A design method for rigid pile composite foundation structure in a region with deep melting interlayer

Abstract

The application discloses a kind of deep melting interlayer development area rigid pile composite foundation structure design method, it is related to rigid pile composite foundation field, including the following steps: step one, in the existing rigid pile bearing capacity calculation process, front-end increase subgrade-ground temperature field analysis;Step two, increase groundwater analysis;Step three, determine the compression modulus of the soil layer of seasonal freeze-thaw layer, (water-rich) melting interlayer, permafrost layer, bearing capacity characteristic value, check the single pile bearing capacity characteristic value of different positions in the cross section of roadbed using different pile length, pile diameter, pile body stiffness material;Step four, carry out zoned unequal design, adjust pile length, pile diameter, pile body stiffness, so that the range of all pile single pile bearing capacity characteristic values in cross section is lower than design allowable value.The application effectively optimizes pile foundation design, reduces material waste, reduces engineering cost, while ensuring the safety and stability of structure.

Description

Technical Field

[0001] This invention relates to the field of rigid pile composite foundation technology, specifically to a design method for rigid pile composite foundation structures in areas with deep melting interlayers. Background Technology

[0002] Permafrost is widely distributed in my country, ranking third in the world in area, with perennial and seasonally frozen soil covering two-thirds of the country's total land area. Perennial permafrost refers to a layer of soil and rock that remains frozen for many years. The soil and rock mass near the surface typically exhibits seasonal freezing and thawing, with significant temperature fluctuations; this is also known as the active layer. Below the active layer lies the perennially frozen soil and rock mass, known as the permafrost layer, where the temperature is stable and remains below 0°C. The foundations in the permafrost region of the Qinghai-Tibet Plateau exhibit a typical stratigraphic sequence of seasonal freeze-thaw layers, (water-rich) thawing interlayers, and permafrost layers. Currently, there is no specific design method for composite foundation structures addressing this stratigraphic combination. Therefore, we propose a design method for rigid pile composite foundation structures in areas with well-developed deep thawing interlayers to solve the above problems. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a design method for rigid pile composite foundation structures in areas with deep melting interlayers. This method solves the problem that there is currently no design method specifically for composite foundation structures with this type of stratum combination.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] A design method for rigid pile composite foundation structures in areas with deep molten interlayers includes the following steps:

[0006] Step 1: Add a roadbed-foundation temperature field analysis to the existing rigid pile bearing capacity calculation process. Measure or predict the freezing and thawing depth of the roadbed and shallow foundation, the morphology of the cross-sectional freezing and thawing area, the degradation rate and warming rate of the underlying permafrost, and determine the soil compression modulus, bearing capacity characteristic value, and pile tip soil resistance characteristic value of each area based on soil type, temperature value, and the range and morphology of the cross-sectional freezing and thawing area.

[0007] Step 2: Add groundwater analysis, measure or predict the thickness, water content and seasonal fluctuation of the water-rich layer of the melting interlayer, and determine the compression modulus and bearing capacity characteristic value of the melting interlayer based on the characteristics of groundwater changes.

[0008] Step 3: Based on the soil layer compression modulus and bearing capacity characteristic values ​​determined in Steps 1 and 2, verify the single pile bearing capacity characteristic values ​​at different locations on the roadbed cross-section when using materials with different pile lengths, diameters, and stiffnesses. Calculate using the following formula:

[0009] ;

[0010] In the formula: It is the characteristic value of the bearing capacity of a single pile, in kN; This is the characteristic value of pile end resistance, in kPa. It is the characteristic value of the soil lateral resistance around the j-th pile, in kPa; It refers to the length of each pile segment divided according to soil layers, in meters; It is the cross-sectional area at the bottom of the pile, in meters. 2 ; It is the perimeter length of the pile, in meters; It is the number of frozen and thawed soil layers;

[0011] Step four: In the cross section of the roadbed, due to the spatial non-uniformity of the physical and mechanical parameters of the foundation soil, when the range of characteristic values ​​of the single pile bearing capacity calculated using the same pile length, pile diameter, and pile stiffness at different locations exceeds the design allowable value, a zoned unequal strength design should be carried out to adjust the pile length, pile diameter, and pile stiffness so that the range of characteristic values ​​of the single pile bearing capacity of all piles in the cross section is lower than the design allowable value.

