CN116341089B - Method for calculating axial allowable bearing capacity of single pile of railway bored friction pile foundation - Google Patents

Method for calculating axial allowable bearing capacity of single pile of railway bored friction pile foundation Download PDF

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CN116341089B
CN116341089B CN202310626212.XA CN202310626212A CN116341089B CN 116341089 B CN116341089 B CN 116341089B CN 202310626212 A CN202310626212 A CN 202310626212A CN 116341089 B CN116341089 B CN 116341089B
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CN116341089A (en
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廖立坚
高璞
王秀艳
苏伟
王雨权
曾银勇
杨智慧
彭建东
李晓波
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China Construction Sixth Engineering Division Co Ltd
China Railway Design Corp
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Abstract

The invention relates to a method for calculating the axial allowable bearing capacity of a single pile of a railway drilling bored friction pile foundation, which comprises the following steps: calculating the calculated length l of the pile body p The method comprises the steps of carrying out a first treatment on the surface of the Calculating a pile body stability coefficient phi; calculating the final concrete center compression strength [ sigma ] c ]The method comprises the steps of carrying out a first treatment on the surface of the Calculating axial allowable bearing capacity P of single pile according to pile body material strength 1 The method comprises the steps of carrying out a first treatment on the surface of the Calculating axial allowable bearing capacity P of single pile according to rock-soil resistance 2 The method comprises the steps of carrying out a first treatment on the surface of the Calculating the axial allowable bearing capacity [ P ] of single pile]When P 1 <P 2 When [ P ]]=P 1 The method comprises the steps of carrying out a first treatment on the surface of the Otherwise [ P ]]=P 2 . According to the invention, the influence of the pile body material strength is considered from three aspects of pile body stability, concrete material strength and reinforcement ratio, and the bearing capacity of opposite side friction resistance and end resistance is respectively improved according to the load type and geological conditions, so that the problem of inaccurate judgment by means of manual experience is solved, the safety of pile foundation design is ensured, and unnecessary waste during engineering design is avoided.

Description

Method for calculating axial allowable bearing capacity of single pile of railway bored friction pile foundation
Technical Field
The invention relates to the technical field of pile foundations, in particular to a method for calculating an axial allowable bearing capacity of a single pile of a railway drilling bored friction pile foundation.
Background
When calculating the axial allowable bearing capacity of a single pile, a designer often relies on experience to determine some calculation parameters due to the vague simple guiding principle, for example, the allowable bearing capacity of the single pile is only improved according to the geological condition of the pile bottom or the bearing platform bottom, the main bearing capacity of the friction pile is provided by means of side friction resistance, the end resistance is small, and the actual condition cannot be reflected due to the improvement of the geological condition of the pile bottom or the bearing platform bottom. In addition, the allowable strength of the pile material has no quantitative calculation formula, 4000kN, 6000kN and 8000kN are respectively taken as the maximum bearing capacity of the pile according to the pile diameters of 1m, 1.25m and 1.5m by default, the actual situation cannot be considered by the numerical value, and the deviation is large.
Disclosure of Invention
The invention aims to solve the defects of the prior art and normalize the design flow of pile foundations, and provides a method for calculating the axial allowable bearing capacity of a single pile of a railway bored friction pile foundation.
The invention adopts the following technical scheme to realize the aim:
the method for calculating the axial allowable bearing capacity of the single pile of the railway bored friction pile foundation comprises the following steps:
s1, calculating the calculated length of the pile bodyl p ；
S2, determining pile body stability coefficientφ；
S3, calculating the initial concrete center compression strength according to the concrete strength gradeσ c0 ]And according to the load type, the compression strength of the final concrete center is obtainedσ c ]；
S4, calculating axial allowable bearing capacity of single pile according to pile body material strengthP 1 ；
S5, calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 And according to the load type and the geological conditionP 2 Carrying out improvement;
s6, calculating the axial allowable bearing capacity of the single pileP]When (when)P 1 <P 2 Time [P]=P 1 The method comprises the steps of carrying out a first treatment on the surface of the Otherwise [P]=P 2 。
In step S1, the pile body is calculated to be longl p Calculated as follows:
；
wherein:
l 0 pile length from the bottom of the bearing platform to the ground, m;
hpile length of the subsurface portion, m;
α-the deformation coefficient of the pile foundation.
