CN1455055A - End-carrying type large-diameter pile pier vertical bearing capacity detecting method - Google Patents

Abstract

The end-bearing type large-diameter pile pier vertical load-bearing capacity detection method includes the following steps: a. according to the geological prospecting material estimating end-bearing capacity and frictional resistance value, designing and making load box; b. welding the load box on the full-length reinforcing cage end portion, hoisting and placing the reinforcing cage into the pile hole; c. cleaning pile hole, check and acceptance and pouring concrete; d. after the concrete strength is reached to 70%, slow-speed retaining loading process or rapid-speed retaining loading process to detect the load-bearing capacity of pile; and e. high-pressure injecting flow state expansion concrete into the load box. Its detection cost is low and its detection data are safe and reliable.

Description

End holds type major diameter pile pier vertical bearing capacity detection method

Affiliated technical field

The invention belongs to technical field of buildings.

Background technology

High-rise, super highrise building day by day increases, the hundreds of tons of major diameter stake bearing capacity, the stake widespread usage of thousands of tons of, vertical static loading test is difficulty relatively, Northwestern Univ USA's building is that honorary professor doctor Jorj.osterberg has invented self-balancing peg method, obtain U.S. deep foundation association Outstanding Contribution Award, and apply very soon all over the world, its principle be utilize the load case (o.cell) of jack type to be contained at the bottom of, upwards push away the frictional resistance of pile body peg by means of the pressure of jack oil pressing system, push the bearing stratum of stake downwards, two times of bearing capacities that are stake of thrust destroy the total bearing capacity that then can not get stake in advance as a side.China south is less for the total bearing capacity of bearing stratum, the long total frictional resistance of pile body is greater than bearing stratum end load, be to make the end resistance of bottom and total frictional resistance that part frictional resistance sum equals balance stake epimere by dress load case (o.cell), then the hole at load case place filled stream expansion concrete and is linked to be integral body by giving pipe laying road high pressure at a certain height in pile body bottom place.

This kind method only is suitable for China south, the geological conditions that sand is more open.For the north and other places, closely knit sand condition, the power of holding is good, and soil layer is more shallow, and pile body length is shorter, and end resistance is much larger than tens of times of pile body frictional resistance several times, because of can not making pile side friction and end resistance self-balancing, and can not detect the bearing capacity of stake.

Summary of the invention

Problem at existing method exists the invention provides a kind of end and holds type major diameter pile pier vertical bearing capacity detection method.

Detect step:

(1) according to geological exploration data, end load, the frictional resistance numerical value of estimation stake design and produce the load case;

The load case is made of upper surface, following bearing plate, cylinder body, fluidised form expansive concrete ascending pipe and output pile tube end settlement measurement pipe and piston.

The plane is identical with the pile body cross section on the load case, and bearing plate determines that by calculating section area is less than the last area of plane (as Fig. 2) under the load case.Test is pressed into load case cylinder body with hydraulic oil by oil pump from seamless steel pipe (conduit 2), in cylinder body, produce high pressure, promote bearing plate pressure ground under the load case, load case upper surface promotes pile body, the stake self-balancing, thereby record pile capacity, the deflection of ground is determined by the reinforcement displacement in the steel pipe that is welded on load case soffit.Behind the EOT, from steel pipe (conduit 1) to the inside and outside injection fluidised form of load case cylinder body expansive concrete.

(2) the load case is welded in elongated reinforcing cage end, and reinforcing bar cage hoisting is put into a hole;

(3) cleaning stake hole, examination, fluid concrete;

(4) after concrete strength generates 70%, maintained load test (ML-test) or maintained load test (ML-test) detection pile capacity at a slow speed fast;

(5) inject the fluidised form expansive concrete to load case high pressure then.

The present invention requires to determine heap(ed) capacity, displacement stable condition and unloading condition:

(1) determining of every grade of heap(ed) capacity: every grade of heap(ed) capacity is 1/8～1/10 of a frictional resistance calculated value.

(2) determining of displacement stable condition:

Twice of stipulated time intrinsic displacement reads data and differs 0.1mm and be considered as at the corresponding levels the loading and finish, and carries out next stage and loads.

(3) unloading condition

The frequency meter frequency declines to a great extent, and stake top displacement increases sharply, and the pile bottom settlements resilience is considered as the termination test condition.

The bearing plate design

Load case upper surface bearing plate is identical with the pile body cross section.Load case soffit bearing plate is by calculate determining, section area is less than bearer plane area (as Fig. 2), and is welded in load case piston, and following bearing plate area is calculated as follows:

A determines pile end groundwork bearing capacity q according to geologic information _p, estimation pile side friction Q _s

B. calculate bearing plate area down:

Bearing plate area under bearing plate under the A-load case

C. descend the bearing plate cross sectional shape identical with stake

The design of load case

Load case cylinder body is cylindrical (as Fig. 1), and diameter of cylinder, wall thickness, piston, Seal Design design identical with jack.Diameter of cylinder is less than the following bearing plate diameter or the length of side.Conduit 1,2 should meet the technical requirements of injecting chutable concrete simultaneously for seamless steel pipe (will satisfy the pressure fuel pump requirement in conduit 2 designs).Conduit 1 root is a convex shape section, is beneficial to concrete and hitherward injects.

