A forward design method for pile foundation bearing and settlement

Abstract

The present invention discloses a forward design method for pile foundation bearing settlement, comprising: S1, acquiring data; S2, calculating the ultimate bearing capacity P; S3, calculating the pile head settlement S Lm ; S4, calculate the ultimate pile head load F p The ultimate pile head settlement S P ; S5. Improve the pile foundation design. The pile foundation bearing and settlement calculation method of the present invention takes the layer-by-layer development of the pile foundation side friction resistance as the theoretical basis, comprehensively considers the coordinated relationship between the bearing capacity and deformation, calculates the pile foundation load-displacement curve to evaluate the bearing and settlement, and overcomes the limitation of the traditional method of calculating the bearing capacity and settlement separately. The method is simple, easy, time-saving and efficient. The obtained pile foundation load-settlement curve can be used for the bearing capacity control and settlement control of the pile foundation project. The calculation is more accurate, which solves the problem of pile foundation design margin redundancy to a certain extent, and can be widely used in the field of pile foundation design in my country.

Description

Technical Field

[0001] The present invention relates to the research field of pile foundation bearing deformation calculation, and in particular to a pile foundation bearing settlement forward design method. Background Art

[0002] Pile foundation is one of the most widely used foundation forms in the field of engineering construction. With the improvement of engineering construction standards and the complexity of construction site geology, the buried depth and pile diameter of pile foundations have gradually increased. The evaluation theory of its vertical bearing capacity is relatively simple, and the calculation method is obviously behind engineering construction. At present, pile foundation verification is mainly divided into two design verification contents: vertical bearing capacity verification and settlement calculation. The vertical bearing capacity is usually calculated by the pile foundation side friction resistance + end resistance method, while the settlement is usually calculated by the layered summation method. The two are independent of each other. The pile foundation design is essentially to verify whether the settlement of the pile head under the ultimate load and working load meets the construction requirements. The drawbacks of the existing methods result in a large design margin. In engineering, there is an urgent need for a pile foundation design method that can quickly and reasonably calculate the relationship between pile foundation load and settlement to verify bearing and settlement. Summary of the invention

[0003] In order to solve the problems of the prior art, the present invention provides a forward design method for pile foundation bearing and settlement.

[0004] To this end, the present invention adopts the following technical solutions:

[0005] A forward design method for pile foundation bearing settlement comprises the following steps:

[0006] S1, get data:

[0007] According to the pile foundation design, the pile foundation data required for the pile foundation design are extracted from the survey report. The pile foundation data include the pile foundation length L and pile foundation radius R, pile foundation unit side friction resistance, pile foundation unit end resistance q t , compression modulus E at the pile bottom s , the number of main reinforcements N of the pile foundation, the diameter d of the main reinforcement of the pile foundation and the concrete material of the pile foundation; using the buried depth spacing Δh to divide the pile length of the pile foundation into I pile nodes, L = (I-1) × Δh; i is used as the number of the pile node, i∈[1,I]; for each of the pile nodes, the corresponding pile foundation unit side friction f is extracted from the pile foundation data si ;

[0008] S2, calculate the ultimate bearing capacity P:

[0009]

[0010] Wherein, A is the cross-sectional area of ​​the pile foundation;

[0011] S3, calculate the pile head settlement S Lm, including the following steps:

[0012] S31, according to the load length l of each pile node i Calculate all pile head loads F Ti , get the pile head load data set;

[0013] Where t = l i / Δh; the load length l i is the distance from the ith pile node to the top of the pile foundation;

[0014] S32, extract M pile head loads from the pile head load data set and record them as F Tm , and then determine F Tm The corresponding load length l m , m is the number of the pile head load; m∈[1,M];

[0015] S33, calculate the compression modulus E of the pile foundation c ,

[0016]

[0017] Among them, E1 is the elastic modulus of the steel bar, A1 is the cross-sectional area of ​​the steel bar, E2 is the compression modulus of concrete, and A2 is the cross-sectional area of ​​concrete;

[0018] S34, use the load length l determined by S32 m Calculate the pile head settlement S caused by the pile head load Lm ;

[0019]

[0020] S4, calculate the ultimate pile head load F p The ultimate pile head settlement S p :

