CN114059573B - Pile foundation rock-socketed depth design method considering bridge full life cycle karst cave erosion amount - Google Patents
Pile foundation rock-socketed depth design method considering bridge full life cycle karst cave erosion amount Download PDFInfo
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Abstract
The invention relates to the field of calculation of bearing capacity of civil engineering bridge pile foundations, in particular to a pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of a bridge, which comprises the following steps: step 1), respectively calculating the rock embedding depth of the pile foundation when the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount are considered; and 2) comparing the pile foundation rock-socketed depth with the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount, and taking the maximum value as a design value. The pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of the bridge can dynamically consider the influence of karst cave corrosion on the value of the pile foundation rock-socketed depth of the bridge, and provides a reference basis for the design calculation of the highway bridge pile foundation in the karst region.
Description
Technical Field
The invention relates to the field of calculation of bearing capacity of civil engineering bridge pile foundations, in particular to a pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of a bridge.
Background
The bridge pile foundation in the karst development area is influenced by the pile body and the underlying karst cave, and the bearing characteristics and the values of all parameters of the bridge pile foundation in the karst development area are different from those of the conventional bridge pile foundation in a large and complex way. A more perfect method is provided for designing and calculating the bridge pile foundation in the conventional environment, but the influence of the karst environment on the stress and the bearing characteristic of the pile foundation is not considered. At present, the design and calculation method and parameter value of the bridge pile foundation in the karst development area are still unclear, so that the research on the design and calculation method and parameter value of the bridge pile foundation in the karst development area is very important.
The karst development area bridge pile foundation passes through the karst cave and the underlying karst cave, and the karst cave can be gradually eroded due to the influence of underground water, mineral substances and the like in the whole service life of the bridge, so that the stress of the pile foundation is greatly influenced.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides the pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of the bridge, which can dynamically consider the influence of karst cave corrosion on the value of the rock-socketed depth of the bridge pile foundation and provide a reference basis for the design calculation of the highway bridge pile foundation in the karst region.
The invention is realized by the following technical scheme:
a pile foundation rock-socketed depth design method considering the full life cycle karst cave erosion amount of a bridge comprises the following steps:
step 1), respectively calculating the rock embedding depth of the pile foundation when the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount are considered;
when the vertical bearing capacity is considered, the method for calculating the rock-socketed depth of the pile foundation comprises the following steps:
(1) When the karst region is drilled or the hole-digging cast-in-place pile passes through the karst cave, the depth h of the embedded rock of the pile foundation r Calculated according to the following formula:
in the formula: [ R ] a ]The allowable value of the axial compression bearing capacity of the single pile, when the self weight of the pile body and the weight of the replacement soil account for the buoyancy, the difference value of the gravity of the replacement soil also accounts for the buoyancy is taken as the load consideration;
c 1 the end resistance performance coefficient is determined according to hole cleaning and rock crushing degree factors;
A p -pile end cross-sectional area, for a pedestal pile, taking the pedestal cross-sectional area;
f rk -pile end rock saturated uniaxial compressive strength standard value, taking clay rock natural humidity uniaxial compressive strength standard value as f rk When the pressure is less than 2MPa, calculating according to the friction pile;
c 2m -coefficient of lateral resistance of the rock formation in which the cavern is located;
m 1 the lateral resistance exertion coefficient of the soil layer where the karst cave is located is determined according to the filling of the karst cave of the pile body and the conditions of the surrounding underground rivers;
u-the perimeter of the pile body of each soil layer or each rock stratum part;
z is the height of the karst cave, and the reaming part is not counted;
f rkm -rock saturated uniaxial compressive strength standard values of rock formations where the karst caves are located;
c 2 the lateral resistance performance coefficient of the rock embedding layer is determined according to the factors of hole cleaning and rock crushing degree;
