A method for predicting the safety of the pile body of hammer-driven piles in granite areas

Abstract

The present invention relates to a method for predicting the safety of the pile body of a hammer-driven pile in a granite area, which can predict the safety of the pile body in this type of area and avoid the damage of the pile body. The key points of the technical solution are as follows: First, determine the weight and maximum stroke of the diesel hammer, detect the diameter and top surface burial depth of the boulder by means of ground penetrating radar or cross-hole seismic CT, determine the radius of the precast pile, the design value of the axial compressive strength of the pile body concrete, the ultimate value of the pile body compressive bearing capacity, the elastic modulus and Poisson's ratio of the granite residual soil, the shear modulus of the granite residual soil, and the instantaneous maximum impact force received by the top surface of the precast pile. Then, determine the lateral frictional resistance of the soil body on the pile body, the lateral frictional resistance of the soil body on the pile body, the dynamic cohesive force of the granite residual soil, and the unit weight of the granite residual soil. Finally, determine the resistance of the soil body under the boulder, and judge whether the pile body will be damaged by comparing the instantaneous maximum impact force with the resistance, so as to achieve the purpose of avoiding the damage of the pile body in advance.

Description

Technical Field

[0001] The present invention relates to the field of infrastructure construction, and particularly relates to a method for predicting the safety of the pile body of a hammer-driven pile in a granite area. Background Art

[0002] There are often a certain number of boulders distributed in the granite weathered residual soil area. When hammer-driven piles are constructed in this area, the pile tip may hit directly above a boulder, resulting in the precast pile being unable to be successfully driven to the designed depth. If the boulder is large in size, under the action of the hammering force, the precast pile cannot sink, and the pile body may be damaged. For the granite weathered residual soil area, the judgment of the safety of the precast pile body is mostly based on engineering experience, and no relevant theoretical method has been seen for guidance so far. Summary of the Invention

[0003] In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for predicting the safety of the pile body of a hammer-driven pile in a granite area, which can not only predict the safety of the pile body in this type of area, avoid damage to the pile body, but also has the advantages of strong processability, convenient use and reliable results.

[0004] To solve the above technical problem, the technical solution of the present invention is: a method for predicting the safety of the pile body of a hammer-driven pile in a granite area, comprising the following steps:

[0005] Step S1: Determine the weight W and the maximum stroke H of the diesel hammer;

[0006] Step S2: Determine the diameter D and the top surface burial depth Z of the boulder under the precast pile body;

[0007] Step S3: Determine the radius a of the precast pile and the design value f of the axial compressive strength of the pile body concrete c ;

[0008] Step S4: Determine the ultimate value N of the compressive bearing capacity of the precast pile body u , wherein, is the precast pile manufacturing process coefficient, taking 0.85; A p is the cross-sectional area of the precast pile body, A p = πa 2 ;

[0009] Step S5: Determine the elastic modulus E and the Poisson's ratio μ of the granite residual soil;

[0010] Step S6: Determine the shear modulus G of the granite residual soil, and determine the instantaneous maximum impact force N received on the top surface of the precast pile max ,

[0011] Step S7: Determine the lateral frictional resistance q of the soil received by the precast pile bodys ;

[0012] Step S8: Determine the resistance Q of the soil on the side wall of the precast pile s , Q s = 2πaZq s ;

[0013] Step S9: Determine the dynamic cohesive force c d and the dynamic internal friction angle

[0014] Step S10: Determine the unit weight γ of the granite residual soil;

[0015] Step S11: Determine the resistance Q of the soil below the boulder p ,

[0016] Q p = 1.2c d N c + 0.6γDN γ

[0017]

[0018]

[0019] Step S12: Judge the safety of the precast pile body. If N max ≥ Q s + Q p , the precast pile body will not be damaged;

[0020] If N max < Q s + Q p , the precast pile body may be damaged and needs to be rejudged. If N max ≤ N u , the precast pile body will not be damaged; If N max > N u , the precast pile body will be damaged.

[0021] Furthermore, in Step S2, use the methods of ground penetrating radar, high-density electrical method or cross-hole seismic CT to detect the diameter D and the top surface burial depth Z of the boulder.

[0022] Furthermore, in Step S3, according to the precast pile construction plan, determine the radius of the precast pile, take precast piles of the same batch and the same quality, cut out standard test blocks, and determine the design value f of the axial compressive strength of the concrete by the concrete compressive strength test c .

[0023] Further, in step S5, typical samples of granite residual soil are taken on-site and transported back to the laboratory for triaxial loading and unloading tests to determine the elastic modulus E or determine the elastic modulus E based on engineering experience, and determine the Poisson's ratio μ.

