Design method for filled-core embankment subgrade structure

Abstract

The present invention belongs to the technical field of road construction applications, and particularly relates to a design method for a core-filled embankment subgrade structure. The present invention provides a design method for a core-filled embankment subgrade structure, which takes the material modulus of the core-filled area, the material modulus of the improvement layer, and the thickness of the improvement layer that can be easily obtained as variables, and combines the mechanical parameters of the materials in the core-filled area and the improvement area and the performance difference degree between the two to determine the model parameters, effectively realizing the calculation of the equivalent rebound modulus of the subgrade surface, thereby realizing the design of the core-filled embankment subgrade structure, and having multiple values such as technology, cost, economy, environmental protection, and carbon reduction, and is suitable for large-scale popularization and use.

Description

Technical Field

[0001] The present invention belongs to the technical field of road construction applications, and particularly relates to a design method for a core-filled embankment subgrade structure. Background Technique

[0002] The Industrial Revolution and the Information Revolution have accelerated the invention and progress of modern high-power construction machinery and automation equipment, greatly promoting the breadth and depth of large-scale engineering activities. While significantly improving the level of human development, they have also left the homeland on which we depend for survival devastated and overburdened. There is only one Earth. Over the years, after suffering the painful lessons of wantonly destroying the environment, humanity has reflected on its actions and summed up experience. Now, protecting the ecological environment, developing carbon reduction technologies, and promoting green construction have become the consensus of humanity. China has a vast territory and a large population. With the advancement of livelihood projects, the hardening of roads has been achieved in every village in China's road network, and the total mileage of highways at all levels ranks first in the world. With the strengthening of national strength and the continuous improvement of people's living standards, China's 15th Five-Year Plan further proposes to transform and upgrade a large number of low-grade highways, and at the same time plans a number of new high-grade highways. The successive highway construction projects have a huge demand for engineering materials.

[0003] For subgrade fillers, the existing design specifications require that the strength of subgrade fillers and the strength of subgrade structures need to meet certain standards. For example, the "Code for Design of Highway Subgrades" (JTG D30-2015) stipulates the CBR control standards for expressways and first-class highways according to highway grades as follows: 8% for the upper roadbed, 5% for the lower roadbed, 4% for the upper embankment, and 3% for the lower embankment, while the CBR control standards for second-class highways are: 6% for the upper roadbed, 4% for the lower roadbed, 3% for the upper embankment, and 2% for the lower embankment. The higher the grade, the higher the requirements for the performance indicators of subgrade fillers. In the design of highway pavement structures, the subgrade structure strength, that is, the resilient modulus of the subgrade top surface, is an important design parameter. The "Code for Design of Highway Asphalt Pavements" (JTG D50-2017) stipulates that the resilient modulus of the subgrade top surface for heavy, extra-heavy, and extremely heavy traffic loads should not be less than 50, 60, and 70 MPa respectively, and the resilient modulus of the roadbed top surface for medium and light traffic loads should not be less than 40 MPa. The higher the traffic load grade, the higher the requirements for the subgrade structure strength.

[0004] In some areas, a large amount of materials distributed along the highway engineering construction are often abandoned because their engineering properties do not meet the requirements of standards and specifications, and instead, high-cost high-quality materials are used. The main reasons for poor fillers include: low material strength, poor water stability and engineering properties; poor particle gradation, difficult to roll compact, and poor structural stability; too high water content, difficult to reach the specified compaction degree, long creep duration in the later stage, and large settlement; excessive content of a certain mineral component, swelling or collapsibility occurring in the later stage, etc. At the same time, the harsh environments of dry-wet cycles and freeze-thaw cycles also pose more requirements on material properties and structural design. Poor fillers include coastal sand in coastal areas, peat soil in marsh areas, over-wet soil in humid areas, collapsible loess on the Loess Plateau, high liquid limit soil in hot and humid areas in the south, aeolian sand in Gobi areas in the north, and so on.

[0005] Through scientific and reasonable technical means, on the premise of ensuring project quality, improving the utilization rate of local materials along the highway, achieving local material utilization and turning waste into treasure, not only can the waste earthwork and the dependence on external high-quality materials be reduced, the excessive excavation of natural mountain bodies or clay resources be reduced, but also the material transportation costs and mechanical equipment can be reduced. It can significantly reduce the construction cost and the damage to the natural environment, and at the same time can effectively practice the concept of green and high-quality development and help achieve the dual-carbon goal.

