CN102277867B - Construction method for collapsible loess foundation - Google Patents

Construction method for collapsible loess foundation Download PDF

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Publication number
CN102277867B
CN102277867B CN 201110123842 CN201110123842A CN102277867B CN 102277867 B CN102277867 B CN 102277867B CN 201110123842 CN201110123842 CN 201110123842 CN 201110123842 A CN201110123842 A CN 201110123842A CN 102277867 B CN102277867 B CN 102277867B
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pile
stake
mud jacking
construction
soil
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CN102277867A (en
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胡长明
李修波
梅源
林�源
赵浩
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Xian University of Architecture and Technology
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Xian University of Architecture and Technology
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Abstract

The invention discloses a construction method for a collapsible loess foundation. The construction method comprises the following steps of: firstly, performing foundation treatment on a loess field with collapsibility by using a super downhole dynamic consolidation (SDDC) pile; secondly, collecting undisturbed soil on site, normally performing an indoor experiment to measure an inter-pile soil compaction coefficient and an SDDC pile body compaction coefficient, evaluating the collapsibility, and if any one of the three indexes cannot meet a design requirement, performing pile compensation construction on the SDDC pile until the design requirement is met; and finally, pouring the pile and mudjacking. The method has the advantages of economy, environment friendliness, high treatment depth, good treatment effect, large bearing potential, high complicated load resistance and the like. By application of the method, various side effects caused by the collapsibility of the deep collapsible loess field can be eliminated, and requirements of upper-part high rise buildings on the bearing capability and settlement of the foundation can be met.

Description

A kind of job practices of collapsible loess foundation
Technical field
The present invention relates to the building lot process field, be specially the job practices of a kind of SDDC of employing stake and filling pile ' s after grouting technical tie-up Combined Treatment loess foundation settlement by soaking.
Background technology
In the northwest, North China regular meeting runs into the Loess Subgrade problem; generally including the low humidity collapsible loess is main purpose to eliminate or to reduce saturated yielding distortion harm; need improve the ground of bearing capacity of foundation soil simultaneously handles problems; and weak loess (the especially saturated loess of high humility; how to be transformed saturation ratio S by the full water of collapsible loess r﹥ 80%) handle problems to improve bearing capacity of foundation soil, to reduce harmful compressive strain the ground that is purpose.Because the many and general cohesive soil of the latter's engineering properties is similar, mainly should consider the compressive strain of ground, can treat by weak cohesive soil, the former should consider mainly that then ground is out of shape by the saturated yielding after the water-soaked.
The processing method of traditional collapsible loess foundation mainly contains following method:
(1) bed course, the compacting of (2) weight top layer, (3) are strong to be rammed, (4) compaction pile, (5) chemical consolidation, (6) pre-immersion, (7) pile foundation.
More than in the processing method to collapsible loess foundation, method (1) and method (2) are handled depth as shallow, should not be used for the deep place of collapsible loess; Method (3) is big to the negative effect of environment, should not reach the urban district around existing building and use; The used filler of method (4) is single, and undesirable to the compacted effect of inter-pile soil, elimination ground settlement by soaking that only can be limited; Method (5) disposal cost costliness generally will not adopt; The place peripheral ground sinks to ftractureing during method (6) immersion, and causes " metalling run out " Durchgangshohle easily, influences the safety of surrounding buildings thing; Method (7) is handled deep Collapsible Loess District, and especially in the self weight collapse loess place, for overcoming the adverse effect that the negative skin friction of pile is brought, required stake is longer, less economical.
More than in the traditional treatment method at collapsible loess foundation, especially to the deep place of self weight collapse loess, still do not have cost-effective method for processing foundation and can satisfy high-rise building (towering structure) to the requirement of bearing capacity of foundation soil and settling amount, therefore, the processing method of seeking a kind of new collapsible loess foundation is the focus that those skilled in the art pay close attention to.
Summary of the invention
At shortcoming or the deficiency that above-mentioned prior art exists, the object of the present invention is to provide a kind of SDDC of employing stake and filling pile ' s after grouting technical tie-up to handle the job practices of collapsible loess foundation.
