Method for calculating vertical bearing capacity of structural steel pile in sandy soil field

Abstract

The invention discloses a method for calculating the vertical bearing capacity of a steel pile in a sandy soil field, which is used for calculating numerical simulation on the vertical bearing capacity of the steel pile in the sandy soil field under the conditions of different pile lengths, cross section areas, cross section shapes and sandy soil compactness on the basis of numerical simulation and field load test results. The vertical bearing capacity of the section steel pile under the conditions of different section steel pile lengths, cross section areas, cross section shapes and sand compactness is obtained, and the pile side friction resistance and the pile end resistance are corrected according to the obtained vertical bearing capacity of the section steel pile; and according to the corrected pile side friction resistance and pile end resistance, the vertical compression resistance and pulling resistance ultimate bearing capacity of the steel pile in the sandy soil site is calculated. According to the method, the defects in the prior art are overcome, and the accuracy and applicability of calculating the vertical bearing capacity of the steel pile in the sandy soil site are high.

Description

Technical Field

[0001] The invention relates to the field of civil engineering, and in particular to a method for calculating the vertical bearing capacity of steel piles in a sandy soil site. Background Art

[0002] At present, the pile types with mature pile foundation design theory and specifications in China mainly include traditional pile types such as precast concrete piles, mud wall drilled (punched) piles, dry operation bored piles, steel pipe piles, and rock-embedded piles. However, the design theory of steel piles mainly refers to conventional steel piles and adopts a semi-empirical and semi-theoretical method, resulting in inaccurate estimation of steel material budgets in the early stages of a large number of projects.

[0003] Nowadays, in civil engineering, steel piles are an important foundation form, and the accurate calculation of their vertical bearing capacity is crucial to the safety and economy of the project. The stress behavior of steel piles in sandy soil sites is relatively complex due to the friction characteristics between particles and the relatively loose structure.

[0004] At present, the calculation methods of the vertical bearing capacity of pile foundations in the domestic pile foundation design specification "Technical Specifications for Building Pile Foundations" (JGJ94-2016) can be divided into two types: in-situ test method and empirical parameter method. The in-situ test method is to determine the relevant geological parameters based on in-situ exploration data such as static penetration, select coefficients according to the specification, and then determine the standard value of the vertical ultimate bearing capacity of a single pile; while the empirical parameter method is to estimate the standard value of the vertical ultimate bearing capacity of a single pile based on the relevant parameter value table in the specification in the absence of relevant static penetration data. The existing calculation methods often find it difficult to fully consider the nonlinear characteristics of sand and the geometric characteristics of steel piles, resulting in deviations in the calculation results. Summary of the invention

[0005] The present invention provides a method for calculating the vertical bearing capacity of steel piles in sandy soil sites, which supplements and improves the method for calculating the ultimate bearing capacity of steel pile foundations in sandy soil sites under vertical loads that is not involved in the prior art, thereby having high accuracy and applicability in calculating the vertical bearing capacity of steel piles in sandy soil sites.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for calculating the vertical bearing capacity of steel piles in a sandy soil field comprises the following steps:

[0008] Step S1: Exploring and testing the sandy soil site to measure the density, internal friction angle, and cohesion parameters of the sandy soil; determining the pile length, cross-sectional area, and cross-sectional shape parameters of different steel piles;

[0009] Step S2: Based on the physical and mechanical properties of sand and the geometric properties of steel piles, a mechanical model of steel piles in sandy soil is established;

[0010] Step S3: Based on the mechanical model, numerical simulation analysis is performed on the influence of the parameter changes of different steel pile lengths, cross-sectional areas, cross-sectional shapes of the steel piles and sand density on the vertical bearing characteristics of the steel piles, so as to obtain the vertical bearing capacity of the steel piles in the sand field under the conditions of different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density;

[0011] Step S4: According to the vertical bearing capacity of the steel piles in the sandy soil field under the conditions of different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density obtained in step S3, calculate the influence coefficient λ1 of the steel pile length, the influence coefficient λ2 of the cross-sectional area, the influence coefficients λ3 and λ4 of the sand density, and the cross-sectional shape parameter λ s1 and λ s2 ;

[0012] Step S5: According to the correction coefficients λ1, λ2, λ3, λ4, λ s1 and λ s2 The side friction and end resistance of steel piles are modified, and a calculation formula for the vertical bearing capacity of steel piles in sandy soil sites is derived.

