Key Technology For Construction Of Deep Foundation Pit And Large Volume Raft Foundation In Water-rich Soft Stratum

China is characterized by rapid urbanization,lack of urban land resources and gradual increase of tall buildings.Due to the complexity of construction environment and working conditions,blindly adopting traditional design and construction schemes is easy to cause engineering safety accidents.Based on the deep foundation pit construction of the commercial and office buildings in Fudi Finance Island,Chengdu,this paper makes an in-depth study on the preliminary geological survey,theoretical analysis of deformation,selection of support structure system,optimization of support parameters and optimization of construction technology for the deep foundation pit construction under the condition of water-rich and weak stratum.The foundation of tall buildings mostly adopts mass concrete.Mass concrete has problems such as too high hydration heat at early stage and internal heat is not easy to diffuse,which results in temperature crack and affects long-term stability.At the same time,the waterproof and impermeable capacity of concrete structures under water-rich conditions plays an important role in construction safety and later operation.Based on the above situation,this paper studies the reduction of hydration heat release rate and hydration heat release energy of mass concrete as well as the enhancement of its waterproof and impermeable ability.Combined with the above problems and research significance,based on the summary and analysis of existing studies,this paper optimized the supporting structure system and parameters of the foundation pit excavation process through theoretical analysis,laboratory test,FLAC3 D numerical simulation and field monitoring,and carried out modification and waterproofing research on the foundation mass concrete material.The main work and results are as follows:(1)The deformation mechanism and influencing factors of deep foundation pit excavation under the condition of water-rich weak stratum are summarized,and the supporting structure system of underground diaphragm wall + internal support with the best waterproof and deformation resistance effect is formulated.Combined with practical engineering cases,using FLAC3 D numerical simulation software of underground continuous wall rigidity and supported the number inside the vertical settlement of soil in the process of excavation and maintenance on the influence of the lateral deformation of the wall,the simulation results show that the underground continuous wall stiffness of subsidence and deformation,supported the influence is obvious,combined with the relevant design specifications,it is concluded that supported the number should not be less than 4.(2)Combined with actual engineering construction site,the general situation of the engineering construction in the region and monitoring scheme in detail,according to the numerical simulation results and monitoring data,through Origin software for the settlement of soil around the foundation pit under different excavation steps and maintain wall lateral deformation data,the results show that the subsidence and deformation can satisfy the requirements of specification,supporting structure and monitoring scheme is reasonable and effective.(3)Through indoor experiment,fly ash and slag power plants is studied when single and joint replacement of cement hydration heat of concrete,and it is concluded that when the dosage of fly ash and slag power plants are 15% when replace cement can effectively reduce the hydration heat release rate and hydration heat of concrete energy,and does not affect the mechanical properties of concrete.Finally combined with the field temperature monitoring data to prove the authenticity of the above research results.(4)Researching new permeable crystallization type concrete surface protective agent(OCSP)in enhancing the performance of the mass concrete waterproof impermeability experimental results show that the concrete show besmear brushs OCSP can effectively reduce the water absorption of concrete and reinforced concrete carbonation resistance,for the increase of capability of waterproof impermeability of concrete under the condition of water provides a new train of thought.