[0024] Further, in step S9, the granite residual soil samples retrieved from the site are subjected to dynamic triaxial tests to determine the dynamic cohesive force c d and the dynamic internal friction angle

[0025] Further, in step S10, the granite residual soil samples retrieved from the site are subjected to density tests. After measuring the density, multiply it by the acceleration of gravity to obtain its unit weight γ.

[0026] Compared with the prior art, the present invention has the following beneficial effects: The method for predicting the safety of the pile body of the hammer-driven pile in the granite area is not only reasonably designed, can predict the safety of the pile body in this type of area, avoid the pile body from being damaged, but also has the advantages of strong processability, convenient use and reliable results.

[0027] The following further elaborates on the present invention in conjunction with specific embodiments. Specific Embodiments

[0028] To make the above features and advantages of the present invention more obvious and understandable, the following specific embodiments are given for detailed description.

[0029] A method for predicting the safety of the pile body of the hammer-driven pile in the granite area includes the following steps:

[0030] Step S1: Determine the weight W and the maximum stroke H of the diesel hammer;

[0031] Step S2: Determine the diameter D and the top surface burial depth Z of the boulder under the precast pile body;

[0032] Step S3: Determine the radius a of the precast pile and the design value f of the axial compressive strength of the pile body concrete c ;

[0033] Step S4: Determine the ultimate value N of the compressive bearing capacity of the precast pile body u , wherein, is the precast pile manufacturing process coefficient, taking 0.85; A p is the cross-sectional area of the precast pile body, A p =πa 2 ;

[0034] Step S5: Determine the elastic modulus E and the Poisson's ratio μ of the granite residual soil;

[0035] Step S6: Determine the shear modulus G of the granite residual soil and the instantaneous maximum impact force N on the top surface of the precast pile. max ,

[0036] Step S7: Determine the lateral frictional resistance q of the soil on the pile body of the precast pile. s ;

[0037] Step S8: Determine the resistance Q of the soil on the side wall of the pile body of the precast pile. s , Q s = 2πaZq s ;

[0038] Step S9: Determine the dynamic cohesive force c and the dynamic internal friction angle d of the granite residual soil.

[0039] Step S10: Determine the unit weight γ of the granite residual soil;

[0040] Step S11: Determine the resistance Q of the soil under the boulder. p ,

[0041] Q p = 1.2c d N c + 0.6γDN γ

[0042]

[0043]

[0044] Step S12: Determine the safety of the pile body of the precast pile. If N max ≥ Q s + Q p , then the pile body of the precast pile will not be damaged;

[0045] If N max < Q s + Q p , then the pile body of the precast pile may be damaged and needs to be rejudged. If N max ≤ N u , then the pile body of the precast pile will not be damaged; if N max > N u , then the pile body of the precast pile will be damaged.

[0046] In the embodiment of the present invention, in step S2, the diameter D and the top surface burial depth Z of the boulder are detected by using methods such as ground penetrating radar, high-density electrical method or cross-hole seismic CT.

[0047] In the embodiment of the present invention, in step S3, according to the precast pile construction plan, determine the radius of the precast pile, take precast piles of the same batch and the same quality, cut out standard test blocks, and determine the design value f of the axial compressive strength of the concrete by the concrete compressive strength test c .

[0048] In the embodiment of the present invention, in step S5, take typical samples of granite residual soil on site, transport them back to the laboratory for triaxial loading and unloading tests, determine the elastic modulus E or determine the elastic modulus E according to engineering experience, and determine the Poisson's ratio μ

[0049] In the embodiment of the present invention, in step S9, conduct dynamic triaxial tests on the granite residual soil samples retrieved from the site to determine the dynamic cohesive force c of the granite residual soil d and the dynamic internal friction angle

[0050] In the embodiment of the present invention, in step S10, conduct density tests on the granite residual soil samples retrieved from the site. After measuring the density, multiply it by the acceleration of gravity to obtain its unit weight γ

[0051] Select a region of granite residual soil, and it is planned to build a high-rise building with a precast pile foundation, and the hammering method is used for construction. When driving the pile, a boulder is encountered at the end of the precast pile. In order to determine the pile body safety of the precast pile, the method of the present invention is used for prediction

