A bridge foundation structure and design method for a steep slope section

Abstract

The present invention relates to the technical field of bridge engineering, and particularly relates to a bridge foundation structure and a design method for a steep slope section. The bridge foundation structure for the steep slope section includes an open excavation foundation and a pile foundation. The pile foundation includes a pile cap and a pile body. The pile foundation is arranged on the side close to the steep slope, and the open excavation foundation is arranged on the side far from the steep slope. The open excavation foundation and the pile cap are cast integrally. The design method includes calculating the longitudinal average stiffness #imgabs0# and the transverse average stiffness #imgabs1# within the full width of the cross-section, calculating the longitudinal stiffness ratio γ xi and the transverse stiffness ratio γ yi , calculating the cross-section stress σ maxi and σ mini after considering the foundation stiffness, and determining the base size and number of layers of the open excavation foundation according to σ maxi <[σ]. Calculating the pile top load N z within the pile foundation range, and determining the length of the pile foundation according to the pile top load N z . The present invention realizes the effective combination of the open excavation foundation and the pile foundation, gives play to the advantages of various foundations, and has the characteristics of saving project investment, occupying less land, having strong terrain adaptability, and causing little environmental damage.

Description

Technical Field

[0001] The invention relates to the technical field of bridge engineering, in particular to a steep slope section bridge foundation structure and a design method. Background Art

[0002] The topographic and geological conditions of steep slopes in mountainous areas (the steep slope mentioned in the present invention refers to a slope greater than or equal to 45 degrees) are complex. When a bridge pier foundation is set on a steep slope with a thin surface cover layer and good geological conditions of the foundation bearing layer, it is more economical to use a conventional open-cut foundation. However, in order to meet the requirement that the foundation is set on a stratum with a good bearing layer, the excavation depth is large, the construction risk is high, and the impact on the natural slope is large. If the base elevation is raised, the open-cut foundation edge will be closer to the stratum boundary line, and the base will be difficult to meet the designed force requirements, which is risky. Especially in steep slopes, the influence of the bank slope stability line must also be considered. The open-cut foundation must be outside the influence range of the bank slope stability. At this time, the open-cut foundation is difficult to adapt to the topographic and geological conditions; when a traditional pile foundation is used, the investment is high. In addition, on the slopes near the river, even if the geological conditions of the foundation bearing layer are good, the long-term scouring of the water flow will easily cause the bottom of the foundation to be scoured and hollowed out when using open excavation foundation, which will affect the force and safety of the structure. When using traditional retaining wall and other protection measures, additional protection investment is required, and there is a certain impact on the environment. Therefore, it is necessary to combine the terrain and geological conditions to study the economically reasonable form of bridge foundation. Summary of the invention

[0003] The purpose of the present invention is to provide a steep slope bridge foundation structure and design method in view of the problems existing in the prior art that when an open-cut foundation is used in a steep slope section, the force on the slope side foundation does not meet the requirements when the burial depth is insufficient; when the burial depth is sufficient, it will lead to a large amount of foundation excavation and a large impact on environmental damage; if a pile foundation is used, it will lead to high project investment.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for designing a steep slope bridge foundation structure, wherein the steep slope bridge foundation structure comprises an open cut foundation and a pile foundation, wherein the pile foundation comprises a pile cap and a pile body, wherein the pile foundation is arranged on a side close to the steep slope, and the open cut foundation is arranged on a side away from the steep slope, wherein the open cut foundation and the pile cap are cast together, and wherein designing the steep slope bridge foundation structure comprises the following steps:

[0006] Step 1: Calculate the average stiffness along the full width of the section and average stiffness in transverse direction C xi is the longitudinal stiffness of the ith foundation segment, C yi is the transverse stiffness of the i-th foundation segment, Lxi is the width of the i-th foundation segment along the bridge, L yi is the transverse width of the i-th foundation segment, L x L is the full width of the foundation along the bridge. y It is the full width of the foundation in the transverse direction of the bridge;

[0007] Step 2: Calculate the stiffness ratio γ along the bridge direction xi and transverse stiffness ratio γ yi , γ xi is the stiffness ratio of the i-th foundation segment along the bridge direction, γ yi is the transverse stiffness ratio of the i-th foundation segment;