Determining of detected pressures and displacement

Detected pressures reads from the oil pump oil meter, and following bearing plate deflection is measured the reinforcement displacement that is welded in down bearing plate in the conduit [1] and measured, and stake top displacement goes out to be installed on the dial gage that stake pushes up and measures.

Determining of pile capacity

Settling amount≤0.012～0.015D or pressure fuel pump descend under the following bearing plate, stake top displacement increases sharply, down during bearing plate displacement resilience the oil meter pressure of correspondence for bearing plate down to the pressure (Po) of ground.The pile capacity formula is:

A wherein _{The stake end}---stake end section area, A _{Pressing plate}---following bearing plate area, Q---pile capacity

Self-balancing given estimate inaccurate situation, pile capacity can suitably be adjusted by (3) bar method in the 3rd.

(1) testing explanation

Oil pump is pressed into load case cylinder body with hydraulic oil from seamless steel pipe [conduit 2], in cylinder body, produce high pressure, promote bearing plate pressure ground under the load case, load case upper surface promotes pile body, the stake self-balancing, thereby record pile capacity, the deflection of ground is determined by the reinforcement displacement in the steel pipe that is welded on load case soffit [conduit 1].Behind the EOT, from conduit to load case cylinder body inside and outside injection fluidised form expansive concrete (as Fig. 1).

Theoretical foundation

(1) damage feature of large diameter pile

The work characteristics of major diameter stake is different with the medium-small diameter stake, and on the basis of a large amount of tests, Meyerhof pointed out in 1988, and the major diameter stake is " a progressive destruction ".Actual is because diameter is big, bearing stratum compression influence is dark, the distortion of sinking is big, the stake end periphery produces the oblique crack of splayed, and bearing stratum breaks away from the stake effect of contraction of earth pillar on every side, enlarges along stretching along with load increases the crack, reaching to a certain degree, stake end soil wedge pushes the crack closed, load continues to increase, and the crack enlarges, and extruding is closed again.Progressive like this destruction, the load subsidence curve is as shown in Figure 5 step-like.This is the characteristics of progressive destruction.Because oblique crack appears in its end points periphery, bearing stratum no longer is subjected to the effect of contraction of earth pillar on it, so osterberg peg method adapts to this kind destruction situation just, just obtains various countries expert's approval and applies.

(2) foundation model is the elastic half-space body, and according to theory of elastic mechanics: the surface action diameter is the circular evenly distributed load P of D ₀The time, the settling amount formula is: $S=\frac{1-{\mathrm{\μ}}^2}{E}D{P}_0$ (1)

E in the formula, μ are the modulus of deformation and the Poisson's ratio of soil.The static load test pile determines that the bearing capacity of stake often is as the criterion with S=1.5D%, so $1.5D\%=\frac{1-{\mathrm{\μ}}^2}{E}D{P}_0$ (2) D gets in the cancelling, $P_0=0.015\frac{E}{1-{\mathrm{\μ}}^2}$ (3)

In like manner, for minor diameter (d) stake, substitution formula (1), $1.5d\%=\frac{1-{\mathrm{\μ}}^2}{E}d{P}_0$ (4)

D in (4) formula of elimination then has: $P_0=0.015\frac{E}{1-{\mathrm{\μ}}^2}$ (5)

The two is identical for formula (3), (5), by similarity relation, so the simulation of available paxilla.So record the bearing capacity formula of each Model Pile be:

A wherein _{The stake end}---stake end section area, A _{Pressing plate}---the bearing plate area

(3) give when balancing each other certainly and estimate unon time, can adjust by the following method:

A. lower end resistance hour, frictional resistance load one displacement curve is extension (as Fig. 4) suitably

B. top frictional resistance hour, end resistance load one displacement curve is extension (as Fig. 3) suitably

Suitably reduce according to extension, still can try to achieve the stake bearing capacity value.

The scope of application:

Along with the fast development of infrastructure, the pile pier basis more and more is applied to the basis of building, structure, the existing more application example of large-scale, high-bearing capacity pile pier, but the pile pier foundation bearing capacity detection of above-mentioned specific condition is failed to solve.The present invention is applicable to the Large Diameter Pile Foundation of end resistance greater than frictional resistance, and the pile pier bearing capacity is high more, and the inventive method can manifest superiority more.The requirement that the deep layer treadmill test of the new basic design specification of the foundation 8.5.5 bar regulation of China's in April, 2002 promulgation is determined is also just meeting this principle.

