Branch pile embankment reinforcing structure suitable for deep soft soil foundation and settlement calculation method of branch pile embankment reinforcing structure

Abstract

The invention discloses a branch pile embankment reinforcing structure suitable for a deep soft soil foundation and a settlement calculation method.The branch pile embankment reinforcing structure comprises a road surface, embankment filling soil, a geogrid, a broken stone hardcore, a solidification layer and squeezing branch piles which are sequentially arranged from top to bottom, and the squeezing branch piles downwards stretch into the soft soil foundation; the top end of the squeezing and expanding branch pile is embedded into the curing layer, and a force bearing disc is squeezed and expanded in the curing layer at the top end of the squeezing and expanding branch pile. The bearing disc is extruded and expanded in the curing layer to play the role of the pile cap, the embankment load is conducted to the branch disc pile, deformation is coordinated to prevent the low embankment from generating a mushroom pavement, in addition, the tedious steps of pile cap construction are avoided, and the bearing capacity of the curing layer is fully transferred.

Description

Technical Field

[0001] The present invention belongs to the field of ground treatment, and particularly relates to a branch-disk pile embankment reinforcement structure suitable for deep soft ground, and also relates to a settlement calculation method for the branch-disk pile embankment reinforcement structure. Background Art

[0002] Deep soft ground not only has characteristics such as high water content, large void ratio, high compressibility, low strength, and high sensitivity, but also due to the excessive depth of soft soil, the settlement stabilization takes a long time and the dissipation of deep pore water pressure is slow, making it difficult to fully treat the foundation. Therefore, it is not suitable to fill embankments on it.

[0003] In recent years, rigid pile composite foundations have become a solution for soft foundation treatment due to their many advantages such as strong settlement control ability, short construction time, easy control of construction quality, and large foundation treatment depth. As a new type of pile foundation with a variable cross-section in the longitudinal direction, the squeezed branch-disk pile, a patent application with the publication number CN201109909Y, discloses a squeezed branch-disk pile, which includes a main pile and multiple branch-disk structures extending outward from the main pile; the branch-disk structure is a protruding branch-disk-shaped bearing structure, and the used squeezing and expanding machine rotates a certain angle and then expands outward, continuously performing multiple times or successively, and finally forms a branch / disk-shaped cavity, and then fills it with concrete. By using a special squeezing and expanding device to add branch-disk structures on the main pile body, the contact area between the branch-disk structures and the pile-side soil is increased to improve the bearing capacity of the pile foundation.

[0004] The squeezed branch-disk pile first emerged in the traditional building field and has been widely used in bridge pile foundation construction in recent years. However, at present, the design methods and structures applied to the soft ground treatment of highway engineering are relatively rare, and as a type of rigid pile, the squeezed branch-disk pile still has the following problems when applied to the treatment of deep soft foundation under embankments:

[0005] ⑴ High cost: Highway construction is a linear project. The extensive use of large-diameter branch-disk piles for soft foundation treatment will lead to an increase in project expenses.

[0006] ⑵ Generate a "mushroom" road surface: For low-fill embankments, due to the differential settlement between the pile and the soil being reflected to the surface layer, local unevenness occurs.

[0007] ⑶ There is a risk of "progressive" failure: That is, the phenomenon that the pile group gradually fails from the road slope toe to the inner side of the road due to the bending / shearing yield of the rigid piles at the slope toe, resulting in the overall instability of the embankment.

[0008] ⑷ "Surplus" bearing capacity: The vertical bearing capacity of rigid piles can fully cope with the vertical load of the embankment. Summary of the Invention

[0009] The first object of the present invention is to provide a branch - disk pile embankment reinforcement structure applicable to deep soft soil foundations, which has simple construction, low cost, can avoid the formation of "mushroom" road surfaces, and can make full use of the bearing capacity of the solidified layer.

[0010] The first object of the present invention is achieved by the following technical measures: A branch - disk pile embankment reinforcement structure applicable to deep soft soil foundations, characterized in that it includes a road surface, embankment fill, geogrid, gravel cushion, solidified layer, and squeezed - expanded branch - disk piles arranged in sequence from top to bottom. The squeezed - expanded branch - disk piles extend downward into the soft soil foundation, the top of the squeezed - expanded branch - disk piles is embedded in the solidified layer, and a bearing disk is squeezed - expanded in the solidified layer at the top of the squeezed - expanded branch - disk piles.

[0011] The present invention squeezes - expands a bearing disk in the solidified layer to play the role of a pile cap: ① transmitting the embankment load to the branch - disk piles; ② coordinating deformation to prevent the appearance of "mushroom road surfaces" on low embankments. In addition, the cumbersome steps of pile cap construction are avoided and the bearing capacity of the solidified layer is fully mobilized.

[0012] For the squeezed - expanded branch - disk piles of the present invention, a "small diameter" is selected for the pile diameter, and the main pile diameter can be selected from 500 mm to 700 mm; and they are arranged under the condition of relatively "large spacing", and the pile spacing can be selected from 2 to 2.5 times the maximum outer diameter of the squeezed - expanded bearing disk.

[0013] The thickness of the solidified layer of the present invention varies with the height of the embankment fill. The thickness of the solidified layer is taken as 0.2 - 0.4 times the height of the embankment fill, and the thickness of the solidified layer does not exceed 4 m.

[0014] The solidified layer of the present invention is thinner at the center of the road and thicker at the two side slope feet.

[0015] The squeezed - expanded branch - disk piles of the present invention are arranged with branch - disk structures along the main piles, and the minimum distance between adjacent branch - disk structures is not less than 8 times the main pile diameter.

[0016] The second object of the present invention is to provide a method for calculating the settlement of the above - mentioned branch - disk pile embankment reinforcement structure applicable to deep soft soil foundations.