[0052] According to the selected precast pile construction machinery, determine that the weight W of the diesel hammer is 72 kN and the maximum stroke H is 2.3 m; detect the diameter D of the boulder below the pile body by the cross-hole seismic CT method to be 1.0 m, and the top surface burial depth Z is 7.3 m; according to the precast pile construction plan, determine the radius a of the precast pile to be 0.2 m, take precast piles of the same batch and the same quality, cut out standard test blocks, and determine the design value f of the axial compressive strength of the concrete by the concrete compressive strength test c to be 24.2 MPa; determine the ultimate value N of the pile body compressive bearing capacity u to be 2584.9 kN; take typical samples of granite residual soil on site, transport them back to the laboratory for triaxial loading and unloading tests, determine the elastic modulus E to be 8000 kPa, and determine the Poisson's ratio μ to be 0.26; determine the shear modulus G of the granite residual soil to be 3174.6 kPa, and determine the instantaneous maximum impact force N max received on the top surface of the precast pile to be 678.7 kN; according to the geotechnical engineering investigation report, obtain the lateral frictional resistance q s of the pile body to be 29 kPa; determine the resistance Q s of the soil on the side wall of the pile body to be 192.6 kN; conduct dynamic triaxial tests on the granite residual soil samples retrieved from the site to determine its dynamic cohesive force c d to be 26 kPa, and the dynamic internal friction angle is 22°; For the granite residual soil samples retrieved from the site, density tests are carried out. After testing the density and multiplying it by the acceleration due to gravity, the unit weight γ is obtained as 18.4 kN / m3; Determine the resistance Q of the soil below the boulder p is 605.4 kN; Judge the safety of the pile body, Q s +Q p is 798.1 kN, that is, N max <Q s +Q p , the pile body may be damaged and needs to be rejudged. Since N max <N u , the pile body will not be damaged.

[0053] The present invention is not limited to the above best implementation mode. Anyone can obtain other various forms of prediction methods for the safety of the pile body of hammer-driven piles in granite areas under the inspiration of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area, characterized in that: It includes the following steps: Step S1: Determine the weight W and the maximum stroke H of the diesel hammer; Step S2: Determine the diameter D and the top surface burial depth Z of the boulder under the precast pile body; Step S3: Determine the radius a of the precast pile and the design value f of the axial compressive strength of the pile body concrete c ; Step S4: Determine the ultimate value N of the compressive bearing capacity of the precast pile u , wherein, is the precast pile manufacturing process coefficient, taking 0.85; A p is the cross-sectional area of the precast pile body, A p = πa 2 ; Step S5: Determine the elastic modulus E and the Poisson's ratio μ of the granite residual soil; Step S6: Determine the shear modulus G of the granite residual soil and determine the instantaneous maximum impact force N on the top surface of the precast pile max , Step S7: Determine the lateral soil friction q acting on the precast pile shaft s ; Step S8: Determine the resistance Q of the soil on the side wall of the precast pile s , Q s = 2πaZq s ; Step S9: Determine the dynamic cohesive force c of the granite residual soil d and the dynamic internal friction angle Step S10: Determine the unit weight γ of the granite residual soil; Step S11: Determine the resistance force Q of the soil mass under the boulder p , Q p = 1.2c d N c + 0.6γDN γ Step S12: Determine the safety of the precast pile body. If N max ≥Q s +Q p , the precast pile body will not be damaged; If N max <Q s +Q p , the precast pile shaft may be damaged and needs to be rejudged. If N max ≤N u , the precast pile shaft will not be damaged; if N max >N u , the precast pile shaft will be damaged.

2. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area according to claim 1, characterized in that: In Step S2, use the methods of geological radar, high-density electrical method or cross-hole seismic CT to detect the diameter D and the top surface burial depth Z of the boulder.

3. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area according to claim 1, characterized in that: In step S3, according to the precast pile construction plan, determine the radius of the precast pile, select precast piles of the same batch and the same quality, cut out standard test blocks, and determine the designed axial compressive strength value f of the concrete through a concrete compressive strength test c .

4. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area according to claim 1, characterized in that: In Step S5, take typical specimens of the granite residual soil on-site, transport them back to the laboratory for triaxial loading and unloading tests to determine the elastic modulus E or determine the elastic modulus E according to engineering experience, and determine the Poisson's ratio μ.

5. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area according to claim 1, characterized in that: In step S9, for the granite residual soil samples retrieved from the site, dynamic triaxial tests are conducted to determine the dynamic cohesive force c d and the dynamic internal friction angle 6. A method for predicting the safety of the pile body of a hammer-driven pile in a granite area according to claim 1, characterized in that: In Step S10, conduct a density test on the granite residual soil specimens retrieved from the site. After measuring the density, multiply it by the acceleration of gravity to obtain its unit weight γ.

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