The Research On Post-Grouting Cement To Increase The Load Capacity For Bored Pile

The pile foundation treatment is an efficient and costly method. So the importaintquestion is how to reduce the cost of this method. Not only for researchers but also for thedesigners, engineer and supervising engineer all try to find solutions for this issue. For thisreason many studieds have been done on cement post-grouting technology to increase theload capacity for bored pile. The post grouting technique has been used in many countries(e.g., Japan, Thailand, and China). Many studies have been using by modeling andexperiments for grouting technique to increase the bearing capacity and strengthen thestability.With the rapid development of high-rise and construction demand is increaseing;drilled grouting pile has been applied broadly, because of its advantages such as simpleconstruction, high loading capacity, less impact on environment, strong adaptability and soon. But the common defects of drilled grouting pile are collapse of hole wall, mud layer bythe side of pile, sediment of porebottom, soil softening and loosing of hole wall, thesecause the insufficiency of loading capacity of single pile.Bored pile with post-grouting grout pour technique is a kind new process which isbased on cast-insitu bored pile technique. It remedies the weakness of the cast-in-situ boredpile. It can increase the bearing capacity of the cast-in-situ bored pile. This research cancontribute some good practical significance, and bring a large economic benefit.Post-grouting pile process includes the following five steps:Step1: construction bored pile.Step2: Installation the steel pipe drilling along the length of the pile.Step3: Pumping high pressure water to clean sediment at the bottom of the pile.Step4: after installation steel caqes conducting concrete bored pile.Step5: the end of the plug pipe to keep the pressure grouting and the same.This dissertation describes the post-grouting mechanism and construction technologyof the bored pile, Through the mechanism of post grouting in different parts of description,theoretically expounds the post grouting technique in the process of grouting and the effectof the grouting mode.And the different soil layer on the grouting effect are described briefly, and studied the filling pile after grouting technique process.The constructionprocess of grouting after a detailed description, and puts forward some problems thatshould be paid attention in the construction and its treatment. The post grouting technologycan eliminate the inherent weakness of bored piles, and increase the capacity of pile.Before the grouting, construction should be determined by testing the groutingparameters.Previous studies showed that the soil condition, the premise of groutingpressure and grouting effect mainly depends on the cement injection.At this point, the ratioof slurry, grouting flow and grouting pump time are also important factors influencing thegrouting technique.In this paper, the parameters of grouting and the standardization process mainlyincludes: choosing grouting materials, slurry density, viscosity and water cement ratio,strength and consolidation time W/C.Parameter calculation mainly includes: groutingpenetration radius, grouting pressure, grouting quantity calculation, calculation strength ofgrouting, grouting sequence and stop condition.Analysis method of the bearing capacity of bored piles, and a method for determiningthe bearing capacity of pile foundation in the specification given different specification isdifferent, the bearing capacity of pile foundation method is presented.Mainly in thehighway bridge and the foundation design specification (JTGD63-2007)(hereinafterreferred to as "specifications") and "technical specification for building pile foundation(JGJ94-2008)(hereinafter referred to as the specification2) mainly introduces methods forthe determination of the pile foundation bearing capacity of bored piles.A specification andspecification2, the bearing capacity of pile foundation are experiencedcomposition.Specification is one with single pile side resistance and the bearing capacity ofthe single pile to represent the single pile bearing, in the calculation of pile side resistance,the soil and pile side friction values on experience.In situ test specification2mainlyintroduces the method and experience method.Bored piles construction include:(1) drilling preparation: the construction survey andlofting, grading, layout of the construction road, water supply, power supply system, theproduction of steel liners and embedment, mud pit excavation and modulation, theselection of drilling rig.(2) the pore forming process: drilling emplacement, drilling hole,hole cleaning.The production of reinforcing cage.(3) the production of reinforcing cage,setting of reinforced protective layer, storage and transportation of reinforcing steel bar cage and reinforcing cage hoisting up and in placed.(4) pouring underwater concreteperfusion preparation, underwater concrete configuration and underwater concreteperfusion.Pile common problem: open deflection and string of pulp and liners falls off, the stringhole, sticking, shrinkage cavity, drills, breaking pile, reinforcing cage up-floating, afterperfusion pile quality defects.The post grouting pile bearing capacity of pile bottom has been applied inconstructions with different geological conditions (sand, clay, gravel). the bearing capacitypiles using the post grouting pile bottom in Hanoi Vietnam, Beijing, Shanghai, Tianjin,Wuhan and other places is analized and compared with piles without using this technology,which shows that bearing capacity of piles is better.Throug further static test on the effect of Post-Grouting technology to increase the loadcapacity for bored pile, the results show that on the same conditions, settlement of pilesusing Post-Grouting technology is smaller than the settlement of