A method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles

Abstract

The present invention discloses a method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles, specifically: determining the maximum dry density and optimal moisture content of mixed fillers corresponding to different construction waste incorporation rates through compaction tests; preparing mixed fillers with different construction waste incorporation rates, with the moisture content being the optimal moisture content, and conducting dry-wet cycle tests; conducting dynamic triaxial tests on mixed filler samples that have undergone preset dry-wet cycle times, obtaining the sample permanent deformation value, obtaining the influence functions of different construction waste incorporation rates, dry-wet cycle times, compaction degree, loading stress, and loading times on permanent deformation; multiplying each influence function to establish a permanent deformation estimation model; and fitting the model parameters according to dynamic triaxial test data. The present invention can conveniently and accurately obtain the permanent deformation of improved construction waste-expansive soil, and scientifically guide its application in roadbed filling. The model has clear physical meaning and simple structure, which reduces the difficulty of the test.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering and relates to a method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles. Background Art

[0002] In the field of road and geotechnical engineering, permanent deformation of roadbed is a hot topic that researchers continue to pay attention to. For the currently commonly used semi-rigid base pavement structure, the permanent deformation of the roadbed is crucial to the stability of the road structure. At the same time, considering the stability and durability of the roadbed during the operation period, the complex and changeable climate environment poses a potential threat to roadbed deformation. According to climate data, the climate in southern Hunan and Jiangxi in my country is hot and humid, and it rains all year round, causing the roadbed to gradually become wet. In addition, the rapid growth of traffic volume in recent years has caused the combined effect of these factors to cause the permanent deformation of the roadbed in the humid and hot southern regions to continue to increase, and its overall bearing capacity has been significantly reduced. Therefore, it is of great significance to study the permanent deformation of roadbed soil in the humid and hot southern regions under long-term cyclic loading.

[0003] Expansive soil is widely distributed in the hot and humid areas of southern my country. With the rapid development of transportation infrastructure construction in the region, it is inevitable to use expansive soil as roadbed filler in areas where road construction materials are scarce. However, expansive soil is a typical special clay soil with fissures and swelling and shrinkage. Its engineering characteristics such as multiple fissures, water absorption expansion, and water loss shrinkage make the expansive soil roadbed prone to varying degrees of stability decline under the repeated action of vehicle loads, thus bringing great harm to the service life of the highway. Domestic and foreign scholars mainly use admixtures (such as cement and quicklime) to treat it, but this improvement method belongs to the category of chemical improvement, has a short effective period, and has certain adverse effects on the environment. At the same time, with the vigorous promotion of infrastructure construction and urbanization in my country, the amount of construction waste generated is growing rapidly. The huge amount of construction waste that is difficult to dispose of has seriously restricted the sustainable development of cities, and the problem of its effective recycling, disposal, and reuse needs to be solved urgently. Therefore, the present invention attempts to use construction waste to improve expansive soil, and provides an effective reference for stability analysis of improved construction waste-expansive soil under the combined effects of complex climate and load through permanent deformation, an important indicator for characterizing the stability performance of roadbed.

[0004] Generally speaking, indoor triaxial test is a generally recognized method for determining permanent deformation. However, considering that the cost of triaxial test is high, time-consuming, and requires professional personnel to operate, we hope to obtain the permanent deformation of improved construction waste-expansive soil under different conditions through a more accurate and rapid method. At present, domestic and foreign scholars usually use three methods to determine permanent deformation: the first is to determine it by empirical method, but the permanent deformation range of each roadbed filler given is large and cannot be quantitatively analyzed. The second is to establish a more complex constitutive model to simulate each cycle process. This method needs to remember the yield surface generated by each cycle process during the calculation process. The calculation amount is large and it is difficult to be widely promoted and applied in engineering. The third method is to use dynamic triaxial test and then use the Tseng model in the Mechanistic-Empirical Pavement Design Guide (MEPDG) specification to estimate the permanent deformation. Although the Tseng model has the characteristics of few model parameters and wide application range, the model does not consider the factors comprehensively and ignores the influence of stress state and physical state. In view of this, it is necessary to establish a simple and effective permanent deformation estimation model for improved construction waste-expansive soil. Summary of the invention

[0005] To solve the above problems, the present invention provides a method for estimating the permanent deformation of improved construction waste-expansive soil under dry-wet cycles, which can conveniently and accurately obtain the permanent deformation of improved construction waste-expansive soil, scientifically guide its application in roadbed filling, and solve the problems existing in the prior art.