In step S2, pile body stability factorφAccording tol p /dIs determined by the value of (a) and (b),dthe diameter of pile foundation, m; the method comprises the following steps:
when (when)l p /dWhen the temperature is less than or equal to 7,φ=1.00；
when 7 < ">l p /dWhen the temperature is less than or equal to 8.5,φ=1.00+(0.98-1.00)/(8.5-7)×(l p /d-7)；
when 8.5 < "l p /dWhen the temperature is less than or equal to 10.5,φ=0.98+(0.95-0.98)/(10.5-8.5)×(l p /d-8.5)；
when 10.5 < "l p /dWhen the temperature is less than or equal to 12,φ=0.95+(0.92-0.95)/(12-10.5)×(l p /d-10.5)；
when 12 < ">l p /dWhen the temperature is less than or equal to 14,φ=0.92+(0.87-0.92)/(14-12)×(l p /d-12)；
when 14 < "l p /dWhen the temperature is less than or equal to 15.5,φ=0.87+(0.81-0.87)/(15.5-14)×(l p /d-14)；
when 15.5 < >l p /dWhen the temperature is less than or equal to 17,φ=0.81+(0.75-0.81)/(17-15.5)×(l p /d-15.5)；
when 17 < ">l p /dWhen the temperature is less than or equal to 19,φ=0.75+(0.70-0.75)/(19-17)×(l p /d-17)；
when 19 < ">l p /dWhen the temperature is less than or equal to 21,φ=0.70+(0.65-0.70)/(21-19)×(l p /d-19)；
when 21 < ">l p /dWhen the temperature is less than or equal to 22.5,φ=0.65+(0.60-0.65)/(22.5-21)×(l p /d-21)；
when 22.5 < >l p /dWhen the temperature is less than or equal to 24,φ=0.60+(0.56-0.60)/(24-22.5)×(l p /d-22.5)；
when 24 < ">l p /dWhen the temperature is less than or equal to 26,φ=0.56+(0.52-0.56)/(26-24)×(l p /d-24)；
when (when)l p /dWhen the temperature is more than or equal to 26,φ=0.52。
in step S3, the initial concrete center compressive strength is calculated from the concrete strength gradeσ c0 ]The method specifically comprises the following steps:
when the concrete strength is C25 [σ c0 ]=6.8MPa；
When the concrete strength is C30 [σ c0 ]=8.0MPa；
When the concrete strength is C35 [σ c0 ]=9.4MPa；
When the concrete strength is C40 [σ c0 ]=10.8MPa；
When the concrete strength is C45 [σ c0 ]=12.0MPa；
When the concrete strength is C50 [σ c0 ]=13.4MPa；
When the concrete strength is C55 [σ c0 ]=14.8MPa；
When the concrete strength is C60，[σ c0 ]=16.0MPa。
In step S3, an improvement coefficient is determined according to the load type, and the final concrete center compressive strength is obtained according to the improvement coefficientσ c ]；
When the load type is dominant [σ c ]=[σ c0 ]；
When the load type is main force plus additional force [ the load type is main force ]σ c ]=1.3×[σ c0 ]；
When the load type is main force+special force [ the load type is the main force ]σ c ]=1.5×[σ c0 ]；
When the load type is principal force+earthquake force [ the following is true ]σ c ]=1.5×[σ c0 ]。
In step S4, calculating the axial allowable bearing capacity of the single pile according to the pile body material strengthP 1 The calculation formula is as follows:
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )；
wherein:
Apile body area, m 2 ；
n-the ratio of the modulus of elasticity of the reinforcement to the modulus of deformation of the concrete;
ρ 0 -minimum pile body reinforcement.
