CN112903969A - Expansive soil strength evaluation model considering physical and chemical effects - Google Patents

Expansive soil strength evaluation model considering physical and chemical effects Download PDF

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CN112903969A
CN112903969A CN202110109614.3A CN202110109614A CN112903969A CN 112903969 A CN112903969 A CN 112903969A CN 202110109614 A CN202110109614 A CN 202110109614A CN 112903969 A CN112903969 A CN 112903969A
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strength
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expansive soil
suction
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钱建固
林志强
彭慧敏
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Tongji University
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract

The invention relates to a swelled ground strength evaluation model considering physical and chemical effects. The model is based on the analysis of the physical and chemical actions between soil particles and water, and firstly, a traditional soil-water characteristic curve is obtained according to the dehumidification or humidification test data of the expansive soil; secondly, calculating the relationship among the total suction force, the adsorption force (namely physical and chemical acting force) and the saturation to obtain the change curve of the total suction force and the adsorption force along with the saturation; and finally, forecasting the strength of the expansive soil under different suction forces by using the strength in saturation and the strength under a reference suction force. Compared with the prior art, the method has the advantages that the obvious physical and chemical effects among the expansive soil, the soil and the water can be considered, the model parameters have physical significance and are easy to determine, and the like, and the problem that the existing strength prediction model can only aim at one soil can be solved.

