Research And Application Of Cast-in-place Pile Foundation Post Grouting Technology Of Super-tall Building In Beijing

This paper has become rather complicated geological conditions of China sincethe20th century, after the second half, especially since the last20years of the20thcentury to the first decade of the21st century, due to the continued rapid growth ofthe national economy, the scale of infrastructure investment escalating constructionsite and environmental conditions, especially making deep foundation pile-basedapplications, research and development has reached an unprecedented level.Pile pressure grouting pile into a pile of the various forms of drilling, diggingholes and punching and the grouting pipe buried in the pile or piles week, will be ableto cure slurry (such as pure cement, cement mortar, a grout admixture doped,chemical slurry, etc.) is uniformly injected into the soil around the body of the bottomof the pile tip or pile. Serous infiltration, filling, displacement, splitting, compactionand consolidation, and other physical or chemical form alone or together, change thephysical and mechanical properties of the soil around the side of the pile tip and pile,the pile tip resistance and the pile side resistance improved to varying degrees, the pilesettlement amount is reduced, the carrying capacity of the pile is improved. Thereasonable process after grouting can not only improve single pile bearing and unevensettlement can reduce the pile settlement amount and pile group, with significanteconomic benefits.Over the last decade, the extensive rise of high-rise buildings and high-risebuildings in the country, large diameter bored pile to get a large number ofapplications, especially in the coastal areas, require high capacity and stability of thebearing capacity of the pile foundation, at the same time to meet the settlement theamount of the request, pile foundation design a new topic. Post grouting Bored pile end (side) meet the large buildings bearing capacity, at the same time to meet theconditions of engineering applications, the use of grouting pile bearing capacity of thepile end (side) can be considered reduce the number of piles, arranged pile of planeposition can increase the spacing of the piles to reduce the pile group effect. Postgrouting Bored pile end (side) work load deformation is small, and thus can reducethe settlement of the differences between the high-rise buildings in the main buildingwith podium. Use the pile tip (side) groutig the good pile tip bearing layers exist in theconstruction of venues premise, is bound to bring new vitality to the development ofhigh-rise buildings.With the progressive development of the domestic construction project at thepresent stage, the support of the state and the cause of building gradually, a largenumber of construction projects being construction. The pile grouting method can beapplied to a variety of complex geological conditions, foundation construction,application market is very huge. Has a very important social and economic benefits,grouting technology in promoting and pile foundation reinforcement technology bythorough and systematic study on the of pile grouting method in the pile foundationconstruction, security and economy of the pile foundation construction also has a veryimportant role in the development of its application value is reflected in the followingaspects.⑴Inheriting all the advantages of the ordinary pile, applicable to a variety ofgeological conditions, no vibration harm, no noise and so on.(2) Creatively proposed and implemented the pile bottom the pile side pressuregrouting construction technology, making the pile capacity compared with the samediameter and length of the ordinary pile, greatly increases. Thus greatly reducing thelength of the pile design, reduce construction costs, the economic benefits are veryobvious. ⑶Settlement is greatly reduced, and apply to the upper structure of the settlementsensitive industrial construction and mechanical equipment foundation.⑷Pile the side pressure grouting even if the pile side mud cake with soil mixedwith the compaction process, the soil and the pile and links into the overall slurryhardened stones will form a wedge in the pile side. These will cause friction betweenthe pile and the soil area increases, improve the lateral friction. This advantage can bemore widely applied in the uplift pile designs.The pile grouting improve pile foundation theory, there are three things:penetration, compaction, splitting grouting (grout) reinforced the role of thefoundation soil.After grouting technology of process parameter selection depends on theimprovement of pile capacity, which after grouting material selection, after groutingpressure allowed value, the post grouting how much pressure time interval, and otherparameters of the pulp is the most critical.Full analysis and evaluation of the text through the geological seismic engineeringfield construction of high-rise buildings in Beijing Fortune Plaza II period, the terrainsurrounding the seismic effects of the regional hydrogeological conditions, site andfoundation bearing capacity value factors, issues related to the research and analysisof the engineering and construction field area in geotechnical engineeringinvestigation, proposed the foundation program and structure construction measuresto resolve the differences between the main high-rise towers and pure basementsubsidence problems put forward the program of large diameter bored piles reliablepile end and take pile lateral groutig, increase pile capacity, to meet the requirementsof the foundation of the project as well as the overall stability.With the help of the general purpose finite element the software ANSYS12.0establish the structural model of the pile-soil system to simulate the static load test process to determine before grouting and after grouting for different strata, differentpile length of the large diameter of the bearing capacity of bored piles improvementdisplacement settlement. As the pile end bearing stratum final1○12layers of sand andgravel layer, using the program should be based on the area construction projects theunderwater drilling pile design and construction experience, take a reliable pile tip,pile lateral the grouting Technology (groutig is pile after the pile, using high-pressureinjection pump embedded in the bottom of the pile or pile side grouting conduit to thebottom of the pile or pile side of the high pressure injection of cement slurry throughthe slurry splitting, the role of filling, compaction, consolidation, the plug real pilebottom of soft soil, to achieve consolidation sediment and the purpose of squeezingsoil; return pulp slurry along the pile lateral diffusion, to strengthen the soil and pileside The skin friction of bored piling technology to improve the pile capacity,anti-friction, reduce the amount of building subsidence), and shall meet the designrequirements to improve in soft ground conditions. Be able to not only improve into ahole, pile quality, and can eliminate the hole bottom sediment, and impact of the holewall mud skin to maintain the stability of the hole wall, so as to improve the bearingcapacity of the foundation piles and reduce the pile foundation settlement.After the end of the project through the pile capacity hydrostatic test, sonictransmission experiments and compressive testing of low strain are fully proved in thesame conditions, the pile bottom pile lateral grouting pile whether from a single pilecarrying capacity, or pile integrity and the pile strain lowering has greatly improved.And to a certain extent, on the bottom of the pile lateral grouting method to reduce thelarge diameter pile some of the original construction defects, to ensure the integrity ofthe pile.High-rise building large-diameter pile grouting technology involves more actualengineering factor is often integrated presence and interaction factor, this article is only for a fixed high-rise buildings in the region of large diameter piles after groutingeffectand computational methods to do a preliminary study. Extensive collection ofengineering data, summarize the achievements in the actual engineering applications,practical experience rise to the theory of the system, to more effectively guide theengineering practice, is still a major research direction in the future.