CN103938660A - Method for determining pile foundation bearing capacity after pile slipping - Google Patents

Abstract

The invention discloses a method for determining pile foundation bearing capacity after pile slipping. According to the method, the influences of pile slipping on bearing capacity are taken into consideration, unit side friction is determined in three areas, and CPT in-situ test indexes and related construction data serve as the foundation of calculation. According to the method, the influences of pile slipping on a soil body are taken into consideration, different calculation methods are adopted for the influences of pile slipping on pile foundation bearing capacity, reliable foundation is provided for detecting whether the pile foundation bearing capacity meets the requirement for the load of the upper portion or not after pile slipping, and it can be ensured that the pile foundation upper structure is safe and stable. The method is high in reliability, low in cost and short in cycle, and labor, material and time are greatly saved. The method has the outstanding advantages for oceanographic engineering. The method conforms to the engineering practice and is simple and clear, calculation is easy, related parameters can be easily determined and are reliable, and the calculation result is made more accurate.

Description

Determine the stake method of bearing capacity of pile foundation afterwards of slipping

Technical field

The present invention relates to a kind of definite method of bearing capacity of pile foundation, particularly a kind of definite stake method of bearing capacity of pile foundation afterwards of slipping.

Background technology

Pile foundation is the most frequently used basis of ocean platform, and in recent years, diameter was greater than 2m, and the great diameter and long steel pipe pile that depth of penetration exceedes 90m is widely adopted.Due to Marine Geology circumstance complication, soil layer difference is large, and a phenomenon of slipping in piling process is very common, and the stake of slipping fast may make pile body destroy, and causes the accident.Can the stake Zhou Tuzhi after stake that slip changes, and bearing capacity of pile foundation is affected, and has certain deviation by bearing capacity of pile foundation and the actual result of the assessment of original method, have scholar still meet design requirement and query slipping a rear bearing capacity of pile foundation.Therefore, determine slip stake after bearing capacity of pile foundation be very necessary.

At present, be to adopt the semi-theoretical method of semiempirical mostly to the bearing capacity calculation of great diameter and long open steel pile tube.What be widely adopted is the computational methods of the API of American Petroleum Institute (API) specification recommends before; In recent years, utilize static sounding (CPT) method, the method for carrying out bearing capacity estimation by setting up relation between CPT index and bearing capacity is subject to more and more scholars' accreditation.

U.S. API(2000,2006) specification separate provision in the design formulas of sand and the resistance of clay king-pile cardinal extremity and side friction.The method, taking laboratory test index as foundation, as native angle of internal friction, normal stress and undrained shear strength etc., is considered some influence factors and revises, and then obtaining bearing capacity of pile foundation.But, marine guidance piling is a dynamic process, bearing capacity of pile foundation is made up of quiet soil resistance and the resistance two parts of breaking ground, API specification fails to take into full account the resistance of breaking ground, some the parameter physical significance relating in formula is indefinite, and one group of index represents the situation of a soil layer, under the large feature of ocean soil property the change of divergence, can make unavoidably computational accuracy reduce.

In recent years, the large quantity research that Chinese scholars has been carried out, found to utilize the CPT method to determine that bearing capacity of pile foundation presents its outstanding advantage.CPT method is a kind of home position testing method, relies on that its fast and easy, cost are low, feature accurately and reliably, no matter there is application widely in land or ocean engineering.The method can be tested in position, can not cause soil disturbance, therefore can react really resistance to shear of soil and change, and makes to predict the outcome more accurately and reliably.At present, in the time adopting CPT method evaluation bearing capacity of pile foundation, often adopt probe to revise static point resistance q _c, set up static point resistance q _cand relation between pile foundation unit's side friction and the resistance of unit end, determine bearing capacity of pile foundation with this.Have a lot of scholars to propose to utilize CPT data to calculate the method for bearing capacity of pile foundation, the most representative have ICP method, Fugro method and a UWA method etc.Physical dimension and effect of depth that these 3 kinds of methods are considered pile body, done different regulations to the assessment of end resistance and side friction respectively.But, prove according to a large amount of case histories in recent years, there is relatively large deviation by slip a rear bearing capacity of pile foundation and the actual conditions of above several method assessment, slip and an impact for bearing capacity generation be can not ignore.Therefore, proposing a kind of definite method of slipping a rear bearing capacity of pile foundation has important.

