CN113722929B - Calculation method of shear strength of unsaturated expansive soil - Google Patents
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- CN113722929B CN113722929B CN202111060456.3A CN202111060456A CN113722929B CN 113722929 B CN113722929 B CN 113722929B CN 202111060456 A CN202111060456 A CN 202111060456A CN 113722929 B CN113722929 B CN 113722929B
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- 239000002689 soil Substances 0.000 title claims abstract description 139
- 238000004364 calculation method Methods 0.000 title claims abstract description 50
- 238000010276 construction Methods 0.000 claims abstract description 10
- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 7
- 238000012360 testing method Methods 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
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- 239000011148 porous material Substances 0.000 claims description 4
- 230000008569 process Effects 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 2
- 238000010008 shearing Methods 0.000 claims 1
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- 238000013461 design Methods 0.000 abstract description 2
- 238000012544 monitoring process Methods 0.000 abstract description 2
- 238000011835 investigation Methods 0.000 abstract 1
- 238000011160 research Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000007791 dehumidification Methods 0.000 description 2
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- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
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Abstract
The invention discloses a calculation method of the shear strength of unsaturated expansive soil, which comprises the following steps: determining a construction engineering site as an unsaturated expansive soil distribution area, on-site distribution monitoring soil body saturation, obtaining unsaturated expansive soil shear strength calculation parameters, effective stress calculation of the unsaturated expansive soil, and calculating the shear strength of the unsaturated expansive soil; the invention is based on the effective stress principle of classical soil mechanics, adopts saturation to uniformly consider the non-saturation and expansibility of the soil body according to the soil-water-force characteristics, comprehensively considers the action of stress, provides a calculation formula of the shear strength of the non-saturated expansion soil, and can provide a scientific, reasonable, simple and feasible shear strength calculation method for engineering investigation and design of the non-saturated expansion soil area so as to simply and effectively reflect the comprehensive influence of the non-saturation and expansibility of the soil body on the shear strength of the soil body, thereby achieving the purposes of reasonably controlling engineering cost, effectively reducing engineering risk, filling standard blank and integrally improving engineering quality.
Description
Technical Field
The invention relates to the technical field of geotechnical engineering stability, in particular to a calculation method of shear strength of unsaturated expansive soil.
Background
The unsaturated expansive soil has extremely complex physical and mechanical properties due to the influence of mineral composition, grain size grading, hydration property, hydraulic property and other factors; especially in the process of increasing the saturation of unsaturated expansive soil, the shear strength of the soil is rapidly reduced due to the change of the volume weight, cohesive force, internal friction angle, matrix suction force, expansive force and other parameter properties of the soil, the stability of related engineering is seriously affected, and the risk of the engineering is greatly increased.
At present, in the construction engineering of unsaturated expansive soil areas, related calculation on the aspect of soil expansion deformation is mainly carried out by adopting 'building technical Specification of expansive soil areas' (GB 50112-2013), so that the calculation content on the aspect of the shear strength of the expansive soil is very little, and the calculation on the shear strength of the unsaturated expansive soil is not yet presented. In view of the situation, in the actual construction engineering of the expansive soil area, the related design mainly uses an empirical method to reduce the related calculation parameters to avoid the risk caused by expansibility, and the related reduction coefficient also lacks perfect theoretical basis and proof of strict logic, so that the value of the coefficient often has great artificial property and uncontrollability, which can lead the engineering cost to be increased sharply and simultaneously the engineering risk to be still not controlled effectively. Therefore, aiming at the huge annual engineering construction quantity and related engineering accidents in the unsaturated expansive soil area, a scientific, reasonable, simple and practical method for accurately obtaining the shear strength of the soil body by considering detailed calculation is urgently needed, and the purposes of reasonably controlling the engineering cost, effectively reducing the engineering risk, filling the standard blank and integrally improving the engineering quality are achieved.
Disclosure of Invention
Aiming at the defect of the existing unsaturated expansive soil shear strength calculation, the invention aims to provide a calculation method of the unsaturated expansive soil shear strength, which is a shear strength calculation method with perfect theoretical basis, simple form, scientific and reasonable, simple and applicable, can effectively solve the defect of the existing unsaturated expansive soil shear strength calculation, can provide higher technical guarantee for actual engineering, and effectively ensures the quality safety of the engineering.