[0013] Preferably, in step S4, under conditions of different steel pile lengths, the pile body side friction resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile body side friction resistance obtained by theoretical calculation, and based on the comparison result, a correction coefficient λ1 of the pile body friction resistance under the condition of varying steel pile lengths in sandy soil sites is obtained.

[0014] Preferably, in step S4, under conditions of different cross-sectional areas of steel piles, the pile end resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile end resistance obtained by theoretical calculation, and based on the comparison result, a correction coefficient λ2 of the pile body friction resistance under the condition of varying pile length of steel piles in sandy soil sites is obtained.

[0015] Preferably, in step S4, under conditions of different sand densities, a standard penetration test is carried out on sand of each density, a relationship model between the standard penetration number N and the sand density ρ is established, and the density ρ is changed to obtain soil bodies with different densities, so as to obtain the pile body friction resistance and pile end resistance of piles in sands with different densities; according to the ratio of the measured values ​​to the predicted values ​​of the pile body friction resistance and pile end resistance under different densities, the pile body friction resistance correction coefficient λ3 and the pile end resistance correction coefficient λ4 under the condition of changing density of the sand site are obtained.

[0016] Preferably, in step S4, under different cross-sectional shapes of steel piles, the pile side friction resistance value and pile end resistance value of the vertical ultimate bearing capacity obtained by numerical simulation in step S3 are compared to obtain the pile body friction resistance correction coefficient λ under the condition of changing cross-sectional shapes of steel piles.s1 and pile tip resistance correction factor λ s2 .

[0017] Preferably, in step S4, for the correction coefficients of the length, cross-sectional area, cross-sectional shape and sand density of the steel pile for which no numerical simulation is performed, linear interpolation calculation is performed based on the obtained correction coefficients of the pile side friction and pile end resistance.

[0018] Preferably, in step S5, the calculation formula for the vertical bearing capacity of steel piles in sandy soil sites includes a formula for the vertical compressive bearing capacity of steel piles and a formula for the vertical tensile bearing capacity of steel piles; wherein,

[0019] The formula for the vertical compressive bearing capacity of steel piles is:

[0020] Q p =λ1λ3λ s1 i∑q sik l i +λ2λ4λ s2 λ p q pk A p

[0021] The pull-out bearing capacity formula of steel pile is:

[0022] Q T =λ1λ3λs1u∑γ i q sik l i

[0023] Where: q sik is the standard value of the ultimate lateral resistance of the i-th layer of soil on the pile side; q pk is the standard value of the ultimate end resistance; u is the circumference of the pile body; l i is the thickness of the i-th layer of soil around the pile; A p is the pile tip area; p is the soil plug effect coefficient at the pile end; i is the pull-out coefficient.

[0024] The present invention provides a method for calculating the vertical bearing capacity of steel piles in sandy soil sites. It has the following beneficial effects: based on numerical simulation and field load test results, the present invention takes into account the changes in the length, cross-sectional area, density of sand and cross-sectional shape of the steel piles, and the calculation formula for the vertical compressive and tensile ultimate bearing capacity of steel pipe piles. The side friction and end resistance of the steel piles are corrected, and finally a corrected method for calculating the vertical compressive and tensile ultimate bearing capacity of steel piles in sandy soil sites is obtained. This method has the advantages of accurate calculation, simple operation and wide application range. In addition, the method for calculating the ultimate bearing capacity of steel pile foundations in sandy soil sites under vertical loads, which is not involved in the prior art, is supplemented and improved, thereby helping to improve the scientificity and economy of the design of medium-sized steel pile foundations in civil engineering and provide a strong guarantee for engineering safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the present invention or the technical solutions in the prior art, the drawings required for describing the prior art are briefly introduced below.

[0026] Figure 1 It is a graph showing the relationship between pile load and relative displacement (QS) under different cross-sectional shapes in the present invention;

[0027] Figure 2 It is a curve diagram of the relationship between the pile body load and the relative displacement (QS) of the H-shaped steel pile under different cross-sectional sizes in the present invention;

[0028] Figure 3 The axial force distribution diagram of the H-shaped steel pile body under different cross-sectional sizes in the present invention;

[0029] Figure 4 The distribution diagram of the side friction resistance of the H-shaped steel pile under different cross-sectional sizes in the present invention;

[0030] Figure 5 The figure is a graph showing the relationship between the pile body load and the relative displacement (QS) of the H-shaped steel pile under different pile lengths in the present invention;