In order to realize above-mentioned task, the present invention is achieved by following technical scheme:
A kind of job practices of collapsible loess foundation is characterized in that, this method at first adopts SDDC stake method that ground is carried out in the loess place with settlement by soaking and handles; Then, gather undisturbed soil at the scene, carry out laboratory test by standard, record the compacted coefficient of inter-pile soil, SDDC stake pile body coefficient of consolidation, and carry out the settlement by soaking evaluation, if having when not satisfying design specifications in three indexs, then carry out the piling construction of SDDC stake, until meeting design requirement; Carry out the filling pile ' s after grouting construction then.
The step of its concrete construction is as follows:
Step 1 is verified geologic information, in conjunction with design parameters, selects suitable drilling construction facility;
Step 2, obstruction is on the ground removed in smooth place, and undreground works and pipeline in the scope of mark disposal field keep levelling of the land;
Step 3 is measured unwrapping wire, makes control axis, piling site boundary and sign;
Step 4, the construction equipment of selecting in the applying step one, impact holing.The drilling construction facility generally adopt the stake machine of band pile frame, and jump bit is selected the overweight hammer of olive shape for use.Pile-forming machine perching, align, after the leveling, the lifting weight arrives design height and (can be promoted to generally that 10m ~ 18m), the overweight hammer of olive shape is automatically-unhooked, pour in the soil by the kinetic energy of the overweight hammer of olive shape, carry out aforesaid operations repeatedly, reach designing requirement until hole depth;
Step 5, the layering filler, ram pile:
To insert a hole by the quantitative filler layering that design is mixed and stirred with standard hopper or dumper, the overweight hammer of the olive shape when using pore-forming then is with filler compaction in layers one by one, until becoming the SDDC stake.And each hole should be rammed and be filled to more than the design elevation of top 0.5m at least; Wherein, the sequence of construction of pore-forming and filling tamped is carried out at interval;
Step 6, construction machinery move to next stake position, and repeating step four, step 5 are all finished until the SDDC stake;
Step 7, pile body filler sample and the inter-pile soil sample of SDDC stake are gathered in the excavation prospect pit, do indoor conventional soil test, and specific requirement is as follows:
(1) it is some to get the pile body filler sample of inter-pile soil and SDDC stake by standard, does indoor conventional soil test, and the coefficient of consolidation that the compacted coefficient that its result should satisfy inter-pile soil is not less than the pile body of 0.93, SDDC stake is not less than 0.97;
(2) settlement by soaking evaluation.For further determining the elimination degree of settlement by soaking, the not disturbed soil sample of Three S's DDC stake centre of form place inter-pile soil is gathered in ground on the scene excavation prospect pit, carry out indoor conventional soil test, according to laboratory test results, judge whether the elimination degree of settlement by soaking meets design requirement.
If above each index meets design requirement, then carry out the construction of filling pile ' s after grouting; Otherwise carry out the piling construction of SDDC stake;
Step 8 before carrying out filling pile construction, adopts the thick C15 concrete of 100mm that cure process is carried out on the ground of adopting the SDDC stake and handling;
Step 9 adopts total powerstation to utilize the crossing point of axes of appointment to do the control point, and to the setting-out of grout pile position, location, the stake position direction range error of castinplace pile is not less than 5mm, and with spike mark is one by one carried out in the stake position;
Step 10 is made reinforcing cage, checks and accepts stand-by.Adopt the pre-pipe laying mud jacking of pile body, namely by the mud jacking degree of depth requirement of design, madjack pipe is fixed on the reinforcing cage, squeezing unit is transferred with reinforcing cage.Adopt screwed connection to avoid welding between the madjack pipe;
Step 11, the pore-forming facility are in place, and keep boring machine steady, not run-off the straight, displacement;
Step 12 is adjusted boring machine, to good grout pile position, starts boring machine with the contraposition circle, reach controlling depth after, carry out hole operation clearly;
Step 13, mobile pore-forming facility are to next grout pile position, and repeating step 11 and step 12 are until the pore-forming operation of finishing all castinplace piles;
Step 14 is transferred the reinforcing bar cage hoisting of making in advance that installs Grouting Pipe, ties up mortar cushion block or plastic clip before reinforcing cage is put into, and during install reinforcing cage, the mating holes position, hangs and directly holds up surely, slowly sinks, and avoids colliding hole wall; When reinforcing cage is put into design attitude, should fix immediately; Weld junction between two sections reinforcing cages, to guarantee the correct position of reinforcing cage, guarantees that protective layer thickness meets the requirements;
Step 15, madjack pipe tries the water.Should do the test of trying the water when every joint madjack pipe is transferred with reinforcing cage, if find that water column descends or water column disappears, should check then whether madjack pipe has sand holes, screwed connection whether to seal.