Summary of the invention

The present invention provides a kind of method of bearing capacity of pile foundation after stake of slipping of determining for solving the technical problem existing in known technology, and the bearing capacity of pile foundation slipping after stake that adopts that the method determines conforms to more with actual conditions.

The technical scheme that the present invention takes for the technical problem existing in solution known technology is: a kind of definite stake method of bearing capacity of pile foundation afterwards of slipping, adopts following steps:

1) carry out static sounding in situ test, to obtain initial probe static point resistance q _c', side friction f _sand pore water pressure u;

2) according to step 1) in data draw stake position place's soil body degree of depth-probe correction static point resistance q _c, side friction f _sand the curve map of pore water pressure u, wherein, q _c=q _c'+u(1-η), in formula, η is probe area correction factor, according to the figure inspection of static sounding result garbled data; According to parameter q _cand f _sdivide soil layer, and complete geologic prospect report;

3) carry out the design of pile foundation according to the API of American Petroleum Institute (API) specification, obtain the final driving depth d of Pile Foundations Design, pile foundation outer diameter D and pile foundation inner diameter D _i;

4) carry out piling construction, the depth H while obtaining slipping stake end;

5) calculate the bearing capacity of pile foundation slipping after stake:

According to existing API specification, bearing capacity of pile foundation Q _uby pile side friction Q _sand end resistance Q _ptwo parts composition, that is:

Q _u=Q _s+Q _p=Σf _iA _si+q _pA _p （1）

Wherein, f _i, q _pthe unit's of being respectively side friction and unit end resistance, A _si, A _pbe respectively a side surface area and stake end surface area, A _si=π Dh _i, A _p=π (D ²-D _i ²)/4, h _ifor corresponding section pile foundation height;

5.1) consider slip stake the impact of bearing capacity is determined to unit side friction:

5.1.1) by slip stake the impact of stake unit's side friction is divided into three regions:

When z/H<0.5, it is complete influence area;

0.5≤z/H≤0.8 o'clock is some effects district;

When z/H>0.8, for without influence area;

Wherein, z is arbitrary depth value, and H is the degree of depth while slipping stake end;

5.1.2) determine the unit side friction of three zoness of different:

5.1.2.1) complete influence area:

f _i=2kPa

5.1.2.2) some effects district:

5.1.2.2.1), in the time of z/d≤0.5, d is the final driving depth of pile foundation,

Sand: $f_i=0.03q_c{A}_r^{0.3}{[\max \left(\frac{h}{D}\right),2]}^{-0.5}\tan {\mathrm{\&delta;}}_{\mathrm{cv}}---\left(2\right)$

Wherein $A_r=1-\left(\frac{D_i^2}{D^2}\right)$

Clay: f _i=(q _c-σ _vo)/k ₁(3)

Wherein k ₁=12+14.9log((q _c-σ _vo)/σ _vo')

In formula (2), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter, h investigates point and a vertical distance for end, and δ cv determines Zhuan – Soil Interface angle of friction by constant volume shear test; σ in formula (3) _vocover soil pressure on total, k ₁for empirical coefficient, σ _vo' be upper earthing body effective stress;

5.1.2.2.2) in the time of z/d>0.5, f _i=2kPa;

5.1.2.3) without influence area:

F _idefinite method sand in cotype (2), cotype in clay (3);

5.2) determine the end resistance q of unit _p:

Sand: q _p=q _c(0.15+0.45A _r) (4)

Wherein $A_r=1-\left(\frac{D_i^2}{D^2}\right)$

Clay: q _p=(q _c-σ _v0)/k ₂(5)

Wherein k ₂=N _kT/ 9

In formula (4), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter; In formula (5), σ _v0cover soil pressure on total, k ₂for empirical coefficient, N _kT=(q _c-σ _vo)/Su, Su is soil body undrained shear strength;

5.3) by step 5.1) definite side friction f of unit _iwith step 5.2) definite end resistance q of unit _pand stake side surface area A _siwith stake end surface area A _psubstitution formula (1) can be determined and slips a rear bearing capacity of pile foundation.

Advantage and good effect that the present invention has are:

1) considered to slip the impact of stake on the soil body, according to slip stake on bearing capacity of pile foundation produce an impact in various degree adopt different computational methods, slip a rear bearing capacity of pile foundation and whether meet upper load requirement reliable basis is provided for detecting, can ensure pile foundation superstructure safety and stability.