In step S4, the ratio of the elastic modulus of the reinforcing steel bar to the deformation modulus of the concretenThe concrete strength grade is determined according to the concrete strength grade, and specifically comprises the following steps:
when the concrete strength is C25, C30 and C35,n=10；
when the concrete strength is C40, C45, C50, C55 and C60,n=8。
in step S4, the minimum reinforcement ratio of the pile bodyρ 0 The method is determined according to the types of the steel bars, and specifically comprises the following steps:
when the type of the reinforcing steel bar is HPB300,ρ 0 =0.55%；
when the type of the reinforcing steel bar is HRB400,ρ 0 =0.50%；
when the type of the reinforcing steel bar is HRB500,ρ 0 =0.45%。
in step S5, calculating the axial allowable bearing capacity of the single pile according to the rock-soil resistanceP 2 The calculation formula is as follows:
P 2 =Σq i F i +q 0 N 0 ；
wherein:
F i -the side friction of each layer of soil;
N 0 -end resistance of the pile bottom;
q i 、q 0 -foundation allowable bearing capacity increase factor, including soil providing side friction resistance and soil providing end resistance.
In the step S5 of the process,q i 、q 0 depending on the load type and geological conditions, the following are specific:
p1, when the load type is dominant:q i 、q 0 1.0;
p2, when the load type is main force plus additional force:q i 、q 0 1.2;
p3, when the load type is main force+special force:
σ 0 is the basic bearing capacity of foundation soil,
when (when)σ 0 >At the time of 500KPa,q i 、q 0 1.4;
when 150KPa<σ 0 When the pressure is less than or equal to 500KPa,q i 、q 0 1.3;
when (when)σ 0 When the pressure is less than or equal to 150KPa,q i 、q 0 1.2;
p4, when the load type is main force+earthquake force:
σ 0 is the basic bearing capacity of foundation soil,
when (when)σ 0 >At the time of 500KPa,q i 、q 0 1.4;
when 150KPa<σ 0 When the pressure is less than or equal to 500KPa,q i 、q 0 1.3;
when (when)σ 0 When the pressure is less than or equal to 150KPa,q i 、q 0 1.2.
The beneficial effects of the invention are as follows: aiming at the problem of calculating the allowable bearing capacity of a single pile, the invention provides a single pile axial allowable bearing capacity calculation formula calculated according to the pile body material strength from the three aspects of pile body stability, concrete material strength and reinforcement ratio, and respectively improves the bearing capacities of side friction resistance and end resistance according to load types and geological conditions, thereby solving the problem of inaccurate judgment by means of manual experience, ensuring the safety of pile foundation design and avoiding unnecessary waste during engineering design. The method is suitable for the design of bored friction pile foundations of bridges such as roads, railways, municipal works and the like.
Drawings
FIG. 1 is a computational flow diagram of the present invention;
FIG. 2 is a schematic view of a friction pile foundation according to embodiment 1 of the present invention;
the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention. The invention is more particularly described by way of example in the following paragraphs with reference to the drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When a component is considered to be "connected" to another component, it can be directly connected to the other component or intervening components may also be present. When an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
as shown in fig. 1, the method for calculating the axial allowable bearing capacity of the single pile of the railway bored friction pile foundation comprises the following steps:
s1, calculating the calculated length of the pile bodyl p ；
S2, determining pile body stability coefficientφ；
S3, calculating the initial concrete center compression strength according to the concrete strength gradeσ c0 ]And according to the load type, the compression strength of the final concrete center is obtainedσ c ]；
S4, calculating axial allowable bearing capacity of single pile according to pile body material strengthP 1 ；
S5, calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 And according to the load type and the geological conditionP 2 Carrying out improvement;
s6, calculating the axial allowable bearing capacity of the single pileP]When (when)P 1 <P 2 Time [P]=P 1 The method comprises the steps of carrying out a first treatment on the surface of the Otherwise [P]=P 2 。
In step S1, the pile body is calculated to be longl p Calculated as follows:
；
wherein:
l 0 pile length from the bottom of the bearing platform to the ground, m;
hpile length of the subsurface portion, m;
α-the deformation coefficient of the pile foundation.
In step S2, pile body stability factorφThe values in table 1 were calculated by the linear difference formula:
table 1 pile body stability factor table
；
Note that: in the tablel p Calculating the length, m, of the pile body;dis pile foundation diameter, m.