[0006] In order to improve the local utilization rate of poor fillers, engineers and researchers have proposed a core-filled embankment subgrade structure, as shown in the attached drawings of the specification Figure 1 shown. That is, the poor filler is enclosed in the core of the subgrade cross-section; on both sides of the slope are side-packing soils with a width of not less than 2m filled in layers synchronously. The side-packing soil materials are selected as clays or gravelly soils with good compactness and high structural strength, which can not only restrain the lateral deformation of the poor filler but also be easy for vegetation and greening, reducing the later-stage rainwater scouring; the upper overlying improvement layer is gravelly soil with good gradation, controllable particle size, good water stability and good structural strength, or materials treated with inorganic binders. While the improvement layer functions to seal the poor filler, it is mainly used to make up for the defects of poor structure and low structural strength of the poor filler, improving the bearing capacity and structural strength of the top surface of the subgrade structure to meet the requirements of design indicators.

[0007] The equivalent resilient modulus of the subgrade top surface is the main index to characterize the subgrade structure strength. In the existing highway standards and specifications, the equivalent resilient modulus of the subgrade top surface is generally obtained through direct resilient tests, back-calculation of deflection tests, or empirical conversion formulas with CBR, etc. For layered structural systems, predecessors have also proposed prediction formulas for the resilient modulus at the top of the structural layer, but these methods are more applicable to the case where the modulus ratio is between 10 and 10,000, that is, the case where the mechanical properties of the lower material and the upper covering layer material differ greatly, such as the subgrade material overlying the pavement base course material, and the empirical solution of the equivalent modulus at the top of the base course can be used.

[0008] Since the above empirical formula is not applicable to the estimation of the equivalent modulus of the subgrade structure top surface, it is necessary to specifically propose an empirical formula that can be used to estimate the equivalent resilient modulus of the subgrade structure top surface of the core-filled embankment, and to achieve the strength control of the core-filled subgrade structure is the problem that needs to be solved currently. Summary of the Invention

[0009] In view of the technical inconvenience problems existing in the strength control of the existing core-filled embankment structure, the present invention proposes a design method that is reasonable in design, simple in method, convenient in operation and can effectively calculate the equivalent resilient modulus of the subgrade structure top surface of the core-filled embankment to achieve the strength control of the core-filled embankment structure.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a design method for a core-filled embankment structure, including the following steps:

[0011] a. First, according to the design document, determine the top surface elevation and cross-section of the embankment, preliminarily determine the areas of the core-filled area, the two side wrapping areas and the overlying improved layer, select the improved layer material and preset the thickness of the improved layer;

[0012] b. Respectively measure the modulus of the materials used in the core-filled area and the modulus of the useful materials in the improved layer;

[0013] c. Then, based on the thickness of the improved layer and the material moduli of the core-filled area and the improved layer, calculate the equivalent resilient modulus of the subgrade structure top surface of the core-filled embankment, and the calculation formula is:

[0014] E t = a ln E0 + b ln E1 + c ln h1 + d

[0015] Wherein, E t is the equivalent resilient modulus of the subgrade structure top surface of the core-filled embankment, E0 is the material modulus of the core-filled area, E1 is the material modulus of the improved layer, h1 is the thickness of the improved layer, and a, b, c, d are model parameters;

[0016] d. By comparing the calculated equivalent resilient modulus of the subgrade structure top surface with the subgrade structure modulus value specified in the design document, determine whether it meets the requirements of the design document. If it does not meet or far exceeds the design standard, return to step a to re-select the improved layer material or re-determine the thickness of the improved layer. If it meets the requirements of the design document and the over-standard does not exceed 20%, then make the calculated equivalent resilient modulus of the subgrade structure top surface of the core-filled embankment approach the subgrade structure modulus value specified in the design document by fine-tuning the thickness of the improved layer, and thereby determine the thickness of the improved layer and the material of the improved layer;

[0017] e. According to the finally determined thickness of the improved layer, determine the upper limit of the core-filled area, thereby completing the structural design and strength control design of the core-filled embankment structure.

