Rail engineering pile board structure roadbed's half steel casing length calculation method

Abstract

The application relates to a method for calculating the length of a semi-steel casing of a rail engineering pile plate structure roadbed, and comprises the following steps: S1, inputting basic parameters; S2, determining the total pile length l, the pile spacing d and the standard value of the pile side friction, if the pile spacing is less than 6 times the pile diameter, executing step S3, if the pile spacing is greater than or equal to 6 times the pile diameter, executing step S4; S3, calculating the group pile effect coefficient eta; S4, determining the correction coefficients zeta, lambda1, lambda, k1 and k2; S5, substituting the obtained data into the semi-steel casing length formula of the pile body; and S6, outputting the result h1. Compared with the prior art, different calculation methods are adopted for single piles or group piles, the length of the steel casing is more accurately determined through analysis of mechanics and group pile effects in the optimal proportion calculation of the semi-steel casing length of the pile body, the material utilization rate is effectively improved, the engineering cost is reduced, and the function of transferring the pile side friction downward during operation is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-speed railway subgrade construction, and particularly relates to a method for calculating the length of a semi-steel casing of a pile-plate structure subgrade for a rail connection project. BACKGROUND

[0002] At present, the composite pile-plate structure, as an economical and reliable pile foundation form, has been widely applied in high-speed railway subgrade projects in China. However, due to the different environments of different railways, corrosion or wear of the pile foundation will occur, which will eventually cause damage to the concrete structure inside the pile foundation and even safety problems. At present, the protection of the pile foundation is mainly through improving the performance of the concrete itself or retaining the steel casing. As for the method of improving the performance of the concrete itself, it will lead to a decrease in economic indicators. As for the method of retaining the steel casing, through the search of Chinese patent CN112211040A, a steel casing reinforced concrete composite pile pile-plate structure and construction method for a rail connection project subgrade, including a reinforced concrete plate, a track structure, a joist and a steel casing reinforced concrete composite pile, the steel casing reinforced concrete composite pile is drilled into the foundation, the top of the steel casing reinforced concrete composite pile is fixedly connected with the joist, which well solves the problem of fast corrosion or wear of the pile foundation. However, this patent does not consider the calculation of the optimal proportion of the length of the semi-steel casing of the pile, the material utilization rate is low, the engineering cost is high, and the pile side friction cannot be transferred downward during operation. SUMMARY

[0003] The present application is to overcome the defects of the prior art and provide a method for calculating the length of a semi-steel casing of a pile-plate structure subgrade for a rail connection project, which determines the length of the semi-steel casing, effectively improves the material utilization rate, reduces the engineering cost, meets the requirements of long-term deformation control near the high-speed railway, and meets the function of transferring the pile side friction downward during operation.

[0004] The object of the present application can be achieved by the following technical solutions:

[0005] A method for calculating the length of a semi-steel casing of a pile-plate structure subgrade for a rail connection project, characterized by comprising the following steps:

[0006] S1 input basic parameters, including: foundation allowable vertical bearing capacity R a , standard value of side friction of each soil layer i of the semi-steel casing section q i1 (kPa), height of each soil layer around the semi-steel casing section l i1 (m), cross-sectional area of the pile end A p (m 2 ), circular area of the variable cross-section at the end of the semi-steel casing A p1 (m 2), the cross-sectional perimeter u (m) of the pile below the semi-steel casing, the cross-sectional perimeter u1 (m) of the pile of the semi-steel casing section, the bottom cleaning coefficient m0, the foundation bearing capacity f of the semi-steel casing section a01 (kPa), the foundation bearing capacity f of the non-semi-steel casing section a0 (kPa), the weighted average coefficient of the bulk density of each soil layer of the semi-steel casing section γ1, and the weighted average coefficient of the bulk density of each soil layer of the non-semi-steel casing section γ2, step S2 is performed;

