CN1760469A - Method for determining treatment of pie body based on bearing capacity of single pile when rejecting hammer in subsequent piling - Google Patents

Abstract

The invention discloses a method for determining and disposing of a pile body based on the bearing capacity of a single pile when hammering is rejected in subsequent pile driving. It belongs to the technology of judging the quality of pile body during the piling process of marine engineering. According to the piling records at the construction site and the theoretical formula, the present invention simulates the continuous piling process through the one-dimensional wave equation, calculates the relationship curve between the penetration of the pile body and the number of hammering, and adjusts Q _s , Q _p , S _f , J _P , _JS calculation parameters make the calculation curve and piling record curve can be well matched, so as to determine the value of _Qs , _Qp , _Sf , _JP , _JS . Based on this, subsequent piling analysis is carried out, and the phenomenon of hammer rejection is simulated by adjusting f and q values. Calculate the actual bearing capacity of the single pile with the finally determined f and q values, compare it with the designed and calculated bearing capacity of the single pile, and determine the disposal of the pile body when the subsequent pile driving rejects the hammer. The present invention has the advantages that the means for obtaining relevant parameters is simple and easy, and has high reliability. The method is also suitable for predicting in the design stage whether hammer rejection will occur when piling continues to stop hammering for a period of time.

Description

Bearing capacity of single pile when refusing to hammer into shape based on subsequent piling determines to dispose the method for pile body

Technical field

The present invention relates to a kind of bearing capacity of single pile when refusing to hammer into shape and determine to dispose the method for pile body based on subsequent piling.Belong to the technology of judging pile quality in the ocean engineering piling process.

Background technology

Carry out piling construction at sea, often need pile extension, change pile hammer or because the problem of aspects such as meteorology, allocation of ships, cause pile body continuously injection arrive projected depth, so stopping in the work progress just occurred and hammered phenomenon into shape.In ocean engineering, proceed piling construction after will stopping to hammer into shape and be called subsequent piling.Stop hammering into shape the back because the recovery and the raising of foundation soil body intensity in piling, what subsequent piling occurs refuses to hammer into shape phenomenon, and promptly the hammering number has has met or exceeded control criterion, and pile body still can't continue injection and reach projected depth.After occurring refusing to hammer phenomenon into shape, determine the bearing capacity of pile body reality, by comparing, thereby rationally determine the method for disposal of pile body with former design bearing capacity by certain means of testing combining with theoretical analysis.Has important economic implications for the marine guidance piling engineering.

Summary of the invention

The purpose of this invention is to provide a kind of bearing capacity of single pile when refusing to hammer into shape based on subsequent piling to determine to dispose the method for pile body.This procedure is simple, and reliability is higher.

The present invention is realized by following technical proposals.Pile driving record according to the job site, according to theoretical formula, by analytical calculation to piling process simulation formula, determine the actual carrying capacity of single pile, compare with former design-calculated bearing capacity of single pile, the method of disposal of pile body when final definite subsequent piling is refused to hammer into shape, this method is characterised in that and comprises following process:

1. adopt following formula to calculate bearing capacity of single pile in the pile foundation design:

Q _D＝∑(f _i·A _si)+q·A _p (1)

In the formula, f _i: the unit side friction of i layer soil, f=ac when soil layer is cohesive soil is when soil layer is non-cohesive soil f=KP ₀' tan δ.Wherein α is a dimensionless factor, and α is calculated by following formula: α=0.5 ψ when ψ≤1.0 ^-0.5ψ＞1.0 o'clock α=0.5 ψ ^-0.25, ψ=c/P wherein ₀', P ₀' by the effective overburden pressure of discussion point; C is the undrained shear intensity of soil, is obtained by original position prospecting test.K is the lateral earth pressure coefficient; Angle of friction between δ soil and the pile lining is obtained by original position prospecting test;

A _Si: the side surface area of i layer soil king-pile, calculate acquisition according to the real size of stake;

Q: unit bearing capacity of pile tip, q=9c when soil layer is cohesive soil; When soil layer is non-cohesive soil q=P ₀' N _q, N wherein _qBe bearing capacity factor, 1 acquisition of tabling look-up;

A _p: the stake end gross area, calculate acquisition according to the real size of stake.