[0017] The second object of the present invention is achieved by the following technical measures: A method for calculating the settlement of the above - mentioned branch - disk pile embankment reinforcement structure applicable to deep soft soil foundations, characterized by including the following steps:

[0018] First, according to the structural form and soil layer characteristics of the branch - disk pile embankment reinforcement structure, select the ground settlement calculation points and determine the vertical load at the top of the squeezed - expanded branch - disk piles.

[0019] Second, for the selected ground settlement calculation points, calculate the stressed length of the squeezed - expanded branch - disk piles at the settlement calculation points according to the vertical load at the top of the piles, and determine the bearing surface of the squeezed - expanded branch - disk piles in the soil layer.

[0020] III. Calculate the ground settlement caused by soil deformation above and below the bearing surface of the squeezed-expanded branch-disk pile respectively. The ground settlement above the bearing surface is calculated according to the pile body compression, and the ground settlement below the bearing surface is calculated according to the soil layer compression;

[0021] IV. Calculate the sum of the pile body compression and the soil layer compression, that is, the final ground settlement deformation of the branch-disk pile embankment reinforcement structure is obtained.

[0022] In step I of the present invention, the ground settlement calculation points are within the settlement control range in the middle of the roadbed or within the sliding stability control range of the slope.

[0023] In step II of the present invention, the bearing surface of the squeezed-expanded branch-disk pile in the soil layer is the position where the axial force of the pile body is 0. When calculating the axial force of the pile body of the squeezed-expanded branch-disk pile, the skin friction of the pile and the bearing capacity provided by the bearing branch-disk structure are considered.

[0024] In step III of the present invention, the ground settlement above the bearing surface is calculated by the following method:

[0025]

[0026] Among them, s 上 is the final ground settlement caused by soil deformation above the bearing surface; L 0 is the stressed length of the squeezed-expanded branch-disk pile; EA is the axial compression stiffness of the pile body of the squeezed-expanded branch-disk pile; F(x) is the axial force distribution along the pile body, which should be calculated according to the soil layer characteristics, the size, spacing and quantity of the branch disks.

[0027] In step III of the present invention, the ground settlement below the bearing surface is calculated by the following method:

[0028]

[0029] Among them, ψ c is the empirical coefficient for calculating the settlement of the pile foundation, and each region should be determined by statistical comparison of local engineering measurement data; l is the number of adjacent piles affecting the ground settlement calculation point; m is the number of soil layers divided within the depth range of the foundation settlement calculation; n is the number of bearing disks above the bearing surface; p i,k is the additional pressure of the i-th bearing disk of the k-th pile near the ground settlement calculation point of the foundation at the bearing surface; E sj is the compression modulus of the j-th soil layer below the bearing surface, and the pressure section from the self-weight pressure of the soil to the sum of the self-weight pressure and the additional pressure of the soil should be taken for calculation; z j 、z j-1 are the distances from the bearing surface to the bottom surfaces of the j-th soil layer and the j-1-th soil layer below; is the average additional stress coefficient within the range from the foundation settlement calculation point caused by the k-th pile to the bottom surfaces of the j-th layer and the (j-1)-th layer of soil, and is adopted according to the average additional stress coefficients of internal points and external points under a uniformly distributed circular ring load surface.

[0030] Compared with the prior art, the present invention has the following remarkable effects:

[0031] ⑴ In the present invention, the squeezed-expanded bearing plates in the solidified layer play the role of a pile cap: ① transmitting the embankment load to the branched-disk pile; ② coordinating the deformation to prevent the appearance of a "mushroom road surface" on a low embankment. In addition, the cumbersome steps of pile cap construction are avoided and the bearing capacity of the solidified layer is fully mobilized.

[0032] ⑵ The present invention effectively combines the solidified layer and the squeezed-expanded branched-disk pile, and uses the pile layout form of "small diameter, large spacing" to give full play to the high bearing performance of the branched-disk pile, achieving the purpose of saving materials, reducing costs and shortening the working hours.

[0033] ⑶ The present invention makes full use of the solidified layer: in the early stage, the solidified layer can be used as a construction platform for structures such as bridge pile foundations and branched-disk piles in the early stage, and at the same time provides a temporary road for heavy-duty vehicles, which will increase the construction efficiency; during the construction stage, the solidified layer provides an anchoring effect for the squeezed-expanded branched-disk pile and its first disk, which is beneficial to the stability of a single pile. In addition, the solidified layer will improve the bearing capacity of the foundation.

[0034] ⑷ The in-situ solidification layout form of the present invention adopts "thin in the middle and thick on both sides". On the one hand, it improves the utilization rate of the solidification material in the middle, and on the other hand, it improves the strength and stiffness of the foundation at the slope foot, inhibiting the progressive failure caused by the bending failure of the side piles.

[0035] ⑸ The calculation method of the present invention fully considers the supporting effect of the squeezed-expanded branched-disk pile on the embankment structure. The self-weight of the embankment and the road surface load are borne by the soil arch structure at the top of the branched-disk pile, and part of the load is transmitted to deeper soil layers through the branched-disk pile, reducing the foundation stress below the ground line, thereby greatly reducing the ground settlement deformation amount and avoiding excessive road surface settlement deformation.

[0036] ⑹ Since the squeezed-expanded branched-disk pile embankment reinforcement structure of the present invention uses the branched-disk pile to reinforce the foundation structure, the stress of the pile-soil system in the foundation is complex. Usually, the finite element method is used to simulate and analyze the ground settlement amount. However, there are some problems in the finite element method, such as the modeling process is relatively cumbersome and it takes more time in the design process. The ground settlement amount calculation method of the squeezed-expanded branched-disk pile embankment reinforcement structure proposed by the present invention has a clear concept, strong operability and can reflect the actual stress characteristics of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0038] Figure 1 is the cross-sectional view of the present invention;

[0039] Figure 2 is the top view of the present invention;

[0040] Figure 3 is the schematic diagram of a single squeezed-expanded branch pile of the present invention;

[0041] Figure 4 is the reinforcement drawing of the squeezed-expanded branch pile of the present invention;

[0042] Figure 5 is the elevation view of the bearing plate of the squeezed-expanded branch pile of the present invention;

[0043] Figure 6 is the plan view of the bearing branch of the squeezed-expanded branch pile of the present invention;

[0044] Figure 7 is the schematic diagram of the transition section of the solidified layer under the road shoulder of the present invention;

[0045] Figure 8 is the flow block diagram of the settlement calculation method of the present invention;

[0046] Figure 9 is the elevation schematic diagram of the settlement calculation method of the present invention;

[0047] Figure 10 is the plan schematic diagram of the settlement calculation method of the present invention;

[0048] Figure 11 is the schematic diagram of the calculation parameters of the settlement calculation method of the present invention.

