Analysis On Factors Of Swelling Soil To The Composite Soil Nailing Wall Foundation Pit Supporting

In order to study the adverse effects of swelling soil on foundation pit,this paper which is based on Yizhou city Commercial Street underpass excavation project engineering in Guangxi,first of all introduces the engineering situation,the original supporting design,the damage form and the initial cause of the accident;And then expounds the expansive soil foundation pit instability theory,through the calculation analysis of expansive soil foundation pit supporting design software for foundation pit soil pressure,overall stability,and the internal force of retaining components of concrete influence;Finally using numerical analysis software to original expansive soil foundation pit,soil reinforcement outside the excavation schemes,reinforced concrete simulation analysis has been made to the supporting structure,and the optimal scheme is put forward.This paper draws the following conclusion:(1)For foundation pit soil reinforcement outside the two solutions,in the case of red clay is not inflation,the original design has been able to meet the requirements of all kinds of limits(deformation demands,supporting pile bearing capacity).But if red clay swelling,calculated in accordance with the original design scheme,showed significant deformation is too large,supporting structure internal force increased significantly,increased by 76%,and maximum displacement of pile maximum bending moment increased by 65%,and pile body's largest shear force increased by 41%.(2)Outside the foundation pit set water measures,soil reinforcement,can effectively control the deformation.In two kinds of reinforcement scheme,the scheme 2(model B2)is the best results;Using scheme 2,deformation meets the requirements,structural internal force is also very close to the soil without inflation.Compared with the model of B1,B2,they share the same quantities.Scheme 2,corresponding(model B2)thought to be more appropriate.(3)For the three options supporting structure reinforcement,without considering the expansion of the red clay,the original design has been able to meet the deformation limit.But if consider red clay swelling,calculated in accordance with the original design scheme,the maximum horizontal displacement of pile is 29.36 mm,pile top displacement is 24.87 mm,exceeds limit 21 mm.Model C horizontal displacement of the pile head is 17.66 mm,21 mm does not exceed the limit,the other two reinforcement model D and E are beyond the limit.(4)In structure reinforcement scheme,the three models of D and E are unable to effectively control the deformation,investigate its reason,may be because the soil expands,buried in the soil anchor and soil nailing can only reduce the relative displacement between them and supporting piles,but cannot reduce the expansion of the support area outside the impact on the support area.In contrast,enhance supporting piles model C can control deformation,its internal force also increases accordingly,equivalent to "hard up".(5)Considered in calculation of several schemes,the corresponding model B2 and model C can effectively control the displacement of retaining structure.Retaining structure,the thinking model of B2 to the "burden",letting the soil around the retaining structure is not inflation,control the influence of the expansive soil from the source.Model C idea is "enhanced",increase the stiffness of supporting pile,soil to make the expands supporting plies deformation decrease.Calculations also show that if the water is too small model B1,the range of water effect is not obvious;If to increase the number of anchor and soil nail,the effect is not good.Suggestions according to the field situation,the model of B2 and model C scheme to select a suitable construction scheme.