[0012] As a further explanation of the present invention, in step one, the calculation of the roadbed-foundation temperature field is obtained by the calculation formula of the upper surface water-thermal boundary; the calculation formula of the upper surface water-thermal boundary is divided into the calculation formula of the upper surface moisture boundary and the calculation formula of the upper surface temperature boundary, and the water-thermal coupling migration model is obtained according to the calculation formulas of the upper surface moisture boundary and the upper surface temperature boundary.

[0013] Furthermore, the formula for calculating the upper surface water boundary includes:

[0014]

[0015]

[0016] In the formula, M is the amount of material melted. It is the melting coefficient. It's the air temperature. It represents the melting temperature, while PE represents the potential evaporation rate. It's radiation levels. It is evaporation potential. All of these are coefficients that affect potential evaporation.

[0017] Furthermore, the formula for calculating the upper surface temperature boundary includes:

[0018]

[0019] In the formula, T is the surface temperature. Ambient temperature, Temperature increment inside the boundary layer The heat transfer coefficient is the coefficient of heat flux passing through. It is solar radiation from the Earth's surface. It is total solar radiation. It's reflectivity. It is the effective utilization rate of solar radiation.

[0020] Furthermore, the calculation formula for the hydrothermal coupled migration model is as follows:

[0021]

[0022] In the formula, It is the surface temperature. It is time. It is thermal conductivity. It is the equivalent volumetric heat capacity. It is a heat source item. It is the soil moisture content. It is the moisture diffusion coefficient. It is a water source item. It is the equivalent volumetric heat capacity of soil with water content. It is a heat source term related to temperature and water content. It is the temperature-dependent moisture diffusivity. This is a temperature-related moisture source item. Furthermore, The term representing non-uniform heat conduction in space is expanded in three-dimensional coordinates as follows: This is used to characterize the spatial diffusion of heat in a non-uniform roadbed medium; It is the spatial gradient of soil moisture content, expressed as ( ), Let the divergence of water migration flux be expressed as ;in, These are the horizontal and vertical coordinates of the cross-section of the composite structure, respectively. For the vertically extended coordinates.

[0023] The derivation of the calculation formula for the hydrothermal coupled migration model is explained below:

[0024] 1. Background and Basic Assumptions of the Derivation

[0025] Based on the laws of conservation of heat and water, the hydrothermal coupling model equations used in this invention are derived step by step from fundamental physical processes. To ensure that the model can accurately describe the nonlinear characteristics of regions with deep melting interlayers, the following basic assumptions are made:

[0026] (1) The material in the model is regarded as a continuous porous medium, and the temperature is defined. and moisture content For macroscopic field variables;

[0027] (2) The heat changes in the material come from heat conduction, internal heat sources and latent heat exchange during the phase change of water;

[0028] (3) Thermal parameters of the medium (thermal conductivity) Specific heat capacity Subject to soil moisture content The significant influence of this exhibits spatial non-uniformity;

[0029] (4) Moisture migration follows a Fick-like diffusion law, and the diffusion coefficient is... Affected by temperature Regulation.

[0030] 2. Derivation of the temperature control equation (energy conservation)

[0031] According to the law of conservation of heat, the rate of increase of heat within a roadbed unit is equal to the sum of the divergence of the heat flux flowing in through conduction and the internal source term:

[0032] ,

[0033] in, The equivalent volumetric heat capacity affected by water content is denoted as . ; It is the net inflow of heat flux; For external heat source items; This is the latent heat of phase change in water.

[0034] Considering the spatial heterogeneity of soil moisture content in areas with deep thawed interlayers, thermal conductivity With water content It exhibits a non-uniform distribution in space, according to Fourier's law of heat conduction:

[0035] ,

[0036] Substituting this into the energy balance equation, we obtain the temperature control equation in the form of preserving the divergence operator:

[0037] ,

[0038] In the formula: The term representing non-uniform heat conduction in space is expanded in three-dimensional coordinates as follows: This is used to characterize the spatial diffusion of heat in a non-uniform roadbed medium; This represents a combined heat source term related to temperature and water content, including latent heat sources generated during the ice-water phase change. Represents the horizontal, vertical, and longitudinal coordinates of the roadbed and foundation in spatial dimensions.

