; The soil disturbance degree SDD under loading conditions is calculated by the following formula: .

[0007] Optionally, in step S1, the average effective stress Including the average effective stress of the soil before disturbance and the average effective stress of the soil after disturbance ,in: Mean effective stress Calculated by the following formula: ; In the formula, , and Represent the effective stresses in the three principal stress directions respectively; Average effective stress of soil before disturbance Calculated by the following formula: ; In the formula, , and They represent the effective stresses in the three principal stress directions before the disturbance; Average effective stress of soil after disturbance Calculated by the following formula: ; In the formula, , and They represent the effective stresses in the three principal stress directions after disturbance.

[0008] Optionally, in step S1, the volume strain Calculated by the following formula: ; In the formula, represents the loading and unloading Poisson’s ratio; ， and represents the stress increments in the three principal stress directions after the disturbance; , and represents the modulus in the three principal stress directions; represents the maximum shear strain; represents the dilatancy angle.

[0009] Optionally, in step S1, the shear strain is characterized by a normalized shear strain obtained by the generalized shear strain and the failure shear strain, wherein: Generalized shear strain Calculated by the following formula: ; In the formula, , , represents the strain increments in the three principal stress directions after disturbance; The failure shear strain is obtained through triaxial consolidated undrained compression tests.

[0010] Optionally, step S2 specifically includes: Step S21, a one-dimensional consolidation test is performed on the soil before disturbance to obtain the soil before disturbance. e - p Curve and e -log p The curve, e - p The structural index is calculated by the curve. e -log p The inherent structural index is calculated from the curve, where: Structural Index Calculated by the following formula: ; In the formula, represents the vertical effective stress; represents the additional void ratio, i.e., vertical effective stress Function of represents the yield stress of soil; Intrinsic structural index Calculated by the following formula: ; In the formula, represents the void ratio of the corresponding ideal remolded soil; Step S22, using the intrinsic structural index Normalized Structural Index Get structural parameters , expressed by the following formula: .

[0011] Optionally, in step S3, there is no clay soil =34, clay soil =31.

[0012] Compared with the prior art, the present invention has the following beneficial effects: (1) The method provided by the present invention comprehensively considers the changes in stress levels and soil structure caused by underground engineering construction, thereby improving the accuracy of disturbance evaluation; (2) The method provided by the present invention introduces structural parameters to characterize the initial structural strength of the soil, and uses volume strain (including shear expansion) and shear strain to reflect the structural changes of the soil after disturbance; empirical parameters related to soil types are obtained through back analysis of underground engineering cases of cohesionless soil and cohesive soil. The method was applied to actual cases to verify its applicability. (3) The method provided by the present invention is applicable to cohesionless soil and cohesive soil with different structural states. At the same time, by considering the change of stress level, the method is applicable to the disturbance evaluation of unloading (releasing the in-situ stress of the soil, such as tunneling and foundation pit excavation) and loading (increasing the average effective stress level, such as ground loading and bag grouting) working conditions. The evaluation results of different working conditions are very consistent with the measured results based on in-situ tests or experiments; (4) The parameters in the method provided by the present invention can be obtained through theoretical methods and numerical simulations to evaluate the disturbance degree of actual underground engineering. Therefore, this method can accurately predict soil disturbance before construction, which has important guiding significance for deformation prediction of actual engineering and optimization of reinforcement schemes. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which: Figure 1 A schematic diagram of key parameters for evaluating soil disturbance degree provided by the present invention; Figure 2 A schematic diagram of structural parameter calculation provided by the present invention; Figure 3 It is a schematic diagram of calculating the disturbance degree of the bottom of a foundation pit in a sandy soil layer provided by the present invention; Figure 4 It is a schematic diagram of calculating the disturbance degree of the underlying stratum during tunnel excavation in soft clay strata provided by the present invention; Figure 5 A schematic diagram of calculating the disturbance degree of soil mass beside bag grouting in silt-sand strata provided by the present invention. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] The terms "first", "second", etc. in the specification and claims of the present invention are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0016] See also Figure 1 As shown, an embodiment of the present invention provides a unified evaluation method for disturbance degree considering soil stress and structural changes, comprising the following steps: Step S1, calculating the average effective stress of the soil used to characterize the stress state of the soil, and the volume strain and shear strain used to characterize the initial structural properties of the soil; Step S2, calculating structural parameters characterizing the initial structural properties of the soil through a one-dimensional consolidation test; Step S3, substituting the calculated soil average effective stress, shear strain, volume strain and structural parameters into the soil disturbance degree evaluation formula, respectively calculating the soil disturbance degree SDD under unloading conditions and loading conditions, to evaluate the soil disturbance caused by underground engineering construction, wherein: The soil disturbance degree SDD under unloading conditions is calculated by the following formula: ; In the formula, represents the average effective stress of soil after disturbance; represents the average effective stress of soil before disturbance; represents structural parameters; represents the generalized shear strain; represents the failure shear strain; represents body strain; An empirical coefficient that represents the contribution of body structure to the change of soil mechanical properties; The soil disturbance degree SDD under loading conditions is calculated by the following formula: .