In order to achieve the above object, the present invention adopts the following solutions: the calculation method of the shear strength of the unsaturated expansive soil comprises the following steps:
(1) According to the definition of the expansive soil in the existing expansive soil region building technical specification, determining the construction engineering field as an unsaturated expansive soil distribution region;
(2) On the basis of the step (1), according to the characteristics of the existing unsaturated expansive soil region construction engineering, the saturation of the soil body is monitored in real time by site distribution;
(3) According to a shear strength test of unsaturated soil expansive soil in saturation, determining calculated values c and phi of soil cohesive force and internal friction angle;
(4) Based on the steps (2) and (3), obtaining VG model calculation parameters from the soil-water characteristic test results, wherein the VG model calculation formula is as follows:
s＝α[(S r0 +ΔS r ) β/(1-β) -1] 1/β
wherein: s is the suction of the substrate, unit kPa, and has: s=u a -u w ，u a For pore air pressure, u w Is pore water pressure; s is S r0 、ΔS r The method is characterized by respectively comprising the following steps of initial saturation of soil mass and incremental saturation, wherein the units are: the%is as follows: 0.ltoreq.DeltaS r ≤1-S r0 The method comprises the steps of carrying out a first treatment on the surface of the Alpha and beta are calculation parameters of the VG model;
and (2) combining the step, and obtaining calculation parameters of the expansion force and the initial saturation and the incremental saturation respectively by an expansion force test, wherein the calculation formula of the expansion force is provided for the first time as follows:
wherein: p (P) s As expansion force, unit: kPa; s is S r0 、ΔS r The method is characterized by respectively comprising the following steps of initial saturation of soil mass and incremental saturation, wherein the units are: the%is as follows: 0.ltoreq.DeltaS r ≤1-S r0 The method comprises the steps of carrying out a first treatment on the surface of the a. b and k are respectively calculated parameters of expansion force and initial saturation and incremental saturation;
(5) Assuming that the unsaturated expansive soil is redistributed in saturation due to the change of water in the initial saturation state, the saturation of the soil is increased by delta S r And the soil body is atThe volume remains unchanged during the process (i.e. without regard to the shear-expansion of the soil). And (3) combining the related calculation formula in the step (4), deriving the effective stress principle of the unsaturated soil expansion soil according to the classical soil mechanics effective stress principle, and providing the following calculation formula of the effective stress principle of the unsaturated soil:
wherein: sigma' is the effective stress of soil mass, unit: kPa; sigma is soil action stress; n is soil porosity, and is determined by an indoor basic geotechnical test;
(6) In combination with the calculated values of the parameters in the steps (3), (4) and (5) and the effective stress of the unsaturated expansive soil, on the premise of coulomb criterion, and in combination with the research of Fredlund, vanapalli and the like, the shear strength calculation formula of the unsaturated expansive soil without considering the influence of the shear expansion of the soil body is provided as follows:
wherein: τ is soil shear strength, unit: kPa; sigma is soil action stress; c. phi is the effective cohesion and the effective internal friction angle of unsaturated expansive soil when saturated.
