| Yangtze River, Minjiang River and a number of water systems brought together in southwest China. Somethimes there were fourth flush pluvial phases along the river, the thickness of which ranged from dozens to hundreds meters.With the implementing of infrastructure construction in the southwest, more and more building yards were build by high-filled in the mountain and hilly topography unit along river. Unlike most building foundations, there would be a large load on the foundation under high filling boby. If the thickness of the foundation was large, the settlement would be very big, which could seariously threaten the safety. Treating the foundation with correct and effective method, increasing the strength and reducing the amount of settlement would be of significance to the construction’s safety.This article based on the Fu Ling power station construction and took the soft foundation with large thickness in the high filled section as the subject of the research, which was focused on the engineering properties of the soft foundation with large thickness. Layered summation and three-dimensional numerical simulation was used to research the settlement of soft foundation with large thickness and its deformation characteristics. The analysis was meant to choose the right ground treatment method and six ground treatment schemes were preliminary designed. Through the theoretical technical feasibility analysis, the treatment effect analysis, the economic analysis and stability of the composite foundation, this article finally proposed a ground treatment scheme which is "gravel pile and removing part of the soft soil". This scheme was proven to be economically viable and had good effect, which could achieve the purpose of project stability ensurance and safe using. The main results achieved in the article are as follows:(1) The soft covering layers in this field are mainly distributed on the slope, the valleys and terraces Ⅰ, which are markedly divisional. they are divided into three types based on their formation and composition characteristics, namely "riverbank type","valley type" and "slope type".(2) The engineering geological condition shows that the laws of the soft foundation’s non-uniformity is obvious, which represent at three aspects:①Soft foundations are non-homogeneous, three types are markedly divisional;②The thickness of each types of soft foundation varies widely, which has the laws that the thickness of the "riverbank type" is bigger than that of the "valley type" while the thickness of the "valley type" is bigger than that of the "slope type";③The components of the soft foundation are non-homogeneous. Silty clay and silt in alluvium and proluvium type is banded along the Yangtze River in the north and northeast of this field; Silty clay in diluvium and proluvium type distributes mainly in valleys and silty clay in eluvium and diluvium type mainly lies on the slope and its top;(3) Based on the results of physical and mechanical test of the undistuebed soil samples, soft soil with large thickness was low liquid limit soil with high water rate, which contented large amount of cosmid, had low mechanical strength and medium compression. their were should be treated in this engineering.(4) Based on the statistical regression annlysis, the correlation between some of the physical parameters of the silty soil, one of the component of the soft foundation with large thickness, were proved to be good. The empirical formulas between water ratio and voids ratio, water ratio and wet density, liquid limit and plasticity index were given as the form of e=0.023w+0.166,ρ=-0.01w+2.217,Ip=0.619Wl-7.186.(5) The result achieved by layered summation was that the largest settlement of the soft foundation with large thickness in profile19-19’lied on the surface of the foundation under the platform with the elevation of190m, the amount of which was1130mm and tapered off towards each side of it.The ground settlement was non-homogeneous.(6) The three-dimensional numerical simulation method was used to analyses the general deformation characteristics of the soft foundation with large thickness, and non-uniformity of the ground settlement was further studied. The largest settlement in areas located in profile19-19’ and its vicinity, in which the lateral displacement was larger; Focusing on the profile19-19’, the largest settlement located in the area under the plateform range from180m to190m, which is close to the result of theoretical calculation. In addition, the foundation’s lateral displacement to outside of the slope was0.72m.(7) According to the non-homogeneous deforamation characteristics, The settlement presented the regularity of maximum settlement position as the center,,gradually reducing to the sides. The area sedimentating most located where thickness of soft foundation was large and load level was relatively small, so the thickness of the soft foundation was the main factor influencing the settlement, while the load level was the secondary fator.(8) Compared with other treatment methods, the gravel pile method and cement mixing pile method were proved to be suitable for this field. Six foundation treatment schemes were compared at the aspects of theoretical technical feasibility, treatment effect, the economics and stability of the foundation. The conclusion was drawn that the scheme gravel pile combined with removing part of the soft soil had good effect to this field and the stability of the foundation was high enough to meet the engineering requirements. |
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