[0007] S2 determines the standard value of the total pile length l, the pile spacing d and the pile side friction, if the pile spacing is less than 6 times the pile diameter, it is in the form of pile group, step S3 is performed, if the pile spacing is greater than or equal to 6 times the pile diameter, it is in the form of single pile, step S4 is performed;

[0008] S3 calculates the group pile effect coefficient η, step S4 is performed;

[0009] S4 determines the correction coefficients ζ, λ1, λ, k1, k2, step S5 is performed;

[0010] S5 substitutes the obtained data into the formula for calculating the length of the pile occupied by the semi-steel casing, step S6 is performed;

[0011] S6 outputs the result h1.

[0012] Further, the group pile effect coefficient η calculation formula in step S3 is:

[0013]

[0014] Wherein:

[0015] λ is the average reduction coefficient considering the stress superposition of pile group; h is the total pile length (m); m is the number of pile group rows, n is the number of pile group columns; r1 is the longitudinal pile spacing; r2 is the transverse pile spacing; is the weighted average value of the internal friction angle of each soil layer within the pile body embedded depth range.

[0016] Further, in step S3, when the pile spacing is less than 6 times the pile diameter, the influence of the group pile effect is considered, and the foundation allowable vertical bearing capacity R a is corrected, that is, the foundation allowable vertical bearing capacity R a is divided by the group pile effect coefficient η.

[0017] Further, in step S4, the corresponding correction coefficient is queried according to the specification issued in the construction of the engineering roadbed.

[0018] Further, the formula for calculating the length of the pile occupied by the semi-steel casing is:

[0019]

[0020] Wherein, R a is the basic allowable vertical bearing capacity; ζ is the side friction correction coefficient of the steel pipe section (considering the compaction effect of the surrounding soil during the steel pipe driving process, ζ>1); m is the number of soil layers of the half-steel casing section; n is the number of soil layers of the concrete section below the half-steel casing; q i1 is the standard value of the side friction of each soil layer i of the half-steel casing section (kPa); q i is the standard value of the side friction of each soil layer i of the non-half-steel casing section (kPa); l i1 is the height of each soil layer around the half-steel casing section (m); l i is the height of each soil layer around the non-half-steel casing section (m); l is the total pile length (m); u1 is the cross-sectional perimeter of the half-steel casing section (m); u is the cross-sectional perimeter of the pile below the half-steel casing (m); A p is the cross-sectional area of the pile end (m 2 ); A p1 is the circular ring area of the variable cross-section at the end of the half-steel casing (m 2 ); λ1, λ are correction coefficients; m0 is the bottom cleaning coefficient; h is the total pile length (m); f a01 is the foundation bearing capacity of the half-steel casing section (kPa); f a0 is the foundation bearing capacity of the non-half-steel casing section (kPa); k1 is the coefficient of the bearing capacity change with depth of the half-steel casing section; k2 is the coefficient of the bearing capacity change with depth of the non-half-steel casing section; γ1 is the bulk weight weighted average coefficient of each soil layer of the half-steel casing section; γ2 is the bulk weight weighted average coefficient of each soil layer of the non-half-steel casing section.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The present application can obtain the optimal half-steel casing length by judging the size of the pile spacing, calculating the group pile effect coefficient η, effectively improving the material utilization rate, reducing the engineering cost, and meeting the function of downward transfer of the pile side friction during operation.

[0023] 2. The present application proposes a half-steel casing length calculation method for the track engineering pile plate structure roadbed, which can greatly reduce the disturbance of the bored pile construction to the surrounding stratum, meet the strict deformation control requirements of high-speed railway, and effectively control the impact of track engineering construction on the existing high-speed railway line structure and train safety.

[0024] 3. The present application can form a constraint on the core reinforced concrete by calculating the optimal length of the half-steel casing, improve the strength of the reinforced concrete material, improve the plasticity and toughness performance, and delay or prevent the half-steel casing from premature local buckling, thereby ensuring the pile quality. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1This is a flowchart of the method for calculating the length of the semi-steel casing according to the present invention.