[0021]

[0022] Among them, F p =P, α = Q / P, β is the average additional stress coefficient; Ψ s is the pile bottom settlement correction coefficient, through E s OK, I s is the stress influence coefficient of pile side friction, I p is the stress influence coefficient of the bottom resistance, the I s and I p It is determined by the ratio of the pile radius R to the pile length L and the Poisson's ratio of the soil at the bottom of the pile; Q is the ultimate pile end resistance, Q = A·q t ;

[0023] S5, Improve pile foundation design:

[0024] The pile head settlement S obtained using S3 Lm The ultimate pile head settlement S obtained by S4 p Draw the load-settlement curve of the pile foundation, determine the working load settlement of the pile foundation in the curve through the pile foundation working load in the pile foundation design, and compare it with the settlement requirements in the design specifications. If it meets the requirements, output the pile foundation design. If not, modify the pile foundation design until the settlement requirements are met.

[0025] Preferably, Δh in S1=0.1 m.

[0026] Preferably, M≥2 in S32.

[0027] Stress influence coefficient I of pile side friction in S4 s Determined by the following formula:

[0028]

[0029] Where n = R / L, C = (n 2 +1) 0.5 , B=(n 2 +4) 0.5 , v is the Poisson's ratio of the soil at the pile base.

[0030] Stress influence coefficient I of bottom resistance in S4 p Determined by the following formula:

[0031]

[0032] The pile foundation bearing settlement calculation method of the present invention takes the pile foundation side friction resistance exerted layer by layer as the theoretical basis, comprehensively considers the coordination relationship between bearing capacity exertion and deformation, and calculates the pile foundation load displacement curve to evaluate the bearing settlement. Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The method of the present invention is based on the layer-by-layer development of the lateral friction resistance of the pile foundation, establishes the correlation between the load and settlement at the pile head, and directly calculates the load-settlement curve required for the pile foundation design, overcoming the limitation of the traditional method of calculating the bearing capacity and settlement separately;

[0034] 2. The method of the present invention is simple, easy, time-saving and efficient. The obtained pile foundation load-settlement curve can be used for the bearing capacity control and settlement control of pile foundation engineering. The calculation is more accurate, which solves the problem of pile foundation design margin redundancy to a certain extent and can be widely used in the field of pile foundation design in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the forward design method for pile foundation bearing and settlement of the present invention;

[0036] Figure 2 is a distribution diagram of unit lateral friction of pile foundation in an embodiment of the present invention;

[0037] Figure 3 is a diagram of the ultimate lateral friction of pile foundation at different depths in an embodiment of the present invention;

[0038] Figure 4 is a curve diagram showing the relationship between the compression modulus at the pile bottom and the pile bottom settlement correction coefficient in an embodiment of the present invention;

[0039] Figure 5 3 is a pile foundation load-settlement curve diagram obtained in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0041] The method of the present invention is used to calculate the pile foundation bearing settlement of a pile foundation project. The method is applicable to any stratum. The site in the following embodiment is a thick Quaternary stratum, the landform type is mainly a tidal flat landform, with the characteristics of alternating marine and terrestrial deposition, and the lithology is mainly composed of silty clay and silt, and the distribution is relatively stable.

[0042] See also Figure 1 The method for calculating the bearing settlement of the pile foundation of the above site includes the following steps:

[0043] S1, get data:

[0044] According to the preliminary pile foundation design, the pile foundation data required for the pile foundation design are extracted from the survey report. The pile foundation data include the pile foundation length L and pile foundation radius R, pile foundation unit side friction resistance, pile foundation unit end resistance q t , compression modulus E s , the number of main reinforcement N of the pile foundation, the diameter d of the main reinforcement of the pile foundation and the concrete material of the pile foundation. Use the buried depth spacing Δh to divide the pile length into I pile nodes, then L = (I-1) × Δh; i is used as the number of the pile node, i∈[1,I]; for each pile node, extract the corresponding pile foundation unit side friction f from the pile foundation data si .

