1. A method for enhancing the water softening resistance of soil is characterized by comprising the following steps: the polymer fiber is mixed with the soil body by adopting a fiber mixing or implanting method.

2. The method for enhancing the water softening resistance of a soil body according to claim 1, wherein the method comprises the following steps: the polymeric fiber is PPF chopped fiber, the length is 16-22mm, the diameter is 0.19 +/-0.1 mm, and the elastic modulus is 3.5 GPa.

3. A method for evaluating the water softening resistance of a soil body, which is used for evaluating the soil body enhanced by the method for enhancing the water softening resistance of the soil body according to claim 1 or 2, and comprises the following steps:

s10, calculating water absorption rate based on the mass of the soil body before and after water saturation, obtaining water absorption rate reduction rate according to the water absorption rate of the reinforced soil body and the water absorption rate of the soil body which is not reinforced, and obtaining a water absorption rate reduction rate assigned value S1 of the soil body according to the water absorption rate reduction rate;

s20, calculating volume expansion rate based on the volume of the soil before and after water saturation, obtaining volume expansion rate reduction rate according to the volume expansion rate of the reinforced soil and the soil without reinforcement, and obtaining soil volume expansion rate reduction rate assigned value S2 according to the volume expansion rate reduction rate;

s30, calculating a softening coefficient based on unconfined compressive strength of the soil before and after water saturation, obtaining a softening coefficient enhancement rate according to the softening coefficient of the reinforced soil and the soil which is not reinforced, and obtaining a soil softening coefficient enhancement rate assigned value S3 according to the softening coefficient enhancement rate;

s40, calculating a comprehensive soil water-softening resistance score S based on the soil water absorption reduction rate assigned value S1, the soil volume expansion rate reduction rate assigned value S2 and the soil softening coefficient enhancement rate assigned value S3, and evaluating the soil water-softening resistance according to the S value.

4. The soil mass water-softening resistance evaluation method of claim 3, wherein the calculating of water absorption based on the mass of the soil mass before and after water saturation comprises:

the water absorption evaluation formula is as follows:wherein W_dThe mass of the soil body in the dry state, W_sIs a soil body inMass in the saturated state.

5. The soil mass water-softening resistance evaluation method according to claim 3 or 4, wherein the step of obtaining the soil mass water absorption reduction rate assigned value S1 according to the water absorption reduction rate comprises the following steps:

obtaining an assigned value S1 of the water absorption rate of the soil body according to the water absorption rate reduction rate by contrasting a water absorption rate reduction rate assigned table;

the water absorption reduction rate assignment table is as follows:

water absorption reduction rate/%) ≤15 15-30 30-45 45-60 60-75 75-90 ≥90 score/S1 5 15 30 45 60 75 90

6. The soil mass water-softening resistance evaluation method according to claim 3, wherein the calculating of the volume expansion rate based on the volume of the soil mass before and after water saturation comprises:

the volume expansion rate evaluation formula is as follows:wherein V_dIs the volume of the soil body in a dry state, V_sThe volume of the soil body in a saturated state.

7. The soil mass water-softening resistance evaluation method according to claim 3 or 4, wherein the step of obtaining the assigned value S2 of the volume expansion rate reduction rate of the soil mass according to the expansion rate reduction rate comprises the following steps:

according to the expansion rate reduction rate, comparing with a volume expansion rate reduction rate assigning table, and obtaining a soil volume expansion rate reduction rate assigning value S2;

the volume expansion rate reduction rate is assigned as follows:

volume swell reduction rate/%) ≤5 5-15 15-25 25-35 35-45 ≥45 score/S2 10 20 40 60 80 95

8. The soil mass water-softening resistance evaluation method of claim 3, wherein the step of calculating the softening coefficient based on the unconfined compressive strength of the soil mass before and after water saturation comprises the following steps:

the softening coefficient evaluation formula is as follows:wherein sigma_fThe unconfined compressive strength, sigma, of the soil body in a dry state_FThe confined compressive strength of the soil body in a saturated state is not limited.