[0018] Preferably, the thickness of the improved layer is 0.4 m to 1.5 m.

[0019] Preferably, in step c, the model parameters a, b, c, and d are determined according to the mechanical parameters of the core filling area material and the improved area material and the performance difference between the two.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0021] The present invention provides a design method for a core-filled embankment subgrade structure. Taking the material modulus of the core filling area, the material modulus of the improved layer, and the thickness of the improved layer that can be conveniently obtained as variables, and combining the mechanical parameters of the core filling area material and the improved area material and the performance difference between the two to determine the model parameters, effectively realizes the calculation of the equivalent resilient modulus of the subgrade surface, thereby realizing the design of the core-filled embankment subgrade structure, and has multiple values such as technology, cost, economy, environmental protection, and carbon reduction, and is suitable for large-scale popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0023] Figure 1 is the existing core-filled embankment subgrade structure;

[0024] Figure 2 is the subgrade structure model and parameter diagram of the improved layer overlying the core-filled embankment with coastal sand;

[0025] Figure 3 is the influence diagram of the coastal sand modulus E0 on the equivalent modulus E t of the subgrade structure top;

[0026] Figure 4 is the influence diagram of the improved layer modulus E1 on the equivalent modulus E t of the subgrade structure top;

[0027] Figure 5 is the influence diagram of the improved layer thickness h1 on the equivalent modulus E t of the subgrade structure top;

[0028] Figure 6 is the subgrade structure model and parameter diagram of the improved layer overlying the core-filled embankment with highly liquid limit over-wet soil. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0030] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed in the following specification.

[0031] Based on the designed subgrade elevation and the cross-sectional dimensions of the embankment structure, how to increase the range of the core filling area is the key to controlling construction costs and promoting green and low-carbon construction. To this end, by determining the equivalent resilient modulus of the subgrade top surface, and then determining the thickness of the improved layer, the upper limit of the core filling area can be determined, thereby achieving the purpose of controlling construction costs and promoting green and low-carbon construction.

[0032] In the present invention, taking the coastal sand in the coastal area and the highly plastic silty red clay in the humid area of the south as examples respectively, the prediction and control methods for the resilient modulus at the top of the core-filled embankment subgrade structure are described.

[0033] Example 1. This example provides a design method for a core-filled embankment subgrade structure with medium-fine coastal sand as the core filling area material.

[0034] First, physical and mechanical property tests are carried out on the medium-fine coastal sand material. A series of tests such as sieving, compaction, California Bearing Ratio (CBR), and resilience tests show that: this sand is mainly composed of medium-fine particles, with a proportion of 95%, the coefficient of uniformity Cu is between 2.0 and 3.0, and the coefficient of curvature Cc is close to 1. Therefore, according to the provisions of the "Code for Highway Geotechnical Tests" (JTG 3430-2020), it does not meet the conditions of Cu>5 and 1<Cc<3, and the gradation is poor; the CBR strength is between 12% and 26%, and the material strength is good; the resilient modulus is 15 MPa to 55 MPa, the structural strength is uneven, and it does not meet the standard requirement of 40 MPa for the subgrade strength of a certain highway grade; the optimum moisture content is 12%, which is quite different from the natural moisture content of 3%. Practice shows that although the CBR strength of the coastal sand material is large, the gradation is poor, the difference between the natural moisture content and the natural moisture content is large, it is easy to permeate water and lose water, the structure becomes loose after losing water on the surface layer, its structural strength is unstable, the deflection value is large, and it is difficult to pass the subgrade strength acceptance standard.

[0035] Since coastal sand is a poor subgrade filler, in order to realize its engineering application, a core-filled embankment subgrade structure with coastal sand filling the core, side wrapping on both sides, and a covering of improved layer on the top is usually adopted. That is, first, a cushion layer with a thickness of about 0.5m is filled on the compacted foundation after surface cleaning. The cushion layer material is graded crushed stone or inorganic binder-treated material with good strength and water stability. The subgrade structure above the cushion layer adopts the form of coastal sand filling the core, side confinement wrapping on both sides, and a top improved layer covering. The wrapping soil and the improved layer are preferably made of materials with good structure such as gravelly soil, clay, or improved materials, as shown in the attached drawings of the specification Figure 1 In the core-filled embankment subgrade structure with coastal sand in this case, the improved layer material is selected as gravelly soil, cement-treated coastal sand, or lime-treated coastal sand. The thickness of the side wrapping is preferably greater than 2m in design.

