Analysis On Long-short Piled Raft Foundation Settlement Of Large Chimneystacks In Soft Soils

With the development of piled-raft foundation, piles with uneven length are used in foundations more and more often due to the uneven bearing stratum under pile toe. Long-short pile foundation is proposed in order to reduce long pile number and to reasonably make use of the good carrying capacity of the bearing stratum of superficial layer.An analysis method for long-short piled raft foundation is introduced including the calculation of additional stress of long-short pile foundation, calculation of underlying stratum settlement, determination of P-S curve for single pile in pile groups and finite-element analysis for raft. A practical project of long-short piled raft foundation in Zhejiang Yuhuan power plant is analyzed with the help of POGAP which is developed based on the above theory.The Yuhuan power plant whose installed capacity is4×1000MW is the first thermal generator set which belongs to million-kilowatt grade that put into commercial operation. The chimneystacks of second-stage is introduced in this paper, and outer barrel which is concrete structure is230meters high, the outer diameter is17.8m, the outer diameter in ground level is31m. The inner barrel is composed of two240m high steel barrel, and the inner diameter is7.2m. Considering the requirement of bearing capacity, pile-raft foundation is selected.Because the area is almost made up of soft soil ground, the choice of foundation treatment method is important, also the economy of project should be considered. Three different kinds of design schemes of piled-raft foundation are compared. In the end, a comparison between calculated settlement and measured settlement is made, and the design scheme of long-short piled raft foundation is found to preferably meet the engineering needs.