[0031] Figure 6 The axial force distribution diagram of the H-type short pile body under different pile lengths in the present invention;

[0032] Figure 7 The distribution diagram of the side friction of H-shaped steel piles with different pile lengths in the present invention;

[0033] Figure 8 is the λ1-L relationship diagram in the present invention;

[0034] Fig. 9 is the λ2-L relationship diagram in the present invention;

[0035] Fig.10 It is the relationship diagram of λ3-N in the present invention;

[0036] Fig.11 is the λ4-N relationship diagram in the present invention;

[0037] Fig.12 This is a stratum distribution diagram in the experimental example of the present invention;

[0038] Fig.13 This is a verification diagram of the bearing capacity formula of medium-sized steel piles in the experimental example of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0040] like Figure 2 As shown, the present invention discloses a method for calculating the vertical bearing capacity of steel piles in sandy soil sites. Based on numerical simulation results, the side friction resistance and pile end resistance of the steel piles are partially corrected, and the vertical bearing capacity of steel piles in sandy soil sites under different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density conditions is proposed.

[0041] The specific steps include:

[0042] Step S1: Exploring and testing the sandy soil site to measure the density, internal friction angle, and cohesion parameters of the sandy soil; determining the pile length, cross-sectional area, and cross-sectional shape parameters of different steel piles; in this embodiment, the basic parameters of the sandy soil and steel piles are shown in Table 1;

[0043] Table 1 Material mechanical parameters

[0044]

[0045] Step S2: Based on the physical and mechanical properties of sand and the geometric properties of steel piles, a mechanical model of steel piles in sandy soil is established;

[0046] Step S3: Based on the mechanical model, numerical simulation analysis is performed on the influence of the parameter changes of different steel pile lengths, cross-sectional areas, cross-sectional shapes of the steel piles and sand density on the vertical bearing characteristics of the steel piles, and the vertical bearing capacity of the steel piles in the sand field under the conditions of different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density is obtained; in the present invention, specific embodiments of numerical simulation calculation are shown in Tables 2 to 4;

[0047] Table 2 Working conditions of different cross-sectional shapes of steel piles in sandy soil sites

[0048]

[0049] Table 3 Working conditions of different cross-sectional dimensions of H-type steel piles in sandy soil sites

[0050]

[0051] Table 4 Working conditions of different H-type steel pile lengths in sandy soil sites

[0052]

[0053] When the cross-sectional perimeter of the steel pile in the sandy soil site is constant, the change law of the vertical ultimate bearing capacity and the change law of the load-settlement curve are as follows: Figure 1 shown.

[0054] When the cross-sectional dimensions of the steel piles in the sandy soil site change, the change law of their vertical ultimate bearing capacity and the change law of the load-settlement curve are as follows: Figure 2 The variation law of the pile axial force distribution curve is shown in Figure 3 The variation law of the pile side friction distribution curve is shown in Figure 4 shown.

[0055] When the length of the steel pile in the sandy soil site changes, the change law of its vertical ultimate bearing capacity and the change law of the load-settlement curve are as follows: Figure 5 The variation law of the pile axial force distribution curve is shown in Figure 6 The variation law of the pile side friction distribution curve is shown in Figure 7 shown.

[0056] Step S4: Under different steel pile length conditions, the pile side friction resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile side friction resistance obtained by theoretical calculation, so that a λ1-L diagram can be established (such as Figure 8 According to the comparison results, the correction coefficient λ1 of the pile friction resistance of the steel pile in the sandy soil field under the condition of changing pile length is obtained, as shown in Table 5.

[0057] Table 5 λ1 recommended value table

[0058]

[0059] Under the conditions of different cross-sectional areas of steel piles, the pile end resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile end resistance obtained by theoretical calculation, so a λ2-L diagram can be established (such as Fig. 9 According to the comparison results, the correction coefficient λ2 of the pile friction resistance of the steel pile in the sandy soil field under the condition of changing pile length is obtained, as shown in Table 6.