[0026] Figure 2 This is a schematic diagram of the cross-sectional structure of the pile-plate structure in this invention.

[0027] Figure 3 This is a schematic diagram of the longitudinal section of the pile-slab structure in this invention;

[0028] Figure 4 It is along Figure 3 Cross-sectional view of line AA in the middle;

[0029] Figure 5 It is along Figure 3 Cross-sectional view of the middle BB line.

[0030] The figure shows: reinforced concrete slab (1), support beam (2), precast semi-steel casing (3), reinforced concrete structural pile (4), spiral stirrup (5), longitudinal reinforcement (6), internal thread of semi-steel casing (7), track structure (8), core reinforced concrete (9), and semi-steel casing reinforced concrete composite pile (10). Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] Example

[0033] like Figure 1 As shown, a method for calculating the length of a semi-steel casing in a roadbed with a pile-slab structure for rail connection projects is characterized by the following steps:

[0034] Input basic parameters for S1, including: allowable vertical bearing capacity of the foundation R. a Standard value of side friction resistance q of each soil layer in the steel casing section i1 (kPa), height of each soil layer around the semi-steel casing section l i1 (m), pile end cross-sectional area A p (m 2 ), the area A of the annular ring at the variable cross-section end of the semi-steel casing p1 (m 2 ), the perimeter of the pile cross-section below the semi-steel casing u (m), the perimeter of the pile cross-section of the semi-steel casing section u1 (m), the bottom cleaning coefficient m0, and the bearing capacity of the foundation of the semi-steel casing section f. a01 (kPa), bearing capacity of the foundation of the non-semi-steel casing section f a0 (kPa), the weighted average coefficient of unit weight of each soil layer in the semi-steel casing section γ1, the weighted average coefficient of unit weight of each soil layer in the non-semi-steel casing section γ2, and execute step S2;

[0035] S2 determines the standard values ​​of total pile length l, pile spacing d, and pile side friction. If the pile spacing is less than 6 times the pile diameter, it is a group pile form, and step S3 is executed. If the pile spacing is greater than or equal to 6 times the pile diameter, it is a single pile form, and step S4 is executed.

[0036] S3 calculates the group pile effect coefficient η, and then proceeds to step S4;

[0037] S4 determines the correction coefficients ζ, λ1, λ, k1, and k2, and then proceeds to step S5;

[0038] S5 Substitute the obtained data into the formula for the length of the pile body occupied by the semi-steel casing, and execute step S6;

[0039] S6 outputs result h1.

[0040] like Figure 2 As shown, this embodiment provides a semi-steel casing reinforced concrete composite pile-slab structure for roadbed connection engineering, including determining the length of the pile body occupied by the semi-steel casing, prefabricating the semi-steel casing (3), reinforced concrete structural pile (4), support beam (2) and reinforced concrete slab (1), the support beam (2) is set below the reinforced concrete slab (1) and fixed or overlapped with it, the top of the semi-steel casing (3) and the reinforced concrete structural pile (4) are fixedly connected to the bottom of the support beam (2), and after the installation of the semi-steel casing (3) is completed, the reinforced concrete structural pile (4) is poured inside it.

[0041] Specifically, the semi-steel casing reinforced concrete composite pile (5) includes a semi-steel casing (3) and a reinforced concrete structural pile (4); the tops of both the semi-steel casing (3) and the reinforced concrete structural pile (4) are fixedly connected to the support beam (2). The semi-steel casing (3) is fitted onto the outside of the reinforced concrete structural pile (4) and forms a clearance fit. That is, the outer diameter of the semi-steel casing is slightly larger than the diameter of the hole formed during pile foundation construction. The length of the semi-steel casing (3) is less than the length of the reinforced concrete structural pile (4). This constitutes two parts: a semi-steel casing that is drilled into the shallower foundation and a reinforced concrete structural pile that is located in the deeper foundation. The semi-steel casing (3) is a segmented splicing structure along its axial direction, that is, a segmented prefabricated assembly structure.