2) adopt CPT in situ test index and the relevant construction data foundation as calculating, reliability is strong, and cost is low, and the cycle is short, can greatly reduce human and material resources and time.This has outstanding advantage for ocean engineering.

3) the method meets engineering reality, and method is simply clear and definite, is easy to calculate, and related parameter all easily determines and reliably, this makes result of calculation more accurate.

In sum, the present invention considers to slip stake impact, utilizes the relevant data of CPT index and piling construction to determine the bearing capacity of pile foundation slipping after stake, makes result of calculation more approach actual conditions.

Brief description of the drawings

Fig. 1-1 is probe correction static point resistance q _cwith change in depth curve map;

Fig. 1-2 is probe side friction f _swith change in depth curve map;

Fig. 1-3 are that pore water pressure u is with change in depth curve map;

Fig. 2 is the bearing capacity of pile foundation correlation curve figure that surveys bearing capacity of pile foundation and obtain according to API and CPT method;

The unit side friction of Fig. 3 when slipping stake the unit side friction that provides of pile body and piling finish while finishing and the correlation curve figure of initial unit side friction;

Fig. 4 is for slipping a rear driving energy measured value and predicted value contrast column diagram;

Fig. 5 is actual measurement bearing capacity and the bearing capacity correlation curve figure that adopts the present invention to calculate.

Detailed description of the invention

For further understanding summary of the invention of the present invention, Characteristic, hereby exemplify following examples, and coordinate accompanying drawing to be described in detail as follows:

Determine the stake method for bearing capacity of pile foundation afterwards of slipping, adopt following steps:

1) carry out static sounding in situ test, to obtain initial probe static point resistance q _c', side friction f _sand pore water pressure u;

While carrying out CPT in-situ test, the plant and instrument using is the Wison-APB stake hole CPT system at the center of reconnoitring.CPT probe cone angle is that 60 °, conehead area are 10cm ², friction sleeve area is 150cm ².Sensor for pore water pressure is arranged on the sharp above 5mm of the shoulder place of probe cone, and the continuous injection stroke of each test is 3m, and penetrating speed is 20mm/s.And all to demarcate CPT probe at indoor and operation field before each CPT operation.

2) refer to Fig. 1-1～Fig. 1-3, draw the stake position place soil body degree of depth-probe according to the data in step 1) and revise static point resistance q _c, side friction f _sand the curve map of pore water pressure u, and divide soil layer, obtain surveying report;

Described probe correction static point resistance q _caccording to gained q in step 1) _c' and u press following formula gained: q _c=q _c'+u(1-η), in formula, η is probe area correction factor.According to the figure inspection of static sounding result garbled data, refer to Fig. 1, the data that obviously there are differences if having should be rejected, and to avoid accidental error, guarantee that data are reliable.According to parameter q _c, f _sdeng division soil layer, and complete geologic prospect report.

Calculating the static point resistance adopting is afterwards all revised q _c, according to relevant regulations, according to the probe of specification described in step 1), here probe area correction factor η is taken as 0.75.

3) carry out the design of pile foundation according to the API of American Petroleum Institute (API) specification, obtain the final driving depth d of Pile Foundations Design, pile foundation outer diameter D and pile foundation inner diameter D _ietc. parameter;

4) carry out piling construction, obtain an actual initial depth, the parameters such as stake end depth H of slipping of slipping of pile body;

5) according to above step parameter, definite rear bearing capacity of pile foundation that slips:

The calculating of a rear bearing capacity of pile foundation of slipping is according to step 2), CPT index q in step 3) and step 4) _c, pile foundations parameter d, D, D _iand slip stake depth H while finishing, adopt with the following method and to determine.

According to existing API specification, bearing capacity of pile foundation Q _uby pile side friction Q _sand end resistance Q _ptwo parts composition, that is:

Q _u=Q _s+Q _p=Σf _iA _si+q _pA _p （1）

Wherein, f _i, q _pthe unit's of being respectively side friction and unit end resistance.A _si, A _pbe respectively a side surface area and stake end surface area, A _si=π Dh _i, A _p=π (D ²-D _i ²)/4, h _ifor corresponding section pile foundation height; Obtain bearing capacity of pile foundation key and will determine exactly the side friction f of unit _iand the end resistance q of unit _p.

