Design method of core filling type fill roadbed structure

Abstract

The invention belongs to the technical field of road construction application, and particularly relates to a design method of a core filling type fill roadbed structure. The invention provides a design method of a core filling type fill subgrade structure, which comprises the following steps of: determining model parameters by taking the material modulus of a core filling area, the material modulus of an improved layer and the thickness of the improved layer which can be conveniently acquired as variables and combining the mechanical parameters of a core filling area material and an improved area material and the performance difference of the two materials; according to the method, the equivalent resilience modulus of the top surface of the roadbed is effectively calculated, so that the core-filling type fill roadbed structure is designed, and the method has multiple values of technology, cost, economy, environmental protection, carbon reduction and the like, and is suitable for large-scale popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of road construction application, and in particular relates to a design method for a core-filling type earthfill roadbed structure. Background Art

[0002] The industrial revolution and information revolution have accelerated the invention and progress of modern high-power engineering machinery and automation equipment, greatly promoted the breadth and depth of large-scale engineering activities, and significantly improved the level of human development, while also leaving the homes on which people depend for survival devastated and overwhelmed. There is only one earth. Over the years, after suffering the painful lessons brought about by wanton destruction of the environment, mankind has learned from its painful experience and summed up its experience. Now, protecting the ecological environment, developing carbon reduction technologies, and promoting green construction have become a consensus of mankind. China has a vast territory and a large population. With the advancement of livelihood projects, my country's road network has achieved hardened access to every village, and the total mileage of roads at all levels has ranked first in the world. With the strengthening of national strength and the continuous improvement of people's living standards, my country's 15th Five-Year Plan further proposed to transform and upgrade a large number of low-grade roads, and at the same time planned a number of new high-grade roads. The road construction that has been carried out has a huge demand for engineering materials.

[0003] For roadbed filling materials, the existing design specifications require that the strength of roadbed filling materials and roadbed structure strength must meet certain standards. For example, the "Highway Roadbed Design Specifications" (JTG D30-2015) stipulates that the CBR control standards for expressways and first-class highways are: 8% for upper roadbed, 5% for lower roadbed, 4% for upper embankment, and 3% for lower embankment according to the highway grade, while the CBR control standards for second-class highways are: 6% for upper roadbed, 4% for lower roadbed, 3% for upper embankment, and 2% for lower embankment. The higher the grade, the higher the performance index requirements for roadbed filling materials. In the design of highway pavement structure, the roadbed structure strength, that is, the rebound modulus of the roadbed top surface is an important design parameter. The "Highway Asphalt Pavement Design Specifications" (JTG D50-2017) stipulates that the rebound modulus of the roadbed top surface for heavy, extra-heavy and extremely heavy loads should be no less than 50, 60 and 70 MPa respectively, and the rebound modulus of the roadbed top surface for medium and light traffic loads should be no less than 40 MPa. The higher the traffic load grade, the higher the requirements for the roadbed structure strength.

[0004] In some areas, a large number of materials distributed along the highway construction are often abandoned because their engineering performance does not meet the requirements of standard specifications, and are replaced by high-quality materials with high costs. The main reasons for poor fillers include: low material strength, poor water stability and engineering performance; poor particle grading, difficult to compact, and poor structural stability; too high water content, difficult to achieve the specified compaction, long creep duration, and large settlement; the content of a certain mineral component exceeds the standard, and expansion or collapse occurs in the later period. At the same time, the harsh environment of dry-wet cycles and freeze-thaw cycles also puts forward more requirements on material performance and structural design. Poor fillers include coastal sand in coastal areas, peat soil in swamp areas, over-wet soil in humid areas, collapsible loess on the Loess Plateau, high liquid limit soil in the humid and hot areas of the south, and aeolian sand in the Gobi area of ​​the north.

[0005] Through scientific and reasonable technical means, while ensuring the quality of the project, the utilization rate of local materials along the highway can be improved, so that local materials can be used and waste can be turned into treasure. This can not only reduce waste and dependence on external high-quality materials, reduce excessive excavation of natural mountains or clay resources, but also reduce material transportation costs and machinery equipment. It can not only significantly reduce construction costs and damage to the natural environment, but also effectively implement the concept of green and high-quality development, and help achieve the dual carbon goals.