[0042] Specifically, the semi-steel casing cast-in-place pile (10) comprises two parts: a semi-steel casing (3) that is drilled into the foundation at a shallow depth and a reinforced concrete structural pile (4) that is located in the foundation at a deeper depth. On the one hand, the precast semi-steel casing (3) can significantly reduce the disturbance of the surrounding strata caused by the construction of the reinforced concrete structural pile (4); on the other hand, the semi-steel casing (3) provides a restraining effect on its core reinforced concrete (9), thereby improving the strength, plasticity, and toughness of the reinforced concrete (9); the presence of the reinforced concrete (9) can delay or prevent premature local buckling of the semi-steel casing (3).

[0043] Specifically, the outer diameter of the prefabricated semi-steel casing (3) is slightly larger than the diameter of the reinforced concrete structural pile (4), forming a clearance fit structure; the semi-steel casing (3) is prefabricated in sections and assembled, the first section of the semi-steel casing (3) has a sharp corner shape to facilitate the rotation of the semi-steel casing (3), and the thickness of the semi-steel casing (3) is usually 12-25mm; the inside of the semi-steel casing (3) is a threaded structure (7) or a built-in shear ring.

[0044] Specifically, during construction, the prefabricated semi-steel casing (3) is first drilled to form a barrier structure, and then drilling, soil removal, steel reinforcement cage placement, and concrete pouring (9) are carried out inside the semi-steel casing (3) to form the semi-steel casing reinforced concrete composite pile (10).

[0045] Specifically, the steel reinforcement cage in the reinforced concrete structural pile (4) includes spiral stirrups (5) and longitudinal reinforcement (6), which are pre-welded or tied.

[0046] Specifically, the determination of the length of the semi-steel casing in the pile body is calculated according to the following formula:

[0047]

[0048] In the formula:

[0049] R a — Allowable vertical bearing capacity of foundation;

[0050] ζ— Steel pipe segment side friction correction coefficient (considering the compaction effect of the surrounding soil during the steel pipe driving process, ζ>1); m— Number of soil layers of semi-steel casing segment;

[0051] n— Number of concrete segments below the semi-steel casing;

[0052] q i1 — Standard value of side friction of each soil layer i of semi-steel casing segment (kPa);

[0053] q i — Standard value of side friction of each soil layer i of non-semi-steel casing segment (kPa);

[0054] l i1 — Height of each soil layer around the semi-steel casing segment (m);

[0055] l i — Height of each soil layer around the non-semi-steel casing segment (m);

[0056] l— Total pile length (m);

[0057] u1— Pile cross-sectional circumference of semi-steel casing segment (m);

[0058] u— Pile cross-sectional circumference below the semi-steel casing (m);

[0059] Ap —Pile tip cross-sectional area (m 2 );

[0060] A p1 —Half-steel casing end variable cross-section circular ring area (m 2 );

[0061] λ1, λ—Correction coefficient;

[0062] m0—Clear bottom coefficient;

[0063] h—Total pile length (m);

[0064] f a01 —Half-steel casing segment foundation bearing capacity (kPa);

[0065] f a0 —Non-half-steel casing segment foundation bearing capacity (kPa);

[0066] k1—Half-steel casing segment bearing capacity changes with depth coefficient;

[0067] k2—Non-steel casing segment bearing capacity changes with depth coefficient;

[0068] γ1—Half-steel casing segment each soil layer bulk density weighted average coefficient;

[0069] γ2—Non-half-steel casing segment each soil layer bulk density weighted average coefficient.

[0070] Specifically, when the pile spacing is less than 6 times the pile diameter, the group pile effect is considered, and the allowable vertical bearing capacity R a should be divided by the group pile effect coefficient η, and the calculation formula is:

[0071]

[0072] Where:

[0073] In the formula:

[0074] h—Pile length;

[0075] m, n—Group pile row and column number;

[0076] r1—Longitudinal pile spacing;

[0077] r2—Lateral pile spacing.