The method comprises the following steps:
when (when)l p /dWhen the temperature is less than or equal to 7,φ=1.00；
when 7 < ">l p /dWhen the temperature is less than or equal to 8.5,φ=1.00+(0.98-1.00)/(8.5-7)×(l p /d-7)；
when 8.5 < "l p /dWhen the temperature is less than or equal to 10.5,φ=0.98+(0.95-0.98)/(10.5-8.5)×(l p /d-8.5)；
when 10.5 < "l p /dWhen the temperature is less than or equal to 12,φ=0.95+(0.92-0.95)/(12-10.5)×(l p /d-10.5)；
when 12 < ">l p /dWhen the temperature is less than or equal to 14,φ=0.92+(0.87-0.92)/(14-12)×(l p /d-12)；
when 14 < "l p /dWhen the temperature is less than or equal to 15.5,φ=0.87+(0.81-0.87)/(15.5-14)×(l p /d-14)；
when 15.5 < >l p /dWhen the temperature is less than or equal to 17,φ=0.81+(0.75-0.81)/(17-15.5)×(l p /d-15.5)；
when 17 < ">l p /dWhen the temperature is less than or equal to 19,φ=0.75+(0.70-0.75)/(19-17)×(l p /d-17)；
when 19 < ">l p /dWhen the temperature is less than or equal to 21,φ=0.70+(0.65-0.70)/(21-19)×(l p /d-19)；
when 21 < ">l p /dWhen the temperature is less than or equal to 22.5,φ=0.65+(0.60-0.65)/(22.5-21)×(l p /d-21)；
when 22.5 < >l p /dWhen the temperature is less than or equal to 24,φ=0.60+(0.56-0.60)/(24-22.5)×(l p /d-22.5)；
when 24 < ">l p /dWhen the temperature is less than or equal to 26,φ=0.56+(0.52-0.56)/(26-24)×(l p /d-24)；
when (when)l p /dWhen the temperature is more than or equal to 26,φ=0.52。
in step S3, the initial concrete center compressive strength is calculated from the concrete strength gradeσ c0 ]Look-up is performed as in table 2.
Table 2 concrete center compressive Strength (MPa)
；
And the improvement is carried out according to the load type and the table 3, so as to obtain the compression strength of the final concrete centerσ c ]。
Table 3 table for coefficient of improvement in compressive strength of concrete center
；
In step S4, calculating the axial allowable bearing capacity of the single pile according to the pile body material strengthP 1 The calculation formula is as follows:
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )；
wherein:
Apile body area, m 2 ；
n-the ratio of the modulus of elasticity of the reinforcement to the modulus of deformation of the concrete;
ρ 0 -minimum pile body reinforcement.
The ratio of the elastic modulus of the steel bars to the deformation modulus of the concrete was determined according to the strength grade of the concrete, as shown in table 4.
TABLE 4 ratio of elastic modulus of reinforcing bars to deformation modulus of concrete
；
Minimum reinforcement ratio of pile bodyρ 0 Determined according to the kind of the reinforcing bars as shown in table 5.
Table 5 pile body minimum reinforcement ratio table
；
Calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 The calculation formula is as follows:
P 2 =Σq i F i +q 0 N 0 ；
wherein:
F i -the side friction of each layer of soil;
N 0 -end resistance of the pile bottom;
q i 、q 0 -foundation allowable bearing capacity increase factor, including soil providing side friction resistance and soil providing end resistance.
q i 、q 0 Depending on the type of load and the geological conditions, see in particular table 6.
Table 6 allowable bearing capacity improvement coefficient of foundation
；
Note that: in the tableσ 0 Is the basic bearing capacity of foundation soil, KPa.
Specific example 1:
some bridge pier adopts a bored cast-in-place friction pile foundation, the diameter of a pile foundation is 1m, the number of piles is 8, the pile length is 36.5m, the ground elevation is 112.335m, the bearing platform bottom elevation is 115.335m, the deformation coefficient of the pile foundation is 0.3447, the pile body is concrete marked with C30, the steel bar adopts HPB300, other specific dimensions and geological conditions are shown in figure 2, and geological parameters are shown in table 7.