Reinforcing cage is placed and is carried out in the metapore that finishes needing again the water surface in the inspection eye after the second time, finished in clear hole, and it is suitable for reading that no abnormal back seals madjack pipe with plug;
Step 10 six, the concreting castinplace pile.With putting a slide tube concreting castinplace pile, before putting the slide tube, check and measure the thickness of loosened soil in the boring again, carry out when reaching designing requirement, concreting is adopted and is carried out continuously, when concreting is pushed up to the stake of castinplace pile, the stake top design elevation that should suitably surpass castinplace pile is to guarantee that after cutting laitance the stake top mark height of castinplace pile adheres to specification.Simultaneously, make the test block of same match ratio, per tour must not be less than one group;
Step 10 seven, packer permeability test, packer permeability test carry out in 24 hours behind pile.Must carry out packer permeability test before the formal mud jacking, to check the unimpeded situation of pipeline and one way valve.
If during the situation that in stake side or stake end reaming takes place, collapse hole or fullness coefficient is bigger, need pay special attention to carry out in advance packer permeability test, carry out guaranteeing to wash open thicker concrete coating in concreting in intact 5 hours.
Break through force value and the unimpeded situation of pipeline by special messenger's record during test;
Step 10 eight, repeating step 14, step 15, step 10 six, step 10 seven are finished the pile work of each castinplace pile, are the ready work of back mud jacking construction simultaneously;
Step 10 nine, back mud jacking construction.Take the mode of secondary grouting, to give full play to the effect of slip casting, obtain better effect.
(1) just annotate: the concrete curing of castinplace pile pile body began mud jacking after 3~5 days, at the bottom of will being injected into by high-pressure pump and pre-buried madjack pipe by the good cement paste of design configurations or go in the stake side soil layer, if compound mud jacking then generally carries out a side pressure slurry earlier, carry out pile base grouting after 12 hours again.Pressure is little when just annotating, slurries by rare to thick.To keep a close eye on the variation of grouting pressure, grouting amount when just annotating, and note slip casting rhythm.Should arrange during pile grouting dial gage detect stake on the amount of lifting, avoid excessive.
(2) secondary grouting: the best Grouting Pipe with slip casting for the first time of the Grouting Pipe of slip casting for the second time is symmetrically distributed.Grouting amount is generally primary 1 ∕, 3~1 ∕ 4 for the second time, and water/binder ratio can suitably improve.
(3) mud jacking of same pile order: earlier last side pipe is carried out mud jacking, descend side pipe then, hold the pipe mud jacking at last; The mud jacking order of same cushion cap stake: stake rear center stake earlier.
Step 2 ten stops mud jacking.Stop total control principle of mud jacking based on the mud jacking amount, pressure is controlled to be auxilliary.But the mud jacking parameter also should be according to the geological conditions choose reasonable, if the stake end during for closely knit gravel boulder bed, should be the major control index with the mud jacking amount; The stake side should be the major control index with mud jacking pressure then when being closely knit loess formation.
After mud jacking finishes immediately to the madjack pipe plug of screwing on, in order to avoid reduce grouting result because of overfall.
Step 2 11, repeating step 19, step 2 ten are finished the construction working of each filling pile ' s after grouting continuously.
The high-rise building (towering structure) that adopts method of the present invention can effectively solve on the deep collapsible loess place requires harsh problem to aspects such as bearing capacity of foundation soil, settling amount, ambient influnences.Can effectively to shorten stake after this method long because adopting again, so its economic benefit of bringing is more remarkable than additive method.
Description of drawings
Fig. 1 is SDDC stake layout schematic diagram;
Fig. 2 is ground processing profiles schematic diagram;
Fig. 3 is that madjack pipe is buried schematic diagram underground.
Mark among the figure is represented respectively: 1, inter-pile soil, 2, the SDDC stake, 3, the ground bottom do not have the natural soil layer of settlement by soaking ,4, castinplace pile, 5, Grouting Pipe.
The present invention is described in detail with embodiment with reference to the accompanying drawings.