[0006] The technical solution adopted in the embodiment of the present invention is a method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles, which is specifically carried out in the following steps:

[0007] S1: Determine the maximum dry density and optimum moisture content of mixed filler corresponding to different construction waste incorporation rates through compaction tests;

[0008] S2: preparing mixed fillers with different incorporation ratios of construction waste and the optimum moisture content, and conducting dry-wet cycle tests;

[0009] S3: Perform a dynamic triaxial test on the mixed filler sample that has undergone a preset number of dry-wet cycles to obtain the permanent deformation value of the sample; obtain the influence function of different construction waste incorporation rates, dry-wet cycles, compaction degree, loading stress, and loading times on permanent deformation;

[0010] S4: Multiply each influence function to establish a permanent deformation prediction model;

[0011] S5: The model parameters are obtained by fitting according to the dynamic triaxial test results.

[0012] Furthermore, in step S3, the permanent deformation influence function of different construction waste incorporation rates is shown in the following formula:

[0013]

[0014] Where: is the influence function corresponding to the number of dry-wet cycles, e is a constant, N DW is the number of dry-wet cycles, and α1 and α2 are model parameters.

[0015] Furthermore, in step S3, the permanent deformation influence function of different dry-wet cycle times is shown in the following formula:

[0016]

[0017] Where: is the influence function corresponding to the mixing rate of construction waste, λ CDW is the incorporation rate of construction waste, b1 and b2 are model parameters.

[0018] Furthermore, in step S3, the permanent deformation influence function of different compaction degrees is shown in the following formula:

[0019] g K =c1+c2K

[0020] Where: g K is the influence function corresponding to the compaction degree, K is the compaction degree, and c1 and c2 are model parameters.

[0021] Furthermore, in step S3, the permanent deformation influence function of different loading stresses is shown in the following formula:

[0022]

[0023] Where: is the influence function corresponding to the loading stress, σ d is the loading stress, d1 and d2 are model parameters.

[0024] Furthermore, in step S3, the permanent deformation influence function of different loading times is shown in the following formula:

[0025]

[0026] Where: g N is the influence function corresponding to the number of loadings, N is the number of loadings, and e1, e2, e3, and e4 are model parameters.

[0027] Furthermore, in step S4, the permanent deformation prediction model established is:

[0028]

[0029] Where: ε p For permanent deformation; N DW is the number of dry-wet cycles; CDW is the mixing rate of construction waste; K is the compaction degree; σ d is the loading stress; N is the number of loading times; α1, α2, b1, b2, c1, c2, d1, d2, e1, e2, e3, and e4 are model parameters.

[0030] Furthermore, in step S3, the load form in the dynamic triaxial test is a half-sine wave, with a frequency of 1 Hz, a loading time of 0.2 s, and an intermittent time of 0.8 s. The confining pressure is selected as 30 kPa, and the loading stress is selected as 20 kPa, 40 kPa, and 60 kPa. After intermittent loading for 10,000 times, the permanent deformation value of the specimen is obtained.

[0031] The beneficial effects of the present invention are:

[0032] 1. The present invention overcomes the limitations of the existing traditional conventional soil permanent deformation prediction model, comprehensively considers the physical properties of improved construction waste (construction waste incorporation rate, compaction degree), the influence of loading and environment on its permanent deformation, and establishes a permanent deformation prediction model that is more suitable for improved construction waste, thereby improving portability and accuracy; at the same time, the model has clear physical meaning and simple structure, which greatly reduces the test time and difficulty, provides obvious engineering convenience for units that do not have the conditions for triaxial testing, and has high market promotion value.

[0033] 2. Compared with the existing standard methods, the present invention is more convenient and accurate, which is convenient for guiding the design and construction of improved construction waste-expansive soil in road structures, providing a reference for the practical application of road resource recycling, and can be extended to the design and detection of other construction waste improved roadbed soils, and has broad application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 is a flow chart of an embodiment of the present invention.

[0036] Figure 2 These are the compaction test results of mixed fillers at different construction waste incorporation rates in the embodiments of the present invention.

[0037] Figure 3 It is a relationship diagram between different construction waste incorporation rates and final permanent deformation values ​​under the conditions of 0 dry-wet cycles, 93% compaction degree, and 40 kPa loading stress in an embodiment of the present invention.

[0038] Figure 4 It is a relationship diagram between different compaction degrees and final permanent deformation values ​​under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, and 40 kPa loading stress in an embodiment of the present invention.

[0039] Figure 5 It is a relationship diagram between different loading stresses and final values ​​of permanent deformation under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, and 93% compaction degree in an embodiment of the present invention.

[0040] Figure 6 It is a relationship diagram between different dry-wet cycle numbers and the final value of permanent deformation under the conditions of 10% construction waste incorporation rate, 93% compaction degree, and 40 kPa loading stress in an embodiment of the present invention.