[0078] —The weighted average value of the internal friction angle of each soil layer within the range of pile body depth.

[0079] A calculation example of the length of the half-steel casing occupied by the pile body is given below:

[0080] The single pile allowable bearing capacity of the semi-steel casing reinforced concrete composite pile is 3000 kN, the steel casing wall thickness is 20 mm, the pile body is poured with C35 reinforced concrete, the pile diameter is 1.0 m, the rectangular arrangement is adopted, the transverse pile spacing is 4.0 m, the longitudinal pile spacing is 5.0 m, and the pile length is 35 m. The raft is made of C50 reinforced concrete, the width is 7.1 m, and the thickness is 1.0 m. Taking the stratum conditions of a typical section of a certain project as an example, the “Code for Design of Foundation and Foundation of Railway Bridges and Culverts” TB 10093-2017 is consulted, a construction area with a length of 50 m is selected, the semi-steel casing reinforced concrete composite pile is arranged in 10 rows and 2 columns, and the stratum conditions of the steel casing reinforced concrete composite pile are shown in Table 1:

[0081] Table 1 Ground soil layer parameters

[0082]

[0083] Further, considering that the pile spacing of the semi-steel casing reinforced concrete composite pile is less than 6 times the pile diameter, the group pile effect coefficient is first calculated:

[0084] Weighted average value of internal friction angle of each soil layer in the range of pile body embedded depth

[0085]

[0086]

[0087]

[0088]

[0089] h is the total pile length (m); m is the number of group pile rows, n is the number of group pile columns; r1 is the longitudinal pile spacing; r2 is the transverse pile spacing; is the weighted average value of the internal friction angle of each soil layer in the range of the pile body embedded depth. Therefore, the actual calculation vertical allowable bearing capacity R of the group pile foundation in the 50 m construction area is a = 3140 kN

[0090] Further, in this embodiment, the compaction effect of the steel pipe on the surrounding soil during the steel pipe driving process is considered, the steel pipe segment side friction resistance correction coefficient ζ = 1.5; the soil condition is good, not easy to collapse and good clear bottom, the clear bottom coefficient m0 = 0.5 is selected, and the correction coefficients λ1, λ in this example are all 1. Assuming that the semi-steel casing penetrates 2 layers and 3 layers of soil, respectively, the relevant parameters are substituted into the following formula for calculation.

[0091]

[0092] The steel casing length calculation results are shown in Table 2:

[0093] Table 2 Trial results

[0094] Steel casing end penetration depth range Results 9.04m ~ 17.19m 40.31m 17.19m ~ 29.53m 26.75m

[0095] Further, according to whether the calculation result accords with the soil depth range, the pile length occupied by the semi-steel casing is set as 27 m.

[0096] The preferred embodiments of the present application are described in detail above. It should be understood that those of ordinary skill in the art can make modifications and variations without departing from the concept of the present application. Therefore, the technical solutions obtained by logical analysis, reasoning or limited experiments based on the prior art according to the concept of the present application should be within the protection scope defined by the claims.