Advantage:

(1) counter force system that does not need counterweight and anchoring pile etc. to form provides detection used pressure with stake self balance, reduces and detects cost;

(2) be subjected to such environmental effects little, can realize detecting;

(3) save the duration, speed up the work;

(4) the detection data security is reliable.

Description of drawings

Fig. 1 is a load box structure schematic diagram of the present invention;

Fig. 2 is a load case work schematic diagram of the present invention;

Fig. 3 is when top frictional resistance hour, the suitable extension view of end resistance load-displacement curve;

Fig. 4 is when bottom end resistance hour, the suitable extension view of frictional resistance load-displacement curve;

Fig. 5 large diameter pile P-S curve map.

The specific embodiment

With φ 300mm stake test is example, and according to method as above, its experimental data sees the following form:

Table 1.1 φ 300mm stake self-balancing detects experimental data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
									The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
			For the first time	1635	0.53	0.6	0.65	0.625							0.39	0.37	0.38
For the second time	1730	1.05							1.16	1.2	1.18	0.64	0.68	0.62
			For the third time	1807	1.50	1.74	1.76	1.75							1	1.05	1.025
The 4th time	1875	1.97							2.28	2.26	2.27	1.32	1.29	1.305
			The 5th time	1941	2.53	2.87	2.83	2.85							1.6	1.63	1.615
The 6th time	1999	3.07							3.4	3.39	3.395	1.95	2.08	2.015
			The 7th time	2039	3.54	3.91	3.91	3.91							2.3	2.32	2.31
The 8th time	1967	2.75							5.47	5.36	5.415	2.28	2.27	2.25

Annotate: the stake degree of depth: the 930mm of nuzzling

Table 1.2 φ 300mm stake self-balancing detects experimental data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
									The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
			For the first time	1630	0.53	0.68	0.65	0.665							0.35	0.34	0.345
For the second time	1735	1.09							1.26	1.21	1.235	0.73	0.75	0.74
			For the third time	1800	1.48	1.86	1.83	1.845							0.99	1	0.995
The 4th time	1891	2.10							2.54	2.5	2.52	1.4	1.42	1.41
			The 5th time	1960	2.71	3.17	3.02	3.095							1.82	1.81	1.815
The 6th time	2030	3.45							3.81	3.67	3.74	2.23	2.22	2.225
			The 7th time	1987	2.93	5.28	5.17	5.225							2.18	2.17	2.13
The 8th time	1914	2.53							6.88	6.75	6.815	2.1	2.1	2.04

Annotate: the stake degree of depth: the 920mm of nuzzling

Table 1.3 φ 300mm stake self-balancing detects experimental data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
									The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
			For the first time	1620	0.49	0.71	0.72	0.715							0.33	0.32	0.325
For the second time	1722	0.99							1.29	1.29	1.29	0.67	0.66	0.665
			For the third time	1798	1.48	1.85	1.85	1.85							0.99	0.98	0.985
The 4th time	1881	2.0							2.44	2.45	2.445	1.35	1.33	1.34
			The 5th time	1942	2.53	3.02	3.01	3.015							1.7	1.69	1.695
The 6th time	2006	3.12							3.59	3.58	3.585	2.04	2.03	2.035
			The 7th time	2042	3.6	4.11	4.08	4.09							2.38	2.33	2.335
The 8th time	1984	3.26							5.58	5.61	5.595	2.29	2.26	2.30

Annotate: the stake degree of depth: the 900mm of nuzzling

Table 2.1 φ 300mm stake contrast test tables of data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Counterweight (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
										The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
				For the first time	1781	0.53	2.0	0.54	0.58							0.56	0.34	0.33	0.335
For the second time	1823	1.15	1.09							1.08	1.085	0.61	0.59	0.60
				For the third time	1840	1.87		1.84	1.86						1.85	1.22	1.23	1.225
The 4th time	1859	2.38	2.40							2.38	2.39	1.69	1.70	1.695
				The 5th time	1881	3.02		3.01	3.05						3.03	1.93	1.94	1.935
The 6th time	1902	3.6	3.54							3.53	3.535	2.33	2.35	2.34
				The 7th time	1922	4.25		4.05	4.07						4.06	2.79	2.81	2.80
The 8th time	1938	4.9	4.67							4.69	4.68	3.24	3.23	3.235
				The 9th time	1951	5.405		5.12	5.15						5.135	3.62	3.62	3.62
The tenth time	1943	5.10	7.21							7.23	7.22	3.56	3.54	3.55
				The tenth once	1941	5.05		9.01	8.99						9.0	3.48	3.45	3.465