9. The soil mass water-softening resistance evaluation method according to claim 3 or 4, wherein the obtaining of the soil mass softening coefficient enhancement rate assigned value S3 according to the softening coefficient enhancement rate comprises:

obtaining a soil body softening coefficient enhancement rate assignment value S3 according to the softening coefficient enhancement rate and a softening coefficient enhancement rate assignment table;

the softening coefficient enhancement rate is given in the following table:

10. the soil body water softening resistance evaluation method according to claim 3, wherein the soil body water softening resistance evaluation according to the S value comprises the following steps:

when S is more than 75 and less than or equal to 100, the soil body has excellent evaluation on the water softening resistance; when S is more than 50 and less than or equal to 75, the soil body has good evaluation on the water softening resistance; when S is more than 25 and less than or equal to 50, the soil body water softening resistance is evaluated to be medium; and when S is more than 0 and less than or equal to 25, the soil body is poor in evaluation of the water softening resistance.

Background

Water has an important influence on the engineering characteristics of the soil body, and the participation of water can cause the volume change and the strength loss of the soil body, and is a main inducing factor of geological disasters such as landslide, debris flow and the like. Common measures for solving the problem of softening of the soil body when meeting water include methods of replacement and filling, cement solidification, anchor rod reinforcement and the like, so that the soil body is physically or chemically reinforced, and the strength and the deformation characteristic of the soil body are improved. The method has good effect in enhancing the strength and stability of the soil body after meeting water, and obtains a great deal of practical benefit, however, the traditional reinforcement methods have the defects of high construction difficulty, high cost and the like.

At present, single indexes such as water absorption rate, volume expansion rate and the like are mainly adopted for evaluating the water softening resistance of the soil body, but the comprehensive evaluation method for the water softening resistance of the soil body is less, the optimal parameters of the reinforcing material cannot be determined, and the indexes need to be systematically evaluated.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in order to solve the problems, a method for enhancing the water softening resistance of soil and an evaluation method are provided.

The technical scheme adopted by the invention is as follows: a method for enhancing the water softening resistance of soil is characterized by comprising the following steps: the polymer fiber is mixed with the soil body by adopting a fiber mixing or implanting method.

The polymer fiber is PPF (polypropylene fiber) chopped fiber, the length is 16-22mm, the diameter is 0.19 +/-0.1 mm, and the elastic modulus is 3.5 GPa. The polypropylene fiber as an artificial synthetic fiber has the advantages of low price, uniform dispersion in soil, good water stability, obvious strength increase and the like, and the polypropylene fiber does not absorb water, thereby having good water softening resistance; compared with plant fibers, the compressive strength of the mixed polypropylene fibers and soil is increased from 352kPa to 500kPa by 42% and the water softening resistance is improved by 65% under the same content.

A soil body water softening resistance evaluation method is used for evaluating a soil body enhanced by the soil body water softening resistance enhancement method, and comprises the following steps:

s10, calculating water absorption rate based on the mass of the soil body before and after water saturation, obtaining water absorption rate reduction rate according to the water absorption rate of the reinforced soil body and the water absorption rate of the soil body which is not reinforced, and obtaining a water absorption rate reduction rate assigned value S1 of the soil body according to the water absorption rate reduction rate;

s20, calculating volume expansion rate based on the volume of the soil before and after water saturation, obtaining volume expansion rate reduction rate according to the volume expansion rate of the reinforced soil and the soil without reinforcement, and obtaining soil volume expansion rate reduction rate assigned value S2 according to the volume expansion rate reduction rate;

s30, calculating a softening coefficient based on unconfined compressive strength of the soil before and after water saturation, obtaining a softening coefficient enhancement rate according to the softening coefficient of the reinforced soil and the soil which is not reinforced, and obtaining a soil softening coefficient enhancement rate assigned value S3 according to the softening coefficient enhancement rate;

s40, calculating a comprehensive soil water-softening resistance score S based on the soil water absorption reduction rate assigned value S1, the soil volume expansion rate reduction rate assigned value S2 and the soil softening coefficient enhancement rate assigned value S3, and evaluating the soil water-softening resistance according to the S value.

The method for calculating the water absorption rate based on the mass of the soil body before and after water saturation comprises the following steps:

water absorption rating scaleThe valence formula is:wherein W_dThe mass of the soil body in the dry state, W_sThe mass of the soil body in a saturated state.

The step of obtaining the assigned value S1 of the water absorption rate reduction rate of the soil body according to the water absorption rate reduction rate comprises the following steps:

obtaining an assigned value S1 of the water absorption rate of the soil body according to the water absorption rate reduction rate by contrasting a water absorption rate reduction rate assigned table;

the water absorption reduction rate assignment table is as follows:

water absorption reduction rate/%)	≤15	15-30	30-45	45-60	60-75	75-90	≥90
								score/S1	5	15	30	45	60	75	90

The volume expansion rate is calculated based on the volume of the soil before and after water saturation, and the method comprises the following steps:

the volume expansion rate evaluation formula is as follows:wherein V_dIs the volume of the soil body in a dry state, V_sThe volume of the soil body in a saturated state.

