Composite foundation settlement calculation method considering karst rock-soil interface grouting

Abstract

The invention relates to a composite foundation settlement calculation method considering karst rock-soil interface grouting, which is characterized in that n layers of covering layers are arranged on a limestone karst area, the thicknesses of soil layers are respectively h1, h2,..., hn, the compression moduli of the corresponding soil layers are respectively Es1, Es2,..., Esn, the pile length of a composite foundation reinforcing pile is L, and the m layer is reinforced; the distance between the bottom face of the reinforcing pile group and the bottom face of each soil layer is Zm, Zm + 1,... and Zn, after karst grouting is considered, the compression modulus increasing coefficients of the soil layers above the bedrock face are lambda1, lambda2,... and lambdan, the lambdan is larger than or equal to 1.0, and the total settlement of the composite foundation is the product of the sum of the settlement S1 of the reinforcing area and the settlement S2 of the underlying layer and the settlement experience correction coefficient ms. According to the method, a composite foundation settlement calculation formula is improved, the soil layer compression modulus improvement coefficient lambda is introduced into the settlement calculation process, the synergistic effect of karst grouting and composite foundation reinforcement is comprehensively considered, and the settlement calculation precision of the high-speed rail karst roadbed composite foundation is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering and transportation infrastructure construction, and in particular relates to a composite foundation settlement calculation method considering grouting at a karst rock-soil interface. Background Art

[0002] In my country, karst geological phenomena are widely distributed, accounting for more than one-third of the country's land area, and are common adverse geological conditions in railway projects. In order to cope with the adverse effects of karst on the stability of railway subgrades, the "Railway Special Subgrade Design Code" (TB10035-2018) puts forward clear requirements for the treatment of karst subgrades. When the thickness of the karst cover layer is greater than 5m, grouting technology should be used to seal the soil-rock interface to form a water-proof curtain; among them, the grouting thickness of the soil layer above the bedrock surface should not be less than 3.0m, and the grouting depth into the bedrock should not be less than 5m. For deep-cover karst areas with a cover layer thickness of ≥30m, foundation treatment measures combining composite foundations and karst grouting are usually adopted. This type of treatment method effectively enhances the bearing capacity and stability of the subgrade and is an important technical means in high-speed railway construction.

[0003] However, current design and calculation methods have significant technical deficiencies when applying a combination of composite foundation and karst grouting treatment measures. High-speed railways have extremely strict requirements for controlling foundation deformation, especially for ballastless tracks, where the permitted post-construction settlement is only 15 mm. “Millimeter-level” settlement control is directly related to the safety and smooth operation of high-speed trains. However, existing settlement design and calculation methods do not fully consider the effect of grouting the soil layer above the bedrock surface on improving the compression modulus of the foundation soil, and ignore the significant impact of the 3m grouting layer on reducing post-construction settlement of the roadbed. As a result, the calculation results cannot meet the requirements for precise millimeter-level settlement control of high-speed railways. Therefore, it is urgent to propose a new settlement calculation method for high-speed railway composite foundations that comprehensively considers the improvement effect of karst grouting on foundation performance to further improve the accuracy of settlement calculation for karst roadbed composite foundations. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a composite foundation settlement calculation method that takes into account grouting at the karst rock-soil interface, aiming to solve the problem in the existing technology that the impact of grouting on the soil layer compression modulus on the settlement calculation is not fully considered, thereby achieving the goal of precise control of millimeter-level settlement of high-speed railway subgrades.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A composite foundation settlement calculation method considering grouting at the karst rock-soil interface. The upper cover layer in the limestone karst area is n layers, and the thickness of each soil layer is h1, h2, ..., h n , the corresponding soil compression modulus is E s1 、E s2,…,E sn The length of the composite foundation reinforcement pile is L, and the reinforcement reaches the mth layer. The distances between the bottom surface of the reinforcement pile group and the bottom surface of each soil layer are Z m 、Z m+1 ,…,Z n After considering karst grouting, the compression modulus of the soil layer above the bedrock surface is increased by λ1, λ2, ..., λ n ,λ n ≥1.0, the total settlement of the composite foundation is:

[0007] S=m s (S1+S2)

[0008] Among them, S1 is the settlement of the reinforced area, S2 is the settlement of the underlying layer, m s is the empirical correction coefficient for settlement.