[0008] Step 3: Calculate the cross-sectional stress σ after considering the combined stiffness maxi and σ mini , σ maxi is the maximum base stress of the ith foundation segment, σ mini is the minimum base stress of the ith foundation segment, N i is the vertical pressure acting on the center of gravity of the bottom surface of the i-th foundation segment, A i is the bottom area of ​​the ith basic segment, M xi is the bending moment along the bridge direction of the ith foundation segment, M yi is the transverse bending moment of the i-th foundation segment, I xi is the moment of inertia along the bridge of the ith foundation segment, I yi is the transverse moment of inertia of the ith foundation segment, x i is the distance from the ith basic segment to the y-axis, y i The distance of the i-th basic segment from the x-axis;

[0009] According to σ maxi <[σ], determine the base size and number of layers of the open-cut foundation, [σ] is the allowable bearing capacity of the foundation;

[0010] Step 4: Calculate the pile top load N within the pile foundation range z , A z =(d+2s 1 )L y , σ 1 , σ 2 Pile foundation range A z The base stress on both sides, d is the pile diameter, s is 1 is the distance between the edge of the pile body and the edge of the pile cap;

[0011] According to the pile top load N z Determine the length of the pile foundation.

[0012] As a preferred embodiment of the present invention, in step 4, according to the pile top load N z Determining the length of the pile foundation involves the following steps:

[0013] If σ 1 , σ 2 When both are greater than 0 and the pile foundation is a column pile,

[0014] Calculate the length H of the pile foundation according to the following formula:

[0015] H=h+h 0 ,

[0016] In the formula, h 0 is the distance from the rock surface to the bottom of the pile cap, and h is the depth of the pile foundation that needs to be embedded in the rock surface. h is calculated according to the following formula:

[0017] N Z ≤[P]=R(C 1 A+C 2 Uh),

[0018] Where [P] is the allowable bearing capacity of the pile foundation, R is the uniaxial compressive strength of rock, and C 1 , C 2 is a coefficient determined according to the degree of rock layer crushing and bottom cleaning conditions, A is the bearing area of ​​the pile bottom, and U is the circumference of the drilled hole of the pile embedded in the rock layer.

[0019] As a preferred embodiment of the present invention, in step 4, according to the pile top load N z Determining the length of the pile foundation involves the following steps:

[0020] If σ 1 , σ 2 When both are greater than 0 and the pile foundation is a friction pile,

[0021] Calculate the length H of the pile foundation according to the following formula:

[0022] H=∑l i ,

[0023] In the formula, l i is the thickness of each soil layer, l i Calculated according to the following formula:

[0024]

[0025] Where [P] is the allowable bearing capacity of the pile foundation, U is the circumference of the pile section, calculated according to the designed pile diameter, and f i is the ultimate friction resistance of each soil layer, m 0 is the reduction coefficient of bored pile bottom bearing force, and A is the pile bottom bearing area.

[0026] As a preferred embodiment of the present invention, in step 4, according to the pile top load N z Determining the length of the pile foundation involves the following steps:

[0027] If σ 1 >0,σ 2 <0, the length H of the pile foundation is calculated according to the following formula:

[0028] H=∑l i ,

[0029] In the formula, l i is the thickness of each soil layer, l i Calculated according to the following formula:

[0030] N Z ≤[P']=0.30U∑a i f i l i ,

[0031] Where [P'] is the allowable bearing capacity of the foundation under axial tension, U is the circumference of the pile section, calculated according to the designed pile diameter, and f i is the ultimate friction resistance of each soil layer, a i is the influence coefficient of the friction resistance around piles in each soil layer.

[0032] The present invention also discloses a steep slope section bridge foundation structure, which is designed by using any of the design methods for a steep slope section bridge foundation structure, and includes an open cut foundation and a pile foundation, wherein the pile foundation includes a pile cap and a pile body, the pile foundation is arranged on a side close to the steep slope, and the open cut foundation is arranged on a side away from the steep slope, and the open cut foundation and the pile cap are cast together.

[0033] As a preferred solution of the present invention, the open-cut foundation includes multiple foundation layers, and the angle between two adjacent foundation layers is less than or equal to 45°.

[0034] As a preferred embodiment of the present invention, the angle between the first foundation layer of the open cut foundation and the pier edge is less than or equal to 35°.

[0035] As a preferred solution of the present invention, an oblique angle or right angle transition is adopted between the open cut foundation and the pile cap.

[0036] As a preferred solution of the present invention, the open cut foundation and the pile cap are arranged with equal thickness.

[0037] As a preferred embodiment of the present invention, the distance s between the edge of the pile body and the edge of the pile cap is 1 Greater than or equal to 0.3 times the pile diameter d.