[0039] 3. Derivation of the water control equation

[0040] The conservation of water can be expressed as the rate of change of water content over time equal to the sum of the divergence of water flux and the source term:

[0041] ,

[0042] Among them, water flux It follows a Fick-like diffusion pattern, and the diffusion coefficient... With temperature Closely related, that is:

[0043] ,

[0044] Substituting the flux expression into the conservation equation yields the typical variable coefficient diffusion operator form, ultimately leading to the water control equation:

[0045] ,

[0046] In the formula: It is the spatial gradient of water content, expressed as ( ), Let the divergence of water migration flux be expressed as ;in, These are the horizontal and vertical coordinates of the roadbed-subgrade cross section, respectively. For the vertically extended coordinates.

[0047] This equation describes the physical process of "first calculating the water content gradient, then multiplying it by the temperature-dependent diffusion coefficient, and then calculating the flux divergence".

[0048] 4. The physical origin of coupling relationships

[0049] This model is classified as a hydrothermal coupling model because of temperature. With water content A two-way feedback relationship is formed between them.

[0050] Temperature affects moisture migration primarily through the moisture diffusivity. The higher the temperature, the faster the diffusion; the evaporation rate increases with temperature, thus increasing water loss. Temperature controlled.

[0051] The effects of moisture on temperature changes are mainly reflected in: moisture content affecting thermal conductivity. Moisture content affects specific heat capacity The latent heat term is caused by the phase change of water. All of the above factors have been incorporated into and Therefore, the coefficients and source terms of the temperature equation are both... The function.

[0052] The two have a naturally strong coupling relationship.

[0053] As a further explanation of the present invention, in step three, the formula for calculating the pile length is:

[0054]

[0055] In the formula, It is the depth of melting or freezing. It is the special thickness of the aquifer. It is an additional safety length;

[0056] The formula for calculating the pile diameter is:

[0057]

[0058] In the formula, This is the design load, and K is the safety factor. It is the allowable bearing capacity of the soil layer;

[0059] The formula for calculating the pile spacing is:

[0060]

[0061] In the formula, d is the pile diameter;

[0062] The formula for calculating the bending stiffness of the pile is:

[0063]

[0064] In the formula, E is the elastic modulus of the pile;

[0065] The formula for calculating the pile cap size is:

[0066]

[0067] In the formula, It is the total load borne by the pile cap. h is the allowable bearing capacity of the soil layer at the bottom of the pile cap, and h is the pile cap embedment depth. It is the weight of soil per unit volume.

[0068] Furthermore, the calculation formula for the design load is as follows:

[0069]

[0070] In the formula, For the bearing capacity at the end of the pile, This refers to the frictional force on the pile side. It is the end area. It is the lateral surface area. It is lateral friction. It is the effective stress. is the total stress, and u is the pore water pressure.

[0071] Compared with existing technologies, this design method for rigid pile composite foundation structures in areas with deep molten interlayers has the following advantages:

[0072] 1. This invention, through preliminary temperature field analysis, can more accurately predict the freezing and thawing states of soil layers, thereby better understanding the physical and mechanical properties of the soil. Based on the physical and mechanical parameters of different soil layers, different pile lengths, diameters, and spacings can be designed to effectively optimize pile foundation design, reduce material waste, lower engineering costs, and ensure the safety and stability of the structure. Furthermore, by analyzing the seasonal fluctuations of groundwater and the characteristics of thawing interlayers, foundation structures adapted to different seasons and climatic conditions can be designed, enhancing the adaptability and durability of the project.

[0073] 2. By optimizing pile foundation design and material selection, this invention can improve the seismic resistance of the foundation, ensure structural safety under extreme conditions such as earthquakes, and, based on detailed temperature and hydrological analysis, formulate more accurate construction plans, reduce uncertainties in the construction process, and thus improve construction efficiency. At the same time, by analyzing the characteristics of different soil layers, soil resources can be utilized more rationally, unnecessary earthwork can be avoided, and environmental impact can be reduced.