The specific embodiment
(the Super Down-hole Dynamic Compaction of the super dynamic compaction of deep layer in the hole, be called for short SDDC), it is to pass through impact holing with kinetic energy, over pressure, the strong compacted mechanism of action, from deep to shallow, successively ram pile by force, kinetic energy at over pressure makes the inter-pile soil side produce very big dynamic passive earth pressure in the rammer process by force, forces the downward and peripheral densification of filler to be extruded, and the inter-pile soil mechanics index of physics is improved fully.Can be widely used in assorted filling out, the processing of all kinds of special foundations such as liquefaction, saturated yielding weakness, expansion.This method applicability is strong, handle that the degree of depth is big, treatment effect good, environmental protection, to advantages such as ambient influnence are little, good in economic efficiency, be familiar with by people gradually in recent years, and treatment effect is good.The present invention introduces the super dynamic compaction of deep layer in the hole in the pile foundation method, and the loess foundation settlement by soaking is handled, and through facts have proved, has obtained satisfied effect.
King-pile of the present invention basis pattern is looked specific requirement, can take stake-patten, stake-beam basis, stake-foundation of wall, stake-raft foundation, stake-box foundation etc., mode such as the corresponding mode of laying out pile can adopt under the post and lay out pile, lay out pile under the wall, full hall lays out pile, local full hall lays out pile.
Referring to Fig. 1, Fig. 2 and Fig. 3, the job practices of collapsible loess foundation of the present invention adopts the settlement by soaking of SDDC stake and castinplace pile (be example with the bored pile) post-grouting technology Combined Treatment collapsible loess foundation, specifically comprises the following steps:
One, the construction of SDDC stake 2.
Step 1 is verified geologic information, in conjunction with design parameters, selects suitable drilling construction facility;
Step 2, obstruction is on the ground removed in smooth place, and undreground works and pipeline in the scope of mark disposal field keep levelling of the land;
Step 3 is measured unwrapping wire, makes control axis, piling site boundary and sign;
Step 4, the construction equipment of selecting in the applying step one, impact holing.The drilling construction facility generally adopt the stake machine of band pile frame, and jump bit is selected the overweight hammer of olive shape for use.Pile-forming machine perching, align, after the leveling, the lifting weight arrives design height and (can be promoted to generally that 10m ~ 18m), the overweight hammer of olive shape is automatically-unhooked, pour in the soil by the kinetic energy of the overweight hammer of olive shape, carry out aforesaid operations repeatedly, reach designing requirement until hole depth;
Step 5, the layering filler is rammed pile.To insert a hole by quantitative filler (can not select bulk stiff materials such as fragment of brick, rubble, concrete block for use as the filler) layering that design is mixed and stirred with standard hopper or dumper, the overweight hammer of olive shape when using pore-forming then is with filler compaction in layers one by one, until becoming SDDC stake 2.Each hole should be rammed and be filled to more than the design elevation of top 0.5m at least; Wherein, the sequence of construction of pore-forming and filling tamped is carried out at interval;
Step 6, the construction machinery displacement.Repeating step four, step 5 are all finished until SDDC stake 2;
Step 7, excavation prospect pit are gathered the pile body filler sample of SDDC stake 2 and the soil body that inter-pile soil 1(top has settlement by soaking) sample, do indoor conventional soil test, specific requirement is as follows:
(1) get inter-pile soil 1 by standard and SDDC stake 2 pile body filler samples are some, do indoor conventional soil test, the coefficient of consolidation that the compacted coefficient that its result should satisfy inter-pile soil 1 is not less than the pile body of 0.93, SDDC stake 2 is not less than 0.97;
(2) settlement by soaking evaluation.For further determining the elimination degree of settlement by soaking, the not disturbed soil sample of Three S's DDC stake 2 centre of form place inter-pile soils 1 is gathered in ground on the scene excavation prospect pit, carry out indoor conventional soil test, according to laboratory test results, judge whether the elimination degree of settlement by soaking meets design requirement.