[0038] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0039] 1. The design method of the steep slope bridge foundation structure of the present invention takes into account the combined stiffness of the open cut foundation and the pile foundation, and calculates the average stiffness along the bridge within the full width of the cross section. and average stiffness in transverse direction The cross-sectional stress σ after considering the foundation stiffness is obtained maxi , σ mini and pile top load N z , can quickly determine the structural dimensions of open cut foundation and pile foundation. It has the advantages of high calculation efficiency and accurate calculation results.

[0040] 2. The steep slope bridge foundation structure described in the present invention makes full use of the original geological conditions, sets up open-cut foundations in places with better geology, and adopts pile foundations in places with worse geology, thereby realizing an effective combination of open-cut foundations and pile foundations, giving full play to the advantages of various foundations, and meeting the structural force requirements while reducing the excavation and destruction of the existing terrain, protecting the ecological environment, and having the characteristics of low engineering investment, small land occupation, strong terrain adaptability, and little damage to the environment.

[0041] 3. The steep slope bridge foundation structure described in the present invention adopts a combined foundation, which can improve the anti-sliding stability of the foundation compared to the open-cut foundation. On the premise of meeting the anti-sliding stability of the foundation, the size of the open-cut foundation can be reduced, thereby reducing the amount of engineering work. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural schematic diagram of the steep slope section bridge foundation structure described in Example 2 of the present invention.

[0043] Figure 2 It is a structural schematic diagram of the steep slope section bridge foundation structure described in Example 3 of the present invention.

[0044] Figure 3 It is a structural schematic diagram of the steep slope section bridge foundation structure described in Example 4 of the present invention.

[0045] Figure 4 It is a structural schematic diagram of the steep slope section bridge foundation structure described in Example 5 of the present invention.

[0046] Figure 5 It is a schematic diagram of the entire cross-section of the foundation described in the present invention being under compression.

[0047] Figure 6 The present invention calculates the pile foundation range A z Schematic diagram of the base stress on both sides.

[0048] Figure 7 It is a schematic diagram of one side of the foundation of the present invention being subjected to tension.

[0049] Icons: 0-bridge pier, 1-open cut foundation, 11-foundation layer, 2-pile foundation, 21-pile cap, 22-pile body, 3-edge of steep slope, 4-edge of open cut foundation. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0051] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] Example 1

[0053] A design method for the foundation structure of a bridge on a steep slope. Figure 1-4 As shown, the steep slope bridge foundation structure includes an open cut foundation 1 and a pile foundation 2, the pile foundation 2 includes a pile cap 21 and a pile body 22, the pile foundation 2 is arranged on the side close to the steep slope, and the open cut foundation 1 is arranged on the side away from the steep slope. The open cut foundation 1 and the pile cap 21 are cast together. The design of the steep slope bridge foundation structure includes the following steps:

[0054] Step 1: Calculate the average stiffness along the full width of the section and average stiffness in transverse direction C xi is the longitudinal stiffness of the ith foundation segment, C yi is the transverse stiffness of the i-th foundation segment, L xi is the width of the i-th foundation segment along the bridge, L yi is the transverse width of the i-th foundation segment, L x L is the full width of the foundation along the bridge. y It is the full width of the foundation in the transverse direction of the bridge;

[0055] Step 2: The open cut foundation 1 and the pile cap 21 are usually considered as rigid bodies, and the stress is considered linearly. However, the bending stiffness C of the open cut foundation 1 m and the combined stiffness of the pile and the cap C Z There is a certain difference. After combining the two, the influence of the stiffness difference needs to be considered to obtain the combined stiffness of the open cut foundation 1 and the pile foundation 2. Based on this, the stiffness ratio γ along the bridge direction is calculated. xi and transverse stiffness ratio γ yi , γ xi is the stiffness ratio of the i-th foundation segment along the bridge direction, γ yi is the transverse stiffness ratio of the i-th foundation segment;

[0056] Step 3: Calculate the cross-sectional stress σ after considering the combined stiffness maxi and σ mini ,like Figure 5 , 7 As shown, σ maxi is the maximum base stress of the ith foundation segment, σ mini is the minimum base stress of the ith foundation segment, N i is the vertical pressure acting on the center of gravity of the bottom surface of the i-th foundation segment, A i is the bottom area of ​​the ith basic segment, M xi is the bending moment along the bridge direction of the ith foundation segment, M yi is the transverse bending moment of the i-th foundation segment, I xi is the moment of inertia along the bridge of the ith foundation segment, I yi is the transverse moment of inertia of the ith foundation segment, x i is the distance from the ith basic segment to the y-axis, y i The distance of the i-th basic segment from the x-axis;

[0057] According to σ maxi <[σ], determine the base size and number of layers of the open-cut foundation, [σ] is the allowable bearing capacity of the foundation;

[0058] Step 4: Calculate the pile top load N within the pile foundation range z , A z =(d+2s 1 )L y , σ 1 , σ 2 Pile foundation range A z The base stress on both sides, d is the pile diameter, s is 1 is the distance between the edge of the pile body and the edge of the pile cap;

[0059] According to the pile top load N z Determine the length of the pile foundation.

