The Analysis Of The Large-scale City Buildings Loads On Land Subsidence

The land subsidence have already been discussing for more than 100a. For a long time, the researchers consider that the main cause of land subsidence is the exploit excessively groundwater. From 1980s on, the governments such as shanghai changed their attitude, and begun to balance the irrigation and exploitation of groundwater in order to reduce the influence of groundwater to land subsidence. However, the researchers found that construction loading become the new important factor of land subsidence. The similar condition occurred in Xi'an city, the behavior of Xi'an ground fissures is not weaker but stronger in some area, which is relate to the land subsidence, and researchers speculate it is caused by the rapidly great large-scale construction.However, the research about great large-scale construction loading has not give any reliable systematic theories. therefore, it is difficult to explain the relation between buildings' loads and land subsidence. Considering the distinguishes between the city large-scale loads and a single building load, and the difference in calculation method, this paper mainly analysis the characteristics of the city large-scale loads and the influence to land subsidence.Firstly, this paper redefine the city large-scale loads, and the distinguish between the city large-scale loads and the normal loads not only reflects in the size of building base but also the lager effecting scope naturally.Secondly, this paper define equivalent effecting load as a index to measure the foundation additional stress, and to discovery the law of transmission and diffusion and attenuation of additional stress by studying the characteristics of the equivalent effecting load. In this paper, the formula of the equivalent effecting load has been embodied tentatively to explain the relation among the density, the height of construction and land subsidence.Thirdly, by the mechanical model calculating, this paper discloses the relationship between the appearance depth of the equivalent effecting load surface which is engendered by lots of a discrete group of buildings on the ground and the distance between buildings. This paper also reveals the distribution scope and extension characteristics of the equivalent effecting load surface.Finally, this paper compared the total settlements respectively generated by a single conventional loads and lager-scale loads within the same stratum, to discovery the difference between lager-scale loads and normal loads, and discuss some questions like the actual calculation depth so as to provide some basis for the rational design of building distance in big cities.