[0009] Preferably, the calculation steps of the settlement of the reinforcement area are:

[0010] S1, calculate the compression modulus E of the soil between piles S and the compression modulus improvement factor of soil between piles Calculate the compression modulus E of the soil between piles according to the depth of composite foundation treatment S and the compression modulus improvement factor of soil between piles

[0011]

[0012] Among them, E Si is the compression modulus of each soil layer, h i is the thickness of each soil layer, λ i Improvement coefficient for compression modulus of each soil layer;

[0013] S2, calculate the compression modulus E of the composite foundation sp :

[0014]

[0015] Among them, E P is the compression modulus of the pile, m r is the area replacement rate;

[0016] S3, calculate the settlement of the reinforced area S1:

[0017]

[0018] Among them, P0 is the additional stress at the bottom of the embankment, P z is the additional stress on the bottom surface of the reinforcement area.

[0019] Preferably, the subjacent layer settlement S2:

[0020]

[0021] Among them, Z i is the distance between the bottom surface of the reinforcement pile group and each layer, α i is the average additional stress coefficient from the bottom surface of the reinforced pile group to the bottom surface of the i-th layer.

[0022] Preferably, the compression modulus λ of each soil layer i The improvement coefficient has a clear regularity with the distance from the grouting area and the properties of the covering soil. The closer the soil layer is to the grouting area, the higher the λ i The larger the value.

[0023] Preferably, the total depth of the covering layer is greater than or equal to 30 meters.

[0024] Preferably, a cushion layer of crushed stone and medium-coarse sand is provided on the top of the reinforcement pile, and several layers of geogrid are provided in the cushion layer.

[0025] Preferably, the geogrid is a bidirectional warp-knitted polyester geogrid.

[0026] Preferably, the grouting thickness of the soil layer above the bedrock surface should not be less than 3.0 meters, and the depth into the bedrock should not be less than 5.0 meters.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] The present invention proposes a composite foundation settlement calculation method that takes into account grouting at the karst rock-soil interface. By proposing the soil layer compression modulus improvement coefficient λ after karst grouting, and according to the regular changes in the distance from the grouting area and the properties of the covering soil, the improvement of the foundation soil performance caused by karst grouting is accurately reflected; the composite foundation settlement calculation formula is improved, the soil layer compression modulus improvement coefficient λ is introduced into the settlement calculation process, and the synergistic effect of karst grouting and composite foundation reinforcement is comprehensively considered, which significantly improves the settlement calculation accuracy of the high-speed railway karst roadbed composite foundation, and can meet the stringent requirements of millimeter-level post-construction settlement control of high-speed railways. This method is highly practical and suitable for the design of high-speed railway roadbeds in deep-cover karst areas. It provides a reliable theoretical basis for settlement control under complex geological conditions, effectively solves the problem that the existing technology does not fully consider the influence of grouting on the foundation soil compression modulus, and provides an important guarantee for the safe and smooth operation of high-speed railways. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic flow chart of a composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to the present invention;

[0030] Figure 2 This is a schematic diagram of the composite foundation structure considering grouting at the karst rock-soil interface of the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the present invention.

[0032] In addition, described feature, structure or characteristic can be combined in one or more embodiments in any suitable manner.In the following description, many specific details are provided so as to provide a full understanding of the embodiments of the present application. However, it will be appreciated by those skilled in the art that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps etc. can be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring the various aspects of the application.

[0033] like Figure 1 As shown, this embodiment discloses a composite foundation settlement calculation method considering grouting at the karst rock-soil interface. The upper covering layer in the limestone karst area is n layers, and the thickness of each soil layer is h1, h2, ..., h n , the corresponding soil compression modulus is E s1 、E s2 ,…,E sn Here, the "cover layer" refers to a series of soil layers located above the bedrock. Its physical properties have an important influence on the settlement calculation, especially the thickness and compression modulus, which determine the deformation characteristics and bearing capacity of each soil layer. The length of the composite foundation reinforcement pile is L, and it is reinforced to the mth layer to form a stable support structure. The distance between the bottom surface of the reinforcement pile group and the bottom surface of each soil layer is Z. m 、Z m+1 ,…,Z n After considering karst grouting, the compression modulus of the soil layer above the bedrock surface is increased by λ1, λ2, ..., λ n ,λ n ≥1.0, the total settlement of the composite foundation is:

[0034] S=m s (S1+S2)

[0035] Among them, S1 is the settlement of the reinforced area, S2 is the settlement of the underlying layer, m s is the empirical correction coefficient for settlement.