[0041] Figure 7 It is a relationship diagram between different loading times and permanent deformation under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, 93% compaction degree, and 40 kPa loading stress in an embodiment of the present invention.

[0042] Figure 8 This is a diagram of the robustness verification results of the model built in the embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with 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 only 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 making creative work are within the scope of protection of the present invention.

[0044] Example

[0045] A method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles, such as Figure 1 As shown, please follow the steps below:

[0046] Step S1: Determine the maximum dry density and optimum moisture content of mixed filler at different construction waste incorporation rates through compaction tests; the specific test method is carried out in accordance with the provisions of the Highway Geotechnical Test Code, and the specific process is as follows:

[0047] First, the construction waste and expansive soil required for the compaction test were dried for 24 hours; secondly, the fillers with preset construction waste incorporation rates (0%, 10%, 20%, 30%, 40%, 50%) were configured; thirdly, the moisture content of the fillers was configured with a gradient difference of 2%, and the fillers were stuffed for 18 hours to make the internal humidity uniform; after the stuffing was completed, the mixed fillers were compacted in three layers using a heavy compaction method, with each layer compacted 98 times; finally, the central part of the molded sample was selected to measure the moisture content and dry density, so as to obtain the maximum dry density and optimal moisture content of the mixed fillers at different incorporation rates. The results are shown in Figure 2. Figure 2 shown.

[0048] Step S2: Prepare mixed fillers with different construction waste incorporation rates, and conduct dry-wet cycle tests; Based on the results of step S1, prepare cylindrical mixed filler samples with compaction degrees of 90%, 93%, and 96%, compaction degrees as the ratio of dry density to maximum dry density, moisture content as the optimal moisture content, construction waste incorporation rates of 0%, 10%, 20%, 30%, 40%, and 50%, and diameters and heights of 10 cm×20 cm, respectively. During the molding process, the actual moisture content and compaction degree of the sample are controlled within 1% of the target value. Then, the molded sample is subjected to dry-wet cycle treatment by a dry-wet alternating test machine. A complete dry-wet cycle cycle is set as follows: Place the sample in a sealed box for humidification treatment until the sample is saturated with water (the humidification saturation process takes about 48 hours), and after saturation, air-dry at a temperature of 25°C until the mass of the sample is reduced to the initial mass before humidification. In order to ensure the accuracy of the test results as much as possible, the number of dry-wet cycles was selected as 0, 1, 3, 6, and 10 using the method of increasing the backward difference.

[0049] Step S3: Perform a dynamic triaxial test on the mixed filler sample that has undergone the dry-wet cycle test, and analyze the permanent deformation characteristics under different construction waste incorporation rates, dry-wet cycle times, compaction degrees, loading stresses, and loading times. After the dry-wet cycle test in step S2 is completed, the dynamic triaxial test is immediately performed on the mixed filler sample. The load form in the dynamic triaxial test is a half-sine wave with a frequency of 1 Hz, a loading time of 0.2s, and an intermittent time of 0.8s. The confining pressure is selected as 30 kPa, and the loading stress is selected as 20 kPa, 40 kPa, and 60 kPa. After 10,000 intermittent loadings, the permanent deformation value of the specimen is obtained. The relationship between different construction waste incorporation rates (0%, 10%, 20%, 30%, 40%, 50%) and the final value of permanent deformation under the conditions of 0 dry-wet cycles, 93% compaction degree, and 40 kPa loading stress is as follows: Figure 3 The relationship between different compaction degrees (90%, 93%, 96%) and the final value of permanent deformation under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, and 40kPa loading stress is shown in Figure 4The relationship between different loading stresses (20 kPa, 40 kPa, 60 kPa) and the final value of permanent deformation under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, and 93% compaction degree is shown in Figure 5 The relationship between the final value of permanent deformation under the conditions of 10% construction waste incorporation rate, 93% compaction degree, and 40kPa loading stress and the number of dry-wet cycles (0, 1, 3, 6, 10) is shown in Figure 2. Figure 6 The relationship between different loading times and permanent deformation under the conditions of 0 dry-wet cycles, 10% construction waste incorporation rate, 93% compaction degree, and 40kPa loading stress is shown in Figure 7 shown.

[0050] Step S4: Based on the results of the dynamic triaxial test in step S3, a permanent deformation prediction model is analyzed and established that comprehensively considers physical influences (incorporation rate of construction waste, compaction degree), loading influences (loading stress, loading times), and environmental influences (number of dry-wet cycles):

[0051]

[0052] Where: ε p For permanent deformation; N DW is the number of dry-wet cycles; CDW is the mixing rate of construction waste; K is the compaction degree; σ d is the loading stress; N is the number of loading times; α1, α2, b1, b2, c1, c2, d1, d2, e1, e2, e3, and e4 are model parameters.