TABLE 7 geological parameter table
；
Pile length from bottom of pile cap to groundl 0 =3m；
Pile length of subsurface portionh=33.5m；
4/α=4/0.3447=11.60<h=33.5；
Length of pile bodyl p =0.5×(l0+4/α)=0.5×(3+11.60)=7.30；
l p /d=7.30/1=7.30, table look-up 1,φ=1+(0.98-1)/(8.5-7)×(7.30-7)=0.996；
according to the table look-up table 4 of C30,n=10；
based on the HPB300 look-up table 5,ρ 0 =0.55%；
then, the axial allowable bearing capacity of the single pile is respectively calculated according to the following 4 load types:
(1) Load type: a main force;
look up table 2 based on C30 and consider the improvement factor of Table 3 [σ c ]=1.0×8=8Mpa；
Calculating the axial allowable bearing capacity of a single pile calculated according to the pile body material strengthP 1 ；
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )=0.7×0.996×8000×π/4×(1+10×0.55%)=4621.57kN；
Calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 ；
The table is checked up to 6, and the result is that,q 1 =1.0，q 2 =1.0，q 3 =1.0，q 4 =1.0，q 5 =1.0，q 0 =1.0；
P 2 =Σq i F i +q 0 N 0 =1.0×371.50+1.0×251.94+1.0×1583.37+1.0×502.66+1.0×589.05+1.0×203.29=3501.61kN；
therefore, under the main force working condition, the axial allowable bearing capacity of the single pileP]=min{P 1 ，P 2 }={4621.57，3941.08}=3501.61kN。
(2) Load type: main force + additional force;
look up table 2 based on C30 and consider the improvement factor of Table 3 [σ c ]=1.3×8=10.4Mpa；
Calculating the axial allowable bearing capacity of a single pile calculated according to the pile body material strengthP 1 ；
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )=0.7×0.996×10400×π/4×(1+10×0.55%)=6008.04kN；
Calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 ；
The table is checked up to 6, and the result is that,q 1 =1.2，q 2 =1.2，q 3 =1.2，q 4 =1.2，q 5 =1.2，q 0 =1.2；
P 2 =Σq i F i +q 0 N 0 =1.2×371.50+1.2×251.94+1.2×1583.37+1.2×502.66+1.2×589.05+1.2×203.29=4201.93kN；
therefore, under the working condition of main force and additional force, the axial allowable bearing capacity of the single pile [P]=min{P 1 ，P 2 }={6008.04，4201.93}=4201.93kN；
(3) Load type: main force + special force;
look up table 2 based on C30 and consider the improvement factor of Table 3 [σ c ]=1.5×8=12.0Mpa；
Calculating the axial allowable bearing capacity of a single pile calculated according to the pile body material strengthP 1 ；
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )=0.7×0.996×12000×π/4×(1+10×0.55%)=6932.36kN；
Calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 ；
(1) Powdery clay, sigma 0 =100 kPa, table look-up 6,q 1 =1.2；
(2) middle sand, sigma 0 =370 kPa, table look-up 6,q 2 =1.3；
(3) coarse sand sigma 0 =430 kPa, table look-up 6,q 3 =1.3；
(4) middle sand, sigma 0 =450 kPa, look-up table 6, q 4 =1.3；
(5) Coarse sand sigma 0 =1000 kPa, table look-up 6,q 4 =1.4；
(5) coarse sand sigma 0 =1000 kPa, table look-up 6,q 0 =1.4；
P 2 =Σq i F i +q 0 N 0 =1.2×371.50+1.3×251.94+1.3×1583.37+1.3×502.66+1.4×589.05+1.4×203.29=4594.44kN；
therefore, under the working condition of main force and special force, the axial allowable bearing force of the single pile [P]=min{P 1 ，P 2 }={6932.36，4594.44}=4594.44kN；
(4) Load type: main force + earthquake force;
look up table 2 based on C30 and consider the improvement factor of Table 3 [σ c ]=1.5×8=12.0Mpa；
Solving the strength of the pile body materialCalculated axial allowable bearing capacity of single pileP 1 ；
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )=0.7×0.996×12000×π/4×(1+10×0.55%)=6932.36kN；
Calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 ；
(1) Powdery clay, sigma 0 =100 kPa, table look-up 6,q 1 =1.2；
(2) middle sand, sigma 0 =370 kPa, table look-up 6,q 2 =1.3；
(3) coarse sand sigma 0 =430 kPa, table look-up 6,q 3 =1.3；
(4) middle sand, sigma 0 =450 kPa, table look-up 6,q 4 =1.3；
(5) coarse sand sigma 0 =1000 kPa, table look-up 6,q 5 =1.4；
(5) coarse sand sigma 0 =1000 kPa, table look-up 6,q 0 =1.4；
P 2 =Σq i F i +q 0 N 0 =1.2×371.50+1.3×251.94+1.3×1583.37+1.3×502.66+1.4×589.05+1.4×203.29=4594.44kN；
therefore, under the working condition of main force and earthquake force, the axial allowable bearing force of the single pile [P]=min{P 1 ，P 2 }={6932.36，4594.44}=4594.44kN。
Aiming at the problem of calculating the allowable bearing capacity of a single pile, the invention provides a single pile axial allowable bearing capacity calculation formula calculated according to the pile body material strength from the three aspects of pile body stability, concrete material strength and reinforcement ratio, and respectively improves the bearing capacities of side friction resistance and end resistance according to load types and geological conditions, thereby solving the problem of inaccurate judgment by means of manual experience, ensuring the safety of pile foundation design and avoiding unnecessary waste during engineering design. The method is suitable for the design of bored friction pile foundations of bridges such as roads, railways, municipal works and the like.