If above each index meets design requirement, then carry out the construction of drill-pouring post-pressure grouting; Otherwise carry out the piling construction of SDDC stake 2;
Step 8 before carrying out bored pile 4 construction, adopts the thick C15 concrete of 100mm that cure process is carried out on the ground of adopting SDDC stake 2 and handling;
Two, bored pile 4 back mud jacking constructions
Step 9 adopts total powerstation to utilize the crossing point of axes of appointment to do the control point, and to 4 position setting-outs of bored pile, location, the stake position direction range error of bored pile 4 is not less than 5mm, and with spike mark is one by one carried out in the stake position;
Step 10, reinforcing cage are made, are checked and accepted:
Adopt the pre-pipe laying mud jacking of pile body, namely by the mud jacking degree of depth requirement of design, Grouting Pipe 5 is fixed on the reinforcing cage, squeezing unit is transferred with reinforcing cage.Adopt screwed connection to avoid welding between the Grouting Pipe 5;
Step 11, auger is in place, and keeps auger steady, not run-off the straight, displacement;
Step 12, straightening boring frame tappet, starts auger and creeps into, is unearthed 4 positions of good bored pile with the contraposition circle, reach controlling depth after, after clear soil is dallied in the bottom, hole, stop to bore, carry brill; The hole quality safeguard measure is:
1) reaches loosened soil thickness deeply with sounding line/hammer gaging hole and should not surpass 100mm;
2) in the retaining hole height of mud liquid level prevent shrinkage cavity, the hole of collapsing;
Step 13, mobile auger is to 4 positions of next bored pile, and repeating step 11 and step 12 are until the pore-forming operation of finishing all bored piles 4;
Step 14 is transferred the reinforcing bar cage hoisting of making in advance that installs Grouting Pipe 5, ties up mortar cushion block or plastic clip before reinforcing cage is put into, and during install reinforcing cage, the mating holes position, hangs and directly holds up surely, slowly sinks, and avoids colliding hole wall; When reinforcing cage is put into design attitude, should fix immediately; Weld junction between two sections reinforcing cages, to guarantee the correct position of reinforcing cage, guarantees that protective layer thickness meets the requirements;
Step 15, Grouting Pipe 5 is tried the water.Should do the test of trying the water when every joint madjack pipe 5 is transferred with reinforcing cage, if find that water column descends or water column disappears, should check then whether madjack pipe 5 has sand holes, screwed connection whether to seal.
Reinforcing cage is placed and is carried out in the metapore that finishes needing again the water surface in the inspection eye after the second time, finished in clear hole, and it is suitable for reading that no abnormal back seals Grouting Pipe 5 with plug;
Step 10 six, concreting.With putting a slide tube concreting, before putting the slide tube, check and measure the thickness of loosened soil in the boring again, carry out when reaching designing requirement, concreting is adopted and is carried out continuously, when concreting is pushed up to the stake of bored pile 4, the stake top design elevation that should suitably surpass bored pile 4 is to guarantee that after cutting laitance the stake top mark height of bored pile 4 adheres to specification.Simultaneously, make the test block of same match ratio, per tour must not be less than one group;
Step 10 seven, packer permeability test: packer permeability test carries out in 24 hours behind pile.Must carry out packer permeability test before the formal mud jacking, to check the unimpeded situation of pipeline and one way valve.
If during the situation that in stake side or stake end reaming takes place, collapse hole or fullness coefficient is bigger, need pay special attention to carry out in advance packer permeability test, carry out guaranteeing to wash open thicker concrete coating in concreting in intact 5 hours.
Break through force value and the unimpeded situation of pipeline by special messenger's record during test;
Step 10 eight, repeating step 14, step 15, step 10 six, step 10 seven are finished the pile work of each bored pile 4, are the ready work of back mud jacking construction simultaneously;
Step 10 nine, back mud jacking construction.Take the mode of secondary grouting, to give full play to the effect of slip casting, obtain better effect.
(1) just annotate: bored pile 4 pile concrete maintenances began mud jacking after 3~5 days, at the bottom of will being injected into by high-pressure pump and pre-buried madjack pipe 5 by the good cement paste of design configurations or go in the stake side soil layer, if compound mud jacking, then generally carry out a side pressure slurry earlier, carry out pile base grouting after 12 hours again.Pressure is little when just annotating, slurries by rare to thick.To keep a close eye on the variation of grouting pressure, grouting amount when just annotating, and note slip casting rhythm.Should arrange during pile grouting dial gage detect stake on the amount of lifting, avoid excessive.
(2) secondary grouting: the Grouting Pipe 5 best Grouting Pipe 5 with slip casting for the first time of slip casting for the second time are symmetrically distributed.Grouting amount is generally primary 1 ∕, 3~1 ∕ 4 for the second time, and water/binder ratio can suitably improve.