[0060] For the force of pile foundation, the pile top load is in N z The average stress within the pile foundation range is considered, that is, the pile foundation range A z The average stress of the inner base, such as Figure 6 shown.

[0061] In step 4, according to the pile top load N z Determining the length of the pile foundation involves the following steps:

[0062] (1) If σ 1 , σ 2Both are greater than 0, that is, when the pile foundation is under pressure on both sides and the pile foundation is a column pile,

[0063] Calculate the length H of the pile foundation according to the following formula:

[0064] H=h+h 0 ,

[0065] In the formula, h 0 is the distance from the rock surface to the bottom of the pile cap, and h is the depth of the pile foundation that needs to be embedded in the rock surface. h is calculated according to the following formula:

[0066] N Z ≤[P]=R(C 1 A+C 2 Uh),

[0067] Where [P] is the allowable bearing capacity of the pile foundation, R is the uniaxial compressive strength of rock, and C 1 , C 2 is a coefficient determined according to the degree of rock layer fragmentation and bottom clearing conditions. The coefficients in Table 6.2.2-7 of the Code for Design of Foundations and Subgrades of Railway Bridges and Culverts (TB 10093-2017) can be used. A is the bearing area of ​​the pile bottom, and U is the circumference of the bored hole of the pile embedded in the rock layer.

[0068] (2) If σ 1 , σ 2 Both are greater than 0, that is, when the pile foundation is under pressure on both sides and the pile foundation is a friction pile,

[0069] Calculate the length H of the pile foundation according to the following formula:

[0070] H=∑l i ,

[0071] In the formula, l i is the thickness of each soil layer, l i Calculated according to the following formula:

[0072]

[0073] Where [P] is the allowable bearing capacity of the pile foundation, U is the circumference of the pile section, calculated according to the designed pile diameter, and f i is the ultimate friction resistance of each soil layer. The coefficients in Table 6.2.2-5 of the Code for Design of Railway Bridge and Culvert Foundations (TB 10093-2017) can be used. m 0 is the reduction coefficient of the bearing capacity at the bottom of bored cast-in-place piles. The coefficient in Table 6.2.2-6 of the Code for Design of Foundations and Subgrades for Railway Bridges and Culverts (TB10093-2017) can be adopted, and A is the bearing area at the bottom of the pile.

[0074] (3) If σ 1 >0,σ 2<0, that is, when one side of the pile foundation is under tension (such as Figure 7 As shown), the length H of the pile foundation is calculated according to the following formula:

[0075] H=∑l i ,

[0076] In the formula, l i is the thickness of each soil layer, l i Calculated according to the following formula:

[0077] N Z ≤[P']=0.30U∑a i f i l i ,

[0078] Where [P'] is the allowable bearing capacity of the foundation under axial tension, U is the circumference of the pile section, calculated according to the designed pile diameter, and f i is the ultimate friction resistance of each soil layer. The coefficients in Table 6.2.2-5 of the Code for Design of Foundations and Subgrades of Railway Bridges and Culverts (TB 10093-2017) can be used. i is the influence coefficient of the friction resistance around piles in each soil layer.

[0079] Example 2

[0080] like Figure 1 As shown, a steep slope bridge foundation structure is designed by the design method as described in Example 1, including an open cut foundation 1 and a pile foundation 2, the pile foundation 2 includes a pile cap 21 and a pile body 22, the pile foundation 2 is arranged on the side close to the steep slope, and the open cut foundation 1 is arranged on the side away from the steep slope, and the open cut foundation 1 and the pile cap 21 are cast together.

[0081] When the bridge span is small (span is less than 24m), the pier height is short (pier height is less than 10m), and the foundation bearing capacity is high (basic bearing capacity>0.5MPa), in order to meet the force requirements of the bridge foundation, the plane size of the open cut foundation 1 is arranged according to the structure, and the number of layers of the open cut foundation 1 is small (generally 1 to 2 layers). However, according to the topographic and geological conditions, the edge 4 of the open cut foundation is close to the edge 3 of the steep slope. Considering the instability of the steep slope under natural conditions, partial or overall fragmentation or collapse will affect the force area at the bottom of the open cut foundation 1, thereby affecting the foundation force and the safety of the structure. Therefore, a pile foundation 2 is set close to the steep slope side, and a combination of the open cut foundation 1 and the pile foundation 2 is adopted.