[0049] In the figure: 1 - squeezed-expanded branch pile; 2 - bearing plate; 3 - bearing branch; 4 - solidified layer; 5 - drainage ditch; 6 - gravel cushion; 7 - geogrid; 8 - embankment fill; 9 - road surface; 10 - soft soil foundation; 11 - branch spacing; 12 - longitudinal reinforcement; 13 - stirrup; 14 - plate height; 15 - plate ring width; 16 - main pile diameter; 17 - branch; 18 - soft foundation treatment area at the toe of the slope; 19 - inner soft foundation treatment area. Specific embodiments

[0050] The present invention will be further described below through the description of specific embodiments. However, this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements according to the basic idea of the present invention, but as long as they do not depart from the basic idea of the present invention, they are all within the protection scope of the present invention.

[0051] Such as Figures 1 to 7As shown in the figure, it is a reinforced structure of a branched - disk pile embankment applicable to deep soft soil foundation of the present invention, including a road surface 9, embankment fill 8, geogrid 7, gravel cushion 6, solidified layer 4, and squeezed - expanded branched - disk pile 1 arranged successively from top to bottom. The squeezed - expanded branched - disk pile 1 extends downward into the soft soil foundation 10, and the top of the squeezed - expanded branched - disk pile 1 is embedded in the solidified layer 4, and a bearing disk 2 is squeezed - expanded in the solidified layer 4 at the top of the squeezed - expanded branched - disk pile 1.

[0052] The solidified layer 4 is a soil layer with certain strength and stiffness formed by mixing a solidifying agent into the surface soil by a special mixing machine; the squeezed - expanded branched - disk pile 1 adopts a squeezing - expanded forming method to add a branched - disk structure along the pile body, and a steel reinforcement cage is put in after the squeezing - expanded construction; the top of the squeezed - expanded branched - disk pile 1 is located in the solidified layer 4, and the branched - disk structure is squeezed - expanded in a soil layer with relatively good soil quality or deep soil layer; in the reinforced structure, a layer of geogrid 7 is arranged at the top and middle of the cushion respectively, and the strength of the geogrid 7 is determined according to the lower soft soil quality and the upper embankment fill; a drainage ditch 5 is arranged on the gravel cushion 6.

[0053] The pile diameter of the squeezed - expanded branched - disk pile 1 is selected as "small diameter", and the main pile diameter can be selected from 500 mm to 700 mm; and it is arranged under the condition of relatively "large spacing", and the pile spacing can be selected as 2 - 2.5 times the maximum outer diameter of the bearing disk.

[0054] The thickness of the solidified layer 4 varies with the height of the embankment fill. The thickness of the solidified layer 4 is taken as 0.2 - 0.4 times the embankment filling height, but the thickness of the solidified layer 4 should not exceed 4 m.

[0055] The layout form of the solidified layer 4 is "thin in the road center and thick at both side slopes".

[0056] The squeezed - expanded branched - disk pile 1 arranges a branched - disk structure along the main pile. The vertical spacing of the branched - disk structure is the branch spacing 11, and the minimum vertical spacing should not be less than 8 times the main pile diameter.

[0057] The construction process of the present invention is as follows:

[0058] 1. Clean the surface soil and implement in - situ solidification: Before on - site construction, vegetation, tree roots, boulders and other obstacles on the site should be removed. In - situ solidification should be implemented by using special solidification equipment such as PMX powerful mixing heads. The solidification range should extend from the road center to 2 - 3 m outside the embankment slope foot.

[0059] 2. Backfill the working cushion with plain soil: To provide upper ballast for subsequent bored pile construction and the extrusion of the bearing disk structure and ensure the stability of the surface working platform. It should be noted that the squeezed - expanded branched - disk pile construction can be carried out only after a certain age period of in - situ solidification; the compaction degree of the working cushion plain soil should reach 80%, and its top surface should also meet the basic requirements of flatness.

[0060] 3. Driving cast-in-place piles with branches and plates: The construction mode of the main piles of the cast-in-place piles with branches and plates is basically the same as that of the traditional bored cast-in-place piles. After forming the equal-diameter main piles, an extrusion and expansion device is used to expand the plates at the corresponding elevations to form branches. After extracting the extrusion and expansion equipment, a prefabricated steel reinforcement cage is put in. It should be noted that the construction of cast-in-place piles with branches and plates has a certain soil squeezing effect. The construction should be carried out from the middle of the subgrade to both sides of the road, from existing (structures) buildings and underground pipelines to far away, from existing ditches and slopes to far away, and from abutment culverts to far away. When necessary, construction methods such as continuous jump driving should be adopted; before the subsequent construction, the quality of the formed cast-in-place piles with branches and plates should be detected according to the relevant specification requirements.

[0061] 4. Constructing the gravel cushion layer and laying geogrid: The geogrid is laid at the top and in the middle of the gravel cushion layer respectively; in specific implementation cases, the thickness of the gravel cushion layer is taken as 0.4m - 0.5m, and the geogrid used is a biaxial geogrid GSL / 500pp.

[0062] 5. Filling and surcharging, unloading: The embankment should be filled and compacted in horizontal layers, and the maximum loose paving thickness of each layer should not exceed 30cm; during the embankment filling process, the filling rate should be controlled to protect the cast-in-place piles with branches and plates and the solidified soil layer in the soft soil foundation; if conditions permit, equal-load preloading should be maintained for more than 3 months.

