Study On The Land Subsidence Induced By City Construction

With the rapid development of cities, the land subsidence caused by large-scale construction has been more and more obvious. The dissertation presents a study of land subsidence under bulk loads of buildings in respects of additional stress in foundation and soil compressive characteristics. First, under the uniform distribution, the buildings are equivalent to line load, strip load, point load and rectangular load, respectively. The characteristics of the additional stress are analyzed on each condition. And then, the distances of some of buildings in Beijing are measured. The buildings'distribution is analyzed by means of statistics. Based on this, under the random distribution, the characteristics of the additional stress are analyzed on conditions of line load and point load, respectively. What's more, the effects of soil compressibility on land subsidence are studied. The effecting scale of land subsidence is also discussed under large-scale buildings. According to the construction of a development area, the effects of buildings on nearby dike are studied. The main conclusions are as follows.1) It is indicated by statistical analysis of some buildings in Beijing that buildings on the pitch in the east-west direction obey Gamma distribution, while in the north-south direction are in obedience to lognormal distribution.2) Whether the buildings are uniformly or stochastically distributed, the characteristics of the additional stress in foundation under large-scale buildings are significantly different from that under single building. The additional stresses are superposed. It seems large-scale uniform loads when the depth is equal to the mean distance between buildings. And the magnitude of the large-scale effecting loads does not decay in a large depth below.3) The subsidence is finite when the modulus of compressibility varies in exponential function way, while it is limited only in the condition of power index greater than 1 in power function way. The scale of buildings affecting the additional stress in a certain depth h0 is limited. If the standard that additional stress can be ignored isσ_h0≤0.01q, then the scope of the buildings from the center to 3.5 h₀ can cause impacts.4) As the distance between buildings and the dike increases, the settlement of the dike is gradually reduced. And the settlement decrease is significant nearby the dike through this method. The settlement can be also reduced by means of transferring surface load to underground where soil is hard when the buildings are closer to the dike. For the homogeneous foundation, it is not useful unless the depth is enough deep.