(3) mud jacking of same pile order: earlier last side pipe is carried out mud jacking, descend side pipe then, hold the pipe mud jacking at last; The mud jacking order of same cushion cap stake: stake rear center stake earlier.
Step 2 ten stops mud jacking.Stop total control principle of mud jacking based on the mud jacking amount, pressure is controlled to be auxilliary.But the mud jacking parameter also should be according to the geological conditions choose reasonable, if the stake end during for closely knit gravel boulder bed, should be the major control index with the mud jacking amount; Should be the major control index with mud jacking pressure then when being closely knit loess formation because of the stake side.
After finishing, gives by mud jacking madjack pipe 5 plug of screwing on immediately, in order to avoid reduce grouting result because of overfall.
Step 2 11, repeating step 19, step 2 ten are finished each bored pile 4 construction working of mud jacking afterwards continuously.
Winter, Pluvial construction precautions:
(1) teletostage is built rod when coagulating soil when temperature is lower than below 0 ℃, should take the heat tracing measure.When building, concrete temperature is carried out by winter constructure scheme regulation.Before reaching design strength 50%, the stake top must not endure cold; When temperature should be taked the slow setting measure to concrete during still in 30 ℃ as the case may be.
(2) the Pluvial strictness is adhered to causing the hole of collapsing with the regulation of boring with concreting in case pour water behind the pore-forming.The on-the-spot various measures that draining must be arranged prevent that the surface water from flowing in the groove, causes slope collapse or basic native depression, boring machine inclination etc.
In addition the Pluvial when the place has ponding or soil moisture in layer higher, it is serious that impact holing is inhaled the hammer phenomenon, can adopt rig boring this moment, but must suitably increase the number of times of ramming to filler in the hole;
When adopting method of the present invention to construct, the filler of SDDC stake 2 is not selected fragment of brick, rubble, concrete block or other bulk stiff materials for use.
During the bored concrete pile foundation design, ground after SDDC stake 2 processing is considered as composite foundation, and a position of not considering SDDC stake 2 arranges that treatment region soil body mechanics index of physics adopts average, and the ground bottom does not have the mechanics index of physics employing geological mapping of the natural soil layer 3 of settlement by soaking the data that provide are provided.
With way of example the present invention is specified above, but the invention is not restricted to above-mentioned specific embodiment.
Be that principle of the present invention is described below.
The super dynamic compaction of deep layer (SDDC) is in pore forming process in the hole, force in the hole undisturbed soil side direction to be extruded, the soil body in the Zhou Yiding scope is squeezed, disturbance and reinventing, when filler, force in the hole filler lateral compression hole wall again, the all soil bodys in larger scope of stake are squeezed again, disturbance and reinventing, strong huge tamping energy volume production living ripple and the dynamic stress of ramming acts on repeatedly, force soil skeleton to produce plastic strain, thereby improve compactness and the shear strength of soil, improve the deformation characteristic of soil, the beading pile body and the interlock of inter-pile soil phase that form, the bearing capacity height, the strong compacted effect during because of pore-forming, it is more effective than additive method that this method is eliminated collapsibility of loess effect aspect.Its reinforcement mechanism mainly contains following 4 points:
(1) in pore-forming and the formation of pile to the compacted effect of the power on former;
(2) pile body filling metathesis (comprise pile body and clamp-on the aggregate of inter-pile soil);
When (3) adopting dirt, the aquation of quicklime and gelatification (chemical replacement).In Collapsible Loess District, when improving soil body physical mechanics proterties, can effectively eliminate settlement by soaking by the ground that the SDDC method is handled.Then, adopt the design and construction of the castinplace pile of post-grouting technology associating at the SDDC pile composite foundation that forms.
Adopt the castinplace pile reinforcement mechanism of compound mud jacking technology to mainly contain in the back mud jacking work progress:
(1) infiltration consolidation;
(2) compacted packing action;
(3) splitting reinforced action;
(4) expand end hole enlargement effect.
Under above-mentioned mechanism effect, the physical mechanics proterties of foundation soil body is further improved, the settlement by soaking of slip casting place loess is further eliminated, the bearing capacity of castinplace pile is largely increased, and the pile foundation settling amount significantly reduces under the identical load.