The design parameters of the inviscid sand soil of table 1

Compactness	The classification of soil	N q
			Close in extremely loose	Sand sandy silt silt	8
Dense reality in the pine	Sand sandy silt silt	12
			In dense reality	The sand sandy silt	20
Closely knit extremely close	The sand sandy silt	40
			Closely knit extremely close	Gravel sand		50

2. adopt the one-dimensional stress wave equation to describe the stressed and distortion of energy pile body from the bottom of pile hammer is delivered to the time in the piling process.

$\frac{{\∂}^{2}u}{\∂x^2}=\frac{1}{C^2}\frac{{\∂}^{2}u}{\∂t^2}+R---\left(2\right)$

In the formula, x: the position coordinates in stake cross section;

The particle displacement in stake cross section, u:x place;

T: time, 0.5t usually _Cr＜t＜t _Cr, t _CrBy formula $t_{\mathrm{cr}}=\frac{\mathrm{\Δl}}{C}$ Determine that wherein Δ l is for calculating the unit length of king-pile, desirable 1.0m;

C: the elastic stress wave velocity of wave, $C=\sqrt{\frac{E}{\mathrm{\ρ}}};$

E: the elasticity modulus of materials of stake;

ρ: the density of material of stake;

R: the soil resistance that pile body is subjected to, R=F (f, q, E _s, F _r, Q _s, Q _p, S _f, γ, J _s, J _p, β);

Wherein

F: the unit pile side friction, by formula f=ac, f=KP ₀' tan δ determines;

Q: the unit bearing capacity of pile tip, by formula q=9c, q=P ₀' N _qDetermine;

E _x: the modulus of compressibility of the soil body is obtained by indoor compression test;

F _r: the soil body destroys than being obtained by indoor quiet triaxial test;

Q _s, Q _p: the maximum flexibility distortion of the soil body is held in stake side, stake, and this value is with soil property classification, loading, unloading, stake end form, directly multiple factor is relevant in stake, and span: 2～5mm finally determines by analyzing;

S _f: the maximal destruction distortion of the soil body, cohesive soil span 5～8mm, cohesionless soil span 8～12mm finally determines by analyzing;

γ: the unit weight of the soil body, adopt core cutter method to measure;

J _P: the damped coefficient of stake end soil, this value is relevant with the soil property classification, and span is 0.4～0.8s/m, finally determines by analyzing;

J _S: the damped coefficient of stake side soil, this value is relevant with the soil property classification, and span is 0.1～0.5s/m, finally determines by analyzing;

β: the tired factor of the soil body, this value is relevant with hammering number, hammering energy and the soil property classification of piling, and the hammering number and the hammering energy of piling are obtained by pile driving record, and span is between 0.0～1.0, finally determines by analyzing.

Soil body grain composition, plastic limit, liquid limit, the compactness that the soil property classification is measured according to laboratory test looked into " the category name table of soil " and determined.

3. in the piling process, can obtain the pile penetration of hammering energy, total hammering number, each hammering by piling recorder; Depth of drive plots curve map.This curve map can reflect the soil layer resistance that the pile body depth of penetration is not subjected to simultaneously in the actual piling process.

4. according to the continuous piling process of formula (2) simulation, with Q _s, Q _p, S _f, J _P, J _SCalculating parameter substitution formula (2) calculates, and realizes the Fitting Analysis to continuous piling process.Obtain the relation curve of pile body pile penetration and hammering number under the hammering energy of setting, and compare, constantly adjust Q with the curve that obtains by piling recorder during the 3rd goes on foot _s, Q _p, S _f, J _P, J _SThe value of calculating parameter is obtained many group pile penetrations and hammering and is counted relation curve.To wherein reach 90% the corresponding Q of curve with the curves degree that recorder obtains _s, Q _d, S _f, J _P, J _SValue is defined as the calculating parameter near the soil layer actual conditions.

