| 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 mixed 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 mixed 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 deterioration 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, this study include the effect of different additives (fly-ash, GGBS) to the soil-cement; furthermore X-ray diffraction and scanning electron microscopy (SEM) are adopted to study the decay of soil-cement mechanical properties and the modification mechanism of additives material;3 In the salt-water area of the Yellow River Delta, the settlement and load characters of cement-soil pile composite foundation will be analysed by numerical method and be compared with normal cement-soil composite foundation, meanwhile some field observation tests will be taken on the foundation's settlement, pile-soil stress ratio etc, to study the influence of salt water environment to the bearing capacity of composite foundation;4 From the structure and material angles, respectively, this paper proposes some durability design schemes suitable for soil-cement pile of salt-water area in the Yellow River Delta.By means of numerical analyses of each scheme of the argument, this paper aim to form a set of durability design schemes on economic and feasible of soil-cement deep mixed piles.Taking advantage of the laboratory test, field test, theoretical analysis, numerical calculation, with comprehensive research methods of geomechanics, engineering and material science, chemistry and mathematical sciences, and multidisciplinary crossover, this paper takes the Yellow River delta underground salt water environment as the typical study objects, and studies the deterioration mechanism of soil-cement pile and durability design.Based on above fundementaly research, this study will put forward to attain the optimal strategy of cement-soil pile durability design and a set of specific measures for salt-water area in the Yellow River Delta, providing theoretical support and technical guidance on the the durability design of composite foundation.This study will gain vast economic benefit and social meaning.This paper was subsidized by Natural Science Foundation of China project (51078222; 50708056) and outstanding youth training project of Shandong University Independent Innovation Fundation. |
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