[0036] The equivalent resilient modulus of the subgrade top surface is the main index to characterize the strength of the subgrade structure. To carry out the strength research on different subgrade structure combinations, taking the equivalent resilient modulus of the subgrade top as the dependent variable, and selecting 3 independent factors of the core filling modulus, the improved layer modulus, and the improved layer thickness as the independent variables, with 4 levels selected for each factor, the subgrade structure model and its parameter combinations are as shown in Figure 2 shown. Then, there are a total of 64 full permutation combinations of the subgrade structure combinations. Among them, the core filling modulus and the improved layer modulus can be obtained through resilient tests or related convertible tests.

[0037] For this subgrade structure form, the following assumptions are made: (1) The improved layer material and the core filling area material are homogeneous, uniform, and continuous isotropic materials, and are infinite in the horizontal direction; (2) The improved layer has a certain thickness while the coastal core filling has an infinite thickness; (3) The displacements, stresses, and strains at infinity in the horizontal and vertical directions are zero; (4) The improved layer and the core filling area are in complete continuous contact.

[0038] For 64 different subgrade structure parameters, based on the theoretical model of the surface of a layered elastic body under the action of a double circular standard axle load Figure 2 and the basic equations, the theoretical solutions of the equivalent modulus of the subgrade top surface, the empirical solutions calculated by the empirical formula, and the errors between the two are listed in Table 1 as follows.

[0039] Table 1 Theoretical solutions and empirical solutions of the equivalent modulus of the core-filled embankment subgrade top surface with coastal sand

[0040]

[0041]

[0042]

[0043] Then, a statistical analysis was conducted on 64 subgrade structure parameters and their top surface resilient moduli. 16 groups of subgrade structures were randomly selected, with the moduli and thicknesses of the improved layers limited, and the changes in the top surface moduli of the subgrades were analyzed by varying the moduli of the lower core filling areas. The changing trend of the equivalent modulus of the subgrade top surface with the modulus of the coastal core filling is as shown in Figure 3 Figure [not shown in the provided text, but should be filled in with the actual figure number]. It can be seen from the figure that the equivalent modulus of the subgrade top surface increases logarithmically with the increase in the modulus of the coastal sand. Increasing the modulus of the core filling can almost equivalently increase the equivalent modulus of the subgrade top surface. The logarithmic curve can well fit the relationship between the two, and the goodness of fit is as high as 0.999.

[0044] Next, 16 groups of subgrade structures were randomly selected. Given the modulus of the core filling area and the thickness of the improved layer, by changing the modulus of the improved layer, the relationship between the equivalent modulus of the subgrade top surface and the modulus of the improved layer can be obtained, as shown in Figure 4 Figure [not shown in the provided text, but should be filled in with the actual figure number]. The equivalent modulus of the subgrade top surface is significantly correlated with the modulus of the improved layer, and the relationship between the two can also be well fitted by a logarithmic curve, with a goodness of fit as high as 0.99. It can also be found from the figure that when the modulus of the core filling is larger and the improved layer is thicker, the increase in the modulus of the improved layer for the equivalent modulus of the subgrade top surface is more significant.

[0045] For different moduli of the core filling area and the improved layer, the relationship between the equivalent resilient modulus of the subgrade top surface and the thickness of the improved layer is as shown in Figure 5 Figure [not shown in the provided text, but should be filled in with the actual figure number]. It can be seen from the figure that the two are also non-linearly logarithmically correlated, with a goodness of fit reaching 0.996, and for different material types, the contribution of the thickness of the improved layer to the equivalent modulus of the subgrade top surface is relatively uniform.

