A method for calculating the embedded depth of soil-rock combined foundation pit support piles

Abstract

The present invention provides a method for calculating the rock-embedded depth of soil-rock combined foundation pit support piles. The calculation method includes: determining the profile parameters of the foundation pit enclosure and the soil and rock layers, and determining the relationship between the foundation pit depth h and the soil layer thickness H; performing a force analysis on the pile body above the bedrock surface, and using a cantilever pile calculation method to calculate the bending moment and shear force of the pile body on the bedrock surface; determining the reaction strength of the rock mass on the side of the pile per unit pile length in the rock-embedded section; and performing a force analysis on the pile body below the bedrock surface, and solving the rock-embedded depth of the support pile based on the equilibrium condition of force and moment. By considering the embedding effect of the bedrock, the present invention derives a calculation formula for the rock-embedded depth of soil-rock combined foundation pit support piles, which has great value for promotion and application.

Description

Technical Field

[0001] The invention relates to a method for calculating the rock embedding depth of soil-rock combined foundation pit support piles, belonging to the technical field of civil engineering. Background Art

[0002] As my country's underground space continues to develop and utilize at an ever-increasing rate, foundation pit projects are becoming increasingly deep, large, dangerous, and heavy. A large number of soil-rock combined foundation pits exist, with upper soil layers and lower moderately weathered, slightly weathered, or fresh bedrock. In these combined soil-rock foundation pits, the support structure plays a crucial role in ensuring the stability of the excavation. However, when determining the rock embedding depth of foundation pit support piles, the underlying rock layer is often treated as if it were soil, failing to fully consider the bedrock's embedding effect. This results in excessively deep rock embedding depths for the support piles, leading to unnecessary waste of resources.

[0003] Therefore, it is a very realistic technical problem to conduct reasonable analysis and calculation on the embedded depth of support piles in soil-rock combined foundation pits and find a calculation method for the embedded depth of support piles that meets both safety and economy. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for calculating the rock embedding depth of soil-rock combined foundation pit support piles. By considering the embedding effect of bedrock to analyze the stress of the support piles, the rock embedding depth of the support piles can be reasonably determined, the support cost can be reduced, and resource waste can be avoided.

[0005] In order to achieve the above technical objectives, the present invention provides a method for calculating the rock embedding depth of soil-rock combined foundation pit support piles, characterized in that the method specifically comprises the following steps:

[0006] Step 1: Determine the soil-rock combined foundation pit support profile and the profile parameters of the soil and rock layers, including the foundation pit depth h, the thickness of the soil layer H, the bulk density γ of the soil, the cohesion c of the soil, and the internal friction angle of the soil Active earth pressure coefficient Passive earth pressure coefficient The bulk density γ′ of the rock mass, the uniaxial compressive strength σ of the rock mass c , uniaxial tensile strength of rock mass σ t , elastic modulus E of rock mass r , Poisson's ratio V of the rock mass r , pile diameter D of the support pile, elastic modulus E of the pile body e When the depth h of the soil-rock combined foundation pit is less than or equal to the soil layer thickness H, the embedded depth of the support piles of the soil-rock combined foundation pit is calculated according to the following calculation process. The following calculation formulas all use the above parameters for calculation;

[0007] Step 2: Perform stress analysis on the pile body above the bedrock surface. Use the cantilever pile calculation method to solve the bending moment M and shear force V of the pile body on the bedrock surface:

[0008]

[0009]

[0010] Step 3: Determine the reaction strength of the rock mass on the side of the pile in the rock-socketed section to the unit pile length. According to the Hoek-Brown rock strength criterion, the reaction strength q of the rock mass on the side of the pile to the unit pile length below the critical depth is:

[0011]

[0012] The critical depth l in formula ③ is calculated by the following formula:

[0013]

[0014] Substituting equation ④ into equation ③, we can get:

[0015]

[0016] Step 4: Perform stress analysis on the pile below the bedrock surface and calculate the rock embedment depth z of the support pile based on the equilibrium condition of force and moment:

[0017]

[0018] Substitute the bending moment M and shear force V of the pile on the bedrock surface calculated in step 2 and the reaction strength q of the rock mass below the critical depth per unit pile length calculated in step 3 into formula ⑥ to calculate the rock embedment depth z of the support pile; where, when V>0, ± is +; when V<0, ± is -.