The obtaining of the assigned value S2 of the soil volume expansion rate reduction rate according to the expansion rate reduction rate comprises the following steps:

according to the expansion rate reduction rate, comparing with a volume expansion rate reduction rate assigning table, and obtaining a soil volume expansion rate reduction rate assigning value S2;

the volume expansion rate reduction rate is assigned as follows:

volume swell reduction rate/%)	≤5	5-15	15-25	25-35	35-45	≥45
							score/S2	10	20	40	60	80	95

The softening coefficient is calculated based on unconfined compressive strength of the soil bodies before and after water saturation, and the method comprises the following steps:

the softening coefficient evaluation formula is as follows:wherein sigma_fThe unconfined compressive strength, sigma, of the soil body in a dry state_FThe confined compressive strength of the soil body in a saturated state is not limited.

The obtaining of the soil softening coefficient enhancement rate assigned value S3 according to the softening coefficient enhancement rate comprises the following steps:

obtaining a soil body softening coefficient enhancement rate assignment value S3 according to the softening coefficient enhancement rate and a softening coefficient enhancement rate assignment table;

the softening coefficient enhancement rate is given in the following table:

the evaluation of the soil body water softening resistance performance according to the S value comprises the following steps:

when S is more than 75 and less than or equal to 100, the soil body has excellent evaluation on the water softening resistance; when S is more than 50 and less than or equal to 75, the soil body has good evaluation on the water softening resistance; when S is more than 25 and less than or equal to 50, the soil body water softening resistance is evaluated to be medium; and when S is more than 0 and less than or equal to 25, the soil body is poor in evaluation of the water softening resistance.

The invention has the beneficial effects that: the invention strengthens the soil body by mixing the polymeric fiber and the soil body, has low cost and good effect, and solves the defects in the current method for improving the water softening resistance of the soil body.

The invention provides an evaluation method for integrating water absorption, volume expansion rate and softening coefficient of a soil body, and provides guidance suggestion for specific mixing amount design for enhancing water softening resistance of the soil body.

Drawings

FIG. 1 is an evaluation flow chart of the soil water softening resistance evaluation method in the embodiment.

Detailed Description

The embodiment provides a method for enhancing water softening resistance of soil, which is implemented by reinforcing a soil body, and mixing polymeric fibers and the soil body by adopting a fiber mixing or implanting method, wherein the polymeric fibers are PPF (polypropylene fiber) chopped fibers, the length of the polymeric fibers is 16-22mm, the diameter of the polymeric fibers is 0.19 +/-0.1 mm, and the elastic modulus of the polymeric fibers is 3.5 GPa.

The polypropylene fiber as an artificial synthetic fiber has the advantages of low price, uniform dispersion in soil, good water stability, obvious strength increase and the like, and the polypropylene fiber does not absorb water, thereby having good water softening resistance; compared with plant fibers, the compressive strength of the mixed polypropylene fibers and soil is increased from 352kPa to 500kPa by 42% and the water softening resistance is improved by 65% under the same content.

The embodiment also provides a method for evaluating the water softening resistance of the soil body, which is used for evaluating the soil body enhanced by the method for enhancing the water softening resistance of the soil body so as to provide reference opinions for designing the specific mixing amount of the fibers for enhancing the water softening resistance of the soil body, and the specific method comprises the following steps:

s00, soil body density 1.50g/cm³Mixing or implanting polyester fibers with the content of 0.2%, 0.4%, 0.6% and 0.8% with the soil body to prepare an unconfined compressive strength test sample, saturating the prepared sample, and carrying out next-step enhancement effect evaluation.

S10, soil water absorption evaluation: the soil bodies before and after saturation are weighed to obtain the mass of the soil bodies before and after saturation, the water absorption rate is calculated based on the mass of the soil bodies before and after saturation, the water absorption rate reduction rate is calculated according to the water absorption rate of the reinforced soil body and the water absorption rate of the soil body which is not reinforced, and the assigned value S1 of the water absorption rate reduction rate of the soil body is obtained according to the water absorption rate reduction rate and a comparison water absorption rate assignment table (table 1).

The water absorption evaluation formula in this example is:wherein W_dThe mass of the soil body in the dry state, W_sThe mass of the soil body in a saturated state.