Description

Expansive soil strength evaluation model considering physical and chemical effects
Technical Field
The invention relates to the field of unsaturated soil strength, in particular to a method for evaluating the strength of expansive soil by considering physical and chemical effects.
Background
The expansive soil distribution occupies 1/10 of the territorial area of China, and more than 20 provinces, cities and autonomous regions all have expansive soil. The original-state expansive soil in actual engineering is mostly in an unsaturated state and has the characteristics of dilatancy, fracture and hyperconjugation. The change of the water content in the expansive soil can be caused by the reciprocating change of rainfall or relative humidity in the natural environment, and the soil body generates obvious deformation, thereby causing natural disasters such as uneven settlement of building foundations, slope collapse, uplift damage of power transmission towers, damage of retaining walls, cutting damage and the like. In addition, the beneficial use of bentonite as an engineering barrier to nuclear waste has also raised the interest of researchers.
Unsaturated expansive soil, a special soil type, has more complex behaviors and different generation mechanisms than general unsaturated soil. The presence of aggregates in unsaturated expansive soil makes the distribution of large and small pores obvious, and generally has the characteristic of multi-scale pore structure, the property of liquid phase in soil changes with the size of the pores and the positions of the liquid phase in the pores, and the physicochemical action among the small pores of clay is obvious.
Due to the high content of strongly hydrophilic minerals (i.e. montmorillonite and illite), their mechanical behavior is particularly sensitive to changes in suction and is strongly influenced by physicochemical interactions between water and clay minerals (Lu and Likos, 2006; Baker and Frydman, 2009). This is why the study of such expansive soils has been an important and challenging problem.
The unsaturated shear strength of expansive soil plays an important role in understanding and explaining the mechanical behavior of expansive soil. Since the unsaturated soil shear strength test adopts suction control equipment, the manufacturing cost is high, the time consumption is long, and trained personnel are needed, so that a simple and indirect method for obtaining the shear strength by using different prediction formulas is provided. Many of these equations use soil-water characteristic curves (SWCC) and saturated shear strength parameters to estimate the unsaturated shear strength of a soil mass (Vanapelli et al, 1996; Oberg and Sallfors, 1997; Khalili et al, 1998; Lee et al, 2003; Tekinsoy et al, 2004; han and Vanapelli, 2016). Other methods of evaluating the strength of the nonlinear failure envelope using a hyperbolic relationship to represent the unsaturated shear strength are known (Shenyu, 1996; Xun, 1997; Miao et al, 2002; Jiang et al, 2004).
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an expansive soil strength evaluation model considering physicochemical action.
The purpose of the invention can be realized by the following technical scheme: firstly, based on the analysis of the physical and chemical actions between soil particles and water, obtaining a traditional soil-water characteristic curve according to the dehumidification or humidification test data of the expansive soil; secondly, calculating the relationship among the total suction force, the adsorption force (namely physical and chemical acting force) and the saturation to obtain the change curve of the total suction force and the adsorption force along with the saturation; and finally, forecasting the strength of the expansive soil under different suction forces by using the strength in saturation and the strength under a reference suction force.
Compared with the prior art, the invention has the following advantages:
(1) expansive soil, a type of special soil, has a significant physicochemical effect between water and clay minerals due to its high content of strongly hydrophilic minerals (i.e., montmorillonite and illite), which is considered in the present evaluation model;
(2) the evaluation model can consider the influence of external force and soil body structure on the expansive soil strength, and can evaluate the expansive soil strength in a direct shear state, a triaxial state, a drainage state or a non-drainage state;
(3) the data required to evaluate the model of the present invention is derived from conventional shear testing, no additional test support (e.g., mercury intrusion testing) is required, and the model parameters are physically meaningful and easily determinable.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is an FX soil-water characteristic curve;
FIG. 3 is the magnitude of the physicochemical effect;
FIG. 4 is a strength evaluation curve of the swelling soil of jujube Yang.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
This example uses the swelling soil of jujube yang as an example to illustrate the applicability and the specific calculation and analysis steps of the evaluation model of the present invention.
As shown in fig. 1, the present invention relates to a swelled ground strength evaluation model considering physicochemical action, the method comprising the steps of:
step 1: determining an FX form soil-water characteristic curve;
the dehumidifying test of the swelling soil of jujube yang was performed to obtain the relationship between the suction force and the saturation as shown in table 1 below.
TABLE 1 dewetting test of swelling soil for jujube
Figure BDA0002916834310000031
Writing an MATLAB applet for parameter fitting by utilizing a fitting formula of the FX soil-water characteristic curve, specifically using a fittype function, and giving a reasonable parameter value range in the FX fitting formula: lower bound is ops ═ 0.4,1,0,0 ]; upper bound is ops.upper ═ 0.5,2000,12, 12; start point is ops.startpoint ═ 0.68,100,1,1 ]; thereby determining the traditional model of the soil-water characteristic curve, as shown in figure 2.
Step 2: determining the magnitude of the physicochemical effect;
according to the derivation of the equilibrium relationship between thermodynamics (Wei, 2014; Ma et a1, 2016, 2019), the physicochemical interaction between pore water and soil particles can be expressed as:
Π＝ΠD-ρwΩl
where ρ iswDensity of water, piDOsmotic pressure, ΩlSurface force potential energy, which can be determined by the following equation:
Figure BDA0002916834310000032
for general engineering problems, the osmotic attraction force pi is small because the ion concentration is not changed greatlyDCan be ignored and simultaneously
Figure BDA0002916834310000033
Relative ratio to-pwΩlIs very small, so the physicochemical effect after simplification can be expressed as:
Π≈-ρwΩl
according to the relation between the adsorption force and the total suction force, an MATLAB small program is written for quantification, and the size of the physical and chemical action (namely, the adsorption force) is obtained by using a quad function and a known FX soil-water characteristic curve formula, as shown in FIG. 3.