[0082] In order to meet the force transmission requirements of pile foundation 2, the thickness of pile cap 21 hz needs to be slightly larger than the thickness of open cut foundation 1 hm, and C is defined as hz-hm, S 1 is the distance between the outer pile edge and the outer pile cap edge, S 2is the distance between the inner pile edge and the inner pile cap edge. Due to the low pier height and high foundation bearing capacity, the pier body size and foundation size of pier 0 are relatively small. At this time, the distance between the pier edge and the pile edge is L>(S 1 +C), at the side of the pier near the pile, the open cut foundation 1 is transitioned to the pile cap 21 with an oblique chamfer v. Preferably, the pile cap 21 is transitioned to the open cut foundation 1 at an oblique angle of 45° (such as Figure 1 ). This structure is suitable for structures with high foundation bearing capacity, small bridge span, high and low piers, and areas with low earthquake intensity. The friction between the bottom of the open-cut foundation and the soil layer can resist the horizontal load. The pile foundation 2 is mainly to prevent the influence of local block falling on the open-cut foundation under natural conditions. The foundation force is mainly borne by the open-cut foundation 1.

[0083] When the open cut foundation 1 is 1 layer, the angle a between the open cut foundation 1 and the pier edge is ≤35°. According to the force requirements, if the number of layers of the open cut foundation 1 is greater than 1, that is, the open cut foundation 1 includes multiple foundation layers 11, the angle b between two adjacent foundation layers 11 is ≤45°, and the angle a between the first foundation layer 11 of the open cut foundation 1 and the pier edge is ≤35°. When the open cut foundation 1 is set in layers, the thickness of each layer is generally not less than 1m, and generally does not exceed 3 layers.

[0084] As a preferred solution, S 1 ≥0.3d, S 2 ≥0.3d, the angle c between the outer side of the pile body 22 and the pier edge is ≤45°. The thickness of the pile cap 21 is hz≥2d, where d is the diameter of the pile body 22.

[0085] During construction, firstly, the terrain at the bridge foundation is leveled according to the terrain and geological conditions, and the pile foundation 2 is constructed first. After the concrete strength of the pile body 22 meets the requirements, the open cut foundation 1 part (including the pile cap 21) is excavated, and the open cut foundation 2 and the pile cap 21 are cast together.

[0086] The present invention adopts a combined foundation, which can improve the anti-sliding stability of the foundation compared to the open-cut foundation. On the premise of meeting the anti-sliding stability of the foundation, the size of the open-cut foundation can be reduced, thereby reducing the amount of engineering work.

[0087] Specifically, for open cut foundation, the horizontal force of the external force acting on the bottom surface of the foundation is resisted by the friction between the bottom surface of the foundation and the foundation. The base friction force is equal to the vertical force ∑P of the base external force multiplied by the friction coefficient f between the foundation and the foundation. Therefore, the foundation sliding stability coefficient is the ratio of the base friction force to the horizontal force ∑T of the base external force, that is:

[0088] After the combined foundation is adopted in the present invention, the pile foundation has a restraining effect on horizontal slip, and the shearing effect of the pile foundation needs to be considered. Therefore, the anti-slip stability coefficient of the combined foundation is calculated as follows:

[0089]

[0090] If ∑T<f∑P, the horizontal force of the foundation can be borne by the friction between the open cut foundation and the base, the foundation will not slip, and the shear force of the pile foundation can be used as a safety reserve. At this time, the size of the open cut foundation can be reduced; if ∑T>f∑P, the horizontal force of the foundation is borne jointly by the open cut foundation and the pile foundation.

[0091] Example 3

[0092] like Figure 2 As shown, a steep slope bridge foundation structure is designed by the design method as described in Example 1, including an open cut foundation 1 and a pile foundation 2, the pile foundation 2 includes a pile cap 21 and a pile body 22, the pile foundation 2 is arranged on the side close to the steep slope, and the open cut foundation 1 is arranged on the side away from the steep slope, and the open cut foundation 1 and the pile cap 21 are cast together.