[0074] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Detailed Implementation

[0075] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0076] Example 1: A design method for rigid pile composite foundation structures in areas with deep molten interlayers, comprising the following steps:

[0077] Step 1: Add a roadbed-foundation temperature field analysis to the existing rigid pile bearing capacity calculation process. Measure or predict the freezing and thawing depth of the roadbed and shallow foundation, the morphology of the cross-sectional freezing and thawing area, the degradation rate and warming rate of the underlying permafrost, and determine the soil compression modulus, bearing capacity characteristic value, and pile tip soil resistance characteristic value of each area based on soil type, temperature value, and the range and morphology of the cross-sectional freezing and thawing area.

[0078] Step 2: Add groundwater analysis, measure or predict the thickness, water content and seasonal fluctuation of the water-rich layer of the melting interlayer, and determine the compression modulus and bearing capacity characteristic value of the melting interlayer based on the characteristics of groundwater changes.

[0079] Step 3: Based on the soil layer compression modulus and bearing capacity characteristic values ​​determined in Steps 1 and 2, verify the single pile bearing capacity characteristic values ​​at different locations on the roadbed cross-section when using materials with different pile lengths, diameters, and stiffnesses. Calculate using the following formula:

[0080] ;

[0081] In the formula: It is the characteristic value of the bearing capacity of a single pile, in kN; This is the characteristic value of pile end resistance, in kPa. It is the characteristic value of the soil lateral resistance around the j-th pile, in kPa; It refers to the length of each pile segment divided according to soil layers, in meters; It is the cross-sectional area at the bottom of the pile, in meters. 2 ; It is the perimeter length of the pile, in meters; It is the number of frozen and thawed soil layers;

[0082] Step four: In the cross section of the roadbed, due to the spatial non-uniformity of the physical and mechanical parameters of the foundation soil, when the range of characteristic values ​​of the single pile bearing capacity calculated using the same pile length, pile diameter, and pile stiffness at different locations exceeds the design allowable value, a zoned unequal strength design should be carried out to adjust the pile length, pile diameter, and pile stiffness so that the range of characteristic values ​​of the single pile bearing capacity of all piles in the cross section is lower than the design allowable value.

[0083] Example 2: A design method for a rigid pile composite foundation structure in an area with a deep melting interlayer, comprising the following steps:

[0084] Step 1: Add a roadbed-foundation temperature field analysis to the existing rigid pile bearing capacity calculation process. Measure or predict the freezing and thawing depth of the roadbed and shallow foundation, the morphology of the cross-sectional freezing and thawing area, the degradation rate and warming rate of the underlying permafrost, and determine the soil compression modulus, bearing capacity characteristic value, and pile tip soil resistance characteristic value of each area based on soil type, temperature value, and the range and morphology of the cross-sectional freezing and thawing area.

[0085] The calculation of the roadbed-foundation temperature field is obtained by the calculation formula of the upper surface water and heat boundary; the calculation formula of the upper surface water and heat boundary is divided into the calculation formula of the upper surface moisture boundary and the calculation formula of the upper surface temperature boundary, and the water and heat coupling migration model is obtained based on the calculation formulas of the upper surface moisture boundary and the upper surface temperature boundary.

[0086] Step 2: Add groundwater analysis, measure or predict the thickness, water content and seasonal fluctuation of the water-rich layer of the melting interlayer, and determine the soil physical and mechanical parameters and bearing capacity characteristic values ​​of the melting interlayer based on the characteristics of groundwater changes.