In sum, adopt the job practices of loess foundation settlement by soaking of the present invention to compare with traditional method, its novelty contribution is:
(1) under effect aspect above-mentioned two, the settlement by soaking of loess foundation is eliminated, and then the pile-side negative friction problem that causes because of the loess foundation settlement by soaking solved, so pile foundation can design by the conventional pile foundation of not considering the negative skin friction of pile;
(2) because castinplace pile has adopted SDDC stake and filling pile ' s after grouting technical tie-up Combined Treatment, so the pile foundation settling amount significantly reduces under the significantly raising of pile capacity, identical load action.Therefore, satisfy can effectively shorten under the prerequisite of code requirement the stake long, significantly increase economic efficiency.To have a bearing capacity big and resist the strong characteristics of complicated weight bearing power because of pile foundation again, carry out appropriate design according to engineering characteristic after, can satisfy top high-rise building (towering structure) to the stability on basis and the requirement of differential subsidence.

Claims (2)

1. the job practices of a collapsible loess foundation is characterized in that, this method at first adopts SDDC stake method that ground is carried out in the loess place with settlement by soaking and handles; Then, gather undisturbed soil at the scene, carry out laboratory test by standard, record the compacted coefficient of inter-pile soil and SDDC stake pile body coefficient of consolidation, and carry out the settlement by soaking evaluation, if having when not satisfying design specifications in three indexs, then carry out the piling construction of SDDC stake, until meeting design requirement; Carry out the construction of filling pile ' s after grouting then; Concrete job practices may further comprise the steps:
Step 1 is verified geologic information, in conjunction with design parameters, selects suitable drilling construction facility;
Step 2, obstruction is on the ground removed in smooth place, and undreground works and pipeline in the scope of mark disposal field keep levelling of the land;
Step 3 is measured unwrapping wire, makes control axis, piling site boundary and sign;
Step 4, the construction equipment of selecting in the applying step one, impact holing, drilling construction facility adopt the stake machine of band pile frame, and jump bit is selected the overweight hammer of olive shape for use, pile-forming machine perching, align, after the leveling, the lifting weight arrives design height, and the overweight hammer of olive shape is automatically-unhooked, pours in the soil by the kinetic energy of the overweight hammer of olive shape, carry out aforesaid operations repeatedly, reach designing requirement until hole depth;
Step 5, the layering filler, ram pile:
To insert a hole by the quantitative filler layering that design is mixed and stirred with standard hopper or dumper, the overweight hammer of the olive shape when using pore-forming then is with filler compaction in layers one by one, until pile; And each hole should be rammed and be filled to more than the design elevation of top 0.5m at least; Wherein, the sequence of construction of pore-forming and filling tamped is carried out at interval;
Step 6, construction machinery move to next stake position, and repeating step four, step 5 are all finished until stake;
Step 7, pile body filler sample and the inter-pile soil sample of excavation prospect pit collecting pile are done indoor conventional soil test, and specific requirement is as follows:
(1) it is some to get the pile body filler sample of inter-pile soil and stake by standard, does indoor conventional soil test, and the compacted coefficient that its result should satisfy inter-pile soil is not less than 0.93, and the coefficient of consolidation of pile body of stake is not less than 0.97;
(2) settlement by soaking evaluation: for further determining the elimination degree of settlement by soaking, the not disturbed soil sample of three stake centre of form place inter-pile soils is gathered in ground on the scene excavation prospect pit, carry out indoor conventional soil test, according to laboratory test results, judge whether the elimination degree of settlement by soaking meets design requirement;
If above each index meets design requirement, then carry out the construction of filling pile ' s after grouting; Otherwise carry out the piling construction of stake;
Step 8 before carrying out filling pile construction, adopts the thick C15 concrete of 100mm that cure process is carried out on the ground of adopting pile and handling;
Step 9 adopts total powerstation to utilize the crossing point of axes of appointment to do the control point, and to the setting-out of grout pile position, location, the stake position direction range error of castinplace pile is not less than 5mm, and with spike mark is one by one carried out in the stake position;
Step 10 adopts the pre-pipe laying mud jacking of pile body, namely by the mud jacking degree of depth requirement of design, madjack pipe is fixed on the reinforcing cage, and squeezing unit is transferred with reinforcing cage, adopts screwed connection to avoid welding between the madjack pipe;