[0045] In one embodiment of the present invention, the pile length L is 47.9m, the pile radius R is 0.5m, the pile concrete is C40 concrete, there are 16 main reinforcement bars (N=16) with a diameter of d=25mm, and Δh=0.1m. Extract the unit lateral friction f of the pile within the pile length range si , unit end resistance at the pile bottom q t and the compression modulus E at the pile bottom s The unit lateral friction of the entire pile foundation is Figure 2 The unit side friction resistance data within the burial depth of 0 to 6 m are shown in Table 1; the unit end resistance of the pile foundation at 47.9 m is q t is 2000kPa, and the compression modulus E at the bottom of the pile s It is 28.68MPa.

[0046] Table 1

[0047]

[0048] S2, calculate the ultimate bearing capacity P:

[0049] First, calculate the ultimate side friction resistance F and ultimate pile end resistance Q of the pile foundation:

[0050]

[0051] Q=A·q t ;

[0052] Where A is the cross-sectional area of ​​the pile foundation;

[0053] Then calculate the ultimate bearing capacity P:

[0054] P=F+Q.

[0055] In the above embodiment: F = 2 × 3.14 × 0.5 × 0.1 × 17248.41 = 5416.00 kN;

[0056] Q=3.14×0.5 2 ×2000=1570.00kN; P=6986kN.

[0057] S3, calculate the pile head settlement S Lm , including the following steps:

[0058] S31, according to the load length l of each pile node i Calculate the pile head load F at all pile shaft nodes Ti , and obtain the pile head load data set. The load length l i For this reason, the distance from the pile shaft node to the top of the pile foundation, the pile head load F Ti The calculation formula is as follows:

[0059]

[0060] Where t = l i / Δh;

[0061] S32, extract M pile head loads from the pile head load data set, denoted as F Tm , and determine the corresponding load length l m, m is the number of the pile head load; m∈[1,M]; M≥2;

[0062] S33, calculate the compression modulus E of the pile foundation c ,

[0063]

[0064] Among them, E1 is the elastic modulus of the steel bar, A1 is the cross-sectional area of ​​the steel bar, E2 is the compression modulus of concrete, and A2 is the cross-sectional area of ​​concrete;

[0065] S34, calculate the pile head settlement S caused by the pile head load using the load length determined in S32 Lm ;

[0066]

[0067] In the above embodiment, the pile head load data set obtained in step S31 is used to draw a relationship diagram between the pile head load and the load length, such as Figure 3 In this embodiment, M=2, the pile head loads are taken as 2400 kN and 4800 kN respectively, and the corresponding load length is obtained.

[0068] Then calculate step S33, the elastic modulus of the steel bar E1 = 211GPa, the cross-sectional area of ​​the steel bar The compression modulus of C40 concrete is E2 = 32.5 GPa, and the cross-sectional area of ​​concrete is A2 = A-A1 = 0.77715 m 2 .

[0069] In addition, if C30 concrete is used for the pile foundation, the compression modulus of C30 concrete is E2 = 30 GPa.

[0070] Calculating the compression modulus of pile foundation

[0071] It can be obtained that the pile head settlement generated when the pile head load is 2400kN is 0.001587m. According to the above calculation steps, the pile head settlement generated when the pile head load is 4800kN is 0.004155m.

[0072] S4, calculate the ultimate pile head load F p The ultimate pile head settlement S p , including the following steps:

[0073] S41, calculate the stress influence coefficient I of the pile side friction resistance s :

[0074]

[0075] Where n = R / L, C = (n2 +1) 0.5 , B=(n 2 +4) 0.5 , v is the Poisson's ratio of the soil at the pile base,

[0076] S42, calculate the stress influence coefficient I of the bottom resistance p :

[0077]

[0078] S43, calculate the ultimate pile head settlement S p :

[0079]

[0080] Among them, F p =P, α = Q / P, β is the average additional stress coefficient; Ψ s is the pile bottom settlement correction factor, which is determined by the compression modulus at the pile bottom.

[0081] S5, Improve pile foundation design:

[0082] The pile head settlement S obtained using S3 Lm The ultimate pile head settlement S obtained by S4 p Draw the load-settlement curve of the pile foundation, determine the working load settlement of the pile foundation in the curve through the pile foundation working load in the pile foundation design, and compare it with the settlement requirements in the design specifications. If it meets the requirements, output the pile foundation design. If not, modify the pile foundation design until the settlement requirements are met.