[0046] From the above, it can be seen that the equivalent modulus of the subgrade top surface has a direct and significant relationship with the modulus of the core filling area, the modulus of the improved layer, and the thickness of the improved layer. According to the above single-factor correlation analysis, the equivalent modulus of the subgrade top surface can be expressed as a multivariate non-linear function of the core filling modulus, the improved layer modulus, and the thickness of the improved layer, and can be approximately fitted by a logarithmic function. Through multivariate non-linear regression of 64 groups of subgrade structure parameters, the obtained empirical regression model is:

[0047] E t = 23.47ln E0 + 60.83ln E1 + 18.59ln h1 - 359.84

[0048] where, E t is the equivalent resilient modulus of the subgrade top surface, E0 is the material modulus of the core filling area, E1 is the material modulus of the improved layer, h1 is the thickness of the improved layer, and 23.47, 60.83, 18.59, and -359.84 are model parameters.

[0049] Through the joint significance test of this model, the goodness of fit can reach 0.96, and the average error between the empirical solution and the theoretical solution is only 0.03%. The probability of the statistical P value is less than 0.05, indicating that the null hypothesis is rejected at the 95% confidence level, and the model is meaningful.

[0050] For a certain highway subgrade top surface resilient modulus design standard of 40 MPa, based on the above prediction model, the structural strength of the coastal sand-filled core subgrade structure can be controlled.

[0051] Specifically, first, according to the design document, determine the top elevation and cross-section of the embankment subgrade, preliminarily determine the areas of the core filling area, the two side wrapping areas, and the overlying improved layer, select the improved layer material and preset the thickness of the improved layer.

[0052] Then, respectively measure the modulus of the material used in the core filling area and the modulus of the material selected for the improved layer through resilient tests or relevant convertible tests.

[0053] Next, calculate the equivalent resilient modulus of the subgrade structure top surface at this time. By comparing the calculated equivalent resilient modulus of the subgrade structure top surface with the subgrade structure modulus value specified in the design document, determine whether it meets the requirements of the design document. If it does not meet or far exceeds the design standard, consider reselecting the improved layer material or redrafting the thickness of the improved layer.

[0054] The designed thickness of the improved layer is generally 0.4 m to 1.5 m. For the situation where the structural strength does not meet the standard, it can be improved first by increasing the thickness of the improved layer. If the thickness of the improved layer needs to exceed 1.5 m, then consider replacing the material of the improved layer. If the modulus of the subgrade structure top exceeds the design standard by more than 20%, it indicates that the performance of the improved layer material is too excellent or the thickness is too large. Cost optimization can be considered appropriately, that is, downgrading the improved material or reducing the thickness of the improved layer. It also determines whether to adjust the thickness of the improved layer or change the material according to the preset thickness of the improved layer at this time.

[0055] If it meets the requirements of the design document and the over-standard does not exceed 20%, there is no need to adjust the material of the improved layer at this time. Recalculate by slightly adjusting the thickness of the improved layer to make the obtained solution tend to be close to the requirements of the design document. That's it. Determine the thickness of the improved layer and the material of the improved layer. The purpose of this step is mainly to consider maximizing the utilization rate of poor fillers. Because the designed subgrade top elevation is determined, that is, the top elevation of the core filling area plus the thickness of the improved layer. The smaller the thickness of the improved layer, the higher the top elevation of the core filling layer, and the greater the core filling thickness, the greater the utilization rate of poor fillers. In this way, the material and transportation costs are lower, and it is also more environmentally friendly.

[0056] Finally, according to the finally determined thickness of the improved layer, determine the upper limit of the core filling area, thereby completing the structural design and strength control design of the filled-core embankment subgrade.

[0057] From the perspective of maximizing the in-situ utilization rate of coastal sand, the strength control design of the subgrade structure can be carried out, that is, while meeting the strength requirements of the subgrade structure, appropriately reducing the thickness of the improvement layer, thereby increasing the filling range of the coastal core filling. Therefore, the strength control design of the highway subgrade structure has multiple values in terms of technology, cost, economy, environmental protection, and carbon reduction.

[0058] Example 2. This example provides a design method for a core-filled embankment subgrade structure with highly plastic red clay as the core filling material in the hot and humid southern regions of China.