[0060] Table 6 λ2 recommended value table

[0061]

[0062]

[0063] The influence of sand density variables on the selection of steel pile parameters is analyzed. Under different sand density conditions, standard penetration tests are carried out on sands of each density, and a relationship model between the standard penetration number N and the sand density ρ is established. The density ρ is changed to obtain soils of different densities, so as to obtain the pile body friction resistance and pile end resistance of piles in sands of different densities. Therefore, λ3-N (such as Fig.10 As shown) and λ4-N relationship diagram (as shown Fig.11 According to the ratio of the measured value to the predicted value of the pile friction resistance and pile end resistance under different compaction degrees, the pile friction resistance correction coefficient λ3 and pile end resistance correction coefficient λ4 under the condition of changing density of the sandy soil site are obtained. See Table 7.

[0064] Table 7. Suggested values ​​of λ3 and λ4

[0065]

[0066] Under different cross-sectional shapes of steel piles, the pile side friction resistance and pile end resistance values ​​of the vertical ultimate bearing capacity obtained by numerical simulation of C-shaped steel piles and grooved steel piles are compared with those of H-shaped steel piles, and the pile body friction resistance correction coefficient λ under the condition of changing cross-sectional shapes of steel piles can be obtained. s1 and pile tip resistance correction factor λ s2 . See Table 8.

[0067] Table 8λ s1 , s2 Recommended value table

[0068]

[0069] For the correction coefficients of the steel pile length, cross-sectional area, cross-sectional shape and sand density that have not been numerically simulated, linear interpolation calculations can be performed based on the obtained correction coefficients of the pile side friction and pile end resistance.

[0070] Step S5: According to the correction coefficients λ1, λ2, λ3, λ4, λ s1 and λ s2 The side friction and end resistance of steel piles are modified, and a calculation formula for the vertical bearing capacity of steel piles in sandy soil sites is derived.

[0071] The calculation formulas for the vertical bearing capacity of steel piles in sandy soil sites include the vertical compressive bearing capacity formula of steel piles and the vertical tensile bearing capacity formula of steel piles; among them,

[0072] The compressive bearing capacity formula of steel pile is:

[0073] Q p =λ1λ3λ s1 u∑q sik li +λ2λ4λ s2 λ p q pk A p

[0074] The pull-out bearing capacity formula of steel pile is:

[0075] Q T =λ1λ3λ s1 u∑γ i q sik l i

[0076] Where: q sik is the standard value of the ultimate lateral resistance of the i-th layer of soil on the pile side; q pk is the standard value of the ultimate end resistance; u is the circumference of the pile body; l i is the thickness of the i-th layer of soil around the pile; A p is the pile tip area; p is the soil plug effect coefficient at the pile end; i is the pull-out coefficient.

[0077] The present invention obtains a method for calculating the vertical bearing capacity of steel piles in sandy soil sites by combining theoretical derivation with numerical analysis. The method has the advantages of accurate calculation, simple operation, and wide application range. The implementation of this method will help improve the scientificity and economy of the design of medium-sized steel pile foundations in civil engineering and provide a strong guarantee for engineering safety.

[0078] Experimental example

[0079] The project is the fourth phase of the 700MW concentrated solar power generation and 250MW solar photovoltaic power generation hybrid-independent power generation project planned to be built in Saih Al Dahal, Dubai, UAE. The NE1-700MW CSP+250MW PV hybrid project is located nearly 50 kilometers southwest of the Mohammad Bin Rashid Al Maktoum Solar Park. The owner of the project is DEWA and the developer is ACWA. Area A consists of a 100MW tower-type CSP unit and a 200MW trough-type CSP unit.

[0080] The strata in the project area are consistent through drilling tests. The strata conditions of the 137 boreholes are basically consistent with the physical parameters of each layer. The physical and mechanical parameter indicators of the main strata are summarized. The specific strata distribution is shown in Fig.12 The main formation physical parameters are shown in Table 9.

[0081] Table 9 Main formation physical parameters

[0082]

[0083] The vertical bearing capacity of steel piles is calculated according to the numerical simulation formula. The correctness of the calculation formula of steel piles is verified by the field load test data. The calculation results are shown in Table 10.