[0093] When the bridge span is large (bridge span is 24m, 32m and above), the pier height is relatively high (pier height is 10m-20m), and the foundation bearing capacity is relatively high (basic bearing capacity>0.5MPa), in order to meet the force requirements of the foundation, the plane size of the open-cut foundation 1 is arranged according to the structure, and the number of layers of the open-cut foundation 1 is relatively small (generally 1-2 layers are used). However, according to the topographic and geological conditions, the edge 4 of the open-cut foundation is close to the edge 3 of the steep slope. Considering the instability of the steep slope under natural conditions, after partial or overall fragmentation or collapse, the force area at the bottom of the open-cut foundation 1 is affected, thereby affecting the foundation force and the safety of the structure. At the same time, due to the high earthquake intensity at the bridge site, in order to meet the anti-slip requirements of the foundation, the friction between the bottom of the open-cut foundation 1 and the stratum cannot resist the horizontal force. Therefore, a pile foundation 2 is set close to the steep slope side, and a combination of the open-cut foundation 1 and the pile foundation 2 is used.

[0094] Since the pile foundation needs to bear a large horizontal load, a pile foundation 2 with a larger pile diameter is used. In order to meet the force transmission requirements of the pile foundation 2, a thicker pile cap size is required. Therefore, the thickness hz of the pile cap 21 is larger than the thickness hm of the open cut foundation 1. Define C = hz-hm, S 1 It is the distance between the edge of the pile body and the edge of the pile cap. Due to the high pier, large size of the pier bottom structure, high bearing capacity of the foundation, and the size of the foundation only according to the structure, the distance between the pier edge and the pile edge L<(S 1 +C), transition from the open cut foundation 1 to the pile cap 21 at the side of the pier near the pile side, at this time, after reserving S1 width on the inner side of the pile, a right angle transition is made with the open cut foundation 1. This structure adopts a combined foundation according to the terrain requirements, fully utilizes the geological conditions, gives full play to the force characteristics of the pile foundation 2 and the open cut foundation 1, and meets the force requirements of the foundation. Preferably, due to the sudden change in the thickness of the foundation, in order to meet the force requirements, the arrangement of the steel bars needs to be strengthened on both sides of the sudden change point.

[0095] When the open cut foundation 1 is 1 layer, the angle a between the open cut foundation 1 and the pier edge is ≤35°. According to the force requirements, if the number of layers of the open cut foundation 1 is greater than 1, that is, the open cut foundation 1 includes multiple foundation layers 11, the angle b between two adjacent foundation layers 11 is ≤45°, and the angle a between the first foundation layer 11 of the open cut foundation 1 and the pier edge is ≤35°. When the open cut foundation 1 is set in layers, the thickness of each layer is generally not less than 1m, and generally does not exceed 3 layers.

[0096] As a preferred solution, S 1 ≥0.3d, the angle c between the outer side of the pile body 22 and the pier edge is ≤45°. The thickness of the pile cap 21 is hz≥2d, where d is the diameter of the pile body 22.

[0097] During construction, firstly, the terrain at the bridge foundation is leveled according to the terrain and geological conditions, and the pile foundation 2 is constructed first. After the concrete strength of the pile body 22 meets the requirements, the open cut foundation 1 part (including the pile cap 21) is excavated, and the open cut foundation 2 and the pile cap 21 are cast together.

[0098] Example 4

[0099] like Figure 3 As shown, a steep slope bridge foundation structure is designed by the design method as described in Example 1, including an open cut foundation 1 and a pile foundation 2, the pile foundation 2 includes a pile cap 21 and a pile body 22, the pile foundation 2 is arranged on the side close to the steep slope, and the open cut foundation 1 is arranged on the side away from the steep slope, and the open cut foundation 1 and the pile cap 21 are cast together.

[0100] When the bridge span is large (bridge span is 24m, 32m and above), the pier height is small (pier height is about 10m), and the foundation bearing capacity is relatively small (basic bearing capacity is about 0.4MPa), at this time, due to the large upper load and small foundation bearing capacity, the plane size of the open cut foundation 1 is arranged according to the structure. In order to meet the force requirements of the foundation, the open cut foundation has more layers (generally 3 layers). However, according to the topographic and geological conditions, the edge 4 of the open cut foundation is close to the edge 3 of the steep slope. Considering the instability of the steep slope under natural conditions, partial or overall fragmentation or collapse will affect the force area of ​​the bottom of the open cut foundation, thereby affecting the foundation force and the safety of the structure. Therefore, a pile foundation 2 is set near the steep slope side, and a combination of the open cut foundation 1 and the pile foundation 2 is adopted.