[0019] A further technical solution of the present invention: in the step one, the foundation pit support piles of the soil-rock combined foundation pit are vertical, the rock layer is a homogeneous and continuous single-layer rock mass, including moderately weathered bedrock, slightly weathered bedrock or fresh bedrock, the soil surface is horizontal, there is no overlying load on the soil surface, and the effect of groundwater is not considered.

[0020] A further technical solution of the present invention is as follows: the calculation process of the bending moment M and shear force V of the pile body on the bedrock surface in step 2 is as follows. Using the cantilever pile calculation method, the bending moment M of the pile body on the bedrock surface can be obtained as:

[0021] M=E a ·h a -E p ·h p ⑦

[0022] The shear force V of the pile on the bedrock surface is:

[0023] V=Ep -E a ⑧

[0024] In the above formulas ⑦ and ⑧, the active earth pressure on the pile side E a for:

[0025]

[0026] E a The distance h between the action point on the pile and the bedrock surface a for:

[0027]

[0028] Passive earth pressure on the pile side E p for:

[0029]

[0030] E p The distance h between the action point on the pile and the bedrock surface p for:

[0031]

[0032] The formula Substitute into ⑦ to get formula ① in step 2;

[0033] Formula ⑨ and Substitute into ⑧ to obtain formula ② in step 2.

[0034] A further technical solution of the present invention is as follows: in the step 2, within the critical depth range, the reaction strength of the pile side rock mass to the unit pile length increases with increasing depth; when the critical depth is exceeded, the reaction strength of the pile side rock mass to the unit pile length remains unchanged.

[0035] A further technical solution of the present invention is as follows: In step 4, a force analysis is performed on the pile body below the bedrock surface, and the following equations are obtained from the equilibrium conditions of force and moment:

[0036]

[0037] The expression of the rock embedment depth z of the support pile is solved through the above equations.

[0038] The present invention fully considers the embedding effect of bedrock based on actual conditions, conducts stress analysis on the upper and lower parts of the pile body on the bedrock surface respectively, establishes equations, and reasonably derives a calculation formula for the embedded rock depth of soil-rock combined foundation pit support piles. The method is economical, reasonable and practical, and has great promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1This is a flow chart for calculating the rock embedment depth of soil-rock combined foundation pit support piles of the present invention;

[0040] Figure 2 Schematic diagram of the soil-rock combined foundation pit in the present invention;

[0041] Figure 3 It is a schematic diagram of the force analysis of the pile body below the bedrock surface in the present invention.

[0042] In the figure: 1—foundation pit support piles, 2—ground, 3—bottom of the foundation pit. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments. Figures 1 to 3 The accompanying drawings are simplified examples and are only used to clearly and concisely illustrate the embodiments of the present invention. The technical solutions shown in the accompanying drawings are specific solutions of the embodiments of the present invention and are not intended to limit the scope of the invention claimed for protection. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0044] The present invention provides a method for calculating the rock embedding depth of soil-rock combined foundation pit support piles, which is characterized by comprising the following steps:

[0045] Step 1: Determine the profile parameters of the foundation pit and the soil and rock layers, including the foundation pit depth h, the thickness of the soil layer H, the bulk density γ of the soil, the cohesion c of the soil, and the internal friction angle of the soil. Active earth pressure coefficient Passive earth pressure coefficient The bulk density γ′ of the rock mass, the uniaxial compressive strength σ of the rock mass c , uniaxial tensile strength of rock mass σ t , elastic modulus E of rock mass r , Poisson's ratio V of the rock mass r , pile diameter D of the support pile, elastic modulus E of the pile body e The following calculations are performed using the above parameters. Determine whether the depth h of the soil-rock combined foundation pit is less than or equal to the soil thickness H, the pit support piles are vertical, and the rock layer is a homogeneous, continuous single layer, including moderately weathered bedrock, slightly weathered bedrock, or fresh bedrock. If these requirements are not met, the condition is not applicable. If these requirements are met, perform the following calculations.