[0084] Table 10

[0085]

[0086] The calculation results of steel piles are established with the results of field load tests. Fig.13 It can be seen that the error of the calculation results of steel piles does not exceed ±20%, which verifies the rationality of the calculation formula for the vertical bearing capacity of steel piles in sandy soil sites.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the vertical bearing capacity of steel piles in sandy soil, characterized by: The following steps are involved: Step S1: Exploring and testing the sandy soil site to measure the density, internal friction angle, and cohesion parameters of the sandy soil; determining the pile length, cross-sectional area, and cross-sectional shape parameters of different steel piles; Step S2: Based on the physical and mechanical properties of sand and the geometric properties of steel piles, a mechanical model of steel piles in sandy soil is established; Step S3: Based on the mechanical model, numerical simulation analysis is performed on the influence of the parameter changes of different steel pile lengths, cross-sectional areas, cross-sectional shapes of the steel piles and sand density on the vertical bearing characteristics of the steel piles, so as to obtain the vertical bearing capacity of the steel piles in the sand field under the conditions of different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density; Step S4: According to the vertical bearing capacity of the steel piles in the sandy soil field under the conditions of different steel pile lengths, cross-sectional areas, cross-sectional shapes and sand density obtained in step S3, calculate the influence coefficient λ1 of the steel pile length, the influence coefficient λ2 of the cross-sectional area, the influence coefficients λ3 and λ4 of the sand density, and the cross-sectional shape parameter λ s1 and λ s2 ; Step S5: According to the correction coefficients λ1, λ2, λ3, λ4, λ s1 and λ s2 The side friction and end resistance of steel piles are modified, and a calculation formula for the vertical bearing capacity of steel piles in sandy soil sites is derived.

2. The method for calculating the vertical bearing capacity of steel piles in sandy soil according to claim 1, characterized in that: In step S4, under the conditions of different steel pile lengths, the pile body side friction resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile body side friction resistance obtained by theoretical calculation, and based on the comparison result, the correction coefficient λ1 of the pile body friction resistance under the condition of varying pile lengths of steel piles in sandy soil sites is obtained.

3. The method for calculating the vertical bearing capacity of steel piles in sandy soil according to claim 1, characterized in that: In step S4, under the conditions of different cross-sectional areas of steel piles, the pile end resistance obtained by numerical simulation in step S3 is compared with the equivalent calculated value of the pile end resistance obtained by theoretical calculation, and based on the comparison result, the correction coefficient λ2 of the pile body friction resistance under the condition of varying pile length of steel piles in sandy soil sites is obtained.

4. The method for calculating the vertical bearing capacity of steel piles in sandy soil according to claim 1, characterized in that: In the step S4, under the conditions of different sand densities, a standard penetration test is carried out on sand of each density, a relationship model between the standard penetration number N and the sand density ρ is established, and the density ρ is changed to obtain soil bodies of different densities, so as to obtain the pile body friction resistance and pile end resistance of the pile in sand of different densities; according to the ratio of the measured value and the predicted value of the pile body friction resistance and pile end resistance under different densities, the pile body friction resistance correction coefficient λ3 and the pile end resistance correction coefficient λ4 under the condition of changing density of the sand site are obtained.

5. The method for calculating the vertical bearing capacity of steel piles in sandy soil according to claim 1 is characterized by: In step S4, under different cross-sectional shapes of steel piles, the pile side friction resistance value and pile end resistance value of the vertical ultimate bearing capacity obtained by numerical simulation in step S3 are compared to obtain the pile body friction resistance correction coefficient λ under the condition of changing cross-sectional shapes of steel piles. s1 and pile tip resistance correction factor λ s2 .

6. The method for calculating the vertical bearing capacity of steel piles in sandy soil field according to claim 1 is characterized by: In step S4, for the correction coefficients of the length, cross-sectional area, cross-sectional shape and sand density of the steel pile for which no numerical simulation is performed, linear interpolation calculation is performed based on the obtained correction coefficients of the pile side friction and pile end resistance.

7. The method for calculating the vertical bearing capacity of steel piles in sandy soil field according to claim 1 is characterized by: In step S5, the calculation formula for the vertical bearing capacity of steel piles in sandy soil sites includes the formula for the vertical compressive bearing capacity of steel piles and the formula for the vertical tensile bearing capacity of steel piles; wherein, The formula for the vertical compressive bearing capacity of steel piles is: Q p =λ1λ3λ s1 u∑g sik l i +λ2λ4λ s2 l p q pk A p The pull-out bearing capacity formula of steel pile is: Q T =λ1λ3λ s1 u∑γ i q sik l i Where: q sik is the standard value of the ultimate lateral resistance of the i-th layer of soil on the pile side; q pk is the standard value of the ultimate end resistance; u is the circumference of the pile body; l i is the thickness of the i-th layer of soil around the pile; A p is the pile tip area; p is the soil plug effect coefficient at the pile end; i is the pull-out coefficient.

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