(2) When karst cave exists under the drilling or hole digging cast-in-place pile in karst area, the depth h of embedded rock of pile foundation r Calculated according to the following formula:
in the formula: h is r -reasonable rock-socketing depth of pile foundation;
[R a ]the allowable value of the axial compression bearing capacity of the single pile, and the difference value of the self weight of the pile body and the weight of the replacement soil are taken into consideration as load;
m 2 -coefficient of performance of end resistance as a function of the thickness of the cavern roof;
c 1 the end resistance performance coefficient is determined according to hole cleaning and rock crushing degree factors;
A p -pile end cross-sectional area, for a pedestal pile, taking the pedestal cross-sectional area;
f rk a standard value of saturated uniaxial compressive strength of the rock at the pile end, and a standard value of natural humidity uniaxial compressive strength of the clay rock, when f rk When the pressure is less than 2MPa, calculating according to the friction pile;
u-the perimeter of the pile body of each soil layer or each rock stratum part;
c 2 the lateral resistance performance coefficient of the rock embedding layer is determined according to the factors of hole cleaning and rock crushing degree;
when the stability of the pile body is considered, the calculation method of the rock-socketed depth of the pile foundation is as follows:
(1) For a circular section pile, the following formula is calculated:
(2) For rectangular section pile
In the formula:
h r -reasonable rock-socketing depth of pile foundation;
M H the bending moment at the top surface of the bedrock is calculated according to the m method during calculation, the transverse load is selected according to the level I of the road, and the vertical load is provided by a design party;
M k counter-moment, M, produced on the contact surface of the pile end section with the bed rock k ＝ασ max W；
α -stress reduction factor, α =0.5; sigma max -maximum lateral stress generated by the rock formation surrounding the pile;
w-modulus of section of pile bottom, W = π d 3 /32；
The vertical ultimate compressive strength of the beta-rock is converted into a reduction coefficient of the horizontal ultimate compressive strength, beta = 0.5-1.0, the joint development of the lateral surface of the rock takes a small value, and the joint development of the lateral surface of the rock takes a large value;
R a -mono pile axial compression load tolerance;
d, designing the diameter of the pile body;
when the full life cycle karst cave corrosion amount is considered, the calculation formula of the pile foundation rock-socketed depth is as follows:
h r ＝E p x design lifetime +0.5m
In the formula, E p The erosion rate of the karst stratum where the pile foundation is located;
karst stratum corrosion rate E of pile foundation p The calculation formula of (c) is as follows:
E p ＝kΔmA p -1 T -1
in the formula:
E p -field erosion rate within the pile length depth L;
k is the section correction factor;
Δ m-absolute erosion amount in a certain burying time, i.e. change in mass W of sample in test time 1 -W 2 ；
A p -shaft surface area;
t-time;
the absolute erosion amount is calculated by the formula:
Δm＝E pl ρAL
where Δ m-absolute erosion amount in a certain burying time, i.e., change in mass W of the sample in the test time 1 -W 2 ；
E pl -field erosion degree;
ρ -formation density;
a-the area of the cross section of the pile end;
l is the pile length depth;
the calculation expression of the field corrosion degree is as follows:
in the formula, E pl -field erosion degree;
h 1 surveying the cumulative height of the eroded rock stratum within the drilling footage range;
h 2 -surveying the borehole footage;
and 2) comparing the pile foundation rock-socketed depth with the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount, and taking the maximum value as a design value.
Preferably, h 1 、h 2 The values of (A) are obtained from borehole survey data.
Preferably, the calculating step of the section correction coefficient k is: taking the annual absolute erosion quantity delta m of a plurality of typical karst measuring points obtained by actual measurement as a known quantity, taking the pile foundation pile diameter d passing through the karst area as a variable, and performing inverse calculation on the section correction coefficient k to obtain a section correction coefficient;
the calculation formula of the section correction coefficient k is as follows:
in the formula, k is a section correction coefficient;
d, designing the diameter of the pile body;
t is time;
E pl -field erosion degree.
Compared with the prior art, the invention has the following beneficial effects:
the pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of the bridge can dynamically consider the influence of karst cave corrosion on the value of the pile foundation rock-socketed depth of the bridge, and provides a reference basis for the design calculation of the highway bridge pile foundation in the karst region.
The method has the advantages that the required parameters are few during calculation and are easy to obtain, the pile foundation rock-socketed depth calculation method is simplified, the calculation accuracy is greatly improved, and certain reference can be provided for the design of the bridge pile foundation in the karst region.