5. with definite calculating parameter Q of the 4th step _s, Q _d, S _f, J _P, J _SValue substitution formula (2), the simulation subsequent piling refuse to hammer into shape phenomenon, step is as follows: only change and the relevant f of pile body resistance R, q, β three parameters, wherein f≤f in subsequent piling is analyzed _MaxAnd q≤q _Max, f _MaxAnd q _MaxFor the maximum value of stake side and end resistance is determined by following formula:

f _max＝Mσ′ (3)

q _max＝Mσ′ (4)

In the formula: M=f/P ₀', σ '=P ₀'+0.5 * Δ u, $\mathrm{\Δu}=c_u[21n\frac{r_1}{r_2}+(1.73A_f-0.58)],$ Wherein Δ u is an excess pore water pressure; c _uBe the not draining intensity of the soil body, record by indoor quiet three experiments; r ₁Radius for soil body elastic-plastic interface; r ₂Be the pile body radius; A _fBe pore pressure parameter.

By increasing f, q and the simulation of β value refuse to hammer into shape the f when phenomenon is finally definite to be refused to hammer into shape, q value.

6. the f that the 5th step was determined, the bearing capacity of single pile that q value substitution formula (1) can obtain subsequent piling when refusing to hammer into shape.This bearing capacity and intrinsic bearing capacity of single pile are compared:

(1) when bearing capacity during, then can cut stake more than or equal to former design load;

(2) though when bearing capacity less than design load, in the time of can meeting design requirement by suitable reduction upper load, also can cut stake;

(3) just need to adopt injection, gaslift when bearing capacity can't meet design requirement, engineering measures such as boring reduce pile driving resistance, till stake is driven into projected depth.

The advantage of this invention is: the obtaining means of (1) relevant parameter is simple and easy to do, need not employ special equipment, can not increase the input of engineering.(2) the present invention can directly determine the bearing capacity that subsequent piling refuses to hammer into shape the back single pile, for the reasonable disposal of pile body provides foundation.The construction delay and the economic loss of blindly constructing and bringing have been avoided.(3) this method can realize sunykatuib analysis, analysis efficiency height by the establishment computer software.(4) whether this method can refuse to hammer phenomenon into shape for continuing to drive piles after prediction piling stops hammering a period of time into shape in the design stage effective way is provided.

Description of drawings

Fig. 1 is a flow chart of the invention process.

Pile body pile penetration and the hammering number curve figure of Fig. 2 for obtaining by piling recorder in the embodiment of the invention work progress.

Pile body pile penetration and hammering number curve figure that Fig. 3 obtains according to one-dimensional stress wave equation simulation piling process continuously for the embodiment of the invention.

Fig. 4 is the comparison diagram of embodiment of the invention Fig. 2 curve map and Fig. 3 curve map.

Pile body pile penetration that Fig. 5 obtains for the analysis of embodiment of the invention subsequent piling and hammering number curve figure.

The specific embodiment

Certain engineering is positioned at China Bohai Sea, adopts the steel pipe pile of diameter 1.524m, and the design depth of penetration is 104m.In squeezing into process, embedded depth stopped making a call to 15 days when reaching about 88.7m, had occurred refusing to hammer into shape phenomenon when carrying out subsequent piling.Engineering data is as follows:

(1) part soil body parameter

Layer name	Soil property is described	The degree of depth		Effective unit weight (kN/m 3)	Design shear strength (kPa)	Per surface frictional force	The unit bearing capacity of pile tip
								Layer top (m)	The layer end (m)
		(kPa)	(MPa)
						1	Very soft to soft silty clay			0.0		7.8	4	0	0.04
			2.0	9.0	7.5			6	0.07
										2.0		9.4	16	8	0.14
			3.0	9.4	16			10	0.14
						2	In closely knit aleuritic texture fine sand			3.0		9.2	δ＝20°，f max＝67.0kPa Nq＝12，q max＝2.9MPa	8	0.31
			4.8	9.2	12			0.51
						3	Very closely knit fine sand		4.8		10.0	δ＝30°，f max＝96kPa Nq＝40，q max＝9.6MPa		20	1.71
			17.1	10.0	77			6.63
						4	In closely knit chiltern flour sand		17.1		10.0		δ＝20°，f max＝67.0kPa Nq＝12，q max＝2.9MPa	48	1.99
			20.1	10.0	57			2.35
						5	Hard slightly to hard silty clay		20.1		10.0	40		40	0.36
			24.2	10.0	70			64					0.63