piles without using Post-Grouting technology, and the loading capacity of piles using Post-Grouting technologyincreases1.6-1.75times.The application of post grouting technology can effectively improve the single boredpile bearing capacity. The Elaborated Mipec apartment engineering geological conditionsafter grouting pile bottom grouting method. Result of single pile bearing capacity increaseof56%or more. Post grouting, can improve the mud by the side of pile and pile bottomsediment, improving quality and reducing settlement and pile end resistance.For different areas and geological the Post grouting technology can increase the pilecapacity differently. By comparing the gravel layer and sand layer the Post groutingtechnology can icrease the pile capacity greatly.Through compression test of single pile, in different places for different strata, such asHanoi, Beijing, tianjin, Shanghai, wuhan, hangzhou and other places.For the bottom of thepile in the silty sand layer and silty clay, selection of grouting water cement ratio of W/C=0.55to0.6, grouting pressure for5-7MPa, after grouting in the pile bottom bearingcapacity of single pile was improved30%~40%.For the pile bottom is located in thepebble stone layer then choose W/C=0.65to0.7after pile bottom grouting, can improvethe bearing capacity of single pile reaches50%~80%.Different soil layer has different grouting range, increasing in bearing capacity of single pile post grouting pile led toimprove effect of pile foundation to the best.For grouting bored piles, the bearing capacity is one of the most important, because itdetermines the working efficiency of the pile.Grouting pile construction measures affectthe quality of filling pile, which greatly affect the bearing capacity of bored piles.Therefore, I pointed out that the cause of the problem, and puts forward some measures toovercome the problems existing in the construction process of bored piles of the grouting,so as to ensure the quality of filling pile and the bearing capacity of the play their best.Because post-grouting pile technology in different soil layer the mechanism ofgrouting and grouting results are different, so it is difficult to give a unified formula ofbearing capacity, but according to the test, with the actual conditions of the formation, setup after grouting process and grouting pile bearing capacity of regional design specification.The pile bottom force-hearing layer contrast, tianjin and Shanghai general with gravelsand, silt and silty sand pile bottom force-hearing layer, the bottom of the pile aftergrouting the bearing capacity of single pile was improved30%~40%.Area of gravel layerare like Hanoi, hangzhou, Beijing and wuhan, only which can improve of single bottompost-grouting pile that led the bearing capacity increased about50%~80%.Gravel, silt, rounded gravel layer, silty sand layer, increase capacity of single pilebottom for this reasons:From perspective of geotechnical medium represented that post grouting in silty sandand medium sand layer of fine grained soils, pressure into the slurry is mainly carried outon the bottom sediment filling reinforcement, slurry infiltration rate is low, mainlyfracturing grouting effect.And represented by gravel and rock layer of coarse grained soil,grout injection, except the bottom sediment filling reinforcing its slurry infiltration rate ishigh, the slurry through the permeability, compaction and filling consolidation effect thepile end point soil and pile end together with expanding head of the hole, is equivalent indepth and bottom of the pile, the increasing of bearing capacity of pile endpoint into thebearing area, thus greatly improve the pile bottom resistance.The pile lateral infiltrationrate is different, compared with the fine grained soil and coarse grained soil, infiltrationrate in coarse grained soil is higher than in the fine grained soils.From the perspective of formed post grouting concretion body after consideration,coarse grained soil formation of the concrete strength higher than that of fine grained soil formation, concrete strength is more conducive to the pile foundation under the load,increase of coarse grained soil is more than in fine grained soils.Thus the bearing capacity of pile bottom by slurry injection to the layer of gravel andspherical gravel layer is larger than that under silty sand and medium sand layer increase.Post-grouting the bottom bearing capacity and strengthening of bored cast-in-situ pileare increasing for the following reasons:(1) The influence of the soil, in the same conditions, the bottom of the pile groutingeffect by different soil. Application of pile bottom grouting is useful in gravel, sand, sandygravel, and other coarse gravel soil.Bearing capacity of single pile can improve at rangefrom60%to80%.When the fine soil, silty sand layer, silt, silty clay, post groutinggenerally increased more than30%.(2) Grouting quantity, in general, the pile bottom layer grouting quantity, the more thegreater the range of the pile foundation bearing capacity increase.For gravel, sand, pebbles,sand coarse gravel soil, etc Grouting with W/C=0.650.7, the fine soil, silty sand layer ofpowder sand, silty clay grouting with W/C=0.55to0.6.(3) The grouting pressure, increasing in grouting preasue led to increase bearingcapacity, the settlement of pile.Grouting pressure should be5to7Mpa.FLAC3D software is used to simulate and caculate the capacity of piles using Post-Grouting technology. The simulatited results are compared with experimental results andcalculated results, the difference of these results is small, and it shows that FLAC3D usingto simulate the capacity of piles is acceptable.In the specific contructions, the measured data of contruction used to predicttheoretically of ultimate bearing capacity of the actual pile foundation of contruction, andthe static test results are used to caculate and design pile foundation of contruction.