Drawings
FIG. 1 is a schematic view of bending moment at the top surface of a bedrock at a minimum depth into a formation;
FIG. 2 is a schematic diagram of lateral stress in a peripile formation at a minimum depth of penetration into the formation;
FIG. 3 is a stress layout diagram of a Z6-1 pile of a bridge in Puyan high-speed ZK284+223 rocks.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The invention discloses a pile foundation rock-socketed depth design method considering the full life cycle karst cave corrosion amount of a bridge, which comprises the following steps:
step 1), respectively calculating the rock embedding depth of the pile foundation when the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount are considered;
when vertical bearing capacity is taken into consideration, h r The internal stress in the range is distributed in a triangular shape, and referring to fig. 1 and 2, the rock-socketed depth calculation method of the pile foundation is as follows:
(1) When the drilling (digging) hole filling pile in karst region passes through karst cave, the depth h of pile foundation embedded rock r Calculated according to the following formula:
in the formula: [ Ra ] -allowable value of axial compressive bearing capacity (kN) of a single pile, and the difference between the self weight of the pile body and the weight of the replacement soil (when the weight of the soil is taken into account of buoyancy, the weight of the replacement soil is also taken into account of buoyancy) as a load;
c 1 the coefficient of end resistance performance determined according to hole cleaning and rock crushing degree factors is adopted according to the table 1;
A p pile end cross-sectional area (m) 2 ) For the pedestal pile, taking the area of the pedestal cross section;
f rk a standard value (kPa) of saturated uniaxial compressive strength of the rock at the pile end, a standard value of uniaxial compressive strength of natural humidity of clay rock, when f rk Calculated according to friction pile when less than 2MPa (f) rki Is the i-th layer f rk A value);
c 2m the coefficient of lateral resistance performance of the rock stratum where the karst cave is located is adopted according to the table 1;
m 1 the lateral resistance exertion coefficient of the soil layer where the karst cave is located is determined according to the filling of the karst cave of the pile body and the conditions of the surrounding underground rivers and is adopted according to the table 2;
u-the perimeter (m) of the pile body of each soil layer or each rock stratum part;
z is the height (m) of the karst cave, and the reaming part is not counted;
f rkm -formation rock saturation uniaxial compressive strength standard (kPa) at which the cavern is located;
c 2 the coefficient of lateral resistance of the rock-inlaid layer, which is determined according to factors of hole cleaning and rock crushing degree, is adopted according to the table 1.
TABLE 1 coefficient c 1 、c 2 Value of
TABLE 2 coefficient of side resistance development m 1 Value of
TABLE 3 terminal resistance coefficient of performance m 2 Value of
(2) When karst area drilling (digging) hole filling pile is under karst cave, pile foundation rock-socketed depth h r Calculated according to the following formula:
in the formula: h is a total of r -pile foundation reasonable rock-socketed depth (m);
[R a ]-the axial compressive bearing capacity tolerance (kN) of the mono-pile, the difference between the pile body weight and the weight of the replacement soil (when the soil weight is taken into account in the buoyancy, the weight of the replacement soil is also taken into account in the buoyancy) as a load consideration;
m 2 the coefficient of performance of the end resistance according to the thickness of the top plate of the karst cave is adopted according to the table 3;
c 1 the coefficient of end resistance performance determined according to hole cleaning and rock crushing degree factors is adopted according to the table 1;
A p pile end cross-sectional area (m) 2 ) For the pedestal pile, taking the area of the pedestal cross section;
f rk -pile end rock saturated uniaxial compressive strength standard value (kPa), clay rock takingStandard value of uniaxial compressive strength of natural humidity, when f rk Calculated according to friction pile when less than 2MPa (f) rki Is the i-th layer f rk A value);
u-pile body perimeter (m) of each soil layer or each rock stratum part;
c 2 the coefficient of lateral resistance of the rock-bedding layer, which depends on the factors of hole cleaning and rock crushing degree, is adopted according to the table 1.
When the stability of the pile body is considered, the calculation method of the rock-socketed depth of the pile foundation is as follows:
(1) For a circular section pile, the following formula is calculated:
(2) For rectangular section pile
In the formula:
h r -pile foundation reasonable rock-socketed depth (m);
M H the bending moment (kN.m) at the top surface of the bedrock is calculated according to the m method, the transverse load is selected according to the level I of the highway, and the vertical load is provided by a design party;
M k counter-moment (kN M) generated on the contact surface of pile end section and bed rock, M k ＝ασ max W；
α -stress reduction factor, α =0.5;
σ max -maximum lateral stress generated by the rock formation surrounding the pile;
w-modulus of pile bottom section, W = π d 3 /32；
Converting the vertical ultimate compressive strength of the beta-rock into a reduction coefficient of the horizontal ultimate compressive strength, wherein beta = 0.5-1.0, and taking a small value for the development of the rock lateral joint and a large value for the non-development of the rock lateral joint;
d, the design diameter (m) of the pile body.
When the full life cycle karst cave erosion amount is considered, the calculation formula of the pile foundation rock-socketed depth is as follows:
h r ＝E p x design lifetime +0.5m
In the formula, E p The erosion rate of the karst stratum where the pile foundation is located.
TABLE 4 section correction factor k value
Karst stratum erosion rate E of pile foundation p The calculation steps are as follows:
(1) Firstly, calculating the field corrosion degree, wherein the calculation expression is as follows:
in the formula, E pl -field erosion degree;
h 1 -investigating the cumulative height (m) of the eroded rock formation (cumulative cavity) within the drilling footage;
h 2 -surveying the borehole footage (m); h is 1 、h 2 The values of (A) are obtained from borehole survey data.