Claims

1. A method for calculating the length of a semi-steel casing for a rail-engineered pile-slab structure roadbed, characterized in that, Comprise the following steps: S1 obtains the basic parameters in the pile-slab structure of the semi-steel casing reinforced concrete composite pile, and executes step S2; S2 Determine the total pile length Pile spacing Determine the pile spacing based on the standard value of pile side friction. Has the preset value been reached? If yes, proceed to step S4; otherwise, proceed to step S3. Wherein, the preset value of pile spacing is 6 times of pile diameter; S3 calculating group pile effect coefficient performing step S4; When the pile spacing is less than 6 times the pile diameter, the influence of pile group effect is considered to determine the allowable vertical bearing capacity of the foundation The allowable vertical bearing capacity of the foundation is modified, i.e. Divided by the pile group effect coefficient ; S4 determining a correction coefficient of side friction of the steel pipe section Zeta , the correction coefficient and , a coefficient of the bearing capacity of the semi-steel casing section varying with depth , a coefficient of the bearing capacity of the non-semi-steel casing section varying with depth , executing step S5; S5 substitutes the coefficient values determined in step S4 into the formula of the length of the pile body occupied by the semi-steel casing, and executes step S6; The formula for calculating the length of the pile body occupied by the semi-steel casing is: in, Based on the allowable vertical bearing capacity; Zeta This is the correction factor for the side friction resistance of the steel pipe section; This refers to the number of soil layers in the semi-steel casing section; This refers to the number of soil layers in the concrete section below the semi-steel casing. For each soil layer of the semi-steel casing section Standard value of side friction resistance; For each soil layer of the non-semi-steel casing section i Standard value of side friction resistance; The height of each soil layer around the semi-steel casing section; The height of each soil layer around the non-semi-steel casing section; Total pile length; The perimeter of the cross-section of the semi-steel casing section of the pile; The perimeter of the pile cross-section below the semi-steel casing; The cross-sectional area of ​​the pile tip; The area of ​​the annulus at the variable cross-section end of the semi-steel casing; , This is a correction factor; This is the bottom-clearing coefficient; The bearing capacity of the foundation for the semi-steel casing section; The bearing capacity of the foundation for the non-semi-steel casing section; This is the coefficient representing the variation of the bearing capacity of the semi-steel casing section with depth; This is the coefficient representing the variation of the bearing capacity of the non-semi-steel casing section with depth; This is the weighted average coefficient of the unit weight of each soil layer in the semi-steel casing section; This is the weighted average coefficient of the unit weight of each soil layer in the non-semi-steel casing section; S6 output result .

2. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 1, characterized in that, The basic parameters in the step S1 include: basic allowable vertical bearing capacity , each soil layer of the semi-steel casing section , side friction standard value , height of each soil layer around the semi-steel casing section , pile end section area , circular ring area at the variable cross-section of the semi-steel casing end , cross-sectional perimeter of the pile below the semi-steel casing , cross-sectional perimeter of the pile of the semi-steel casing section , bottom cleaning coefficient , foundation bearing capacity of the semi-steel casing section , foundation bearing capacity of the non-semi-steel casing section , bulk weight weighted average coefficient of each soil layer of the semi-steel casing section , bulk weight weighted average coefficient of each soil layer of the non-semi-steel casing section .

3. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 1, characterized in that, The standard value of the pile side friction resistance in step S2 is selected according to the properties of different soil layers and relevant specifications.

4. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 1, characterized in that, The group pile effect coefficient in step S3 The calculation formula is: wherein: , , to consider the average reduction coefficient of stress superposition of group piles; to the total pile length; to the number of rows of group piles, to the number of columns of group piles; to the longitudinal pile spacing; to the transverse pile spacing; to the weighted average value of the internal friction angle of each soil layer within the pile body embedded depth range.

5. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 1, characterized in that, The corresponding correction coefficient is queried according to the specifications issued in the engineering roadbed construction in step S4.

6. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 3, characterized in that, The side friction correction coefficient Zeta The confidential effect of the steel pipe driving process on the surrounding soil is considered, Zeta 1.

7. The method for calculating the length of the semi-steel casing of the rail engineering pile slab structure roadbed according to claim 1, characterized in that, The pile-slab structure of the semi-steel casing reinforced concrete composite pile in step S1 comprises: a reinforced concrete slab, a semi-steel casing above the reinforced concrete slab and a reinforced concrete structure pile, a joist below the reinforced concrete slab, the top of the semi-steel casing and the reinforced concrete structure pile are fixedly connected with the joist, and the semi-steel casing is sleeved outside the reinforced concrete structure pile.

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