[0083] In the above embodiment,

[0084] n=0.01099, v=0.38, α=0.2247, B=2.00003, C=1.0006, Ψ s =0.65,

[0085] Ψ s By consulting Figure 4 The relationship between the compression modulus at the pile bottom and the pile bottom settlement correction coefficient is obtained.

[0086] I s =25.6458,I p =0.1078;

[0087]

[0088] S P =0.009516m;

[0089] Draw a curve graph based on the calculated pile head settlement of 0.001587m, 0.004155m and the ultimate pile head settlement of 0.009516m, such as Figure 5 The working load of the pile foundation is 3500kN. Figure 5 The corresponding settlement intercepted on the curve is 0.0026m, which meets the settlement requirement of no more than 0.015m. Figure 5 The test results of the actual test piles of the pile foundation are also given. The calculated results are in good agreement with the test results, which verifies the accuracy of the design method.

Claims

1. A forward design method for pile foundation bearing settlement, characterized in that: The following steps are involved: S1, get data: According to the pile foundation design, the pile foundation data required for the pile foundation design are extracted from the survey report. The pile foundation data include the pile foundation length L and pile foundation radius R, pile foundation unit side friction resistance, pile foundation unit end resistance q t , compression modulus E at the pile bottom s , the number of main reinforcements N of the pile foundation, the diameter d of the main reinforcement of the pile foundation and the concrete material of the pile foundation; using the buried depth spacing Δh to divide the pile length of the pile foundation into I pile nodes, L = (I-1) × Δh; i is used as the number of the pile node, i∈[1,I]; for each of the pile nodes, the corresponding pile foundation unit side friction f is extracted from the pile foundation data si ; S2, calculate the ultimate bearing capacity P: Wherein, A is the cross-sectional area of ​​the pile foundation; S3, calculate the pile head settlement S Lm , including the following steps: S31, according to the load length l of each pile node i Calculate all pile head loads F Ti , get the pile head load data set; Where t = l i / Δh; the load length l i is the distance from the ith pile node to the top of the pile foundation; S32, extract M pile head loads from the pile head load data set and record them as F Tm , and then determine F Tm The corresponding load length l m , m is the number of the pile head load; m∈[1,M]; S33, calculate the compression modulus E of the pile foundation c , Among them, E1 is the elastic modulus of the steel bar, A1 is the cross-sectional area of ​​the steel bar, E2 is the compression modulus of concrete, and A2 is the cross-sectional area of ​​concrete; S34, use the load length l determined by S32 m Calculate the pile head settlement S caused by the pile head load Lm ; S4, calculate the ultimate pile head load F p The ultimate pile head settlement S p : Among them, F p =P, α = Q / P, β is the average additional stress coefficient; Ψ s is the pile bottom settlement correction coefficient, through E s OK, I s is the stress influence coefficient of pile side friction, I p is the stress influence coefficient of the bottom resistance, the I s and I p It is determined by the ratio of the pile radius R to the pile length L and the Poisson's ratio of the soil at the bottom of the pile; Q is the ultimate pile end resistance, Q = A·q t ; S5, Improve pile foundation design: The pile head settlement S obtained using S3 Lm The ultimate pile head settlement S obtained by S4 p Draw the load-settlement curve of the pile foundation, determine the working load settlement of the pile foundation in the curve through the pile foundation working load in the pile foundation design, and compare it with the settlement requirements in the design specifications. If it meets the requirements, output the pile foundation design. If not, modify the pile foundation design until the settlement requirements are met.

2. The forward design method for pile foundation bearing and settlement according to claim 1, characterized in that: Δh in S1 = 0.1 m.

3. The forward design method for pile foundation bearing and settlement according to claim 1 is characterized in that: M≥2 in S32.

4. The forward design method for pile foundation bearing and settlement according to claim 1, characterized in that: Stress influence coefficient I of pile side friction in S4 s Determined by the following formula: Where n = R / L, C = (n 2 +1) 0.5 , B=(n 2 +4) 0.5 , v is the Poisson's ratio of the soil at the pile base.

5. The forward design method for pile foundation bearing and settlement according to claim 4 is characterized in that: Stress influence coefficient I of bottom resistance in S4 p Determined by the following formula:

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