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1、Environmental effects induced by excavationAbstract: Based on 3D Biots consolidation theory and nonlinear Duncan-Changs model, a 3D FEM (finite element method) program is developed considering the coupling of groundwater seepage and soil skeleton deformation during excavation. The comparison between
2、 the analysis result considering the variation of water head difference and that without considering it shows that the pore water pressure distribution of the former is distinctly different from that of the latter and that the foundation pit deformations of the former are larger than those of the la
3、tter, so that the result without considering the variation of water head difference is unreliable. The distribution rules of soil horizontal and vertical displacements around the pit and excess pore water pressure are analyzed in detail in time and space, which is very significant for guiding underg
4、round engineering construction and ensuring environment safety around the pit.Key words: Environmental effect, Excavation, Deformation, Excess pore water pressureIntroductionWith the development of city construction, much underground space is utilized and many deep foundation pits sequentially appea
5、r. Excavation need not only ensure the stability and the safety of a pit, but also control the movement of soil stratum around and protect it from being damaged. Especially in some Chinese coastal areas, such as Shanghai, Guangzhou and Hang Zhou, the soil strata are very soft and soil soften saturat
6、ed, therefore excavation will result enlarge soil stratum movement. Movement induced by excavation greatly influences the safety of buildings, subways, underground pipelines and other municipal constructions around a pit, so the consequent environmental effects have become key problems in excavation
7、 and caused much attention. Hou and Chen(1989) investigated the rule of displacement in soil medium surrounding deep excavations and presented method to evaluate the ground surface settlement. With the wide application of finite element technology ,finite element analysis was used in many deep excav
8、ations and some basic rules of environmental effects of excavation were analyzed and investigated(Whittle et al., 1993; Ou and Lai, 1994; Zhang et al.,1999; Ping et al., 2001). The effect of ground settlement and lateral deflection induced by deep excavation son damage of buried pipelines was also d
9、iscussed(Duan and Shen, 2005). Zdravkovic etal.(2005) studied the effect of excavation on the surrounding areas and provided a detailed assessment of wall and ground movements. In addition, Xie etal.(2002) theoretically confirmed that the changes ineffective stresses resulted from dewatering during
10、excavation and seepage were the main factors inducing settlement of ground surface by comparing the calculating results with the field measurements. Shi and Peng (2006) further presented a new method of calculating ground surface settlement caused by foundation pit excavation and dewatering based on
11、 the stochastic medium theory, seepage theory and soil consolidation theory .However, due to the complexity of excavation and groundwater seepage, study on environmental effects of excavation is not yet profound. By the effective stress analysis, not only groundwater seepage including seepage induce
12、d by unloading and seepage induced by the water head difference between the inside and outside of a pit, but also the coupling of groundwater seepage and soil skeleton deformation can be taken into account, so in this paper 3D consolidation finite element equations are derived, and the corresponding
13、 finite element program is further developed. Some useful conclusions are drawn by analyzing the influences of the water head difference between the inside and outside of a pit on excess pore water pressure and the pit deformations and then investigating the time and space variations of environmenta
14、l effect.Finite element equationsBiots 3D consolidation finite element equations (Xie and Zhou, 2002) are as follows:, （1）where K is the element consolidation matrix, Uis the increment column matrix of unknown terms of element node, and R is the increment column matrix of equivalent load and water r
15、unoff of element node. The sub matrix of K can be expressed as:where is the integral constant, t is the time increment, and the calculation of, and can be found in (Xie and Zhou, 2002). The sub matrixes of U and Rcan be expressed as:where ui, vi and wi are the displacement increments of element node
16、 i, pi is the pore water pressure increment of element node i, Rxi, Ryi and Rzi are the equivalent load increments of element node i, and Rpi is the equivalent water runoff increment of element node i. Since groundwater seepage by excavation in soft soil not only includes negative excess pore water pressure induced by unloading, but also involves the water head difference between the inside and outside of a pit, so Eqs.(3) and (4)