[0101] Pile foundation 2 is mainly to prevent the local block falling of the slope under natural conditions from affecting the open cut foundation 1. The foundation force is mainly borne by the open cut foundation 1. Therefore, the pile diameter of pile foundation 2 is arranged according to the minimum pile diameter required by the construction process. In order to meet the force transmission requirements, the thickness of pile cap 21 hz is smaller than the thickness of open cut foundation 1 hm. In addition, due to the short pier height and relatively small pier bottom size, the distance L≥S between the inner side of the pile and the nearest side of the pier 1 , S 1It is the distance between the edge of the pile body and the edge of the pile cap. In order to reduce the amount of foundation engineering and foundation excavation, the open cut foundation and the pile cap adopt a right-angle transition. At this time, the open cut foundation reinforcement configuration of the transition section needs to be strengthened.

[0102] The open cut foundation 1 includes multiple foundation layers 11, the angle b between two adjacent foundation layers 11 is ≤45°, and the angle a between the first foundation layer 11 of the open cut foundation 1 and the pier edge is ≤35°. When the open cut foundation 1 is layered, the thickness of each layer is generally not less than 1m, and generally no more than 3 layers are set.

[0103] As a preferred solution, S 1 ≥0.3d, the angle c between the outer side of the pile body 22 and the pier edge is ≤45°. The thickness of the pile cap 21 is hz≥2d, where d is the diameter of the pile body 22.

[0104] During construction, firstly, the terrain at the bridge foundation is leveled according to the terrain and geological conditions, and the pile foundation 2 is constructed first. After the concrete strength of the pile body 22 meets the requirements, the open cut foundation 1 part (including the pile cap 21) is excavated, and the open cut foundation 2 and the pile cap 21 are cast together.

[0105] Example 5

[0106] like Figure 4 As shown, a steep slope bridge foundation structure is designed by the design method as described in Example 1, including an open cut foundation 1 and a pile foundation 2, the pile foundation 2 includes a pile cap 21 and a pile body 22, the pile foundation 2 is arranged on the side close to the steep slope, and the open cut foundation 1 is arranged on the side away from the steep slope, and the open cut foundation 1 and the pile cap 21 are cast together.

[0107] When the span of the bridge is large (span of 24m, 32m and above), the pier height is high (pier height of 20m and above), and the bearing capacity of the foundation is relatively small (basic bearing capacity of about 0.4MPa), at this time, due to the large upper load and small foundation bearing capacity, the plane size of the open-cut foundation 1 is arranged according to the structure. In order to meet the force requirements of the foundation, the open-cut foundation 1 has more layers (generally 3 layers). However, according to the topographic and geological conditions, the edge 4 of the open-cut foundation is close to the edge 3 of the steep slope. Considering the instability of the steep slope under natural conditions, partial or overall fragmentation or collapse will affect the force area at the bottom of the open-cut foundation 1, thereby affecting the foundation force and the safety of the structure. At the same time, due to the high earthquake intensity at the bridge site, in order to meet the anti-slip requirements of the foundation, the friction between the bottom of the open-cut foundation 1 and the stratum cannot resist the horizontal force. Therefore, a pile foundation 2 is set near the steep slope side, and a combination of the open-cut foundation 1 and the pile foundation 2 is adopted.

[0108] Since the pile foundation 2 needs to bear a large horizontal load, a pile foundation 2 with a larger pile diameter is used. In order to meet the force transmission requirements of the pile foundation 2, a thicker pile cap 21 needs to be used. At the same time, due to the high pier height and large pier bottom size, the distance L between the inner side of the pile and the nearest side of the pier is less than S. 1 , S 1 It is the distance between the edge of the pile body and the edge of the pile cap. The pile cap 21 is set to be equal in thickness to the open cut foundation 1, hz = hm. This solution has a straight base, which is convenient for construction control. At the same time, the pile cap 21 is equal in thickness to the open cut foundation 1, and there is no sudden change in load transfer, and the force bearing performance is good.

[0109] The open cut foundation 1 includes multiple foundation layers 11, the angle b between two adjacent foundation layers 11 is ≤45°, and the angle a between the first foundation layer 11 of the open cut foundation 1 and the pier edge is ≤35°. When the open cut foundation 1 is layered, the thickness of each layer is generally not less than 1m, and generally no more than 3 layers are set.

[0110] As a preferred solution, S 1 ≥0.3d, the angle c between the outer side of the pile body 22 and the pier edge is ≤45°. The thickness of the pile cap 21 is hz≥2d, where d is the diameter of the pile body 22.