[0017] In step S1, the average effective stress Including the average effective stress of the soil before disturbance and the average effective stress of the soil after disturbance ,in: Mean effective stress Calculated by the following formula: ; In the formula, , and Respectively represent the effective stresses in the three principal stress directions, which can be obtained through the measured values ​​of the soil pressure sensor and pore water pressure sensor before and after the field test or the relevant soil arch theory; Average effective stress of soil before disturbance Calculated by the following formula: ; In the formula, , and They represent the effective stresses in the three principal stress directions before the disturbance; Average effective stress of soil after disturbance Calculated by the following formula: ; In the formula, , and They represent the effective stresses in the three principal stress directions after disturbance.

[0018] Volumetric strain Calculated by the following formula: ; In the formula, represents the loading and unloading Poisson’s ratio; ， and represents the stress increments in the three principal stress directions after the disturbance; , and The moduli in the three principal stress directions (load and unload modulus or compression modulus, depending on the unloading or loading condition); represents the maximum shear strain, ; represents the dilatancy angle, which can be obtained through triaxial consolidated drained compression test.

[0019] The shear strain is characterized by the normalized shear strain obtained by the generalized shear strain and the failure shear strain, where: Generalized shear strain Calculated by the following formula: ; In the formula, , , represents the strain increments in the three principal stress directions after disturbance; Failure shear strain is used to evaluate the shear strain state. When the shear strain reaches the failure shear strain, it means that the bond between soil particles has been completely destroyed. The failure shear strain can be obtained through triaxial consolidation undrained compression test.

[0020] Step S2 specifically includes: Step S21, a one-dimensional consolidation test is performed on the soil before disturbance to obtain the soil before disturbance. e - p Curve and e -log p For details, see Figure 2 As shown. e - p The structural index is calculated by the curve. e -log p The inherent structural index is calculated from the curve, where: Structural Index ,Right now Figure 2 The area of ​​CDE is calculated by the following formula: .

[0021] In the formula, represents the vertical effective stress; represents the additional void ratio, i.e., vertical effective stress Function of represents the yield stress of soil; It can be seen from the above formula that the structural index is the additional void ratio In the interval [0, ] is the integral value on .

[0022] Intrinsic structural index ,Right now Figure 2 The area of ​​ABCD is calculated by the following formula: ; In the formula, represents the void ratio of the corresponding ideal remolded soil; It can be seen from the above formula that the inherent structural index yes e - p In the curve [0, ] is the area enclosed by the ideal reshaped soil on the surface and the horizontal axis.

[0023] Step S22, using the intrinsic structural index Normalized Structural Index Get structural parameters , expressed by the following formula: .

[0024] In step S3, the cohesionless soil is obtained by back analysis of the vertical unloading test of Fujian standard sand. =34, obtained by reverse analysis of Shanghai soft clay shield tunneling =31.

[0025] The feasibility of the unified evaluation method for disturbance degree taking into account soil stress and structural changes provided by the present invention is verified by using a specific example below.

[0026] (1) Centrifugal model test of foundation pit excavation in dry sand stratum The test was conducted on a ZJU-400 geotechnical centrifuge of a university. The effective rotation radius of the centrifuge was 4.5 m, and the centrifugal acceleration was maintained at 60g during the test. The internal dimensions of the rigid model box used in the test were 1000 mm×400 mm×1000mm (length×width×height). The prototype dimensions of the foundation pit depth and width were 24 m and 15 m, respectively. The soil used in the test was Fujian standard sand with a relative density of 75%. The test used a micro-soil pressure sensor to measure the soil pressure with a measurement accuracy of 1 kPa, and installed multiple pairs of bending elements to measure the shear wave velocity. The corresponding shear modulus can be obtained from the measured shear wave velocity.