[0006] In order to improve the utilization rate of poor fill materials on site, engineers and researchers proposed a core-filled roadbed structure, as shown in the attached figure of the specification. Figure 1 As shown. The poor filling material is sealed in the center of the cross section of the roadbed; the sides of the slope are filled with edge soil with a width of not less than 2m, which is made of clay or gravel with good compaction and high structural strength. It can not only restrict the lateral deformation of the poor filling material, but also facilitate vegetation and greening, reducing the subsequent rain erosion; the overlying improvement layer is gravel soil with good gradation, controllable particle size, good water stability and good structural strength, or materials treated with inorganic binders. The improvement layer has the function of sealing the poor filling material, and is mainly used to make up for the defects of poor structural properties and low structural strength of the poor filling material, improve the bearing capacity and structural strength of the top surface of the roadbed structure, and make it meet the requirements of the design indicators.

[0007] The equivalent elastic modulus of the top surface of the roadbed is the main indicator of the strength of the roadbed structure. In the existing highway standards and specifications, the equivalent elastic modulus of the top surface of the roadbed is generally obtained through direct rebound test, back calculation of bending test or empirical conversion formula of CBR. For layered structural systems, predecessors have also proposed prediction formulas for the top elastic modulus of the structural layer, but these methods are more applicable to the case where the modulus ratio is between 10 and 10000, that is, the mechanical properties of the lower material and the upper covering layer material are very different, such as the roadbed material overlying the pavement base material, and the equivalent modulus of the top surface of the base can be used for empirical solution.

[0008] Since the above empirical formula is not suitable for estimating the equivalent modulus of the top surface of the roadbed structure, a special empirical formula that can be used to estimate the equivalent rebound modulus of the top surface of the core-fill roadbed structure is proposed, and the strength control of the core-fill roadbed structure is achieved, which is a problem that needs to be solved at present. Summary of the invention

[0009] Aiming at the technical inconveniences existing in the strength control of the existing core-fill roadbed structure, the present invention proposes a design method which has reasonable design, simple method, convenient operation and can effectively calculate the equivalent rebound modulus of the top surface of the core-fill roadbed structure to realize the strength control of the core-fill roadbed 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 of a core-filled earthwork roadbed structure, comprising the following steps:

[0011] a. First, determine the top elevation and cross section of the fill roadbed according to the design documents, preliminarily determine the core filling area, the side edge area and the overlying improvement layer area, select the improvement layer material and preset the thickness of the improvement layer;

[0012] b. by respectively measuring the modulus of the material used in the core filling area and the modulus of the useful material of the improved layer;

[0013] c. Then, the equivalent elastic modulus of the top surface of the core-filled embankment is calculated based on the thickness of the improved layer and the material modulus of the core-filled area and the improved layer. The calculation formula is:

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

[0015] Among them, E t is the equivalent rebound modulus of the 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, and d are model parameters;

[0016] d. By comparing the calculated equivalent elastic modulus of the top surface of the roadbed with the roadbed structural modulus value specified in the design documents, determine whether it meets the requirements of the design documents. If it does not meet or far exceeds the design standards, return to step a and reselect the material of the improved layer or re-plan the thickness of the improved layer. If it meets the requirements of the design documents and exceeds the standard by no more than 20%, the thickness of the improved layer is fine-tuned to make the calculated equivalent elastic modulus of the top surface of the core-filled roadbed and the roadbed structural modulus value specified in the design documents close to each other, and the thickness of the improved layer and the material of the improved layer are determined accordingly;

[0017] e. According to the final 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 filling roadbed.

[0018] Preferably, the thickness of the modified layer is between 0.4m and 1.5m.

[0019] Preferably, in step c, the model parameters a, b, c, d are determined based on the mechanical parameters of the core filling area material and the improved area material and the degree of difference in their performance.

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

[0021] The present invention provides a design method for a core-fill roadbed structure. The method takes the material modulus of the core-fill area, the material modulus of the improved layer and the thickness of the improved layer, which can be easily obtained, as variables. The model parameters are determined by combining the mechanical parameters of the core-fill area material and the improved area material and the performance difference between the two. The method effectively realizes the calculation of the equivalent rebound modulus of the top surface of the roadbed, thereby realizing the design of the core-fill roadbed structure. The method has multiple values ​​such as technology, cost, economy, environmental protection and carbon reduction, and is suitable for large-scale promotion 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 following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 It is an existing core-fill roadbed structure;

[0024] Figure 2 The structural model and parameter diagram of the improved layer of the coastal sand core-filled embankment;

[0025] Figure 3 is the modulus of coastal sand E0 to the equivalent modulus of the roadbed structure top E t The influence diagram of

[0026] Figure 4 is the equivalent modulus E1 of the improved layer to the top of the roadbed structure t The influence diagram of

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

[0028] Figure 6 This is the structural model and parameter diagram of the improved layer roadbed overlying the high liquid limit over-wet soil core-fill embankment. DETAILED DESCRIPTION

[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 may be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the limitations of the specific embodiments disclosed in the following specification.