5.1) considered to slip the impact of stake on bearing capacity.It is considered herein that, the stake of slipping produces the impact of can not ignore to bearing capacity of pile foundation, and a rear bearing capacity that slips obviously reduces, and refers to Fig. 2.Driven pile energy is that bearing capacity of pile foundation the most directly embodies, and as seen from Figure 4, a rear driven pile total energy measured value that slips is significantly less than total energy predicted value (2000MJ), also can illustrate that slipping a rear bearing capacity of pile foundation reduces.The analysis found that bearing capacity reduce be mainly reflected in pile side friction reduce above, that is to say that slipping stake mainly exerts an influence to pile side friction, and little on end resistance impact.

5.1.1) the side friction comparative analysis of the side friction when slipping stake the side friction that provides of pile body and piling finish while finishing when not having to slip, refer to Fig. 3, it is considered herein that slip stake can be divided into three regions to stake unit's side friction by Different Effects degree: when z/H<0.5, be complete influence area; 0.5≤z/H≤0.8 o'clock is some effects district; When z/H>0.8, for without influence area.Wherein, z is arbitrary depth value, and H is the degree of depth while slipping stake end.

5.1.2), while calculating for the unit side friction of three zoness of different, adopt following methods:

5.1.2.1) complete influence area:

This region slips stake to the having the greatest impact of bearing capacity, and the side friction that slips after stake is very little, thinks f _i=2kPa.

5.1.2.2) some effects district:

5.1.2.2.1), in the time of z/d≤0.5, d is the final driving depth of pile foundation,

Sand: $f_i=0.03q_c{A}_r^{0.3}{[\max \left(\frac{h}{D}\right),2]}^{-0.5}\tan {\mathrm{\&delta;}}_{\mathrm{cv}}---\left(2\right)$ Wherein $A_r=1-\left(\frac{D_i^2}{D^2}\right)$

Clay: f _i=(q _c-σ _vo)/k ₁(3) k wherein ₁=12+14.9log((q _c-σ _vo)/σ _vo')

In formula (2), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter, h investigates point and a vertical distance for end, and δ cv determines Zhuan – Soil Interface angle of friction by constant volume shear test.σ in formula (3) _vocover soil pressure on total, k ₁for empirical coefficient, σ _vo' be upper earthing body effective stress.

5.1.2.2.2), in the time of z/d>0.5, side friction is a very little numerical value, specifies now f _i=2kPa.

5.1.2.3) without influence area:

It is considered herein that in this regional extent, the stake of slipping is little on the impact of pile foundation side friction, can ignore, and f _idefinite method sand in cotype (2), cotype in clay (3).

5.3) determine the end resistance q of unit _p:

Owing to slipping stake on bearing capacity of pile tip impact not quite, bearing capacity of pile tip is definite to be calculated as follows.

Sand: q _p=q _c(0.15+0.45A _r) (4) wherein

Clay: q _p=(q _c-σ _v0)/k ₂(5) k wherein ₂=N _kT/ 9

In formula (4), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter.In formula (5), σ _v0cover soil pressure on total, k ₂for empirical coefficient, N _kT=(q _c-σ _vo)/Su, Su is soil body undrained shear strength.

Determine the side friction f of Liu Zhuanhou pile foundation unit according to said method _iand the end resistance q of unit _p, by step 5.1) and definite side friction f of unit _iwith step 5.2) definite end resistance q of unit _pand stake side surface area A _siwith stake end surface area A _psubstitution formula (1), can determine and slip a rear bearing capacity of pile foundation.

The present invention be directed to the definite method of a rear bearing capacity of slipping, as long as stake or prediction occurred to slip slips after stake occurs, can estimate the bearing capacity of pile foundation slipping under stake impact by the present invention.As seen from Figure 4, to squeeze into total energy predicted value be 2000MJ in stake, and a rear hammering energy measured value that slips obviously reduces, and therefore slips after stake and can slight reduction hammering energy be squeezed in soil by pile body, estimates that result more approaches objective reality.

As seen from Figure 5, the bearing capacity of pile foundation and the measured value that obtain with the present invention are more approaching, and precision is higher.If the bearing capacity of pile foundation after stake that slips of determining according to the present invention is greater than the bearing capacity of designing requirement, and there is certain safety factor, pile foundation superstructure safety; If contrary, explanation is slipped a rear bearing capacity of pile foundation and is reduced, and has not reached designing requirement, now must adopt remedial measures, as add or minimizing upper load, to ensure superstructure safety and stability.