(2) Calculating the field corrosion rate according to the pile foundation corrosion amount, wherein the calculation expression is as follows:
E p ＝kΔmA p -1 T -1
in the formula:
E p site erosion Rate in the range of pile Length L (mg (cm)) 2 ·a) -1 )；
k is the section correction factor;
Δ m-Absolute erosion amount (mg) in a certain burying time, i.e. change in mass W of sample in test time 1 -W 2 ；
A p Pile body surface area (cm) 2 )；
T-time (a).
The calculation formula of the absolute corrosion amount is as follows:
Δm＝E pl ρAL
where Δ m-absolute erosion amount (g) in a certain burying time, i.e., change in mass W of the sample in the test time 1 -W 2 ；
E pl -field erosion degree;
rho-formation Density (g/cm) 3 )；
A-area of pile end section (cm) 2 )；
L is the pile length depth.
The calculation step of the section correction coefficient k is as follows: and (3) taking the annual absolute erosion amount delta m of a plurality of typical karst measuring points obtained by actual measurement as a known quantity and the pile foundation diameter d passing through the karst area as a variable, and performing inverse calculation on the section correction coefficient k to obtain the section correction coefficient.
The calculation formula of the section correction coefficient k is as follows:
in the formula, k is a section correction coefficient;
d, designing the diameter (cm) of the pile body;
t-time (a);
E pl -field erosion degree.
And 2) comparing the pile foundation rock-socketed depth with the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount, and taking the maximum value as a design value.
Example 1
Referring to fig. 3, the calculation is carried out by taking a Puyan high-speed ZK284+223 Yan Lian bridge Z6-1 pile as an embodiment, wherein the pile length is 32.5m and the pile diameter is 2.0m. According to the geological survey data, a karst cave with the height of about 1.6m is arranged in the position range of 38.7-40.3 m of the designed pile length, the karst cave is filled with grey brown cohesive soil containing gravels, is wet, soft-plastic, is slightly filled with gravels and is loose, the karst cave with the height of about 5.6m is arranged in the position range of 43.8-49.4 m, the soil layers on the pile side are sequentially distributed with 22.1m cohesive soil su clay =55kPa; crumbFully weathered 5.4m Su conglomerate =100kPa; middle weathered limestone 5.0m, q Su rock ＝220kPa，q qu rock =1800kPa, as shown in fig. 2.
Based on the general engineering profile, the rock-socketed depth obtained by adopting the three rock-socketed depth calculation methods is shown in table 2.
TABLE 2 comparison of rock-socketed depth calculation results
The actual engineering is that the rock-socketed depth is 5.0m, the operation is more than 2 years up to now depending on the engineering bridge, the operation is safe, no potential safety hazard exists, the bearing capacity of the pile foundation is calculated to be 15.6MN, and the stress of the pile foundation is measured to be in a safe range.
Claims (3)
1. A pile foundation rock-socketed depth design method considering the full life cycle karst cave erosion amount of a bridge is characterized by comprising the following steps of:
step 1), respectively calculating the rock embedding depth of the pile foundation when the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount are considered;
when the vertical bearing capacity is considered, the method for calculating the rock-socketed depth of the pile foundation comprises the following steps:
(1) When the karst region is drilled or the hole-digging cast-in-place pile passes through the karst cave, the depth h of the embedded rock of the pile foundation r Calculated according to the following formula:
in the formula: [ R ] a ]The allowable value of the axial compression bearing capacity of the single pile, when the self weight of the pile body and the weight of the replacement soil account for the buoyancy, the difference value of the gravity of the replacement soil also accounts for the buoyancy is taken as the load consideration;
c 1 the coefficient of performance of end resistance is determined according to factors of hole cleaning and rock crushing degree;
A p pile end cross-sectional area, for club-footed piles, taking the club-footed cross-sectionArea;
f rk -pile end rock saturated uniaxial compressive strength standard value, taking clay rock natural humidity uniaxial compressive strength standard value as f rk When the pressure is less than 2MPa, calculating according to the friction pile;
c 2m the lateral resistance performance coefficient of the rock stratum where the karst cave is located;
m 1 the lateral resistance exertion coefficient of the soil layer where the karst cave is located is determined according to the filling of the karst cave of the pile body and the conditions of the surrounding underground rivers;
u-the perimeter of the pile body of each soil layer or each rock stratum part;
z is the height of the karst cave, and the reaming part is not counted;
f rkm -rock saturated uniaxial compressive strength standard values of rock formations where the karst caves are located;
c 2 the lateral resistance performance coefficient of the rock embedding layer is determined according to the factors of hole cleaning and rock crushing degree;