Annotate: the stake degree of depth: the 900mm of nuzzling

Table 2.2 φ 300mm stake contrast test tables of data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Counterweight (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
										The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
				For the first time	1798	0.63	2.0	0.64	0.66							0.65	0.30	0.31	0.305
For the second time	1818	1.19	1.15							1.17	1.16	0.64	0.63	0.635
				For the third time	1841	1.93		1.94	1.93						1.935	1.04	1.05	1.045
The 4th time	1861	2.46	2.72							2.74	2.73	1.63	1.62	1.625
				The 5th time	1889	3.10		3.21	3.23						3.22	1.90	1.89	1.895
The 6th time	1911	3.81	3.74							3.78	3.76	2.35	2.34	2.345
				The 7th time	1925	4.30		4.10	4.12						4.11	2.80	2.82	2.81
The 8th time	1937	4.83	4.49							4.48	4.485	3.04	3.06	3.05
				The 9th time	1952	5.42		4.92	4.93						4.925	3.35	3.37	3.36
The tenth time	1966	6.0	5.53							5.55	5.54	3.92	3.96	3.94
				The tenth once	1959	5.79		7.64	7.68						7.66	3.84	3.80	3.82

Annotate: the stake degree of depth: the 930mm of nuzzling

Table 2.3 φ 300mm stake contrast test tables of data

Load number of times	Frequency meter reading (HZ)	Stake end pressure (KN)	Counterweight (KN)	Pile deflection (mm)			Pile bottom settlements (mm)
										The 1# dial gage	The 2# dial gage	Average	The 1# dial gage	The 2# dial gage	Average
				For the first time	1792	0.61	2.0	0.72	0.73							0.725	0.30	0.29	0.295
For the second time	1813	1.21	1.26							1.28	1.27	0.66	0.67	0.665
				For the third time	1839	1.85		1.88	1.92						1.90	1.20	1.18	1.19
The 4th time	1860	2.41	2.36							2.38	2.37	1.64	1.66	1.65
				The 5th time	1891	3.19		3.16	3.15						3.155	2.08	2.10	2.09
The 6th time	1910	3.78	3.67							3.69	3.68	2.41	2.43	2.42
				The 7th time	1922	4.25		4.0	3.96						3.98	2.89	2.87	2.88
The 8th time	1932	4.65	4.49							4.52	4.505	3.18	3.16	3.17
				The 9th time	1950	5.32		4.94	4.93						4.935	3.52	3.51	3.515
The tenth time	1961	5.80	5.40							5.41	5.405	4.02	4.05	4.035
				The tenth once	1955	5.61		7.73	7.74						7.735	3.94	3.92	3.93

Annotate: the stake degree of depth: the 910mm of nuzzling

The contrast of table 3 φ 300m pile capacity experimental data

Self-balancing detects	The stake type	Pile No.	End resistance	Frictional resistance	Bearing capacity	Pile capacity
							φ300	1#	5.1674	3.54	8.7074	8.6786
	2#	5.0360	3.444	8.48
					3#	5.2550		3.5933	8.8483
	Contrast test	The stake type	Pile No.	Jack pressure						Counterweight weight	Bearing capacity		Pile capacity
φ300					1#	5.405	2.0	8.81	9.47
		2#	6.0	10.0
					3#	5.8		9.6
		Error	8.36％

Unit: KN

Claims (2)

1, a kind of end holds type major diameter pile pier vertical bearing capacity detection method, comprises following steps:

A. according to geological exploration data, end load, the frictional resistance numerical value of estimation stake design and produce the load case;

B. the load case is welded in elongated reinforcing cage end, reinforcing bar cage hoisting is put into a hole;

C. clear up stake hole, examination, fluid concrete;

D. after concrete strength generates 70%, maintained load test (ML-test) or maintained load test (ML-test) detection pile capacity at a slow speed fast;

E. inject the fluidised form expansive concrete to load case high pressure;

The condition that requires to determine comprises; Heap(ed) capacity, displacement stable condition and unloading condition;

F. every grade of heap(ed) capacity is 1/8～1/10 of a frictional resistance calculated value;

G. determining of displacement stable condition, the data that read of stipulated time intrinsic displacement differ 0.1mm and are considered as at the corresponding levels the loading and finish, and carry out next stage and load;

H. unloading condition, the frequency meter frequency declines to a great extent, and the top displacement is little increases in stake, and the pile bottom settlements resilience is considered as the termination test condition.

2, end according to claim 1 holds type major diameter pile pier vertical bearing capacity detection method, it is characterized in that the load case injects conduit, output duct, stake end settlement measurement pipe and piston by last plane, lower plane, cylinder body, fluidised form expansive concrete and forms, the plane is identical with the pile body cross section on the load case, following bearing plate area is less than the last area of plane, cylinder body is cylindrical, diameter of cylinder is less than following bearing plate diameter, and a stake end settlement measurement pipe root is a convex shape section, and piston is positioned at the bottom of cylinder body.

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