[0063] Preferably, the plan view of the subgrade treated with extrusion-expanded cast-in-place piles with branches and plates in a specific implementation case is as Figure 2 , preferably, the spacing S of the cast-in-place piles with branches and plates can be determined according to the embankment filling height and the foundation stiffness; in principle, due to the existence of the branch and plate structure, the pile spacing of the extrusion-expanded cast-in-place piles with branches and plates should be larger than that of the conventional bored cast-in-place piles; in engineering examples, the pile length of the cast-in-place piles with branches and plates is 35m, the main pile diameter is 0.5m, the width of the bearing plate ring is 1.5m, the pile spacing of the cast-in-place piles with branches and plates on the inner side of the road is set to 4.0m, and the pile spacing at the shoulder slope toe is set to 3.0m.

[0064] The layout of the bearing plates 2 and the bearing branches 3 can be referred to Figure 3 , in principle, when the plate-forming condition in the soft soil foundation 10 is poor, the bearing branches 3 should be tried to be arranged in the deep soft soil, and the bearing plates borrow the solidified layer 5 as the bearing layer to play a role. In actual cases, the deep bearing branches and the top bearing plates are extruded and expanded successively from bottom to top. Among them, the bearing branches 3 are selected to be arranged in a 6-star branch layout in the soft soil layer, the width of the branch is required to be 0.25m, and the net distance between the branches is 4.0m (8 times the main pile diameter 16); the height of the bearing plate 14 is set to 1.0m and is arranged in the solidified layer, and the geometric center of the bearing plate should be located in the upper middle part of the solidified layer as much as possible.

[0065] As described in the previous construction process, the prefabricated steel reinforcement cage is put in immediately after the extrusion and expansion of the cast-in-place piles with branches and plates; Figure 4 is the elevation view of the steel reinforcement cage of the cast-in-place piles with branches and plates. Small-spacing stirrups 13 and longitudinal bars 12 are arranged at the top of the pile, and large-spacing stirrups 13 are arranged 2m below the pile top. In the case, the length of the longitudinal bars is about 70% of the pile length.

[0066] Preferably, a foundation transition section is provided under the shoulder position of the present invention, and its form is as follows Figure 7 shown. The area outside the shoulder is the toe soft foundation treatment area 18 (abbreviated as "toe treatment area"), and the area inside is the inner soft foundation treatment area 19 (abbreviated as "inner treatment area"). During the implementation process, it should be ensured that the thickness of the solidified layer in the inner treatment area 19 is greater than 2.0 m, and the thickness of the solidified layer in the toe treatment area 18 is greater than 3.0 m. The transition of the thickness of the solidified layer in the two areas is achieved by controlling the mixing depth of the in-situ solidification machine, and the spacing of the squeezed-expanded branch disk piles 1 changes from sparse to dense; in order to inhibit the progressive failure of the embankment system in the deep soft foundation, in addition to adjusting the pile spacing and the thickness of the solidified layer, the amount or specification of the longitudinal bars 12 in the toe treatment area 18 will be increased. In actual cases, the toe treatment area 18 uses longitudinal bars of 8@14 mm, while the inner treatment area uses longitudinal bars of 6@12 mm.

[0067] As Figure 8 shown, a method for calculating the settlement of a branch disk pile embankment reinforcement structure applicable to deep soft soil foundation as described above includes the following steps:

[0068] 1. According to the structural form and soil layer characteristics of the branch disk pile embankment reinforcement structure, select the ground settlement calculation points and determine the vertical load on the pile top of the squeezed-expanded branch disk piles;

[0069] Determine the vertical load borne by the pile top of the branch disk piles according to the geometric dimensions and road surface form of the squeezed-expanded branch disk pile embankment; determine the height and soil mechanics characteristics of each soil layer according to the soil distribution in the subgrade; the selected ground settlement calculation points for calculation can be within the settlement control range in the middle of the subgrade or within the slope sliding stability control range. The pile top loads of the branch disk piles at different settlement calculation points may be different.

[0070] In this step, the branch disk pile embankment reinforcement structure includes embankment fill and a squeezed-expanded branch disk pile structure arranged below the ground line. Selecting the settlement calculation points is to determine the specific ground settlement positions to be calculated; according to the structural form and geometric dimensions of the embankment fill and the road surface structure, the self-weight of the embankment structure and the equivalent road surface load borne by the pile top of the branch disk piles can be determined; according to the soil distribution of the foundation below the ground line, the thickness of each soil layer can be reasonably divided and its soil mechanics parameters can be clarified, which is convenient for the calculations in the subsequent Step 2 and Step 3.

[0071] In specific implementation, the load distribution above the ground line and the characteristics of the foundation soil layers below the ground line have a greater impact on the final ground settlement deformation. The load at the pile top of the squeezed branch and plate pile can include the overfilled load of the embankment soil. The squeezed branch and plate piles within the settlement control range in the middle of the subgrade can be considered to uniformly bear the self-weight of the embankment structure, and the squeezed branch and plate piles within the slope sliding stability control range can be considered to bear the self-weight of the embankment structure according to a gradient distribution. Each soil layer of the foundation is divided according to the characteristics of the same type of soil mass. The soil layer thickness should be divided as finely as possible, but the calculation workload should also be considered. The depth of the foundation settlement calculation should be determined according to trial calculations.

[0072] II. For the selected ground settlement calculation points, calculate the bearing length of the squeezed branch and plate piles at the settlement calculation points according to the vertical load at the pile top, and determine the bearing surface of the squeezed branch and plate piles in the soil layer. The vertical load at the pile top includes the self-weight of the embankment fill, the equivalent load of the road surface, etc. The bearing surface of the squeezed branch and plate piles in the soil layer is the position where the axial force of the pile body of the branch and plate pile is 0. The calculation of the axial force of the pile body of the branch and plate pile should consider the skin friction of the pile side and the bearing capacity provided by the bearing branch and plate structure.