[0036] In this embodiment, the calculation steps of the reinforcement area settlement are as follows:

[0037] S1, calculate the compression modulus E of the soil between piles S and the compression modulus improvement factor of soil between piles Calculate the compression modulus E of the soil between piles according to the depth of composite foundation treatment S and the compression modulus improvement factor of soil between piles

[0038]

[0039]

[0040] Among them, E Si is the compression modulus of each soil layer, h i is the thickness of each soil layer, λ i Improvement coefficient for compression modulus of each soil layer;

[0041] S2, calculate the compression modulus E of the composite foundation sp :

[0042]

[0043] Among them, E P is the compression modulus of the pile, m r is the area replacement rate;

[0044] S3, calculate the settlement of the reinforced area S1:

[0045]

[0046] Among them, P0 is the additional stress at the bottom of the embankment, P z is the additional stress on the bottom surface of the reinforcement area.

[0047] In this embodiment, the settlement of the underlying layer S2 is:

[0048]

[0049] Among them, Z i is the distance between the bottom surface of the reinforcement pile group and each layer, α i is the average additional stress coefficient from the bottom surface of the reinforced pile group to the bottom surface of the i-th layer.

[0050] Furthermore, the compression modulus of each soil layer is increased by the coefficient λ i The regularity is obvious with the distance from the grouting area and the properties of the covering soil. The closer the soil layer is to the grouting area, the higher the λ iThe larger the value. This is because during the grouting process, the slurry fills the pores of the soil layer and gradually solidifies, resulting in a significant increase in the density and strength of the soil layer near the grouting area, which is manifested as an increase in the compression modulus. As the distance from the grouting area increases, the penetration range of the slurry gradually weakens, so the improvement coefficient gradually decreases, but it still has an important impact on the settlement calculation. By adopting a variety of methods such as field tests and indoor tests, the compression modulus improvement coefficient of each soil layer above the bedrock surface after karst grouting is determined. During the test, by collecting and testing soil layer samples near the grouting area, it was found that the value of the soil layer compression modulus improvement coefficient is closely related to the distance from the grouting area and the soil properties of the covering soil. In addition, the soil properties of the covering soil, such as moisture content, particle size distribution and density, will also affect λ i In the experiment, the analysis of these parameters is to determine the i It provides a reliable theoretical basis and further verifies the significant effect of grouting on improving foundation soil performance.

[0051] In this embodiment, the total depth of the overburden is greater than or equal to 30 meters. This method is suitable for deep-cover karst areas, where the geological conditions are complex and traditional methods have difficulty accurately assessing settlement behavior. The grouting thickness of the soil layer above the bedrock surface should not be less than 3.0 meters, and the depth of grouting into the bedrock should not be less than 5.0 meters. This grouting design ensures the reinforcement effect of the contact area between the overburden and the bedrock, thereby forming a stable water-proof curtain, which not only improves the compressive capacity of the soil layer above the bedrock surface, but also effectively prevents the infiltration of groundwater from affecting the stability of the structure.

[0052] A cushion layer of crushed stone and medium-coarse sand is set on the top of the reinforcement pile, and several layers of geogrid are set in the cushion layer. Specifically, the roadbed fill body includes a cushion layer of crushed stone and medium-coarse sand of not less than 0.4 meters laid on the top of the reinforcement pile, 1 to 2 layers of geogrid are set in the cushion layer, and then the upper roadbed is filled in layers to form the roadbed fill body. The setting of the crushed stone and medium-coarse sand cushion layer not only provides a stable construction platform for the upper roadbed, but also avoids the influence of water softening on the foundation by enhancing the drainage performance. At the same time, arranging 1 to 2 layers of geogrid in the cushion layer further improves the tensile strength and overall stability of the cushion layer, helps to disperse the load and reduce local stress concentration, thereby extending the service life of the entire roadbed structure. Specifically, the geogrid adopts a two-way warp-knitted polyester geogrid, the material of which has excellent tensile strength and durability, and can significantly improve the overall stability of the cushion layer. The bidirectional warp knitting design provides uniform support in the cushion layer, effectively dispersing the upper load, avoiding deformation of the roadbed structure due to local stress concentration, and thus enhancing the overall roadbed structure's anti-deformation ability.