[0087] Step 3: Based on the compression modulus, bearing capacity characteristic values, etc., determined in Steps 1 and 2, verify the single pile bearing capacity characteristic values ​​at different locations on the roadbed cross-section when using materials with different pile lengths, diameters, and stiffnesses, calculated using the following formula:

[0088] ;

[0089] In the formula: It is the characteristic value of the bearing capacity of a single pile, in kN; This is the characteristic value of pile end resistance, in kPa. It is the characteristic value of the soil lateral resistance around the j-th pile, in kPa; It refers to the length of each pile segment divided according to soil layers, in meters; It is the cross-sectional area at the bottom of the pile, in meters. 2 ; It is the perimeter length of the pile, in meters; It is the number of frozen and thawed soil layers;

[0090] Step four: In the cross section of the roadbed, due to the spatial non-uniformity of the physical and mechanical parameters of the foundation soil, when the range of characteristic values ​​of the single pile bearing capacity calculated using the same pile length, pile diameter, and pile stiffness at different locations exceeds the design allowable value, a zoned unequal strength design should be carried out to adjust the pile length, pile diameter, and pile stiffness so that the range of characteristic values ​​of the single pile bearing capacity of all piles in the cross section is lower than the design allowable value.

[0091] As a further explanation of Embodiment 2 of the present invention, the formula for calculating the upper surface water boundary in step one includes:

[0092]

[0093]

[0094] In the formula, M is the amount of material melted. It is the melting coefficient. It's the air temperature. It represents the melting temperature, while PE represents the potential evaporation rate. It's radiation levels. It is evaporation potential. All of these are coefficients that affect potential evaporation.

[0095] As a further explanation of Embodiment 2 of the present invention, the formula for calculating the upper surface temperature boundary in step one includes:

[0096]

[0097] In the formula, T is the surface temperature. Ambient temperature, Temperature increment inside the boundary layer The heat transfer coefficient is the coefficient of heat flux passing through. It is solar radiation from the Earth's surface. It is total solar radiation. It's reflectivity. It is the effective utilization rate of solar radiation.

[0098] As a further explanation of Embodiment 2 of the present invention, the calculation formula of the hydrothermal coupling migration model in step one is as follows:

[0099]

[0100] In the formula, It is the surface temperature. It is time. It is thermal conductivity. It is the equivalent volumetric heat capacity. It is a heat source item. It is the soil moisture content. It is the moisture diffusion coefficient. It is a water source item. It is the equivalent volumetric heat capacity of soil with water content. It is a heat source term related to temperature and water content. It is the temperature-dependent moisture diffusivity. This is a temperature-related moisture source item. Furthermore, The term representing non-uniform heat conduction in space is expanded in three-dimensional coordinates as follows: This is used to characterize the spatial diffusion of heat in a non-uniform roadbed medium; It is the spatial gradient of soil moisture content, expressed as ( ), Let the divergence of water migration flux be expressed as ;in, These are the horizontal and vertical coordinates of the cross-section of the composite structure, respectively. For the vertically extended coordinates.

[0101] As a further explanation of Embodiment 2 of the present invention, the formula for calculating the pile length in step three is as follows:

[0102]

[0103] In the formula, It is the depth of melting or freezing. It is the special thickness of the aquifer. It is an additional safety length;

[0104] The formula for calculating the pile diameter is:

[0105]

[0106] In the formula, This is the design load, and K is the safety factor. It is the allowable bearing capacity of the soil layer;

[0107] The formula for calculating the pile spacing is:

[0108]

[0109] In the formula, d is the pile diameter;

[0110] The formula for calculating the bending stiffness of the pile is:

[0111]

[0112] In the formula, E is the elastic modulus of the pile;

[0113] The formula for calculating the pile cap size is:

[0114]

[0115] In the formula, It is the total load borne by the pile cap. h is the allowable bearing capacity of the soil layer at the bottom of the pile cap, and h is the pile cap embedment depth. It is the weight of soil per unit volume.

[0116] Furthermore, the calculation formula for the design load is as follows:

[0117]

[0118] In the formula, For the bearing capacity at the end of the pile, This refers to the frictional force on the pile side. It is the end area. It is the lateral surface area. It is lateral friction. It is the effective stress. is the total stress, and u is the pore water pressure.