[0073] In this step, after the ground settlement calculation points are determined, the pile top load of the branch and plate piles at the settlement calculation points can be determined according to Step 1. According to the pile top load of the squeezed branch and plate piles, the structural form of the bearing branches and plates, and the characteristics of the soil layer where the pile body is located, the axial force distribution state of the pile body can be calculated, and the actual bearing length of the branch and plate piles can be determined. The position where the axial force of the pile body is 0 corresponds to the bearing surface. The position where the axial force of the pile body is 0 is the bearing surface. At the bearing surface, the pile body does not provide a reaction force. The surface reaction force transmitted to the bearing surface after the skin friction of the pile side and the end resistance of the branch and plate provide the bearing force of the pile body.

[0074] In specific implementation, the axial force state of the pile body of the squeezed branch and plate piles is mainly affected by the skin friction of the pile side and the bearing capacity of the soil at the end of the bearing branch and plate. Domestic codes such as "Code for Design of Highway Bridge and Culvert Foundations" (JTG 3363-2019), "Squeezed Branch and Plate Piles for Bridges" (JT / T 855-2013), and "Technical Specification for Squeezed Branch and Plate Piles of Guangdong Highway Bridges" (T / GDHS 002-2020) all provide calculation formulas for the skin friction of the pile side and the bearing capacity of the soil at the end of the bearing branch and plate. It should be noted that the skin friction provided by the side of the bearing branch is usually not included as a safety reserve. It should be noted that when the force at the pile end is not 0, the bearing surface should be the pile end position.

[0075] III. According to the position of the bearing surface of the squeezed branch and plate piles, calculate the ground settlement caused by the deformation of the soil mass above and below the bearing surface respectively. The ground settlement above the bearing surface is calculated according to the compression of the pile body, and the ground settlement below the bearing surface is calculated according to the compression of the soil layer.

[0076] Calculate the ground settlement caused by the deformation of the soil mass above the bearing surface. Considering that the settlement of the soil mass above the bearing surface is restricted by the squeezed branch pile, it should be indirectly calculated through the vertical compression of the pile body and obtained by the following formula:

[0077]

[0078] Among them, s 上 is the final ground settlement caused by the deformation of the soil mass above the bearing surface; L 0 is the stressed length of the squeezed branch pile; EA is the axial compression stiffness of the pile body of the squeezed branch pile; F(x) is the axial force distribution along the pile body, which should be calculated according to the soil layer characteristics, the size, spacing and quantity of the branch plates.

[0079] Calculate the ground settlement caused by the deformation of the soil mass below the bearing surface. It should be calculated according to the sum of the compression amounts of each soil layer below the bearing surface and obtained by the following formula:

[0080]

[0081] Among them, ψ c is the empirical coefficient for calculating the settlement of the pile foundation. Each region should determine it according to the statistical comparison of local engineering measurement data; l is the number of adjacent piles (including this pile) that have an impact on the ground settlement calculation point; m is the number of soil layers divided within the depth range of the foundation settlement calculation; n is the number of bearing plates (branches) above the bearing surface; p i,k is the additional pressure at the bearing surface of the i-th bearing plate (branch) of the k-th pile near the ground settlement calculation point of the foundation; E sj is the compression modulus of the j-th soil layer below the bearing surface, and the pressure section from the self-weight pressure of the soil to the sum of the self-weight pressure and the additional pressure of the soil should be taken for calculation; z j 、z j-1 are the distances from the bearing surface to the bottom surfaces of the j-th soil layer and the j-1-th soil layer below; is the average additional stress coefficient within the range from the ground settlement calculation point on the foundation above the bearing surface caused by the k-th pile to the bottom surfaces of the j-th soil layer and the j-1-th soil layer, and it is adopted according to the average additional stress coefficients of the internal points and external points under the uniformly distributed circular ring load surface.

[0082] In this step, since the mechanisms of soil deformation above and below the bearing surface are different, different settlement calculation methods should be adopted. Above the bearing surface, the vertical load at the pile top is mainly transmitted through the pile body of the rammed bulb pile. During the downward transmission of the pile top load along the pile body, the load is gradually dispersed into each soil layer through the side friction of the pile and the end resistance of the bearing bulbs. In any soil layer above the bearing surface, there are loads transmitted to both the pile body and the soil layer simultaneously, and the stress state of the pile-soil system is relatively complex. The settlement should be considered to be indirectly obtained from the compression of the pile body. Below the bearing surface, there is no load transmission within the pile body, and the pile top load is completely transmitted to the bearing surface. The settlement deformation amount should be obtained by calculating the compression of each soil layer below the bearing surface.

[0083] In specific implementation, the axial force distribution along the pile body of the rammed bulb pile is a variable. After obtaining the pile body axial force function according to the standard method, the compression of the pile body can be obtained by integration. The soil layer thickness below the bearing surface should be reasonably divided, and the total compression of the soil layer can be calculated by the one-way compression layer summation method.

[0084] IV. Calculate the sum of the compression of the pile body and the compression of the soil layer, and the final ground settlement deformation amount of the rammed bulb pile embankment reinforcement structure can be obtained.

[0085] In this step, the final ground settlement deformation amount of the rammed bulb pile embankment reinforcement structure is the sum of the deformations of the soil mass (pile body) above and below the bearing surface, including the compression of the pile body and the compression of the soil.

[0086] In specific implementation, according to the calculation results of the compression of the pile body above the bearing surface and the compression of the soil mass below the bearing surface obtained in Step 3, the two can be superimposed to obtain the final total settlement deformation amount. It should be noted that when calculating the compression of the soil mass below the bearing surface by the one-way compression layer summation method, the empirical coefficient ψ for pile foundation settlement calculation should be considered. c This coefficient value should be determined by statistical comparison of local engineering measurement data in each region.