[0111] During construction, firstly, the terrain at the bridge foundation is leveled according to the terrain and geological conditions, and the pile foundation 2 is constructed first. After the concrete strength of the pile body 22 meets the requirements, the open cut foundation 1 part (including the pile cap 21) is excavated, and the open cut foundation 2 and the pile cap 21 are cast together.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for the bridge foundation structure in a steep slope section, characterized in that, the bridge foundation structure in the steep slope section includes an open cut foundation (1) and a pile foundation (2). The pile foundation (2) includes a pile cap (21) and a pile body (22). The pile foundation (2) is arranged close to the steep slope side, and the open cut foundation (1) is arranged on the side away from the steep slope. The open cut foundation (1) and the pile cap (21) are integrally cast. Designing the bridge foundation structure in the steep slope section includes the following steps: Step 1: Calculate the average stiffness in the longitudinal direction of the bridge within the full width of the cross-section and the average stiffness in the transverse direction of the bridge , , , is the longitudinal stiffness of the i th basic segment, is the transverse stiffness of the i th basic segment, is the longitudinal width of the i th basic segment, is the transverse width of the i th basic segment, is the full longitudinal width of the foundation, is the full transverse width of the foundation; Step 2: Calculate the longitudinal stiffness ratio along the bridge and the transverse stiffness ratio along the bridge , , , where i is the longitudinal stiffness ratio along the bridge of the th basic segment, i is the transverse stiffness ratio along the bridge of the Step 3: Calculate the section stress considering the combined stiffness and , , , is the maximum base stress of the i th basic segment, is the minimum base stress of the i th basic segment, is the vertical pressure acting at the centroid of the bottom surface of the i th basic segment, is the bottom surface area of the i th basic segment, is the longitudinal bridge moment of the i th basic segment, is the transverse bridge moment of the i th basic segment, is the longitudinal bridge moment of inertia of the i th basic segment, is the transverse bridge moment of inertia of the i th basic segment, is the distance of the i th basic segment from the y axis, The i th basic segment's distance from the x axis; According to , determine the base size and number of layers of the open excavation foundation, which is the allowable bearing capacity of the foundation; Step 4: Calculate the pile top load within the pile foundation scope , , , , are the base stresses on both sides of the pile foundation scope , d is the pile body diameter is the distance between the pile body edge and the pile cap edge; According to the pile top load Determine the length of the pile foundation.

2. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, In the fourth step, according to the pile top load determining the length of the pile foundation includes the following steps: If and are both > 0 and the pile foundation is a column pile, Calculate the length of the pile foundation according to the following formula H , H = h + h 0 ， In the formula, h 0 is the distance from the rock surface to the bottom surface of the pile cap, h is the depth value that the pile foundation needs to be embedded into the rock surface, h which is calculated according to the following formula. ， Wherein, is the allowable bearing capacity of the pile foundation, is the uniaxial compressive strength of the rock, , are coefficients determined according to the fragmentation degree of the rock layer and the bottom cleaning condition, is the bearing area at the pile bottom, is the drilling perimeter of the pile embedded in the rock layer.

3. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, In the fourth step, according to the pile top load Determining the length of the pile foundation includes the following steps: If and are both > 0 and the pile foundation is a friction pile, Calculate the length of the pile foundation according to the following formula H , ， wherein, is the thickness of each soil layer, which is calculated according to the following formula: ， In the formula, is the allowable bearing capacity of the pile foundation, is the perimeter of the pile cross-section, calculated according to the designed pile diameter, is the ultimate skin friction of each soil layer, is the reduction coefficient of the bearing force at the bottom of the bored cast-in-place pile, is the bearing area at the pile bottom.

4. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, In the fourth step, according to the pile top load Determining the length of the pile foundation includes the following steps: If > 0, < 0, then calculate the length of the pile foundation according to the following formula H , ， In the formula, is the thickness of each soil layer, which is calculated according to the following formula: ， In the formula, is the allowable bearing capacity for axial tension of the foundation, is the perimeter of the pile cross-section, calculated according to the designed pile diameter, is the ultimate skin friction of each soil layer, is the influence coefficient of the pile shaft skin friction of each soil layer.

5. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, the open cut foundation (1) includes a plurality of foundation layers (11), and the included angle between two adjacent foundation layers (11) is less than or equal to 45°.

6. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 5, characterized in that, the included angle between the first foundation layer (11) of the open cut foundation (1) and the pier edge is less than or equal to 35°.

7. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, an oblique angle or a right angle transition is adopted between the open cut foundation (1) and the pile cap (21).

8. According to the design method for the bridge foundation structure in a steep slope section as claimed in claim 1, characterized in that, the open cut foundation (1) and the pile cap (21) are provided with the same thickness.

9. According to the design method for the bridge foundation structure in a steep slope section as claimed in any one of claims 1-8, characterized in that, The distance between the pile side edge and the pile cap edge is greater than or equal to 0.3 times the pile body diameter d .

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