[0119] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A design method for rigid pile composite foundation structures in areas with deep molten interlayers, characterized in that, Includes the following steps: Step 1: Add a roadbed-foundation temperature field analysis to the existing rigid pile bearing capacity calculation process. Measure or predict the freezing and thawing depth of the roadbed and shallow foundation, the morphology of the cross-sectional freezing and thawing area, the degradation rate and warming rate of the underlying permafrost, and determine the soil compression modulus, bearing capacity characteristic value, and pile tip soil resistance characteristic value of each area based on soil type, temperature value, and the range and morphology of the cross-sectional freezing and thawing area. Step 2: Add groundwater analysis, measure or predict the thickness, water content and seasonal fluctuation of the water-rich layer of the melting interlayer, and determine the compression modulus and bearing capacity characteristic value of the melting interlayer based on the characteristics of groundwater changes. Step 3: Based on the soil layer compression modulus and bearing capacity characteristic values ​​determined in Steps 1 and 2, verify the single pile bearing capacity characteristic values ​​at different locations on the roadbed cross-section when using materials with different pile lengths, diameters, and stiffnesses. Calculate using the following formula: ； In the formula: It is the characteristic value of the bearing capacity of a single pile, in kN; This is the characteristic value of the pile end resistance, in kPa. It is the characteristic value of the soil lateral resistance around the j-th pile, in kPa; It refers to the length of each pile segment divided according to soil layers, in meters; It is the cross-sectional area at the bottom of the pile, in meters. 2 ; It is the perimeter length of the pile, in meters; It is the number of frozen and thawed soil layers; Step four: In the cross section of the roadbed, due to the spatial non-uniformity of the physical and mechanical parameters of the foundation soil, when the range of characteristic values ​​of the single pile bearing capacity calculated using the same pile length, pile diameter, and pile stiffness at different locations exceeds the design allowable value, a zoned unequal strength design should be carried out to adjust the pile length, pile diameter, and pile stiffness so that the range of characteristic values ​​of the single pile bearing capacity of all piles in the cross section is lower than the design allowable value.

2. The design method for rigid pile composite foundation structures in areas with deep molten interlayers as described in claim 1, characterized in that: In step one, the calculation of the roadbed-foundation temperature field is obtained by the calculation formula of the upper surface water and heat boundary; the calculation formula of the upper surface water and heat boundary is divided into the calculation formula of the upper surface moisture boundary and the calculation formula of the upper surface temperature boundary, and the water and heat coupling migration model is obtained based on the calculation formulas of the upper surface moisture boundary and the upper surface temperature boundary.

3. The design method for rigid pile composite foundation structures in areas with deep melting interlayers as described in claim 2, characterized in that: The formula for calculating the upper surface water boundary includes: ； ； In the formula, M is the amount of material melted. It is the melting coefficient. It's the air temperature. It represents the melting temperature, while PE represents the potential evaporation rate. It's radiation levels. It is evaporation potential. All of these are coefficients that affect potential evaporation.

4. The design method for rigid pile composite foundation structures in areas with deep melting interlayers as described in claim 2, characterized in that: The formula for calculating the upper surface temperature boundary includes: ； In the formula, T is the surface temperature. Ambient temperature, Temperature increment inside the boundary layer The heat transfer coefficient is the coefficient of heat flux passing through. It is solar radiation from the Earth's surface. It is total solar radiation. It's reflectivity. It is the effective utilization rate of solar radiation.

5. The design method for rigid pile composite foundation structures in areas with deep molten interlayers according to claim 2, characterized in that: The calculation formula for the hydrothermal coupled migration model is as follows: ； In the formula, It is the surface temperature. It is time. It is thermal conductivity. It is the equivalent volumetric heat capacity. It is a heat source item. It is the soil moisture content. It is the moisture diffusion coefficient. It is a water source item. It is the equivalent volumetric heat capacity of soil with water content. It is a heat source term related to temperature and water content. It is the temperature-dependent moisture diffusivity. It is a temperature-related moisture source item; in addition, The term representing non-uniform heat conduction in space is expanded in three-dimensional coordinates as follows: This is used to characterize the spatial diffusion of heat in a non-uniform roadbed medium; It is the spatial gradient of soil moisture content, expressed as ( ), Let the divergence of water migration flux be expressed as ;in, These are the horizontal and vertical coordinates of the cross-section of the composite structure, respectively. For the vertically extended coordinates.

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