[0087] In this step, according to the structural form and stress characteristics of the rammed bulb pile embankment reinforcement structure, the specific position of the pile bottom bearing surface is determined by calculating the actual stressed length of the rammed bulb pile. Different vertical settlement calculation methods are selected according to the deformation characteristics of the soil mass in the upper and lower parts of the bearing surface.

[0088] Since the rammed bulb pile embankment reinforcement structure of the present invention uses rammed bulb piles to reinforce the foundation structure, the stress state of the pile-soil system in the foundation is complex. Usually, the finite element method is used for the simulation analysis of the ground settlement amount. However, the modeling process of the finite element method is relatively cumbersome and consumes more time in the design process. The ground settlement amount calculation method for the rammed bulb pile embankment reinforcement structure proposed by the present invention has a clear concept, strong operability, and can reflect the actual stress characteristics of the structure.

[0089] In one embodiment, in the above step 1, by obtaining the structural form of the squeezed branch disk pile embankment reinforcement structure and the soil layer characteristics, selecting the ground settlement calculation points to be calculated, and determining the pile top load of the squeezed branch disk pile, it further includes: determining the vertical load borne by the pile top of the branch disk pile according to the geometric dimensions and road surface form of the squeezed branch disk pile embankment; determining the height and soil mechanics characteristics of each soil layer according to the soil distribution in the foundation; the ground settlement calculation points to be calculated can be within the settlement control range in the middle of the subgrade or within the slope sliding stability control range, and the pile top loads of the branch disk piles at different settlement calculation points may be different.

[0090] In this embodiment, as Figure 9 shown, determine the pile top load of the squeezed branch disk pile according to the filling height of the embankment and the unit weight of the filling and road surface structure materials; according to the soil layer distribution characteristics below the ground line, divide the soil layer thickness according to the calculation parameters required in step 2 and step 3.

[0091] In specific implementation, since the ground settlement amount in the middle of the subgrade is the largest, usually the ground settlement calculation points are selected in the middle range of the subgrade. It is approximately considered that the self-weight of the embankment filling and the equivalent road surface load are evenly distributed on the pile tops of each branch disk pile within this range, and thus the load-bearing situation of the pile top can be quickly determined; as Figure 10 shown, the distances between the branch disk pile and the adjacent piles are S 1 and S 2 , respectively. First, clarify the pressure surface load values of the embankment filling, road surface structure, and equivalent road surface load transmitted to the ground line, then the pressure surface load of the area shared by each pile is the pressure surface load of S 1 S 2 ; divide the soil bodies with similar soil mechanics characteristics into the same soil layer, and the soil layer thickness below the bearing surface should be divided appropriately to avoid excessive calculation amount in the calculation of step 3.

[0092] This embodiment provides the parameters required in the calculations of step 2 and step 3 by clarifying the pile top load value-taking principle and soil layer thickness division principle of the branch disk pile.

[0093] In one embodiment, in the above step 2, according to the selected ground settlement calculation points, calculate the stressed length of the squeezed branch disk pile at the settlement calculation points, and determine the bearing surface of the squeezed branch disk pile in the soil layer, including: for the selected ground settlement calculation points, the stressed length of the squeezed branch disk pile at the settlement calculation points should be calculated according to the vertical load at the pile top. The vertical load at the pile top includes the self-weight of the embankment filling, the equivalent road surface load, etc.; the bearing surface of the squeezed branch disk pile in the soil layer is the position where the axial force of the pile body of the branch disk pile is 0, and the calculation of the axial force of the pile body of the branch disk pile should consider the side friction resistance of the pile and the bearing capacity provided by the bearing branch disk structure.

[0094] In this embodiment, the pile top load is determined through Step 1. According to the pile top load and the soil layer distribution characteristics, the axial force distribution of the pile body is calculated by the standard method. For example, the "Code for Design of Subgrade and Foundation of Highway Bridges and Culverts" (JTG 3363-2019) stipulates the calculation methods for the side friction resistance of the pile and the bearing capacity of the soil at the branch and disk ends. The end of the axial force distribution at the pile bottom is taken as the bearing surface.

[0095] In specific implementation, the axial force distribution of the pile body is determined according to the pile top load and the calculation methods for the side friction resistance of the branch and disk pile and the bearing capacity of the soil at the branch and disk ends stipulated in the code. The position where the pile top load is completely offset by the side friction resistance of the pile and the bearing capacity of the soil at the branch and disk ends is the bearing surface.

[0096] Through the calculation and analysis of the axial force distribution state of the pile body of the squeezed branch and disk pile in this embodiment, the position of the bearing surface of the branch and disk pile in the soil body is determined, providing the parameters required in the calculation of Step 3.

[0097] In one embodiment, for the above-mentioned Step 2, the side friction resistance of the branch and disk pile is calculated as follows:

[0098]

[0099] wherein, R 1 is the characteristic value of the axial compressive bearing capacity of a single pile provided by the side friction resistance of the pile; u is the perimeter of the pile body; n is the number of soil layers; q ik is the standard value of the side friction resistance between each soil layer corresponding to l i and the pile side; l i is the thickness of the i-th soil layer below the bottom surface of the pile cap or the local scour line. When branches and disks are provided in this soil layer, 1.5 times the height of each branch and disk should be subtracted.

[0100] In one embodiment, for the above-mentioned Step 2, the bearing capacity of the soil at the branch and disk ends of the branch and disk pile is calculated as follows:

[0101]

[0102] wherein, R 2 is the characteristic value of the axial compressive bearing capacity of a single pile provided by the bearing capacity of the soil at the branch and disk ends; m is the total number of branches and disks; A pj is the area of the j-th branch or disk (deducting the area of the main pile); q rj is the characteristic value of the bearing capacity of the soil at the end of the j-th branch or disk; m 0 is the bottom cleaning coefficient; λ is the correction coefficient; f aj is the characteristic value of the bearing capacity of the soil at the branch and disk; k 2 is the depth correction coefficient of the characteristic value of the bearing capacity; γ 2 is the weighted average unit weight of the soil layers above the pile tip, disk tip and branch tip; h j is the buried depth of the branch and disk end.