[0053] In summary, the present invention discloses a composite foundation settlement calculation method that takes into account grouting at the karst rock-soil interface. By adopting a variety of methods such as field tests and indoor tests, the compression modulus improvement coefficient of each soil layer above the bedrock surface after karst grouting is determined. By proposing the soil layer compression modulus improvement coefficient and introducing it into the composite foundation settlement calculation formula, combined with the cover layer depth, grouting thickness, bedrock depth and soil layer characteristics, the improvement effect of grouting on soil layer performance is accurately described. This method defines in detail the value range and variation law of the soil layer compression modulus improvement coefficient, and combines the settlement of the pile reinforcement area and the settlement of the underlying layer to improve the settlement calculation formula and achieve high-precision settlement prediction. By adopting the method of the present invention, the calculation accuracy of karst grouting for roadbed reinforcement can be significantly improved, especially for composite foundation treatment measures in deep-cover karst areas, providing a scientific basis for millimeter-level settlement control of high-speed railways. While ensuring the stability and safety of the roadbed, the present invention optimizes the foundation treatment scheme, reduces construction and later maintenance costs, and improves engineering efficiency and quality. The present invention has important guiding significance for the construction of foundation engineering in karst areas, provides reliable technical support for infrastructure with strict requirements on settlement, such as high-speed railways and bridges, and further promotes the development of foundation treatment technology in karst geological environments. It fills the research gap in the existing technology that does not fully consider the impact of grouting on soil performance, and provides the industry with an innovative calculation method with strong practicality and wide adaptability.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the present invention as described above. For the sake of simplicity, they are not provided in detail. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions described in the above embodiments, or to make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite foundation settlement calculation method considering grouting at the karst rock-soil interface, characterized in that: There are n layers of covering layer in the limestone karst area, and the thickness of each soil layer is h1, h2, ..., h n , the corresponding soil compression modulus is E s1 、E s2 ,…,E sn The length of the composite foundation reinforcement pile is L, and the reinforcement reaches the mth layer. The distances between the bottom surface of the reinforcement pile group and the bottom surface of each soil layer are Z m 、Z m+1 ,…,Z n After considering karst grouting, the compression modulus of the soil layer above the bedrock surface is increased by λ1, λ2, ..., λ n ,λ n ≥1.0, the total settlement of the composite foundation is: S=m s (S1+S2) Among them, S1 is the settlement of the reinforced area, S2 is the settlement of the underlying layer, m s is the empirical correction coefficient for settlement.

2. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 1 is characterized in that: The calculation steps of the settlement of the reinforcement area are as follows: S1, calculate the compression modulus E of the soil between piles S and the compression modulus improvement factor of soil between piles Calculate the compression modulus E of the soil between piles according to the depth of composite foundation treatment S and the compression modulus improvement factor of soil between piles Among them, E Si is the compression modulus of each soil layer, h i is the thickness of each soil layer, λ i Improvement coefficient for compression modulus of each soil layer; S2, calculate the compression modulus E of the composite foundation sp : Among them, E P is the compression modulus of the pile, m r is the area replacement rate; S3, calculate the settlement of the reinforced area S1: Among them, P0 is the additional stress at the bottom of the embankment, P z is the additional stress on the bottom surface of the reinforcement area.

3. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 2 is characterized in that: The subsurface settlement S2: Among them, Z i is the distance between the bottom surface of the reinforcement pile group and each layer, α i is the average additional stress coefficient from the bottom surface of the reinforced pile group to the bottom surface of the i-th layer.

4. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 3 is characterized in that: The compression modulus of each soil layer is increased by the coefficient λ i The regularity is obvious with the distance from the grouting area and the properties of the covering soil. The closer the soil layer is to the grouting area, the higher the λ i The larger the value.

5. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 3 is characterized in that: The total depth of the covering layer is greater than or equal to 30 meters.

6. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 1 is characterized in that: A crushed stone and medium-coarse sand cushion layer is provided on the top of the reinforcement pile, and several layers of geogrids are provided in the cushion layer.

7. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 6 is characterized in that: The geogrid is a bidirectional warp-knitted polyester geogrid.

8. The composite foundation settlement calculation method considering grouting at the karst rock-soil interface according to claim 1 is characterized in that: The grouting thickness of the soil layer above the bedrock surface should not be less than 3.0 meters, and the depth into the bedrock should not be less than 5.0 meters.

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