(2) pile body partial parameters

External diameter (mm)	Wall thickness (mm)	Fy (kN/cm 2)	q (kN/m)	A (cm 2)	W (cm 3)	r (cm)
							1524	32	35.5	11.55	1499.92	54797.54	52.75

(3) partial data that writes down by recorder (PIR-D type) in the piling construction process

Pile penetration (ft)	Hammering number (bl/dist)	Total hammering number (-)	The hammering energy of every hammer (kJ)	Hammering number/minute (-)	Total energy (kJ)
						0209.0 0210.0 0211.0 0212.0 0213.0 0214.0 0215.0 0216.0	193 091 082 070 059 069 053 036	00193 00284 00366 00436 00495 00564 00617 00653	391.5 422.4 425.1 434.0 434.9 435.6 436.3 441.5	051 050 048 048 048 048 048 048	0075562 0114003 0148865 0179247 0204905 0234958 0258082 0273975

Above pile driving record is depicted as curve sees Fig. 2.

(4) record piling construction process

Divide three sections and carry out piling construction, in the piling process, when the embedded depth of stake reaches about 88.7m, stopped making a call to 15 days, phenomenon when carrying out subsequent piling, occurred refusing to hammer into shape.

Stake	Length (m): 50.5m	Material: steel
			Pile cutoff: 1st	External diameter (mm): 1524
	Hammer	Model: S-800			Pile cover:
Energy			Type: P1500W	Dolly:

1. bearing capacity of single pile designing and calculating

Calculating bearing capacity of single pile according to formula (1) is 41.8MN.

2. continuous drivability analysis

According to the one-dimensional stress wave equation simulation process of driving piles continuously, analyze the pile body pile penetration and the hammering number curve figure that obtain and see Fig. 3.Result of calculation is compared with pile driving record, constantly adjust calculating parameter, finally obtain satisfied curve-fitting results and see Fig. 4, the final calculating parameter of determining is as follows:

Layer name	γ(kN/m 3)	E x(MPa)	F r	S f(mm)	Q s(mm)	Q p(mm)	J P(s/m)	J S(s/m)
									1-1	8.4	0.3	0.90	5	4.0	4.5	0.60	0.5
1-2	9.4	0.5	0.85	5.5	4.0	4.5	0.55	0.45
									2	9.2	1.0	0.70	8	2.5	2.5	0.49	0.38
3	10	1.5	0.65	9	2.5	2.5	0.49	0.23
									4	10	1.8	0.65	9	2.8	2.8	0.48	0.22
5	10	0.9	0.70	8	2.8	2.8	0.49	0.17

3. subsequent piling analysis

Determine because the soil compaction of stake acts on the super quiet pore water stress that produces in its surrounding soil and the growth of argillic horizon intensity by the 5th step.Adjust f repeatedly, g, β value simulation subsequent piling refuses to hammer into shape phenomenon, pile body pile penetration and hammering number curve figure see Fig. 5 when obtaining refusing to hammer into shape, by the successful as can be known simulation of curve refusing in the subsequent piling hammer phenomenon into shape.The final part soil layer parameter of determining sees the following form.

Level number	Plastic zone R (m)	Pore water Δ u (kPa)	Effective stress σ '=P 0’+Δu (kPa)	The side friction f ' that analysis obtains=M σ ' (kPa)	The side friction q ' that analysis obtains=M σ ' (MPa)
						1-1	9.495	28.126	29.6631	7.02	0.06
1-2	6.236	70.495	60.2473	26.68	0.18
						5	3.955	211.49	341.306	92.67	0.56

4. determine bearing capacity of single pile

With the f that determines in the previous step, the bearing capacity of single pile of q value substitution formula (1) when obtaining refusing to hammer into shape is 42.5MN.

5. judge the method for disposal of pile body

Since the bearing capacity of single pile that sunykatuib analysis is determined be 42.5MN greater than intrinsic bearing capacity of single pile 41.8MN, therefore can cut stake, cutting a pile length is 14.7m.