[0059] In the southern regions of China, there is a large amount of highly plastic red clay. The dry highly plastic red clay has a relatively high resilient modulus, often greater than 100 Mpa. However, due to the relatively high rainfall and large air humidity in the southern regions, the natural moisture content of the highly plastic red clay is generally much higher than the optimum moisture content and the plastic limit moisture content, usually being over-wet soil. The compaction degree and strength of the structure after compaction of the un-air-dried over-wet soil are difficult to meet the compaction standard and strength standard specified in the design, and generally need to be improved with inorganic binders before being used in engineering. In actual engineering, due to geographical and climatic factors, the over-wet soil cannot be air-dried for a sufficient period of time to reduce the moisture content. If all of it is improved with lime, there will be a problem of relatively high construction cost. To make full use of the over-wet highly plastic soil as subgrade filling, its engineering value can only be realized through reasonable subgrade structure design. Considering that the over-wet highly plastic red clay belongs to poor subgrade filling, to realize its engineering application, a core-filled embankment subgrade structure with over-wet soil core filling, side wrapping, and upper improvement layer is usually adopted. Its subgrade structure model and its parameter combinations are as Figure 6 shown.

[0060] Similar to Example 1, first, according to the design document, determine the top elevation and cross-section of the embankment subgrade, preliminarily determine the areas of the core filling area, the side wrapping areas on both sides, and the upper improvement layer, select the improvement layer material and preset the thickness of the improvement layer.

[0061] Next, respectively measure the modulus of the material used in the core filling area and the modulus of the useful material in the improvement layer through rebound tests or related convertible tests (such as obtaining the resilient modulus by converting the CBR obtained from the California Bearing Ratio test). Then, based on the thickness of the improvement layer and the material moduli of the core filling area and the improvement layer, calculate the equivalent resilient modulus of the top surface of the core-filled embankment subgrade. The calculation formula is:

[0062] E t = 21.61ln E0 + 58.79ln E1 + 20.79ln h1 - 353.38

[0063] where, E tis the equivalent resilient modulus of the subgrade top surface, E0 is the material modulus of the core filling area, E1 is the material modulus of the improvement layer, h1 is the thickness of the improvement layer, and 20.7, 21.61, 58.79, and -353.28 are model parameters.

[0064] After verification, the average error between this solution and the theoretical solution is only 0.036%, and the fitting degree reaches 0.97. The significance test shows that the P value is less than 0.05. This empirical model is effective and the prediction effect is very good.

[0065] Next, calculate the equivalent resilient modulus of the subgrade top surface at this time. By comparing the calculated equivalent resilient modulus of the subgrade top surface with the subgrade structure modulus value specified in the design document, determine whether it meets the requirements of the design document. If it does not meet or far exceeds the design standard, consider reselecting the improvement layer material or redetermining the thickness of the improvement layer.

[0066] The designed thickness of the improvement layer is generally 0.4m to 1.5m. For the case where the structural strength does not meet the standard, it can be improved by increasing the thickness of the improvement layer first. If the thickness of the improvement layer needs to exceed 1.5m, then consider replacing the improvement layer material. If the subgrade structure top modulus exceeds the design standard by more than 20%, it indicates that the performance of the improvement layer material is too good or the thickness is too large. Cost optimization can be considered appropriately, that is, degrading the improvement material or reducing the thickness of the improvement layer. Whether to adjust the thickness of the improvement layer or change the material is also determined according to the preset thickness of the improvement layer at this time.

[0067] If it meets the requirements of the design document and the over-standard does not exceed 20%, there is no need to adjust the improvement layer material at this time. Recalculate by slightly adjusting the thickness of the improvement layer to make the obtained solution tend to be close to the requirements of the design document, and then the thickness of the improvement layer and the improvement layer material can be determined. The purpose of this step is mainly to maximize the utilization rate of poor fillers.

[0068] Finally, according to the finally determined thickness of the improvement layer, determine the upper limit of the core filling area, thereby completing the structural design and strength control design of the core-filled embankment subgrade.

[0069] Through the analysis of the resilient modulus of the top surface of the core-filled embankment subgrade structure with the above two types of poor fillers, it can be seen that the top modulus of the core-filled embankment subgrade is closely related to the modulus of the core filling area, the modulus of the improvement layer, and the thickness of the improvement layer. The equivalent modulus of the structure top can be predicted conveniently, quickly, and accurately through an empirical formula. In the formula, a, b, c, and d are model parameters. In engineering practice, the specific values of the parameters can be slightly adjusted according to material differences to reduce the error between the empirical value and the theoretical value. Therefore, the final determined formula is:

[0070] E t = alnE0 + blnE1 + clnh1 + d

[0071] Et is the equivalent resilient modulus of the subgrade top surface, E0 is the material modulus of the core filling area, E1 is the material modulus of the improvement layer, h1 is the thickness of the improvement layer, and a, b, c, d are model parameters. Among them, the model parameters a, b, c, d vary according to the mechanical parameters of the core filling area material and the improvement area material and the performance difference between the two, and are determined by fitting a large number of theoretical solutions. The specific process is as follows:

[0072] First, select three factors: the modulus E0 of the core filling area, the modulus E1 of the improvement layer, and the thickness h1 of the improvement layer. Each factor is evenly selected with no less than four levels within a reasonable value range. Taking four levels for each factor as an example, there are a total of 4×4×4 = 64 types of different subgrade structure types.

[0073] Then, perform multivariate non-linear fitting on the 64 subgrade structure parameters and the analytical solutions of the resilient modulus at the top of the structure, and the values of the parameters a, b, c, d can be obtained. Among them, the parameters a, b, c respectively represent the influence degree of the modulus at the top of the subgrade structure by the modulus E0 of the core filling area, the modulus E1 of the improvement layer, and the thickness h1 of the improvement layer. The larger the parameter, the greater the influence of this factor on the structure modulus, and the parameter d is a constant term.

[0074] This empirical formula can quickly and conveniently obtain the modulus of the subgrade top surface, which is basically applicable to general subgrade fillers and common improvement layer materials, and for the case of 1≤E1 / E0≤10, relatively accurate empirical solutions can be obtained.

[0075] If the mechanical parameters of different subgrade fillers do not differ much, a set of model parameters can be used for approximate solution, or more accurate empirical formula model parameters can be proposed for this specific material. For example, the empirical formula using the core filling material as coastal sand can also be used to calculate the modulus of the subgrade top with the core filling material as high liquid limit red clay. The average error of the 64 groups of empirical solutions of the resilient modulus at the top of the subgrade structure is 1.33%, and the error range is acceptable. While the average error of the empirical solutions obtained using the empirical formula specifically for high liquid limit red clay is only 0.036%, and the error will become very small.

[0076] The above are only the preferred embodiments of the present invention, and are not limitations on the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A design method for a core-filled embankment subgrade structure, characterized in that, It includes the following steps: a. First, according to the design document, determine the top elevation and cross-section of the embankment subgrade, preliminarily determine the areas of the core filling area, the side wrapping areas on both sides, and the overlying improved layer, select the materials for the improved layer and preset the thickness of the improved layer; b. Respectively measure the modulus of the materials used in the core filling area and the modulus of the materials used in the improved layer through tests; c. Then, based on the thickness of the improved layer and the material moduli of the core filling area and the improved layer, calculate the equivalent resilient modulus of the top surface of the core-filled embankment subgrade. The calculation formula is: E t = a ln E0 + b ln E1 + c ln h1 + d Among them, E t is the equivalent resilient modulus of the top surface of the filled-core embankment subgrade, E0 is the material modulus of the filled-core area, E1 is the material modulus of the improved layer, h1 is the thickness of the improved layer, and a, b, c, and d are model parameters; d. By comparing the calculated equivalent resilient modulus of the top surface of the core-filled embankment subgrade with the subgrade structure modulus value specified in the design document, determine whether it meets the requirements of the design document. If it does not meet or far exceeds the design standard, return to step a to re-select the materials for the improved layer or re-determine the thickness of the improved layer. If it meets the requirements of the design document and the over-standard does not exceed 20%, make the calculated equivalent resilient modulus of the top surface of the core-filled embankment subgrade approach the subgrade structure modulus value specified in the design document by fine-tuning the thickness of the improved layer, and thereby determine the thickness of the improved layer and the materials for the improved layer; e. According to the finally determined thickness of the improved layer, determine the upper limit of the core filling area, thereby completing the structural design and strength control design of the core-filled embankment subgrade.

2. The design method of a core-filled embankment subgrade structure according to claim 1, characterized in that The thickness of the improved layer is 0.4m to 1.5m.

3. The design method of a core-filled embankment subgrade structure according to claim 2, characterized in that, In step c, the model parameters a, b, c, and d are determined according to the mechanical parameters of the materials in the core filling area and the improved area and the performance difference degree between the two.

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