(2) When karst cave exists under the drilling or hole digging cast-in-place pile in karst area, the depth h of embedded rock of pile foundation r Calculated according to the following formula:
in the formula: h is r -reasonable rock-socketing depth of pile foundation;
[R a ]the allowable value of the axial compression bearing capacity of the single pile, and the difference value of the self weight of the pile body and the weight of the replacement soil are taken into consideration as load;
m 2 -an end-stop performance factor as a function of the cavern roof thickness;
c 1 the coefficient of performance of end resistance is determined according to factors of hole cleaning and rock crushing degree;
A p -pile end cross-sectional area, for a pedestal pile, taking the pedestal cross-sectional area;
f rk a standard value of saturated uniaxial compressive strength of the rock at the pile end, and a standard value of natural humidity uniaxial compressive strength of the clay rock, when f rk When the pressure is less than 2MPa, calculating according to the friction pile;
u-the perimeter of the pile body of each soil layer or each rock stratum part;
c 2 the lateral resistance performance coefficient of the rock embedding layer is determined according to the factors of hole cleaning and rock crushing degree;
when the stability of the pile body is considered, the method for calculating the rock-socketed depth of the pile foundation is as follows:
(1) For a circular section pile, the following formula is calculated:
(2) For rectangular section pile
In the formula:
h r -reasonable rock-socketing depth of pile foundation;
M H the bending moment at the top surface of the bedrock is calculated according to an m method during calculation, the transverse load is selected according to the level I of the highway, and the vertical load is provided by a design party;
M k counter-moment, M, produced on the contact surface of the pile end section with the bed rock k ＝ασ max W；
α -stress reduction factor, α =0.5; sigma max -maximum lateral stress generated by the rock formation surrounding the pile;
w-modulus of section of pile bottom, W = π d 3 /32；
Converting the vertical ultimate compressive strength of the beta-rock into a reduction coefficient of the horizontal ultimate compressive strength, wherein beta = 0.5-1.0, and taking a small value for the development of the rock lateral joint and a large value for the non-development of the rock lateral joint;
R a -mono pile axial compression load tolerance;
d, designing the diameter of the pile body;
when the full life cycle karst cave corrosion amount is considered, the calculation formula of the pile foundation rock-socketed depth is as follows:
h r ＝E p x design lifetime +0.5m
In the formula, E p The corrosion rate of the karst stratum where the pile foundation is located;
the karst stratum erosion rate E of the pile foundation p The calculation formula of (c) is as follows:
E p ＝kΔmA p -1 T -1
in the formula:
E p -field erosion rate within the pile length depth L;
k is the section correction factor;
Δ m-Absolute erosion amount in a certain burying time, i.e. change W in sample mass in a test time 1 -W 2 ；
A p -shaft surface area;
t is time;
the calculation formula of the absolute corrosion amount is as follows:
Δm＝E pl ρAL
where Δ m-absolute erosion amount in a certain burying time, i.e., change W in mass of sample in test time 1 -W 2 ；
E pl -field erosion degree;
ρ -formation density;
a, the cross section area of the pile end;
l is the pile length depth;
the calculation expression of the field corrosion degree is as follows:
in the formula, E pl -field erosion degree;
h 1 surveying the cumulative height of the eroded rock stratum within the drilling footage range;
h 2 -surveying the borehole footage;
and 2) comparing the pile foundation rock-socketed depth with the vertical bearing capacity, the pile body stability requirement and the full life cycle karst cave corrosion amount, and taking the maximum value as a design value.
2. The method for designing the rock-socketed depth of the pile foundation according to the full-life-cycle karst cave erosion amount of the bridge, of claim 1, wherein h is 1 、h 2 The values of (A) are obtained from borehole survey data.
3. The method for designing the rock-socketed depth of the pile foundation in consideration of the full-life-cycle karst cave erosion amount of the bridge according to claim 1, wherein the step of calculating the section correction coefficient k comprises the following steps: taking the annual absolute erosion amount delta m of a plurality of typical karst measuring points obtained by actual measurement as a known quantity, taking the pile foundation diameter d passing through the karst area as a variable, and performing inverse calculation on the section correction coefficient k to obtain a section correction coefficient;
the calculation formula of the section correction coefficient k is as follows:
in the formula, k is a section correction coefficient;
d, designing the diameter of the pile body;
t is time;
E pl -field erosion degree.
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| JP2007270542A (en) * | 2006-03-31 | 2007-10-18 | Doyu Daichi Co Ltd | Road bridge foundation design method |
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