Design Of Deep Foundation Of Shanghai Eighth People Hospital's Ward Building

Along with the fast development of construction industry in China, the problem about engineering design of retaining and protection of foundation is becoming a hot technical issue in the field of geotechnical engineering. However, foundation engineering is a subject of high integrity, not only needs the knowledge about geotechnical engineering , but also requires about structural engineering . Especially , excavation of foundation pit limited by geological conditions of construction site and surrounding buildings and so on ; influenced by deformation of underground infrastructure ; and also must considered its applicability and economy at the same time ,during the construction in large and medium city . So selective preference and design the scheme of retaining and protection of foundation is extremely significant. This article analyzed and researched the support schemes in accordance with the project of The ShangHai Eighth People Hospital′s ward building . According to the demand of the pit depth , combined with the engineering geological conditions ( hard in upward side and soft in lower side , the majority is clay soil and silty sand ) of building site ; combined with the main mechanical index ( natural moisture content ,plasticity index ,liquidity index ,compression factor ,modulus of compressibility and number of standard penetration test and so on ) in each layer of soil , and added the condition of the peripheral circumstance about building site , the article analyzed and researched the retaining and protection of foundation schemes used immerged sheet pile ,single deep anchored sheet pile ,SMW technique and soil nailing wall individually . As the result of preliminary design and argument from the article, this four support schemes are all feasible. But the total cost of construction with SMW technique and soil nailing wall is lower which would saving the 28% of the cost than the other two schemes .And it is quite marked on cost advantage and social benefit, has simple construction method and safe reliability also. At the same time, considered the complexity and particularity of the condition about foundation pit environment it determined to use the SMW technique to support one side of the pit for removal the effect on underground railway and pipeline. The other three sides because of the construction condition are better so chosen the soil nailing wall (plus the foundation dewatering) that the stability is assurance. The design of SMW technique mainly compared with concrete diaphragm wall and bored pile. Expounded that mainly characteristic of the SMW technique .There is small peripheral ground effect ; highly water stop ability ; extensive usage ; suitability of various strata ; lower cost ; little environmental contamination and so on . Excavate the pit at weak foundation, appears phenomenon of foundation base soil dislocated swelling and underneath of the pile wall displaced to internal pit or inclined often, this is mainly due to the weight amount of soil behind the pile wall exceeds the ground bearing capacity of the base, and the state of elastic equilibrium of foundation soil be destroyed, the soil body after a pile wall took place flowed, the pit bottom rebounded swelling. For prevent this phenomenon from occurring, must checking the degree of safety that swelling of the pit bottom. Through the design andconstruction of the SMW technique, totally meet the necessity requirements. The SMW technique meet the requirements through the checking of safety against overturning, the checking of safety against swelling, and the calculation of inner force and strength. Soil nailing wall is a new retaining structure for soil excavation and slope stability that developed in recent years. Soil nailing wall composed of reinforced soil, slender metallic member rod for prevent in-situ soil slipped and concrete slab that attached to the sloping surfaces. form a retaining wall similar to gravity . Therefore, it is resist soil pressure that transmitted from the back wall and other applied force. Thus the excavation of sloping surfaces could maintain stability. Every layer of soil nail under action of designed inner force should meet the following strength conditions: 41. 12 ysddfF N≤πThe inner stability safety faction of soil nailing wall is: ∑[ ]∑+??????=++????????+????????+????????iiikhkkiikjjhkkiiijy WQSCARSWQRF αααβ?αβ()sincos()costansintancos Through a series of analysis for soil nail's length , aperture , withdrawal resistance of grouting material , stability of inner and external ,and checking of the against slipping and overturning totally meet the necessity requirements . Because soil nailing wall is a method of retaining and protection offoundation suitable for artificial backfill that above of groundwater level or through artificial precipitation, for clay soil and weak cemented. So this foundation pit needs the artificial precipitation. The design of dewatering project mainly according to the characteristic of ground place in this article, for instance, the permeability coefficient of water bearing layer is small, the seep of collecting water is slowly. Hence for reaching the precipitation requirement of dewatering must adopt the combination of light well points dewatering and electro-osmotic well points dewatering method. The general budget of the foundation engineering in the article is $1,410,000 . It has a marked on economic benefits. Particularly, monitoring the deformation due to the excavation of foundation .It is must achieve requirements that the tests of primary material. Inspection and monitoring of soil nailing wall ought to follow the requirements of . It is must make a point of quality inspection and strength tests that construction with the SMW technique. The selective preference, the design and the construction of retaining and protection of foundation in this article have passed the quality inspection and monitoring, and all measure up to engineering requirements. The selective preference ,the design and the construction of retaining and protection of foundation in this article is safe reliability in technology ,quite marked on cost advantage and social benefit , have passed the quality inspection and monitoring . It is well in engineeringdesign and construction quality, short construction period, lower cost and completely achieved the expectant purpose.