[0031] Based on the designed subgrade elevation and the cross-sectional dimensions of the filled 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 development. For this reason, 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, so as to achieve 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 liquid limit 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] Embodiment 1. This embodiment 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 show that: this sand is mainly composed of medium-fine group 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 "Highway Geotechnical Test Regulations" (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] In view of the fact that coastal sand is a poor roadbed filler, in order to realize its engineering application, a core-filled roadbed structure with coastal sand filling, two-side edging and an improved layer on top is usually adopted, that is, firstly, a cushion layer with a thickness of about 0.5m is built on the compacted foundation after surface cleaning. The cushion layer material is graded crushed stone or inorganic binder treatment material with good strength and water stability. The roadbed structure above the cushion layer adopts the form of coastal sand filling, two-side side limit edging and top surface improvement layer covering. The edging soil and the improved layer are preferably made of crushed stone soil, clay or improved materials with good structural properties, as shown in the attached figure of the specification. Figure 1 As shown. In the coastal sand core-filled roadbed structure of this case, the improved layer material is crushed stone soil, cement-treated coastal sand or lime-treated coastal sand. The thickness of the edge on both sides is preferably designed to be greater than 2m.

[0036] The equivalent elastic modulus of the top surface of the roadbed is the main indicator to characterize the strength of the roadbed structure. In order to carry out the strength study of different roadbed structure combinations, the equivalent elastic modulus of the top surface of the roadbed is taken as the dependent variable, and the core modulus, the improved layer modulus and the improved layer thickness are selected as three independent factors as independent variables. Each factor has 4 levels. The roadbed structure model and its parameter combination are shown in the figure. Figure 2 As shown in the figure, there are 64 combinations of roadbed structure combinations. Among them, the core filling modulus and the improved layer modulus can be obtained through rebound tests or related convertible tests.

[0037] The following assumptions are made for this roadbed structure: (1) The improved layer material and the core filling area material are homogeneous, uniform, continuous, isotropic materials, and infinite in the horizontal direction; (2) The improved layer has a certain thickness and the coastal core filling has infinite thickness; (3) The displacement, stress, and strain 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] A theoretical model based on double-circle standard axle load acting on layered elastic body surface for 64 different roadbed structural parameters Figure 2 The theoretical solution of the equivalent modulus of the roadbed top surface obtained by the basic equation, the empirical solution calculated by the empirical formula, and the errors between the two are listed in Table 1.

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

[0040]

[0041]

[0042]

[0043] Then, the 64 roadbed structural parameters and their top surface rebound modulus were statistically analyzed. 16 groups of roadbed structures were randomly selected, and the modulus and thickness of the improved layer were limited. The change of the roadbed top surface modulus was analyzed by changing the modulus of the lower core filling area. Figure 3 As shown in the figure, it can be seen that the equivalent modulus of the roadbed top increases logarithmically with the increase of the coastal sand modulus. Increasing the core filling modulus can almost equivalently increase the equivalent modulus of the roadbed top surface. The logarithmic curve can fit the relationship between the two very well, with a fitting degree of up to 0.999.

[0044] Next, 16 groups of roadbed structures were randomly selected. Given the core-filling area modulus and the thickness of the improved layer, the relationship between the roadbed top equivalent modulus and the improved layer modulus can be obtained by changing the improved layer modulus, as shown in Figure 4 As shown in the figure, the equivalent modulus of the roadbed 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 fitting degree of up to 0.99. It can also be found from the figure that when the core fill modulus is larger and the improved layer is thicker, the improved layer modulus will significantly improve the equivalent modulus of the roadbed top surface.

[0045] For different core filling area modulus and improvement layer modulus, the relationship between the equivalent rebound modulus of the roadbed top surface and the thickness of the improvement layer is as follows: Figure 5 As shown in the figure, it can be seen that the two are also nonlinearly logarithmically correlated, and the fitting degree can reach 0.996. Moreover, for different material types, the contribution of the thickness of the improved layer to the equivalent modulus of the top surface of the roadbed is relatively uniform.

[0046] From the above, it can be seen that the equivalent modulus of the roadbed 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 roadbed top surface can be expressed as a multivariate nonlinear function of the core filling modulus, the modulus of the improved layer and the thickness of the improved layer, and can be approximated by a logarithmic function. By performing multivariate nonlinear regression on 64 groups of roadbed structural parameters, the empirical regression model obtained is:

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

[0048] Among them, E t is the equivalent rebound modulus of the top surface of the roadbed, 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] By conducting a joint significance test on the model, its fit can reach 0.96, and the average error between the empirical solution and the theoretical solution is only 0.03%. The statistical P value probability is less than 0.05, indicating that the null hypothesis is rejected at a 95% confidence level and the model is meaningful.