[0103] In one embodiment, in the above step 3, according to the position of the bearing surface of the squeezed branch pile, the ground settlement amounts caused by the soil deformation above and below the bearing surface are calculated respectively, including: determining the position of the bearing surface according to the calculation, calculating the settlement amount above the bearing surface according to the pile body compression amount, and calculating the settlement amount below the bearing surface according to the soil layer compression amount.

[0104] In this embodiment, as Figure 11 shown, a calculation model for the settlement deformation amount of a single branch pile is established; in the calculation model diagram: L i is the distance from the i-th bearing disk (branch) above the bearing surface to the bearing surface; D is the diameter of the bearing disk (branch); d is the diameter of the main pile; F 0,k is the vertical load borne by the top of the k-th pile, including the self-weight of the embankment fill, the converted load of the road surface, etc.; F i,k is the axial force of the pile body below the i-th bearing disk (branch) of the k-th pile; E sj is the compression modulus of the j-th soil layer below the bearing surface, and the pressure section from the self-weight pressure of the soil to the sum of the self-weight pressure and the additional pressure of the soil should be taken for calculation; m is the number of soil layers divided within the calculation depth of the foundation deformation; n is the number of bearing disks (branches) above the bearing surface; z j 、z j-1 are the distances from the bearing surface to the bottom surfaces of the j-th soil layer and the j-1-th soil layer below; is the internal friction angle of the soil layer where the i-th bearing disk (branch) of the k-th pile is located; since there are many parameters involved in the calculation process of the settlement deformation amount of the branch pile, and the relationships between the various parameters affect each other, the calculation model diagram can better identify the relationships between the various parameters, and at the same time make the calculation process clearer.

[0105] In specific implementation, taking the bearing surface as the demarcation line, the soil settlement amount within the range above the bearing surface is indirectly obtained by calculating the pile body compression amount, and the pile body compression amount is calculated according to the pile body axial force distribution obtained in step 2; the soil settlement amount within the range below the bearing surface is the sum of the soil layer compression amounts, and the one-way compression layer summation method is used for calculation; in addition to this pile, the influence of adjacent piles on the settlement calculation point should be considered.

[0106] In this embodiment, according to the force characteristics of the branch pile embankment reinforcement structure, taking the bearing surface as the demarcation line, different methods are used to calculate the foundation settlement amount.

[0107] In one embodiment, in the above step 3, the soil settlement amount within the range above the bearing surface is calculated through the following method:

[0108]

[0109] Among them, s 上 is the final ground settlement amount caused by the soil deformation within the range above the bearing surface; L 0$L$ is the bearing length of the squeezed branch pile; $EA$ is the axial compression stiffness of the pile body of the squeezed branch pile; $F(x)$ is the axial force distribution along the pile body, which should be calculated according to the soil layer characteristics, the size, spacing and quantity of the branch plates.

[0110] In this embodiment, $F(x)$ is the axial force distribution along the pile body, which is obtained according to Step 2.

[0111] In one embodiment, in the above Step 3, the soil settlement amount within the range below the bearing surface is calculated in the following manner:

[0112]

[0113] Among them, $s$ 下 is the final ground settlement amount caused by the soil deformation within the range below the bearing surface; $\psi$ c is the empirical coefficient for calculating the pile foundation settlement, and each region should determine it according to the statistical comparison of local engineering measured data; $l$ is the number of adjacent piles (including this pile) that have an impact on the foundation settlement calculation point; $m$ is the number of soil layers divided within the range of the foundation deformation calculation depth; $n$ is the number of bearing plates (branches) above the bearing surface; $p$ i,k is the additional pressure at the bearing surface of the $i$-th bearing plate (branch) of the $k$-th pile near the foundation settlement calculation point; $E$ sj is the compression modulus of the $j$-th soil layer below the bearing surface, and the pressure section from the self-weight pressure of the soil to the sum of the self-weight pressure and the additional pressure of the soil should be taken for calculation; $z$ j ,$z$ j-1 is the distance from the bearing surface to the bottom surface of the $j$-th soil layer and the $(j - 1)$-th soil layer below; is the average additional stress coefficient within the range from the foundation settlement calculation point on the bearing surface caused by the $k$-th pile to the bottom surface of the $j$-th soil layer and the $(j - 1)$-th soil layer.

[0114] In this embodiment, $p$ i,k is the additional pressure at the bearing surface of the $i$-th bearing plate (branch) of the $k$-th pile near the foundation settlement calculation point. The additional pressure on the bearing surface is a hollow circular ring area and is calculated in the following manner; when the pile tip of the branch pile is stressed, the bearing surface should be selected at the bottom surface of the pile tip, and the additional pressure transmitted from the pile tip to the bearing surface should be considered.

[0115]

[0116] Among them, $p$ i,k is the additional pressure at the bearing surface of the $i$-th bearing plate (branch) of the $k$-th pile near the foundation settlement calculation point; $F$ i,k is the axial force of the pile body below the $i$-th bearing plate (branch) of the $k$-th pile; $D$ is the diameter of the bearing plate (branch); $d$ is the diameter of the main pile; is the internal friction angle of the soil layer where the $i$-th bearing plate (branch) of the $k$-th pile is located.

[0117] In this embodiment, is the average additional stress coefficient within the range from the foundation settlement calculation point caused by the k-th pile to the bottom surfaces of the j-th layer and the (j - 1)-th layer of soil, and is adopted according to the average additional stress coefficients of internal points and external points under a uniformly distributed circular ring load surface. It can be indirectly obtained based on a similar corner point method using the average additional stress coefficients of internal points and external points under a uniformly distributed circular load surface, and is calculated through the following method:

[0118]

[0119] Wherein, is the average additional stress coefficient of an external point under a uniformly distributed circular load surface; is the average additional stress coefficient of an internal point under a uniformly distributed circular load surface; θ 0 is the angle between the connecting line of the external point and the tangent point of the circle and the horizontal line; ρ 1 (θ), ρ 2 (θ) is the distance from the external point (pole) to the intersection point of the straight line passing through the external point and the circle, ρ 1 (θ)>ρ 2 (θ); ρ 3 (θ) is the distance from the internal point (pole) to the circle, ρ 1 (θ)>ρ 2 (θ).