While the invention has been described above with reference to the accompanying drawings, it will be apparent that the invention is not limited to the above embodiments, but is intended to cover various modifications, either made by the method concepts and technical solutions of the invention, or applied directly to other applications without modification, within the scope of the invention.

Claims (4)

1. The method for calculating the axial allowable bearing capacity of the single pile of the railway bored friction pile foundation is characterized by comprising the following steps of:
s1, calculating the calculated length of the pile bodyl p ；
Length of pile bodyl p Calculated as follows:
；
wherein:
l 0 pile length from the bottom of the bearing platform to the ground, m;
hpile length of the subsurface portion, m;
α-the deformation coefficient of the pile foundation;
s2, determining pile body stability coefficientφ；
Pile body stability factorφAccording tol p /dIs determined by the value of (a) and (b),dthe diameter of pile foundation, m; the method comprises the following steps:
when (when)l p /dWhen the temperature is less than or equal to 7,φ=1.00；
when 7 < ">l p /dWhen the temperature is less than or equal to 8.5,φ=1.00+(0.98-1.00)/(8.5-7)×(l p /d-7)；
when 8.5 < "l p /dWhen the temperature is less than or equal to 10.5,φ=0.98+(0.95-0.98)/(10.5-8.5)×(l p /d-8.5)；
when 10.5 < "l p /dWhen the temperature is less than or equal to 12,φ=0.95+(0.92-0.95)/(12-10.5)×(l p /d-10.5)；
when 12 < ">l p /dWhen the temperature is less than or equal to 14,φ=0.92+(0.87-0.92)/(14-12)×(l p /d-12)；
when 14 < "l p /dWhen the temperature is less than or equal to 15.5,φ=0.87+(0.81-0.87)/(15.5-14)×(l p /d-14)；
when 15.5 < >l p /dWhen the temperature is less than or equal to 17,φ=0.81+(0.75-0.81)/(17-15.5)×(l p /d-15.5)；
when 17 < ">l p /dWhen the temperature is less than or equal to 19,φ=0.75+(0.70-0.75)/(19-17)×(l p /d-17)；
when 19 < ">l p /dWhen the temperature is less than or equal to 21,φ=0.70+(0.65-0.70)/(21-19)×(l p /d-19)；
when 21 < ">l p /dWhen the temperature is less than or equal to 22.5,φ=0.65+(0.60-0.65)/(22.5-21)×(l p /d-21)；
when 22.5 < >l p /dWhen the temperature is less than or equal to 24,φ=0.60+(0.56-0.60)/(24-22.5)×(l p /d-22.5)；
when 24 < ">l p /dWhen the temperature is less than or equal to 26,φ=0.56+(0.52-0.56)/(26-24)×(l p /d-24)；
when (when)l p /dWhen the temperature is more than or equal to 26,φ=0.52；
s3, calculating the initial concrete center compression strength according to the concrete strength gradeσ c0 ]And according to the load type, the compression strength of the final concrete center is obtainedσ c ]；
Initial concrete center compression Strength [σ c0 ]The method specifically comprises the following steps:
when the concrete strength is C25 [σ c0 ]=6.8MPa；
When the concrete strength is C30 [σ c0 ]=8.0MPa；
When the concrete strength is C35 [σ c0 ]=9.4MPa；
When the concrete strength is C40 [σ c0 ]=10.8MPa；
When the concrete strength is C45 [σ c0 ]=12.0MPa；
When the concrete strength is C50 [σ c0 ]=13.4MPa；
When the concrete strength is C55 [σ c0 ]=14.8MPa；
When the concrete strength is C60 [σ c0 ]=16.0MPa；
Final concrete center compressive strength [σ c ]The method specifically comprises the following steps:
when the load type is dominant [σ c ]=[σ c0 ]；
When the load type is main force plus additional force [ the load type is main force ]σ c ]=1.3×[σ c0 ]；
When the load type is main force+special force [ the load type is the main force ]σ c ]=1.5×[σ c0 ]；
When the load type is principal force+earthquake force [ the following is true ]σ c ]=1.5×[σ c0 ]；