6. marine high strain dynamic test result

Calibrate mutually for the bearing capacity of single pile of determining with this method, carried out marine original position high strain dynamic test test, measure bearing capacity of single pile.The PAL foundation pile dynamic test instrument that test adopts U.S. PDI company to produce.Along pile body strain transducer and acceleration transducer are installed axially.Two sensors symmetry respectively are installed in both sides, the same plane of following pile body, stake top, and the center sensor position is about 17.6-19.2m with distance between pushing up.According to condition of construction, the hammering energy in the test is 1000kJ, and 9 signals of hammering into shape are gathered in the equal hammering of every pile 9 times.The signal quality of each hammer of more every pile, choosing wherein, the signal of a hammer carries out waveform fitting, drawing high strain dynamic test result of the test bearing capacity of single pile is that the definite bearing capacity of single pile 42.5MN of 44.5MN and the method that adopts the present invention's proposition is very approaching, and the reliability of this method has been described.

Claims (1)

1. the bearing capacity of single pile when refusing to hammer into shape based on subsequent piling determines to dispose the method for pile body, this method is according to the pile driving record of job site, according to theoretical formula, by analytical calculation to piling process simulation formula, determine the actual carrying capacity of single pile, compare with former design-calculated bearing capacity of single pile, finally determine the method for disposal of pile body when subsequent piling is refused to hammer into shape, this method is characterised in that and comprises following process:

1) adopt following formula to calculate bearing capacity of single pile in the pile foundation design:

Q _D＝∑(f _i·A _si)+q·A _p (1)

In the formula, f _i: the unit side friction of i layer soil, f=α c when soil layer is cohesive soil is when soil layer is non-cohesive soil f=KP ₀' tan δ, wherein α is a dimensionless factor, α is calculated by following formula: α=0.5 ψ when ψ≤1.0 ^-0.5ψ＞1.0 o'clock α=0.5 ψ ^-0.25, ψ=c/P wherein ₀', P ₀' by the effective overburden pressure of discussion point; C is the undrained shear intensity of soil, is obtained by original position prospecting test, and K is the lateral earth pressure coefficient; δ is the angle of friction between soil and the pile lining, is obtained by original position prospecting test;

A _Si: the side surface area of i layer soil king-pile, calculate acquisition according to the real size of stake;

Q: unit bearing capacity of pile tip, q=9c when soil layer is cohesive soil; When soil layer is non-cohesive soil q=P ₀' N _q, N wherein _qBe bearing capacity factor, 1 acquisition of tabling look-up;

A _p: the stake end gross area, calculate acquisition according to the real size of stake;

The design parameters of the inviscid sand soil of table 1 Compactness The classification of soil N _q Close in extremely loose Sand sandy silt silt 8 Dense reality in the pine Sand sandy silt silt 12 In dense reality The sand sandy silt 20 Closely knit extremely close The sand sandy silt 40 Closely knit extremely close Gravel sand 50

2) adopt the one-dimensional stress wave equation to describe the stressed and distortion of energy pile body from the bottom of pile hammer is delivered to the time in the piling process,

$\frac{{\∂}^{2}u}{\∂x^2}=\frac{1}{C^2}\frac{{\∂}^{2}u}{\∂t^2}+R---\left(2\right)$

In the formula, x: the position coordinates in stake cross section;

The particle displacement in stake cross section, u:x place;

T: time, 0.5t usually _Cr＜t＜t _Cr, t _CrBy formula $t_{\mathrm{cr}}=\frac{\mathrm{\Δl}}{C}$ Determine that wherein Δ l is for calculating the unit length of king-pile, desirable 1.0m;

C: the elastic stress wave velocity of wave, $C=\sqrt{E/\mathrm{\ρ}};$

E: the elasticity modulus of materials of stake;

ρ: the density of material of stake;

R: the soil resistance that pile body is subjected to, R=F (f, q, E _S, F _r, Q _S, Q _p, S _f, γ, J _S, J _P, β);