[0120] In one embodiment, in the above step four, the final ground settlement deformation amount of the squeezed branch and plate pile embankment reinforcement structure is the sum of the pile body compression amount and the soil layer compression amount, including: the final total ground settlement deformation amount should be the settlement amount calculated within the range above the bearing surface plus the settlement amount calculated within the range below the bearing surface.

[0121] In this embodiment, the final ground settlement amount of the squeezed branch and plate pile embankment reinforcement structure is obtained through step four.

[0122] Specifically, the final ground settlement amount of the squeezed branch and plate pile embankment reinforcement structure is obtained by adding the soil deformation amounts within the ranges above and below the bearing surface.

[0123] This embodiment obtains the final ground settlement amount of the squeezed branch and plate pile embankment reinforcement structure.

[0124] In one embodiment, in the above step four, the final ground settlement deformation amount is calculated through the following method:

[0125] s = s 上 + s 下

[0126] Wherein, s is the final settlement amount of the foundation settlement calculation point; s 上 is the final ground settlement amount caused by the soil deformation within the range above the bearing surface; s下 The final ground settlement caused by the deformation of the soil mass within the range below the bearing surface.

[0127] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A branch pile embankment reinforcement structure suitable for deep soft soil foundation, characterized by: The invention comprises a road surface, embankment filling, geogrid, crushed stone cushion, solidification layer and extruded branch plate piles arranged in sequence from top to bottom. The extruded branch plate piles extend downward into a soft soil foundation. The top of the extruded branch plate piles is embedded in the solidification layer. A load-bearing plate is extruded in the solidification layer at the top of the extruded branch plate piles.

2. The branch pile embankment reinforcement structure suitable for deep soft soil foundation according to claim 1 is characterized in that: The main pile diameter of the extruded branch plate pile is 500 mm to 700 mm, and the pile spacing of the extruded branch plate pile is 2 to 2.5 times the maximum outer diameter of the extruded bearing plate.

3. The branch pile embankment reinforcement structure suitable for deep soft soil foundation according to claim 2 is characterized in that: The solidified layer is thinner at the center of the road and thicker at the toes of the slopes on both sides.

4. The branch pile embankment reinforcement structure suitable for deep soft soil foundation according to claim 3 is characterized in that: The branch plate piles are arranged with branch plate structures along the main piles, and the minimum spacing between adjacent branch plate structures is not less than 8 times the diameter of the main piles.

5. A settlement calculation method for a branch pile embankment reinforcement structure suitable for deep soft soil foundation as claimed in claim 1, characterized in that The following steps are involved:

1. According to the structural form of the branch pile embankment reinforcement structure and the soil characteristics, select the ground settlement calculation point and determine the vertical load on the top of the squeezed branch pile; 2. For the selected ground settlement calculation point, calculate the force-bearing length of the squeezed-branch pile at the settlement calculation point according to the vertical load on the pile top, and determine the bearing surface of the squeezed-branch pile in the soil layer; 3. According to the position of the bearing surface of the squeezed branch pile, the ground settlement caused by the deformation of the soil above and below the bearing surface is calculated respectively. The ground settlement above the bearing surface is calculated according to the compression of the pile body, and the ground settlement below the bearing surface is calculated according to the compression of the soil layer; 4. Calculate the sum of the compression of the pile body and the compression of the soil layer to obtain the final ground settlement deformation of the branch pile embankment reinforcement structure.

6. The settlement calculation method according to claim 5, characterized in that: In the step 1, the ground settlement calculation point is within the control range of the middle settlement of the roadbed or within the control range of the slope sliding stability.

7. The settlement calculation method according to claim 6, characterized in that: In step 2, the bearing surface of the squeezed branch pile in the soil layer is the position where the axial force of the branch pile is 0. The calculation of the axial force of the branch pile takes into account the pile side friction and the bearing capacity provided by the load-bearing branch structure.

8. The settlement calculation method according to claim 7, characterized in that: In step 3, the ground settlement above the supporting surface is calculated by the following formula: Among them, s 上 is the final ground settlement caused by soil deformation above the supporting surface; L0 is the load-bearing length of the squeezed branch pile; EA is the axial compressive stiffness of the squeezed branch pile; F(x) is the axial force distribution along the pile body, which should be calculated based on the soil characteristics, branch size, spacing and number.

9. The settlement calculation method according to claim 8, characterized in that: In step 3, the ground settlement below the supporting surface is calculated by the following formula: Among them, ψ c is the empirical coefficient for pile foundation settlement calculation, which should be determined in each region based on the statistical comparison of local engineering measured data; l is the number of adjacent piles that affect the foundation settlement calculation point; m is the number of soil layers divided within the depth range of foundation deformation calculation; n is the number of bearing plates above the support surface; p i,k is the additional pressure on the bearing surface of the i-th bearing plate of the k-th pile near the foundation settlement calculation point; E sj is the compression modulus of the jth layer of soil below the supporting surface, which should be calculated from the pressure section from the soil's own weight pressure to the sum of the soil's own weight pressure and the additional pressure; j 、z j-1 is the distance from the support surface to the bottom of the jth soil layer and the j-1th soil layer below; It is the average additional stress coefficient in the range from the calculation point of foundation settlement on the supporting surface caused by the kth pile to the bottom surface of the jth layer of soil and the j-1th layer of soil. It is adopted according to the average additional stress coefficient of the internal and external points under the uniformly distributed circular load surface.

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