Research On Support Mechanism And Design Method Of The Ribbed Support Structure

Foundation pit support belongs to temporary construction in buildings.The design safety factor of foundation pit support is usually low.When the support capacity of the foundation pit is insufficient,it can lead to instability,collapse,and even damage to adjacent buildings.Endangering the safety of construction personnel and mechanical equipment.Therefore,conducting corresponding basic research on the deep foundation pit support system is an urgent requirement in engineering practice.This article considers the characteristics of deep excavation engineering.A new type of steel sheet pile composite support-ribbed support structure has been proposed.The ribbed support structure consists of steel sheet piles and rib plates welded vertically to the steel sheet piles.The front row sheet piles can provide anti overturning bending moment.The rear ribs can significantly improve the structural bending stiffness.The rear ribs can mobilize the self stability performance of the soil through synergistic action.The support structure can form a sheet pile rib plate soil overall bending resistance structure to resist soil pressure.The rib support structure has a high stiffness.The design dimensions of ribbed support structures can be flexibly adjusted according to engineering requirements.It has the advantages of high regional applicability and high reuse rate.Existing engineering cases have proven that the rib support structure has good support performance.However,its support mechanism has not been thoroughly studied.Lack of relatively systematic structural design methods.This article adopts a combination of model testing,numerical simulation,and theoretical research methods.Conduct research on the support performance and influencing factors of ribbed support structures.We have studied the support mechanism and design method of ribbed support structures,and the main achievements are as follows:(1)Sandbox model tests were conducted on steel sheet pile support and ribbed support.The measured data of ground settlement of the foundation pit,horizontal displacement of pile top of support model,and structural stability are analyzed.Studied the support performance of different forms of support structures.The influence of ribbed plate design parameters on the structural stability of ribbed support is studied.The test results show that under the same excavation depth conditions,the horizontal displacement of the pile top,bending deformation of the pile body,and ground settlement deformation of the foundation pit of the ribbed support are all smaller than those of the steel sheet pile support.Ribbed support has better support performance.The greater the ribbed width or the smaller the ribbed spacing of ribbed support,the better the structural stability.There is a critical range of ribbed design parameters.There is also a corresponding relationship between the critical range of different parameters.(2)Geological surveys and indoor geotechnical tests were conducted on the loess site.Determined the relevant calculation parameters of the soil.A standardized model for ribbed support was established using PLAXIS.The influence of structural design parameters such as ribbed width,ribbed spacing,structural section thickness,effective cohesion of soil,and effective internal friction angle of soil on ribbed support performance is studied by Control variates.The numerical simulation results indicate that there is a critical range for each structural design parameter of ribbed support.The critical values of structural design parameters can be determined by combining engineering economic indicators.Under the calculation conditions in this article,the width of the rib plate should be set between 1.6m and 2.4m.The spacing between ribs should be set between 2.4m and 4.8m.When the effective cohesion of the soil is less than 14.3k Pa or the effective internal friction angle of the soil is less than 19.4 °,reinforcement measures should be taken for the soil.(3)Based on practical engineering in sandy and expansive soil areas,a threedimensional model of foundation pit excavation was established using finite element software PLAXIS and ADINA.Studied the support performance of steel sheet pile support and ribbed support under the influence of the spatial effect of foundation pit and soil expansion.The calculation results of the example engineering show that in sandy soil areas,compared with steel sheet pile support,the horizontal displacement extreme value of the foundation pit soil of the ribbed support structure is reduced by 71.11%,the bending moment extreme value of the sheet pile is reduced by 35.43%,and the bending moment distribution is more uniform.In the expansive soil area,under the action of gravity and expansion force,compared with steel sheet pile support,the maximum horizontal displacement of the foundation pit soil of the ribbed support structure decreased by 33.40%,and the maximum vertical tensile stress of the sheet pile of the ribbed support structure decreased by 44.76%.(4)The cross-sectional bending stiffness of the ribbed support structure was calculated.The calculation results show that compared with steel sheet pile support,the ribbed support structure with a rib width of 0.8m and a rib spacing of 0.8m increases the cross-sectional bending stiffness by 19.24 times.Revealed the support mechanism,bending resistance effect,anchor pulling effect,and self stabilization effect of ribbed support structures.The rib support structure is reasonable and feasible.(5)Based on the design method of steel sheet pile support,a design method for ribbed support structure is proposed.A maximum horizontal displacement prediction formula for ribbed support structures was proposed,which can consider the width and spacing of the ribs.