[0053] in:

[0054]

[0055]

[0056] g K =c1+c2K (4)

[0057]

[0058]

[0059]

[0060] Where: is the influence function corresponding to the number of dry-wet cycles; is the influence function corresponding to the mixing rate of construction waste; g K is the influence function corresponding to the compaction degree; is the influence function corresponding to the loading stress; g N is the influence function corresponding to the number of loading times.

[0061] Step S5: The model parameters are obtained by fitting the test data of step S3, and the permanent deformation of the improved construction waste-expanding soil mixed filler under different dry-wet cycle times, construction waste incorporation rate, compaction degree, loading stress, and loading times is reasonably estimated through the estimation model established in step S4. This fitting step is a prior art, and the fitting results are shown in Table 1.

[0062] Table 1 Statistics of estimated model parameters

[0063] Model parameters Numeric Model parameters Numeric <![CDATA[α1]]> 0.39 <![CDATA[d1]]> 0.71 <![CDATA[α2]]> 0.76 <![CDATA[d2]]> 0.29 <![CDATA[b1]]> 1.8 <![CDATA[e1]]> 0.47 <![CDATA[b2]]> -0.39 <![CDATA[e2]]> 0.22 <![CDATA[c1]]> -1.47 <![CDATA[e3]]> 0.26 <![CDATA[c2]]> 2.10 <![CDATA[e4]]> -0.05

[0064] In order to determine the applicability of the method for estimating permanent deformation of construction waste-expansive soil under dry-wet cycles proposed in the present invention, the present invention conducts robustness verification on the newly-created model formula (1). A robustness verification scatter plot is drawn with the measured value of permanent deformation as the horizontal axis and the estimated value as the vertical axis. The results are as follows: Figure 8 As shown in Figure 2, it is not difficult to see that most of the scattered points are concentrated around the straight line y=x. 2 It is 0.97, the model has high accuracy and meets engineering needs.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles, characterized in that: Follow these steps: S1: Determine the maximum dry density and optimum moisture content of mixed filler corresponding to different mixing rates of construction waste through compaction test; S2: Prepare mixed filler samples with different incorporation rates of construction waste and conduct dry-wet cycle tests; S3: Perform dynamic triaxial tests on mixed filler samples that have undergone a preset number of dry-wet cycles to obtain permanent deformation values ​​of samples under different construction waste incorporation rates, different dry-wet cycles, different compaction degrees, different loading stresses, and different loading times, and then obtain the influence functions of different construction waste incorporation rates, dry-wet cycles, compaction degrees, loading stresses, and loading times on permanent deformation; S4: Multiply each influence function to establish a permanent deformation prediction model; S5: The model parameters are obtained by fitting the test data of S3, and the permanent deformation of the improved construction waste-expansive soil mixed filler under different dry-wet cycle times, construction waste incorporation rate, compaction degree, loading stress, and loading times is reasonably estimated through the estimation model established in S4; In step S3, the permanent deformation influence function of different mixing rates of construction waste is shown in the following formula: ， Where: is the influence function corresponding to the number of dry-wet cycles, is a constant, is the number of dry-wet cycles, , are model parameters; In step S3, the permanent deformation influence function of different dry-wet cycle times is shown in the following formula: ， Where: is the influence function corresponding to the incorporation rate of construction waste, is the construction waste incorporation rate, , are model parameters; In step S3, the permanent deformation influence function of different compaction degrees is shown in the following formula: ， Where: is the influence function corresponding to the compaction degree, is the compaction degree, are model parameters; In step S3, the permanent deformation influence function of different loading stresses is shown in the following formula: , Where: is the influence function corresponding to the loading stress, is the loading stress, are model parameters; In step S3, the permanent deformation influence function of different loading times is shown in the following formula: , Where: is the influence function corresponding to the number of loading times, is the number of loads, e 1. e 2. e 3. e 4 is the model parameter; In the step S3, the load form in the dynamic triaxial test is a half-sine wave with a frequency of 1 Hz, a loading time of 0.2 s, and an intermittent time of 0.8 s; the confining pressure is selected as 30 kPa, and the loading stress is selected as 20 kPa, 40 kPa, and 60 kPa. After intermittent loading for 10,000 times, the permanent deformation value of the specimen is obtained.

2. The method for estimating permanent deformation of improved construction waste-expansive soil under dry-wet cycles according to claim 1, characterized in that: In step S4, the permanent deformation prediction model established is: , Where: For permanent deformation; is the number of dry-wet cycles; is the construction waste incorporation rate; is the degree of compaction; is the loading stress; is the number of loads; α 1. α 2. b 1. b 2. c 1. c 2. d 1. d 2. e 1. e 2. e 3. e 4 is the model parameter.

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