The beneficial effects of the invention are as follows: firstly, in the step (4), the calculation relation between the matrix suction representing the unsaturated soil characteristics and the total saturation is given; secondly, providing a calculation relation between the expansion force and the initial saturation and between the expansion force and the incremental saturation; the unsaturation and expansibility of the soil body can be uniformly calculated by the saturation of the soil body through the two calculation relations; then uniformly considering the unsaturation and expansibility of the soil body by an effective stress calculation method of the unsaturated expansive soil; and finally, on the basis of the steps (1) to (5), providing a calculation method of the shear strength of the unsaturated expansive soil on the basis of the coulomb criterion, thereby calculating and obtaining the shear strength of the unsaturated expansive soil. The shear strength of any saturation degree under the soil body humidification condition can be calculated by each parameter of the unsaturated soil shear strength calculation formula obtained by each test (if the shear strength under the dehumidification condition is calculated, only the expansion force calculation term is needed to be ignored). Based on the effective stress of saturated soil mechanics, the unsaturated property and the expansibility of the soil body are uniformly considered by adopting the saturation according to the soil-water-force characteristics, and the effect of the stress is comprehensively considered, so that a calculation formula of the shear strength of the unsaturated expansive soil is provided, the foundation can be scientifically and reasonably provided for the construction engineering of the unsaturated expansive soil area, the influence of the unsaturated property and the expansibility of the soil body on the shear strength of the soil body can be simply and effectively reflected, the reasonable control of the engineering cost is achieved, and the aims of effectively reducing the engineering risk, filling the standard blank and integrally improving the engineering quality are fulfilled.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a soil grading curve of the present invention;
FIG. 2 is a graph showing the soil-water characteristics of the present invention;
FIG. 3 is an expansion force curve of the present invention;
fig. 4 is a schematic diagram of a flow chart for calculating the shear strength of unsaturated expansive soil.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The technical scheme of the present invention is further defined below in conjunction with the specific embodiments, but the scope of the claimed invention is not limited to the description.
Based on the effective stress of saturated soil mechanics, the unsaturated property and the expansibility of the soil body are uniformly considered by adopting the saturation according to the soil-water-force characteristics, and the effect of the stress is comprehensively considered, so that a calculation formula of the shear strength of the unsaturated expansive soil is provided, the foundation can be scientifically and reasonably provided for the construction engineering of the unsaturated expansive soil area, the influence of the unsaturated property and the expansibility of the soil body on the shear strength of the soil body can be simply and effectively reflected, the reasonable control of the engineering cost is achieved, and the aims of effectively reducing the engineering risk, filling the standard blank and integrally improving the engineering quality are fulfilled.
The specific calculation steps are as follows:
(1) Firstly, confirming that the research soil body is distributed on the unsaturated expansive soil field. The physical and mechanical properties of soil bodies in the unsaturated expansive soil engineering sites in a certain region are shown in table 1 by taking unsaturated expansive soil distributed in three-level places in the certain region as an object, and the grading curve is shown in fig. 1.
TABLE 1 physical and mechanical Properties index of soil in unsaturated expansive soil field in certain region
(2) Determining the initial saturation of the soil body as S according to the field data and the soil body saturation monitoring r0 =70.74%, the saturation of the soil after change is S r1 = 80.61%, delta saturation Δs r ＝9.87％；
(3) According to the shear strength test of unsaturated soil expansive soil in saturation, the calculated values c and phi of the soil cohesive force and the internal friction angle are determined, and the specific parameter values of the embodiment are shown in table 2.
TABLE 2 saturated shear parameter values at different net axial pressures
| Cohesive force/kPa | Internal friction angle/° |
| 30.18 | 13.42 |
(4) Firstly, according to the soil-water characteristic test of the soil body in the unsaturated expansive soil field, a test curve is shown in figure 2; by calculating the formula s=α [ (S) for the experimental results and the VG model r0 +ΔS r ) β/(1-β) -1] 1/β Fitting the available fitting parameters are shown in table 3:
TABLE 3 soil-water characteristic fitting parameters
| α | β | Fitting coefficient R 2 |
| 228.22 | 1.69 | 0.991 |
Then, according to the expansion force test of the soil body in the unsaturated expansion soil field, a test curve is obtained as shown in figure 3, and the test result and the expansion force calculation formula are calculatedFitting, the fitting parameters obtained are shown in Table 4:
table 4 expansion force fitting parameters
| a | b | k | Fitting coefficient R 2 |
| 258.92 | 2.41 | 8.20 | 0.995 |
(5) According to the obtained parameters and the net confining pressure, a calculation formula is calculated according to the effective principle of unsaturated expansive soil
The effective stress of the unsaturated expansive soil is calculated, and the calculation results are shown in Table 5:
TABLE 5 effective stress of unsaturated expansive soil
| Net axial pressure/kPa | 50 | 100 | 150 | 200 |
| Effective stress/kPa | 153.13 | 203.13 | 253.13 | 303.13 |
(6) Combining the parameters alpha, beta, a, b, k, c, phi and the effective stress of the unsaturated expansive soil obtained in the steps (3), (4) and (5), and combining the effective stress with the calculation type
The shear strength of the unsaturated soil expansive soil was calculated as shown in table 6:
TABLE 6 calculated values of shear strength of unsaturated expansive soil
| Net axial pressure/kPa | 50 | 100 | 150 | 200 |
| Shear Strength/kPa | 94.69 | 106.59 | 118.49 | 130.39 |
In summary, the shear strength of any saturation degree under the condition of soil humidification can be calculated by each parameter of the unsaturated soil shear strength calculation formula obtained by each test (if the shear strength under the condition of dehumidification is calculated, only the expansion force calculation term needs to be ignored).