Step 11, the pore-forming facility are in place, and keep boring machine steady, not run-off the straight, displacement;
Step 12 is adjusted boring machine, to good grout pile position, starts boring machine with the contraposition circle, reach controlling depth after, carry out hole operation clearly;
Step 13, mobile pore-forming facility are to next castinplace pile position, and repeating step 11 and step 12 are until the pore-forming operation of finishing all castinplace piles;
Step 14 is transferred the reinforcing bar cage hoisting of making in advance that installs Grouting Pipe, ties up mortar cushion block or plastic clip before reinforcing cage is put into, and during install reinforcing cage, the mating holes position, hangs and directly holds up surely, slowly sinks, and avoids colliding hole wall; When reinforcing cage is put into design attitude, should fix immediately; Weld junction between two sections reinforcing cages, to guarantee the correct position of reinforcing cage, guarantees that protective layer thickness meets the requirements;
Step 15, madjack pipe tries the water: should do the test of trying the water when every joint madjack pipe is transferred with reinforcing cage, if find that water column descends or water column disappears, should check then whether madjack pipe has sand holes, screwed connection whether to seal;
Reinforcing cage is placed and is carried out in the metapore that finishes needing again the water surface in the inspection eye after the second time, finished in clear hole, and it is suitable for reading that no abnormal back seals madjack pipe with plug;
Step 10 six, concreting: with putting a slide tube concreting, before putting the slide tube, check and measure the thickness of loosened soil in the boring again, carry out when reaching designing requirement, concreting is adopted and is carried out continuously, when concreting is pushed up to the stake of castinplace pile, should suitably surpass the stake top design elevation of castinplace pile, to guarantee that after cutting laitance the stake top mark height of castinplace pile adheres to specification; Simultaneously, make the test block of same match ratio, per tour must not be less than one group;
Step 10 seven, packer permeability test: packer permeability test carries out in 24 hours behind pile, must carry out packer permeability test before the formal mud jacking, to check the unimpeded situation of pipeline and one way valve, if during the situation that in stake side or stake end reaming takes place, collapse hole or fullness coefficient is bigger, need pay special attention to carry out in advance packer permeability test, carry out guaranteeing to wash open thicker concrete coating in concreting in intact 5 hours; Break through force value and the unimpeded situation of pipeline by special messenger's record during test;
Step 10 eight, repeating step 14, step 15, step 10 six, step 10 seven are finished the pile work of each castinplace pile, are the ready work of back mud jacking construction simultaneously;
Step 10 nine, back mud jacking construction: take the mode of secondary grouting, comprising:
(1) just annotate: the concrete curing of castinplace pile pile body began mud jacking after 3~5 days, at the bottom of will being injected into by high-pressure pump and pre-buried madjack pipe by the good cement paste of design configurations or go in the stake side soil layer, if adopt compound mud jacking, then carry out a side pressure slurry earlier, carry out pile base grouting after 12 hours again; Pressure is little when just annotating, slurries by rare to thick; To keep a close eye on the variation of grouting pressure, grouting amount when just annotating, and note slip casting rhythm, should arrange during pile grouting dial gage detect stake on the amount of lifting, avoid excessive;
(2) secondary grouting: the Grouting Pipe of slip casting for the second time is symmetrically distributed with the Grouting Pipe of slip casting for the first time, and grouting amount is generally primary 1 ∕, 3~1 ∕ 4 for the second time, and water/binder ratio suitably improves;
(3) mud jacking of same pile order: earlier last side pipe is carried out mud jacking, descend side pipe then, hold the pipe mud jacking at last; The mud jacking order of same cushion cap stake: stake rear center stake earlier;
Step 2 ten stops mud jacking: the total control principle that stops mud jacking is that pressure is controlled to be auxilliary based on the mud jacking amount, but the mud jacking parameter is according to the geological conditions choose reasonable, if the stake end during for closely knit gravel boulder bed, should be the major control index with the mud jacking amount; The stake side should be the major control index with mud jacking pressure then when being closely knit loess formation;
After mud jacking finishes immediately to the madjack pipe plug of screwing on, in order to avoid reduce squeezing quality because of overfall;
Step 2 11, repeating step 19, step 2 ten are finished the construction working of each filling pile ' s after grouting continuously.
2. the method for claim 1 is characterized in that, the filler of described pile is not selected fragment of brick, rubble, concrete block or other bulk stiff materials for use.
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