Although by reference to the accompanying drawings the preferred embodiments of the present invention are described above; but the present invention is not limited to above-mentioned detailed description of the invention; above-mentioned detailed description of the invention is only schematic; be not restrictive; those of ordinary skill in the art is under enlightenment of the present invention; not departing from the scope situation that aim of the present invention and claim protect, can also make a lot of forms, within these all belong to protection scope of the present invention.

Claims (1)

1. determine the stake method for bearing capacity of pile foundation afterwards of slipping, it is characterized in that, adopt following steps:

1) carry out static sounding in situ test, to obtain initial probe static point resistance q _c', side friction f _sand pore water pressure u;

2) according to step 1) in data draw stake position place's soil body degree of depth-probe correction static point resistance q _c, side friction f _sand the curve map of pore water pressure u, wherein, q _c=q _c'+u(1-η), in formula, η is probe area correction factor, according to the figure inspection of static sounding result garbled data; According to parameter q _cand f _sdivide soil layer, and complete geologic prospect report;

3) carry out the design of pile foundation according to the API of American Petroleum Institute (API) specification, obtain the final driving depth d of Pile Foundations Design, pile foundation outer diameter D and pile foundation inner diameter D _i;

4) carry out piling construction, the depth H while obtaining slipping stake end;

5) calculate the bearing capacity of pile foundation slipping after stake:

According to existing API specification, bearing capacity of pile foundation Q _uby pile side friction Q _sand end resistance Q _ptwo parts composition, that is:

Q _u=Q _s+Q _p=Σf _iA _si+q _pA _p （1）

Wherein, f _i, q _pthe unit's of being respectively side friction and unit end resistance, A _si, A _pbe respectively a side surface area and stake end surface area, A _si=π Dh _i, A _p=π (D ²-D _i ²)/4, h _ifor corresponding section pile foundation height;

5.1) consider slip stake the impact of bearing capacity is determined to unit side friction:

5.1.1) by slip stake the impact of stake unit's side friction is divided into three regions:

When z/H<0.5, it is complete influence area;

0.5≤z/H≤0.8 o'clock is some effects district;

When z/H>0.8, for without influence area;

Wherein, z is arbitrary depth value, and H is the degree of depth while slipping stake end;

5.1.2) determine the unit side friction of three zoness of different:

5.1.2.1) complete influence area:

f _i=2kPa

5.1.2.2) some effects district:

5.1.2.2.1), in the time of z/d≤0.5, d is the final driving depth of pile foundation,

Sand: $f_i=0.03q_c{A}_r^{0.3}{[\max \left(\frac{h}{D}\right),2]}^{-0.5}\tan {\mathrm{\&delta;}}_{\mathrm{cv}}---\left(2\right)$

Wherein $A_r=1-\left(\frac{D_i^2}{D^2}\right)$

Clay: f _i=(q _c-σ _vo)/k ₁(3)

Wherein k ₁=12+14.9log((q _c-σ _vo)/σ _vo')

In formula (2), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter, h investigates point and a vertical distance for end, and δ cv determines Zhuan – Soil Interface angle of friction by constant volume shear test; σ in formula (3) _vocover soil pressure on total, k ₁for empirical coefficient, σ _vo' be upper earthing body effective stress;

5.1.2.2.2) in the time of z/d>0.5, f _i=2kPa;

5.1.2.3) without influence area:

F _idefinite method sand in cotype (2), cotype in clay (3);

5.2) determine the end resistance q of unit _p:

Sand: q _p=q _c(0.15+0.45A _r) (4)

Wherein $A_r=1-\left(\frac{D_i^2}{D^2}\right)$

Clay: q _p=(q _c-σ _v0)/k ₂(5)

Wherein k ₂=N _kT/ 9

In formula (4), q _crevise static point resistance for probe, D is pile foundation external diameter, D _ifor pile foundation internal diameter; In formula (5), σ _v0cover soil pressure on total, k ₂for empirical coefficient, N _kT=(q _c-σ _vo)/Su, Su is soil body undrained shear strength;

5.3) by step 5.1) definite side friction f of unit _iwith step 5.2) definite end resistance q of unit _pand stake side surface area A _siwith stake end surface area A _psubstitution formula (1) can be determined and slips a rear bearing capacity of pile foundation.