| Excavation engineering is one of the most sophisticated technologies in civil engineering.Foundation pit excavation not only need to ensure its own safety and reliability,but also must ensure the normal use of buildings,structures and underground pipeline around excavation.There are dense buildings and the widely distributed soft soil in coastal area.The soft soil has the characteristics of high void ratio,high compressibility,weak permeability,large deformation and low bearing capacity.Therefore,with the characteristics of the consolidation and secondary consolidation properties of the soft soil,the deformation of the inside and outside of the foundation pit will increase gradually,especially in the long intermittent time of construction stagnations and untimely support,which often leads to excavation engineering accidents.This paper,based on site monitoring data,indoor experimental study of soil secondary consolidation characteristics and the finite element numerical simulation analysis method,studied the effect of the intermittent time of construction and soil secondary consolidation on the deformation of foundation pit excavation,and analyzed its deformation law when pitted normally or periodically as well as considering the influence of soil secondary consolidation.This paper discussed from below four points.(1)Through the analysis of field inspection date of pit excavation,the excavation pile and horizontal displacement were changed by 'bulging' type,and increased along with the deepening of excavation depth,and decrease along with the increasing distance away from boundary of the foundation pit.Surface subsidence increased gradually with the increase of excavation depth,and the sedimentation rate presented as gradually increase and then decrease.Field excavation data can provide relevant parameters for subsequent numerical modeling and the basis for analyzing the results of calculation.(2)The secondary consolidation deformation characteristics of soil was analyzed through the secondary consolidation test.The result showed that loading ratio,pre-pressure are the main factors of secondary consolidation coefficient:Coefficient of secondary consolidation Ca increased with the increase of loading ratio R and decreased with the decrease of R;when the loading ratio was a fixed value,the increment of secondary consolidation coefficient would gradually slow and indicate a trend of decrease with the increase of load;When the load was less than the pre-pressure,secondary consolidation coefficient of soil would gradually increase with the increase of load but the increment gradually decreased;when the load was larger than the pre-pressure,the secondary consolidation coefficient significantly increased with the increase of load;In addition,secondary consolidation coefficient decreased with the increase of preloading load.(3)The deformation of foundation pit under normal excavation was simulated through the finite element numerical analysis software.The study showed that the settlement of surface was presented as the type of "groove" while the horizontal displacement curve of pile presented as "bulging".The deformation gradually increased with the process of foundation pit excavation,and decreased with the increase of excavation layers.(4)The changing rule of the foundation pit horizontal displacement and ground settlement under the condition of different intermittent time was researched through the numerical simulation of finite element analysis software.It showed that the changing rule in the excavation process can be simulated well both in normal excavation simulation and in the foundation pit excavation simulation considering the consolidation.By contrast,the foundation pit excavation simulation that with the consolidation consideration is more consistent with the actual situation;the intermittent time of the foundation pit excavation has certain influence on the displacement of soil and pile,and the displacement will increase gradually as the growth of the intermittent time. |
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