And step 3: determining the saturation intensity and the intensity under the reference suction force;
and carrying out a triaxial shear test under a saturated condition on the jujube yang expansive soil and an unsaturated triaxial shear test under a suction force of 200kPa, wherein the confining pressure is set to be 50kPa and 200 kPa. The test data are shown in table 2.
TABLE 2 triaxial test data of swelling soil for jujube
Figure BDA0002916834310000041
It should be noted that the reference suction force may be a random value, which has little effect on the result. But all strength tests should be accurate.
And 4, step 4: evaluating the unsaturated strength of the jujube yang expansive soil;
the expansive soil is mostly in an unsaturated state under the engineering condition, and the strength of unsaturated soil can be divided into saturation strength and strength contributed by suction:
Q＝Qsat+Qs
Qsatis the strength of saturated soil, QsIs an increase in the strength of the suction contribution. Wherein the intensity caused by the suction force can be expressed as:
Qs＝ASr(s-Π)
wherein Λ represents the contribution of external force, testing technique and soil structure to the strength, SrIs saturation, s is suction, pi is physicochemical action, i.e. adsorption. The intensity at a certain reference suction is:
Qref＝Qsat+ΛSr，ref(sref-Πref)
and (3) obtaining a strength formula of the expansive soil after eliminating the lambda by using the strength formula under the reference suction force:
Figure BDA0002916834310000042
according to the strength evaluation model of the expansive soil, a strength evaluation curve of the jujube yang expansive soil is obtained, as shown in fig. 4.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. An evaluation model for expansive soil strength prediction considering physicochemical action, comprising the steps of:
s1: carrying out a dehumidification test or humidification data of the expansive soil, and obtaining a soil-water characteristic curve of the expansive soil by using an FX model (a model known in the field);
s2: analyzing and calculating the physical and chemical actions between the expansive soil particles and water so as to obtain the relationship among the total suction force, the adsorption force and the saturation;
s3: performing a swelling soil saturation strength test and a strength test under a reference suction force, and providing experimental data for S4;
s4: and deducing to obtain an intensity evaluation formula under any suction by using the saturation intensity and the reference intensity, and making an evaluation curve of the intensity, namely an evaluation model.
2. The evaluation model for expansive soil strength prediction considering physicochemical effects as claimed in claim 1, wherein the detailed contents of step S1 are:
according to the dehumidifying test or humidifying test data of the expansive soil, an MATLAB applet is compiled by utilizing a fitting formula of an FX soil-water characteristic curve to perform parameter fitting, a fittype function is specifically used, and a reasonable parameter value range in the FX fitting formula is given: lower bound is ops ═ 0.4,1,0,0 ]; upper bound is ops.upper ═ 0.5,2000,12,12 ]; start point is ops.startpoint ═ 0.68,100,1,1 ]; thereby determining the traditional model of the soil-water characteristic curve.
3. The evaluation model for expansive soil strength prediction considering physicochemical effects as claimed in claim 1, wherein the detailed contents of step S2 are:
for general engineering problems, the osmotic suction is ignored, and the physicochemical action between the soil body and water is considered to be zero when the soil body is completely saturated; on the basis of the simplification, the physicochemical action between the expansive soil and the water is analyzed to obtain a change curve among the total suction force, the adsorption force and the saturation degree.
4. The evaluation model of expansive soil strength prediction considering physicochemical effect according to claim 2, wherein the determination method of physicochemical effect in step S2 is: by utilizing a thermodynamic correlation equilibrium theory, determining the thermodynamic relationship of microscopic acting forces such as van der Waals force, ionization force, hydration force and the like, and obtaining the physicochemical action in the expansive soil as follows:
Π＝ΠD-ρwΩl
where ρ iswDensity of water, piDOsmotic pressure, ΩlSurface force potential energy, determined by the following equation:
Figure FDA0002916834300000021
Figure FDA0002916834300000022
for general engineering problems, the change of ion concentration is not large, so that the osmotic suction force is piDNeglect while at the same time
Figure FDA0002916834300000023
Relative ratio to-pwΩlIs very slight, and the physicochemical effect after simplification is expressed as:
Π≈-ρwΩl
and further analyzes the relationship between the adsorption force and the total suction force.
5. The model of claim 2, wherein in step S2, an MATLAB applet is written to quantify the relationship between suction force and total suction force, and the magnitude of suction force is determined using the known FX soil-water characteristic curve formula using the quad function.
6. The evaluation model for expansive soil strength prediction considering physicochemical effects according to claim 3, wherein the selected reference suction force is a random value having little influence on the result.
7. The evaluation model of expansive soil strength prediction considering physicochemical effects as claimed in claim 4, wherein the strength of unsaturated soil is divided into saturation strength and suction contribution strength, Q ═ Q-sat+Qs，QsatIs the strength of saturated soil, QsIs an increase in the intensity of the suction contribution, where the intensity caused by suction is denoted as Qs＝ΛSr(S-pi), where Λ represents the contribution of external forces, testing techniques and soil structures to the strength, SrSaturation, s suction, pi physicochemical action, i.e. adsorption; strength under a certain reference suction is Qref＝Qsat+ΛSr，ref(sref-∏ref)。
8. The evaluation model of expansive soil strength prediction considering physicochemical effects as set forth in claim 4, wherein: and (3) obtaining a strength formula of the expansive soil after eliminating the lambda by using the strength formula under the reference suction force:
Figure FDA0002916834300000024
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CN115310026A (en) * 2022-10-12 2022-11-08 海南浙江大学研究院 Bentonite expansive force prediction method and system considering ionic hydration energy

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CN114547864A (en) * 2022-01-21 2022-05-27 湖北工业大学 Prediction method for tensile strength of unsaturated cohesive soil
CN115310026A (en) * 2022-10-12 2022-11-08 海南浙江大学研究院 Bentonite expansive force prediction method and system considering ionic hydration energy
CN115310026B (en) * 2022-10-12 2022-12-30 海南浙江大学研究院 Bentonite expansive force prediction method and system considering ionic hydration energy

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