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

[0051] Specifically, first determine the top surface elevation and cross-section of the fill roadbed based on the design documents, preliminarily determine the core filling area, the side edge areas and the overlying improved layer area, select the improved layer material and preset the thickness of the improved layer.

[0052] Then, the modulus of the material used in the core-filling area and the modulus of the material selected for the improved layer are determined by a rebound test or a related convertible test.

[0053] Next, calculate the equivalent elastic modulus of the top surface of the roadbed structure at this time. By comparing the calculated equivalent elastic modulus of the top surface of the roadbed structure with the modulus value of the roadbed structure 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 material of the improved layer or re-planning the thickness of the improved layer.

[0054] The design thickness of the improved layer is generally 0.4m to 1.5m. If the structural strength does not meet the standard, it can be improved by increasing the thickness of the improved layer. If the thickness of the improved layer needs to exceed 1.5m, you can consider replacing the material of the improved layer. If the top modulus of the roadbed structure exceeds the design standard by more than 20%, it means that the performance of the improved layer material is too good or the thickness is too large. You can consider appropriate cost optimization, 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 based on the preset thickness of the improved layer at this time.

[0055] If the requirements of the design documents are met and the excess does not exceed 20%, there is no need to adjust the material of the improved layer. The thickness of the improved layer can be fine-tuned and recalculated to make the solution close to the requirements of the design documents. The thickness of the improved layer and the material of the improved layer can be determined. The purpose of this step is to maximize the utilization rate of poor fillers. Because the top elevation of the designed roadbed 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, the greater the core filling thickness, and the maximum utilization rate of poor fillers. In this way, the material and transportation costs are also lower, and it is more environmentally friendly.

[0056] Finally, the upper limit of the core-fill area is determined based on the thickness of the improved layer finally determined, thereby completing the structural design and strength control design of the core-fill roadbed.

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

[0058] Example 2: This example provides a design method for a core-filled roadbed structure using high liquid limit red clay as a core-fill material in a hot and humid southern region.

[0059] A large amount of high liquid limit red clay is distributed in southern my country. The rebound modulus of dry high liquid limit red clay is relatively high, often greater than 100Mpa. However, due to the heavy rainfall and high air humidity in southern China, the natural moisture content of high liquid limit red clay is generally much higher than the optimum moisture content and plastic limit moisture content. It is usually over-wet soil. After the over-wet soil is compacted without drying, its compaction and strength are difficult to meet the compaction and strength standards specified in the design. It generally needs to be improved with inorganic binders before it can be used in engineering. In actual engineering, due to geographical and climatic factors, over-wet soil cannot be dried for a long enough time to reduce the moisture content. If all of it is improved by adding ash, it will face the problem of high construction costs. In order to make full use of over-wet high liquid limit soil as roadbed filler, its engineering value can only be realized through reasonable roadbed structure design. In view of the fact that over-wet soil of high liquid limit red clay is a poor roadbed filler, in order to realize its engineering application, a core-fill roadbed structure with over-wet soil core filling, two-side edging and overlying improvement layer is usually adopted. Its roadbed structure model and its parameter combination are as follows Figure 6 shown.

[0060] As in Example 1, first determine the top elevation and cross section of the fill roadbed according to the design documents, preliminarily determine the core filling area, the two side edge areas and the overlying improvement layer area, select the improvement layer material and preset the thickness of the improvement layer

[0061] Next, the modulus of the material used in the core filling area and the modulus of the useful material in the improved layer are measured by rebound test or related convertible test (such as the modulus of resilience obtained by converting the CBR obtained by the California Bearing Ratio Test). Then, the equivalent modulus of resilience of the top surface of the core-filled embankment is calculated based on the thickness of the improved layer and the material modulus of the core filling area and the improved layer. The calculation formula is:

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

[0063] Among them, E tis the equivalent rebound modulus of the top surface of the roadbed, 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 20.7, 21.61, 58.79 and -353.28 are model parameters.

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

[0065] Next, calculate the equivalent elastic modulus of the top surface of the roadbed at this time. By comparing the calculated equivalent elastic modulus of the top surface of the roadbed with the roadbed 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 material of the improved layer or re-planning the thickness of the improved layer.