[0027] Vertical and horizontal earth pressure sensors are buried at 1.2m, 6m and 11m below the bottom of the foundation pit to monitor the changes in earth pressure during the test. A one-dimensional consolidation test is performed on the soil before the test to obtain its e - p Curve and e -log p Curve, its structural parameter can be obtained as 0.067; Fujian standard sand reference loading and unloading modulus The measured value is 103MPa, from which the loading and unloading modulus at each stress level can be obtained; the volume strain and shear strain can be calculated by the calculation formula; according to the back analysis results, the empirical coefficient of Fujian standard sand Take 34, substitute the required parameters into the soil disturbance degree calculation formula proposed by this method, and the corresponding disturbance degree can be obtained. The results obtained by this method are compared with the measured disturbance degree based on the shear modulus and the disturbance degree calculated by considering only the stress level change, as shown in Figure 3 As shown, it can be seen that the method provided by the present invention has a good fitting effect with the measured disturbance degree, and overcomes the limitation of underestimating soil disturbance by only considering the stress level.

[0028] (2) Field test case of shield tunneling in soft clay strata Combination Figure 4 As shown in the figure, the shield tunnel of a subway is assembled with prefabricated reinforced concrete segments. The outer diameter of the tunnel lining is 6.2m and the thickness is 0.35m. At the monitoring section, the top of the tunnel is buried at a depth of 5.5m. The strata at the construction site are mainly divided into four soil layers. The shallow layer is a fill with a thickness of 1.9m, 1.9-10m is silty clay, 10-18.5m is silty clay, and the lower part is a silty clay layer. The tunnel is mainly located in the silty clay layer and the silty clay layer. Before and after excavation, a static penetration test (CPT) was carried out on the soil of the center line of the tunnel. According to the cone tip resistance results, the measured strength attenuation rate of the soil at a depth of 13m and 15.1m from the surface can be obtained. The soil here is a silty clay layer.

[0029] The average effective stress of the soil after tunneling was obtained by numerical simulation of the shield tunneling process, and the one-dimensional consolidation test of the silty clay before the test was carried out. e - p Curve and e -log p Curve, its structural parameter can be obtained as 0.304; silty clay reference loading and unloading modulus The measured value is 21.1 MPa, from which the loading and unloading modulus at each stress level can be obtained; the volume strain and shear strain can be calculated by the calculation formula; according to the back analysis results, the empirical coefficient of silty clay is Take 31, substitute the required parameters into the soil disturbance degree calculation formula, and the disturbance degree at a depth of 13m and 15.1m from the surface can be calculated. The results obtained by this method are compared with the measured disturbance degree based on undrained shear strength calculation and the disturbance degree calculated by considering only the stress level change. Figure 4 As shown, it can be seen that the method provided by the present invention has a good fitting effect with the measured disturbance degree, and the maximum relative error is 3.5%.

[0030] (3) Case study of bag grouting in silt-sand strata The soil used in the test is a remolded sample of silt mixed with sand. The remolded sample is obtained from the soil sample obtained from the site through constant temperature drying, soil fragmentation, block grinding, vacuum stirring, and consolidation. The porosity ratio e 0=0.8, natural moisture contentw =28.7%. The built grouting indoor experimental system can restore the in-situ stratum stress, simulate the actual boundary conditions, and monitor the physical and mechanical properties of the soil such as stress, deformation and stiffness in real time. Figure 5 As shown in the figure (the figure shows the right half of the model test), the model barrel is 600 mm high and 600 mm in inner diameter (radius is 300 mm). Grouting holes are evenly opened at the front end of the grouting pipe. A rubber bag is installed on the outer sleeve of the pipe. The bag is fixed to the groove of the outer wall by wire, which can realize the time-sharing and segmented expansion of the upper and lower areas. The length of the upper and lower grouting areas is 100 mm. The buried position of the grouting pipe is as follows: Figure 5 As shown in the figure (the top of the grouting area is 100mm away from the pressure plate, and the bottom of the grouting area is 300mm away from the bottom of the model barrel), the servo loading device at the top of the model barrel applies pressure to the pressure plate P v The pore pressure penetration test (CPTU) was carried out before and after the bag grouting to obtain the cone tip resistance and excess pore water pressure of the soil, thereby determining the undrained shear strength of the soil.