S4, calculating axial allowable bearing capacity of single pile according to pile body material strengthP 1 ；
Axial allowable bearing capacity of single pileP 1 The calculation formula is as follows:
P 1 =0.7·φ·[σ c ]·A·(1+nρ 0 )；
wherein:
Apile body area, m 2 ；
n-the ratio of the modulus of elasticity of the reinforcement to the modulus of deformation of the concrete;
ρ 0 -minimum pile body reinforcement ratio;
s5, calculating axial allowable bearing capacity of single pile according to rock-soil resistanceP 2 And according to the load type and the geological conditionP 2 Carrying out improvement;
axial allowable bearing capacity of single pileP 2 The calculation formula is as follows:
P 2 =Σq i F i +q 0 N 0 ；
wherein:
F i -the side friction of each layer of soil;
N 0 -end resistance of the pile bottom;
q i 、q 0 -foundation allowable bearing capacity increase factor, including soil providing side friction resistance and soil providing end resistance;
s6, calculating the axial allowable bearing capacity of the single pileP]When (when)P 1 <P 2 Time [P]=P 1 The method comprises the steps of carrying out a first treatment on the surface of the Otherwise [P]=P 2 。
2. The method for calculating axial allowable bearing capacity of a single pile of a bored friction pile foundation for railways according to claim 1, wherein in step S4, the ratio of the modulus of elasticity of the reinforcing steel bar to the modulus of deformation of the concretenThe concrete strength grade is determined according to the concrete strength grade, and specifically comprises the following steps:
when the concrete strength is C25, C30 and C35,n=10；
when the concrete strength is C40, C45, C50, C55 and C60,n=8。
3. the method for calculating the axial allowable bearing capacity of a single pile of a railway bored friction pile foundation according to claim 2, wherein in step S4, the minimum reinforcement ratio of the pile body isρ 0 The method is determined according to the types of the steel bars, and specifically comprises the following steps:
when the type of the reinforcing steel bar is HPB300,ρ 0 =0.55%；
when the type of the reinforcing steel bar is HRB400,ρ 0 =0.50%；
when the type of the reinforcing steel bar is HRB500,ρ 0 =0.45%。
4. the method for calculating the axial allowable bearing capacity of a single pile of a railway bored friction pile foundation according to claim 3, wherein the steps ofIn step S5, the processing unit,q i 、q 0 depending on the load type and geological conditions, the following are specific:
p1, when the load type is dominant:q i 、q 0 1.0;
p2, when the load type is main force plus additional force:q i 、q 0 1.2;
p3, when the load type is main force+special force:
σ 0 is the basic bearing capacity of foundation soil,
when (when)σ 0 >At the time of 500KPa,q i 、q 0 1.4;
when 150KPa<σ 0 When the pressure is less than or equal to 500KPa,q i 、q 0 1.3;
when (when)σ 0 When the pressure is less than or equal to 150KPa,q i 、q 0 1.2;
p4, when the load type is main force+earthquake force:
σ 0 is the basic bearing capacity of foundation soil,
when (when)σ 0 >At the time of 500KPa,q i 、q 0 1.4;
when 150KPa<σ 0 When the pressure is less than or equal to 500KPa,q i 、q 0 1.3;
when (when)σ 0 When the pressure is less than or equal to 150KPa,q i 、q 0 1.2.
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CN108222084A (en) * 2018-01-12 2018-06-29 上海城乡建筑设计院有限公司 A kind of Analysis of Bearing Capacity method of pile body under engineering pile test pile operating mode
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