VG model reference: van Genuchten M T V.A closed-form equation for predicting the hydraulic conductivity of unsaturated soils [ J ]. Soil Science Society of America Journal,1980,44 (5): 892-898.
Shear strength calculation Fredlund study reference: fredlund D G, morgensystem N R, widger R A. The Shear Strength of Unsaturated Soils [ J ]. Canadian Geotechnical Journal,1978,15 (3): 313-321.
Shear strength calculation Vanapalli research reference: vanapalli S K, fredlund D G, pufahl DE, et al model for the prediction of shear strength with respect to soil suction [ J ]. Canadian Geotechnical Journal,1996,33 (2): 379-392.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. The calculation method of the shear strength of the unsaturated expansive soil comprises the following steps:
(1) According to the definition of the expansive soil in the existing expansive soil region building technical specification, determining the construction engineering field as an unsaturated expansive soil distribution region;
(2) On the basis of the step (1), according to the characteristics of the existing unsaturated expansive soil region construction engineering, the saturation of the soil body is monitored in real time by site distribution;
(3) According to the shear strength test of unsaturated soil expansive soil in saturation, determining the calculated values of soil cohesive force and internal friction anglec、Φ；
(4) Based on the steps (2) and (3), obtaining VG model calculation parameters from the soil-water characteristic test results, wherein the VG model calculation formula is as follows:
wherein:s is the suction of the substrate, unit kPa, and has:，u a in order to achieve the pore air pressure, the air pressure is,u w is pore water pressure;S r0 、ΔS r the method is characterized by respectively comprising the following steps of initial saturation of soil mass and incremental saturation, wherein the units are: the%is as follows: />；α、βAll are calculation parameters of VG model;
and (2) combining the step, and obtaining calculation parameters of the expansion force and the initial saturation and the incremental saturation respectively by an expansion force test, wherein the calculation formula of the expansion force is provided for the first time as follows:
wherein:P s as expansion force, unit: kPa;S r0 、ΔS r the method is characterized by respectively comprising the following steps of initial saturation of soil mass and incremental saturation, wherein the units are: the%is as follows:；a、b、kthe calculation parameters of the expansion force, the initial saturation and the incremental saturation are respectively calculated;
(5) Assuming that the saturation of the unsaturated expansive soil is redistributed due to the change of water in the initial saturation state, the saturation of the soil body is increased by deltaS r And the volume of the soil body is kept unchanged in the processThe effective stress principle of the unsaturated soil expansion soil is obtained according to the deduction process of the classical soil mechanics effective stress principle by combining the related calculation formula in the step (4) without considering the shearing and expanding property of the soil, and the following effective stress principle calculation formula of the unsaturated soil expansion soil is provided:
wherein:the unit is the effective stress of soil: kPa;σ acting stress on soil body;nthe porosity of the soil body is determined by an indoor basic geotechnical test;
(6) In combination with the calculated values and the effective stress of the parameters in the steps (3), (4) and (5), on the premise of coulomb criteria, a calculation formula of the shear strength of the unsaturated expansive soil without considering the influence of the shear expansibility of the soil body is provided as follows:
wherein:t the shear strength of soil is as follows: kPa;σ acting stress on soil body;cphi is the effective cohesion and the effective internal friction angle of unsaturated expansive soil when saturated.
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