[0031] The average effective stress of the soil after tunnel excavation is obtained by the buried earth pressure sensor, and the one-dimensional consolidation test is carried out on the soil before the test to obtain its e - p Curve and e -log p Curve, its structural parameter can be obtained as 0.213; the compression modulus of silt-sand remolded soil The measured value is 4.75 MPa; the volume strain and shear strain can be calculated by the calculation formula; according to the back analysis results, the empirical coefficient of silt inclusion is Take 31, substitute the required parameters into the soil disturbance degree calculation formula, and obtain the Figure 5 As shown in the figure, the radial distance between point A and the expansion point is 240 mm) and the disturbance degree is -60.6%. The measured disturbance degree calculated based on the undrained shear strength is -53.0%. It can be seen that the method provided by the present invention has a good fitting effect with the measured disturbance degree, and the relative error is 14.3%.

[0032] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0033] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A unified evaluation method for disturbance degree considering soil stress and structural changes, characterized in that: The steps include: Step S1, calculating the average effective stress of the soil used to characterize the stress state of the soil, and the volume strain and shear strain used to characterize the initial structural properties of the soil; Step S2, calculating structural parameters characterizing the initial structural properties of the soil through a one-dimensional consolidation test; Step S3, substituting the calculated soil average effective stress, shear strain, volume strain and structural parameters into the soil disturbance degree evaluation formula, respectively calculating the soil disturbance degree SDD under unloading conditions and loading conditions, to evaluate the soil disturbance caused by underground engineering construction, wherein: The soil disturbance degree SDD under unloading conditions is calculated by the following formula: ； In the formula, represents the average effective stress of soil after disturbance; represents the average effective stress of soil before disturbance; represents structural parameters; represents the generalized shear strain; represents the failure shear strain; represents body strain; An empirical coefficient that represents the contribution of body structure to the change of soil mechanical properties; The soil disturbance degree SDD under loading conditions is calculated by the following formula: 。 2. The method according to claim 1, characterized in that In step S1, the average effective stress Including the average effective stress of the soil before disturbance and the average effective stress of the soil after disturbance ,in: Mean effective stress Calculated by the following formula: ； In the formula, , and Represent the effective stresses in the three principal stress directions respectively; Average effective stress of soil before disturbance Calculated by the following formula: ； In the formula, , and They represent the effective stresses in the three principal stress directions before the disturbance; Average effective stress of soil after disturbance Calculated by the following formula: ； In the formula, , and They represent the effective stresses in the three principal stress directions after disturbance.

3. The method according to claim 2, characterized in that In step S1, the volume strain Calculated by the following formula: ； In the formula, represents the loading and unloading Poisson’s ratio; ， and represents the stress increments in the three principal stress directions after the disturbance; , and represents the modulus in the three principal stress directions; represents the maximum shear strain; represents the dilatancy angle.

4. The method according to claim 3, characterized in that In step S1, the shear strain is characterized by the normalized shear strain obtained by the generalized shear strain and the failure shear strain, where: Generalized shear strain Calculated by the following formula: ； In the formula, , , represents the strain increments in the three principal stress directions after disturbance; The failure shear strain is obtained through triaxial consolidated undrained compression tests.

5. The method according to claim 4, characterized in that Step S2 specifically includes: Step S21, a one-dimensional consolidation test is performed on the soil before disturbance to obtain the soil before disturbance. e - p Curve and e -log p The curve, e - p The structural index is calculated by e -log p The inherent structural index is calculated from the curve, where: Structural Index Calculated by the following formula: ； In the formula, represents the vertical effective stress; represents the additional void ratio, i.e., vertical effective stress Function of represents the yield stress of soil; Intrinsic structural index Calculated by the following formula: ； In the formula, represents the void ratio of the corresponding ideal remolded soil; Step S22, using the intrinsic structural index Normalized Structural Index Get structural parameters , expressed by the following formula: 。 6. The method according to claim 5, characterized in that In step S3, there is no clay soil =34, clay soil =31.

Images