Study Of Settlement And Loading Capacity Of Deep Cement-soil Mixed Pile Composite Foundation In Yellow River Delta Salt-water Area

The Yellow River Delta is a new-formed land, with the wide distribution of the sedimentary soil mainly composed of low liquid limit powder soil, sand-contained sub-clay and silty soil, all of which above show poor engineering properties and even parts have developed the underconsolidated soils. To reduce the excessive uneven settlement brought by the upper buildings, for instance the high-fill subgrade, soil-cement deep mixing pile of foundation reinforcement is frequently adopted. However in the Yellow River Delta areas, there exists a large scale of salty water, groundwater and subsurface soil with high level of salinity. Previous research has shown that the durability of cement-soil mixed with salt-water is poor, which may cause the bearing capacity of mixing pile composite foundation decay, and eventually lead to the excessive settlement of upper buildings such as roadbed (this settlement probably induce the phenomenon of bridge head bump) or instability and failure of composite foundation. Those distresses will result in the uncoordinated phenomenon between the short life of the composite foundation and the long life of upper structure design, bringing in state-owned assets waste.This paper,based on the survey data on the quality of groundwater and the mechanical properities of soils spreading around the Yellow River Delta regions systematically study the decay of cement-soil characteristics and its mechanical properties of composite foundation,exploring a comprehensive methods including test, theory numerical analysis and etc.1. This research chooses Binzhou-Dezhou Highway K15+155.5～K15+205.5 as the testing area to analyse the characteristics of soil and water of salt-water area in the Yellow River Delta.2. Based on the laboratory test, this paper studies the regulations over time on the soil-cement mechanics properties of salt water area in the Yellow River Delta, compared with the normal soil-cement, meanwhile.3. The model simulation test with the ratio of 1:50 was conducted to study the settlement and bearing capacity of cement pile composite foundation in the salt-water area of the Yellow River delta. And it was found that the cemen-soil degradation caused settlement increase obviously and bearing capacity of the composite foundation decay, then the design scheme taking the durability of cement-soil into account. In the meanwhile, pile defection will speed up cement-soil degradation in the salt-water area, leading to the settlement of the mixing composite foundation increases obviously, so it's necessary to pay more attention to controlling construction quality in the Yellow River delta; At last, it's wise to decrease the length of pile in the edge, for it can save the construction cost without affecting the composite foundation bearing capacity.Based on above fundementaly research, this study provided theoretical support and technical guidance on the the durability design of composite foundation. And it will gain vast economic benefit and social meaning.This work was supported by the Chinese Natural Science Foundations (Nos.51078222,50708056 and 50978207) and Independent Innovation Foundation of Shandong University, IIFSDU (No.2010JQ001).