Research On The Force Mechanism And Design Of A Combined Retaining Structure

With the development of urban construction,land resources are becoming more and more precious,and it is more and more common to build buildings on the slopes of mountains and hills.It is very important to rationally develop and utilize land resources with complex terrain such as slopes and valleys.When developing and utilizing slopes and valleys,due to the large fluctuations in the terrain,it is necessary to cut high and fill low.Setting up an upright retaining structure at the red line of the land and leveling the site with backfill can effectively improve the land utilization rate,but it will face the problem of high fill slopes.Based on the high-fill slope project in the slope zone,a project in Mangshi,Yunnan Province adopted a combined retaining structure(CRS),which integrates the advantages of counterfort retaining wall and gravity retaining wall.Where the bearing capacity of the foundation is insufficient,a pile foundation is added.The tierod is set at the top of the CRS to control the lateral displacement of the wall and improve stability.The CRS occupies a small area and has stable performance,which is of certain research value.For the CRS,this paper mainly do the following research :(1)By analyzing the force of the CRS,the calculation formulas of the anti-slipping stability and anti-overturning stability coefficients of the CRS under the two conditions of no pile and with piles are deduced.(2)Midas/GTS modeling was used to analyze the variation of displacement and axial force of tie-rod of the CRS with backfilling construction under pileless and pile-added conditions,and the slope stability,base pressure and pile foundation force were analyzed.The research shows that:(1)The slope stability coefficient of the retaining system is 1.30 when there is no pile.The slope stability coefficient is 1.728 with piles and tie-rod,which is 1.33 times of that without piles.The slope stability coefficient is 1.347 when the piles are added and the tie-rod are not added,and the slope stability is increased to 1.28 times when the tie-rod are not added.Both pile and tie-rod rod can effectively improve slope stability.(2)The bending moment values of the front and rear piles are equal,the shear force of the rear piles is much larger than that of the front piles,and the horizontal force is mainly borne by the rear piles;(3)In the case of pile addition,the tie rod can reduce the horizontal displacement of the top of the wall by 74.27 %,and the horizontal displacement of the bottom of the wall by 23.87 %.The tie rod can effectively control the horizontal displacement of the CRS.(3)The influence of the CRS’s base burial depth,tie-rod stiffness,pile foundation position,and c and φ values of backfill on the displacement and force of the CRS is analyzed.The research shows that:(1)Increasing the depth of the basement reduces the displacement of the CRS to a certain extent and increases slope stability coefficient;(2)In the case of no tie rods,the rear pile foundation moves outward,which can effectively reduce the displacement of the CRS and improve slope stability coefficient;(3)The increase of the c and φ values of the fill,the horizontal displacement of the CRS decreases slowly,the vertical displacement increases slowly and linearly,and the slope stability coefficient is improved to a certain extent,but the improvement effect is limited.(4)In the case of one-time backfilling without zoning,the tie-rod construction node has a great influence on the displacement of the CRS,and the force of the tie-rod and pile foundation.In the case of no pile,it is more appropriate to add tie rods when backfilling to 11 m or 12m;In the case of pile addition,it is more appropriate to add tie rods when backfilling to 12 m or 13 m.(5)Suggestions are made on the design and construction of the CRS.