Wherein

F: the unit pile side friction, by formula f=α c, f=KP ₀' tan δ determines;

Q: the unit bearing capacity of pile tip, by formula q=9c, q=P ₀' N _qDetermine;

E _x: the modulus of compressibility of the soil body is obtained by indoor compression test;

F _r: the soil body destroys than being obtained by indoor quiet triaxial test;

Q _s, Q _p: the maximum flexibility distortion of the soil body is held in stake side, stake, and this value is with soil property classification, loading, unloading, stake end form, directly multiple factor is relevant in stake, and span: 2～5mm finally determines by analyzing;

S _f: the maximal destruction distortion of the soil body, cohesive soil span 5～8mm, cohesionless soil span 8～12mm finally determines by analyzing;

γ: the unit weight of the soil body, adopt core cutter method to measure;

J _P: the damped coefficient of stake end soil, this value is relevant with the soil property classification, and span is 0.4～0.8s/m, finally determines by analyzing;

J _S: the damped coefficient of stake side soil, this value is relevant with the soil property classification, and span is 0.1～0.5s/m, finally determines by analyzing;

β: the tired factor of the soil body, this value is relevant with hammering number, hammering energy and the soil property classification of piling, and the hammering number and the hammering energy of piling are obtained by pile driving record, and span is between 0.0～1.0, finally determines by analyzing;

Soil body grain composition, plastic limit, liquid limit, the compactness that the soil property classification is measured according to laboratory test looked into " the category name table of soil " and determined;

3) in the piling process, can obtain the pile penetration of hammering energy, total hammering number, each hammering by piling recorder; Depth of drive plots curve map, and this curve map can reflect the soil layer resistance that the pile body depth of penetration is not subjected to simultaneously in the actual piling process;

4) according to the continuous piling process of formula (2) simulation, with Q _s, Q _p, S _f, J _P, J _SCalculating parameter substitution formula (2) calculates, and realizes the Fitting Analysis to continuous piling process, obtains the relation curve of pile body pile penetration and hammering number under the hammering energy of setting, and with the 3rd) curve that obtained by piling recorder in going on foot compares, and constantly adjusts Q _s, Q _p, S _f, J _P, J _SThe value of calculating parameter is obtained many group pile penetrations and hammering and is counted relation curve, will wherein reach 90% the corresponding Q of curve with the curves degree that recorder obtains _s, Q _d, S _f, J _P, J _SValue is defined as the calculating parameter near the soil layer actual conditions;

5) with the 4th) definite calculating parameter Q of step _s, Q _d, S _f, J _P, J _SValue substitution formula (2), the simulation subsequent piling refuse to hammer into shape phenomenon, step is as follows: only change and the relevant f of pile body resistance R, q, β three parameters, wherein f≤f in subsequent piling is analyzed _MaxAnd q≤q _Max, f _MaxAnd q _MaxFor the maximum value of stake side and end resistance is determined by following formula:

f _max＝Mσ′ (3)

q _max＝Mσ′ (4)

In the formula: M=f/P ₀', σ '=P ₀'+0.5 * Δ u, $\mathrm{\Δu}=c_u[2\ln \frac{r_1}{r_2}+(1.73A_f-0.58)],$ Wherein Δ u is an excess pore water pressure; c _uBe the not draining intensity of the soil body, record by indoor quiet three experiments; r ₁Radius for soil body elastic-plastic interface; r ₂Be the pile body radius; A _fBe pore pressure parameter;

By increasing f, q and the simulation of β value refuse to hammer into shape the f when phenomenon is finally definite to be refused to hammer into shape, q value;

6) with the 5th) f that determines of step, the bearing capacity of single pile that q value substitution formula (1) can obtain subsequent piling when refusing to hammer into shape compares this bearing capacity and intrinsic bearing capacity of single pile:

(1) when bearing capacity during, then can cut stake more than or equal to former design load;

(2) though when bearing capacity less than design load, in the time of can meeting design requirement by suitable reduction upper load, also can cut stake;

(3) just need to adopt injection, gaslift when bearing capacity can't meet design requirement, engineering measures such as boring reduce pile driving resistance, till stake is driven into projected depth.

Images