[0046] Step 2: Perform a stress analysis on the pile body above the bedrock surface. Use the cantilever pile calculation method to solve the bending moment and shear force of the pile body on the bedrock surface. The specific calculation process is as follows:

[0047] First, if Figure 2 Calculate the active earth pressure E on the pile sidea for:

[0048]

[0049] E a The distance h between the action point on the pile and the bedrock surface a for:

[0050]

[0051] Calculate the passive earth pressure E on the pile side p for:

[0052]

[0053] E p The distance h between the action point on the pile and the bedrock surface p for:

[0054]

[0055] Using the cantilever pile calculation method, the bending moment M of the pile on the bedrock surface can be obtained as:

[0056] M=E a ·h a -E p ·h p (Formula 5)

[0057] Substituting (Equation 1) to (Equation 4) into (Equation 5) yields:

[0058]

[0059] Using the cantilever pile calculation method, the shear force V of the pile on the bedrock surface can be obtained as:

[0060] V=E p -E a (Equation 7)

[0061] Substituting (Equation 1) and (Equation 3) into (Equation 7) yields:

[0062]

[0063] Step 3: Determine the reaction strength of the rock mass on the side of the pile to the unit pile length in the rock-embedded section. Within the critical depth range, the reaction strength of the rock mass on the side of the pile to the unit pile length increases with increasing depth. Beyond the critical depth, the reaction strength of the rock mass on the side of the pile to the unit pile length remains unchanged.

[0064] According to the design theory and method of rock-socketed anti-slide piles, the critical depth l is determined as:

[0065]

[0066] Among them, the equivalent shear modulus of rock mass G * The calculation formula is:

[0067] Substituting (Equation 10) into (Equation 9) yields the formula for calculating the critical depth l:

[0068]

[0069] According to the Hoek-Brown rock strength criterion, the reaction strength q of the rock mass on the pile side below the critical depth to the unit pile length is:

[0070]

[0071] Substituting (Equation 11) into (Equation 12) yields:

[0072]

[0073] Step 4: Perform stress analysis on the pile below the bedrock surface and calculate the rock embedment depth of the support pile based on the equilibrium condition of force and moment:

[0074]

[0075] According to the equation group, the expression of the rock embedded depth z of the support pile is solved:

[0076]

[0077] Wherein, when V>0, ± is taken as +; when V<0, ± is taken as -; substitute the bending moment (Equation 6) and shear force (Equation 8) of the pile on the bedrock surface, and the reaction strength of the rock mass on the pile side per unit pile length below the critical depth (Equation 13) into (Equation 14) to calculate the value, which is the appropriate rock embedment depth z of the support pile.

[0078] The present invention is further described below with reference to a specific embodiment: In a soil-rock combined foundation pit project in a certain province or city, the foundation pit depth h = 6m, the thickness of the clay soil H = 9m, and the soil bulk density γ = 19kN / m 3 , soil cohesion c=20kN / m 2 , soil internal friction angle Active earth pressure coefficient Passive earth pressure coefficient The bulk density of the rock mass is γ′ = 23 kN / m 3 , uniaxial compressive strength of rock mass σ c =30MPa, uniaxial tensile strength of rock mass σ t =1.2MPa, elastic modulus E of rock mass r =90MPa, Poisson's ratio V of rock mass r=0.25; the supporting piles are bored piles with a diameter of 0.8m, and the elastic modulus of the pile body is E e =31.5GPa.

[0079] Considering the foundation pit section per unit length; the foundation pit depth h = 6m in the embodiment is less than the clay thickness H = 9m, the rock embedment depth of the support piles in the embodiment can be calculated according to the above calculation method. Substituting the above values into the above (Equation 6) to calculate the bending moment M of the pile body on the bedrock surface:

[0080]

[0081] Substituting the above values into the above (Equation 8), the shear force V of the pile on the bedrock surface is calculated as:

[0082]

[0083] According to the Hoek-Brown rock mass strength criterion, the reaction strength q of the rock mass on the pile side per unit pile length below the critical depth is calculated according to (Equation 13):

[0084]

[0085] Then the stress analysis of the pile below the bedrock surface is carried out, such as Figure 3 As shown in the figure, the rock embedment depth of the support pile is solved by the equilibrium condition of force and moment:

[0086]

[0087] According to the equation group, the expression of the rock embedded depth z of the support pile is solved:

[0088]

[0089] When V > 0, ± is taken as +; when V < 0, ± is taken as -. Substituting the calculated bending moment M (191.06 kN·m) and shear force V (23.30 kN) of the pile on the bedrock surface, and the reaction strength q (720.26 kN / m) of the rock mass below the critical depth relative to the unit pile length, into (Equation 14), the support pile rock embedment depth z is calculated to be 1.7 m.