[0066] The design thickness of the improved layer is generally 0.4m to 1.5m. If the structural strength does not meet the standard, it can be improved by increasing the thickness of the improved layer. If the thickness of the improved layer needs to exceed 1.5m, you can consider replacing the material of the improved layer. If the top modulus of the roadbed structure exceeds the design standard by more than 20%, it means that the performance of the improved layer material is too good or the thickness is too large. You can consider appropriate cost optimization, 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 based on the preset thickness of the improved layer at this time.

[0067] If the requirements of the design documents are met and the excess does not exceed 20%, there is no need to adjust the material of the improved layer. The thickness of the improved layer can be fine-tuned and recalculated to make the solution close to the requirements of the design documents. The thickness of the improved layer and the material of the improved layer can be determined. The purpose of this step is mainly to maximize the utilization rate of poor fillers.

[0068] Finally, the upper limit of the core-fill area is determined based on the thickness of the improved layer finally determined, thereby completing the structural design and strength control design of the core-fill roadbed.

[0069] By analyzing the top rebound modulus of the core-filled roadbed structure with the above two types of poor fillers, it can be seen that the top modulus of the core-filled roadbed is closely related to the modulus of the core-filled area, the modulus of the improved layer and the thickness of the improved layer. The empirical formula can be used to conveniently and accurately predict the equivalent modulus of the top of the structure. In the formula, a, b, c, and d are model parameters. In actual engineering, the specific values ​​of the parameters can be fine-tuned according to the differences in materials to reduce the error between the empirical value and the theoretical value. To this end, the final formula is determined as:

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

[0071] Et is the equivalent rebound modulus of the top surface of the roadbed, 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 a, b, c, d are model parameters. Among them, the model parameters a, b, c, d are different according to the mechanical parameters of the core filling area material and the improved area material and the difference in performance between the two, and are determined by fitting a large number of theoretical solutions. The specific process is as follows:

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

[0073] Then, multivariate nonlinear fitting was performed on the 64 roadbed structure parameters and the analytical solutions of the top rebound modulus of the structure to obtain the values ​​of parameters a, b, c, and d. The parameters a, b, and c represent the degree to which the top modulus of the roadbed structure is affected by the modulus of the core filling area E0, the modulus of the improved layer E1, and the thickness of the improved layer h1, respectively. The larger the parameter, the greater the influence of the factor on the structural modulus. Parameter d is a constant term.

[0074] This empirical formula can quickly and conveniently calculate the modulus of the top surface of the roadbed. It is basically applicable to general roadbed fillers and commonly used improved layer materials, and for the case of 1≤E1E0≤10, a more accurate empirical solution can be obtained.

[0075] If the mechanical parameters of different roadbed filling materials are not very different, a common set of model parameters can be used for approximate solution, or more accurate empirical formula model parameters can be proposed for the specific material. For example, the empirical formula for the core material of coastal sand can also be used to calculate the top modulus of the roadbed with the core material of high liquid limit red clay. The average error of the empirical solution of the top rebound modulus of the 64 groups of roadbed structures obtained is 1.33%, which is an acceptable error range. The average error of the empirical solution obtained using the empirical formula specifically for high liquid limit red clay is only 0.036%, which is very small.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A design method for a core-filled embankment structure, characterized in that: The following steps are involved: a. First, determine the top elevation and cross section of the fill roadbed according to the design documents, preliminarily determine the core filling area, the side edge area and the overlying improvement layer area, select the improvement layer material and preset the thickness of the improvement layer; b. Determine the modulus of the material used in the core filling area and the modulus of the material used in the improved layer through experiments; c. Then, the equivalent elastic modulus of the top surface of the core-filled embankment is calculated based on the thickness of the improved layer and the material modulus of the core-filled area and the improved layer. The calculation formula is: E t lnE0+blnE1+clnh1+d Among them, E t is the equivalent rebound modulus of the 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, and d are model parameters; d. By comparing the calculated equivalent elastic modulus of the top surface of the core-filled roadbed with the roadbed structural modulus value specified in the design documents, determine whether it meets the requirements of the design documents. If it does not meet or far exceeds the design standard, return to step a, reselect the material of the improved layer or re-plan the thickness of the improved layer. If it meets the requirements of the design documents and exceeds the standard by no more than 20%, fine-tune the thickness of the improved layer to make the calculated equivalent elastic modulus of the top surface of the core-filled roadbed and the roadbed structural modulus value specified in the design documents close to each other, and determine the thickness of the improved layer and the material of the improved layer accordingly; e. According to the final 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 filling roadbed.

2. The design method of a core-fill roadbed structure according to claim 1, characterized in that: The thickness of the improved layer is between 0.4m and 1.5m.

3. The design method of a core-fill roadbed structure according to claim 2 is characterized in that: In the 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 difference in performance between the two.

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