TABLE 1 Water absorption Rate reduction assigning Table

Water absorption reduction rate/%)	≤15	15-30	30-45	45-60	60-75	75-90	≥90
								score/S1	5	15	30	45	60	75	90

In this example, the water absorption reduction rates of the soil bodies doped with different polymer fiber contents are 37.80%, 47.63%, 63.26% and 68.37%, respectively, and further the water absorption assigned values of the soil bodies reinforced with different polymer fiber contents obtained from table 1 are S1_0.2＝30，S1_0.4＝45，S1_0.660 and S1_0.8＝60。

S20, evaluating the volume expansion rate of the soil body: measuring the volumes of the soil bodies before and after saturation by adopting a drainage method to obtain the volumes of the soil bodies before and after saturation, calculating volume expansion rates based on the volumes of the soil bodies before and after saturation, calculating volume expansion rate reduction rates according to the volume expansion rate of the reinforced soil body and the volume expansion rate of the soil body which is not reinforced, and obtaining a soil body volume expansion rate reduction rate assigned value S2 according to the volume expansion rate reduction rates and a volume expansion rate reduction rate assigned table (table 2).

The volume expansion rate evaluation formula in this example is:wherein V_dIs the volume of the soil body in a dry state, V_sThe volume of the soil body in a saturated state.

TABLE 2 volume expansion rate reduction rate assignment table

Volume swell reduction rate/%)	≤5	5-15	15-25	25-35	35-45	≥45
							score/S2	10	20	40	60	80	95

In this example, the volume expansion rate reduction rates of the soil bodies doped with different polymer fiber contents are respectively 9.67%, 14.41%, 18.71% and 27.58%, and further the volume expansion rate assigned values of the soil bodies reinforced with different polymer fiber contents obtained from Table 2 are respectively S2_0.2＝20，S2_0.4＝20，S2_0.640 and S2_0.8＝60。

S30, soil softening coefficient evaluation: the unconfined compressive strength tests are carried out on soil body samples before and after water saturation to obtain the unconfined compressive strength of the soil body before and after water saturation, the softening coefficient is calculated based on the unconfined compressive strength of the soil body before and after water saturation, the softening coefficient enhancement rate is calculated according to the softening coefficient of the enhanced soil body and the softening coefficient of the soil body which is not enhanced, and the soil body softening coefficient enhancement rate assignment value S3 is obtained according to the softening coefficient enhancement rate by contrasting a softening coefficient enhancement rate assignment table (table 3).

The evaluation formula of the softening coefficient in the embodiment is as follows:wherein sigma_fThe unconfined compressive strength, sigma, of the soil body in a dry state_FThe confined compressive strength of the soil body in a saturated state is not limited.

TABLE 3 softening coefficient enhancement rate assignment table

In this example, the softening coefficient reduction rates of the soil body reinforced by the polymer fibers with different contents are 153.08%, 170.86%, 181.58% and 182.74%, respectively, and the softening coefficient increase rates of the soil body reinforced by the polymer fibers with different contents are S3 respectively obtained from Table 2_0.2＝75，S3_0.4＝75，S3_0.690 and S3_0.8＝90。

S40, calculating a comprehensive soil water-softening resistance score S based on the soil water absorption rate reduction rate assigned value S1, the soil volume expansion rate reduction rate assigned value S2 and the soil softening coefficient enhancement rate assigned value S3, wherein the evaluation formula is (S1+ S2+ S3)/3, and evaluating the soil water-softening resistance according to the S value.

In the embodiment, when S is more than 75 and less than or equal to 100, the evaluation of the water softening resistance of the soil body is excellent; when S is more than 50 and less than or equal to 75, the soil body has good evaluation on the water softening resistance; when S is more than 25 and less than or equal to 50, the soil body water softening resistance is evaluated to be medium; and when S is more than 0 and less than or equal to 25, the soil body is poor in evaluation of the water softening resistance.

In this example, the assigned values of the added polymer fibers with different contents are S1+ S2+ S3)/3 according to the formula S_0.2＝(S1_0.2+S2_0.2+S3_0.2)＝41.67，S_0.4＝(S1_0.4+S2_0.4+S3_0.4)＝46.67，S_0.6＝(S1_0.6+S2_0.6+S3_0.6)＝63.33，S_0.8＝(S1_0.8+S2_0.8+S3_0.8) 70.00, and further determining that the effect of adding the polymeric fibers with different contents to enhance the water softening resistance of the soil body is respectively medium, good and good.