[0090] In this embodiment, the inventors of this application used a method that treated the underlying rock layer as a soil layer for calculation, resulting in a rock-embedded depth of 2.4m for the supporting piles in their calculation group. Compared to the calculation method that treats the underlying rock layer as a soil layer, the soil-rock combined foundation pit supporting pile rock-embedded depth calculation method provided in this embodiment can more accurately calculate the rock-embedded depth of the supporting piles, is economical and practical, and has great potential for widespread application.

[0091] The above is merely one embodiment of the present invention, and its description is relatively specific and detailed. However, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present invention, and such modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for calculating the rock embedding depth of soil-rock combined foundation pit support piles, characterized in that: The specific steps of the method are as follows: Step 1: Determine the soil-rock combined foundation pit support profile and the profile parameters of the soil and rock layers, including the foundation pit depth h, the thickness of the soil layer H, the bulk density γ of the soil, the cohesion c of the soil, and the internal friction angle of the soil Active earth pressure coefficient Passive earth pressure coefficient The bulk density γ′ of the rock mass, the uniaxial compressive strength σ of the rock mass c , uniaxial tensile strength of rock mass σ t , elastic modulus E of rock mass r , Poisson's ratio V of the rock mass r , pile diameter D of the support pile, elastic modulus E of the pile body e When the depth h of the soil-rock combined foundation pit is less than or equal to the soil layer thickness H, the embedded depth of the support piles of the soil-rock combined foundation pit is calculated according to the following calculation process. The following calculation formulas all use the above parameters for calculation; Step 2: Perform stress analysis on the pile body above the bedrock surface. Use the cantilever pile calculation method to solve the bending moment M and shear force V of the pile body on the bedrock surface: Step 3: Determine the reaction strength of the rock mass on the side of the pile in the rock-socketed section to the unit pile length. According to the Hoek-Brown rock strength criterion, the reaction strength q of the rock mass on the side of the pile to the unit pile length below the critical depth is: The critical depth l in formula ③ is calculated by the following formula: Substituting equation ④ into equation ③, we can get: Step 4: Perform stress analysis on the pile below the bedrock surface and calculate the rock embedment depth z of the support pile based on the equilibrium condition of force and moment: Substitute the bending moment M and shear force V of the pile on the bedrock surface calculated in step 2 and the reaction strength q of the rock mass below the critical depth per unit pile length calculated in step 3 into formula ⑥ to calculate the rock embedment depth z of the support pile; where, when V>0, ± is +; when V<0, ± is -.

2. The method for calculating the rock embedment depth of soil-rock combined foundation pit support piles according to claim 1, characterized in that: In the step 1, the foundation pit support piles of the soil-rock combined foundation pit are vertical, the rock layer is a homogeneous and continuous single-layer rock mass, including moderately weathered bedrock, slightly weathered bedrock or fresh bedrock, the soil surface is horizontal, there is no overlying load on the soil surface, and the effect of groundwater is not considered.

3. The method for calculating the rock embedding depth of soil-rock combined foundation pit support piles according to claim 1 is characterized in that The calculation process of the bending moment M and shear force V of the pile body on the bedrock surface in step 2 is as follows: the bending moment M of the pile body on the bedrock surface is calculated according to formula 7 using the cantilever pile calculation method: M=E a ·h a -E p ·h p ⑦ The shear force V of the pile on the bedrock surface is calculated according to formula ⑧: V=E p -E a ⑧ In the above formulas ⑦ and ⑧, the active earth pressure on the pile side E a for: E a The distance h between the action point on the pile and the bedrock surface a for: Passive earth pressure on the pile side E p for: E p The distance h between the action point on the pile and the bedrock surface p for: Formula 9~ Substitute into ⑦ to get formula ① in step 2; Formula ⑨ and Substitute into ⑧ to obtain formula ② in step 2.

4. The method for calculating the rock embedment depth of soil-rock combined foundation pit support piles according to claim 1, characterized in that: In the step 2, within the critical depth range, the reaction strength of the pile side rock mass to the unit pile length increases with increasing depth; when exceeding the critical depth, the reaction strength of the pile side rock mass to the unit pile length remains unchanged.

5. The method for calculating the rock embedment depth of soil-rock combined foundation pit support piles according to claim 1, characterized in that: In step 4, the pile body below the bedrock surface is subjected to stress analysis, and the following equations are obtained from the equilibrium conditions of force and moment: The expression of the rock embedment depth z of the support pile is solved through the above equations.

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