Study On Settlement Deformation Law And Multi-stage Slope Stability Of High Embankmentin By Expansive Soil In Ankang Airport

In recent years,with the rapid development of China’s economic construction and transportation industry,in order to solve the problem of uneven distribution of airports,dense east and sparse west,the "14th Five-Year Plan" of civil aviation has clearly pointed out that the central and western regions and southern regions should be strengthened.The central and western regions and southern regions are mostly mountainous and hilly regions with large topography,complex geological conditions and large quantities of earth-rock material engineering.There are problems of foundation and filling body settlement deformation and stability control of high-fill slope in filling engineering,and these problems are more prominent for high-fill expansive soil.Ankang Airport is located in the expansive soil area,and the amount of excavation and filling is about 30 million m3,and the maximum filling height is 47m.Therefore,the study on the settlement deformation law of expansive soil high filling and the stability of multi-stage slope in Ankang Airport has important reference value for the comparison and selection of filling construction scheme and slope protection mode.Through theoretical analysis,test data and monitoring data analysis,numerical simulation,the settlement deformation of high fill and stability of multi-stage slope in expansive soil hill area are studied.The main work and conclusions are as follows:(1)The foundation soil in Ankang Airport is mainly composed of Holocene silty clay and Pliocene mudstone.The silty clay has moderate to weak expansibility.The foundation soil bearing capacity is not enough and the settlement is large,so foundation soil is treated by dynamic compaction and dynamic replacement with partition.Using local materials,the expansive soil with high natural moisture content in the excavation area is selected as the filling material.The conventional filling method is difficult to reach the prescribed degree of compaction,so the layered rolling compaction method is adopted to fill.Through indoor geotechnical test,plate load test,heavy dynamic penetration test,compaction degree of fill body and other test methods,the effect of foundation treatment and compaction degree of fill body are tested,indicating that the method of foundation treatment and compaction process of fill body adopted in this project is reasonable.(2)In order to test the effect of foundation treatment and compaction of fill body,and predict the final settlement amount and settlement stability time of fill body after construction,46 settlement observation points are laid on the surface of fill body,and leveling method is adopted to observe the settlement after construction.The results show that the height of the fill body and the mechanical properties of the foundation affect the post-construction settlement,and the greater the compressibility of the foundation,the higher the height of the fill,the greater the post-construction settlement.The maximum post-construction settlement of the channel area occurs at B25 point(filling height 40.55m)with a settlement of 150.9mm(390d after construction),and the maximum post-construction settlement of the apron occurs at B7 point with a settlement of 52.1mm(390d after construction).The settlement curve shows that the deformation of the fill body gradually tends to be stable.The post-construction settlement meets the requirements of Geotechnical Engineering Design Code for Civil Airport(M/T5027-2013).Exponential model,hyperbolic model,parabola model,Gompertz model and Logistic growth model were used to carry out regression analysis on the monitoring data of the top surface settlement of the fill above Luojiahe culvert,which showed that the prediction results of exponential regression model were closer to the monitoring data.The final settlement of the fill at B25 point was predicted by this model to be 166.2mm.(3)In order to understand the stable state of the multi-stage slope during construction and after construction,101 surface displacement monitoring points or deep-hole displacement monitoring points were set up on the slope,and the horizontal displacement and settlement of the bridle way surface and deep were monitored by total station instrument,stratified settlement instrument and inclinometer.The results show that the maximum settlement is 80.0mm(210d during construction,372d after construction)at the depth of 5m in the 31st#measuring hole in the second grade bridle way on the north side of Luojiahe culvert fill,and the corresponding height of the fill above the second grade bride-way is 26.90m.JC59 at grade 5 bridle way on the south side of Luojiahe culvert fill has the largest surface settlement,with a value of 155.0mm(62d during construction and 372d after construction),and the corresponding height of fill above grade 5 bridle way is 8.00m.The maximum horizontal displacement of JC17 point on the surface of the secondary bridle way in the south slope is 89.4mm(268d during construction and 372d after construction),and the height of the filling body above the secondary bridle way is 32.00m.At JC48 point of grade 4 bridgway on the north slope of Luojiahe culvert fill,the horizontal displacement of deep stratification at the depth of 0.50m is the largest,with a value of 62.5mm(84d during construction,372d after construction),and the height of fill above grade 4 bridgway is 10.00m.The horizontal displacement and depth of deep layer of slope are negatively correlated during construction and after construction,and the horizontal displacement and settlement of slope surface tend to be stable gradually.According to the specification and engineering experience,the slope is judged to be in a stable state as a whole.(4)In order to analyze the deformation law and stability of the multi-stage slope during construction,stress and strain analysis and stability evaluation of the slope should be carried out.Taking the sixth level slope at the south side of Luojiahe culvert filling body as the research object,the finite element numerical analysis method is adopted to carry out inverse analysis on the calculated parameters according to the monitoring data,and the calculation model is corrected.Combined with strength reduction method,the deformation,safety factor and sliding surface position of graded slope during slope filling are studied.The results show that the vertical displacement increases with the filling height and the maximum settlement location is 18m away from the top of foundation,which is 0.38 times of filling height.The sliding surface of multistage slope presents a combination of arc at the upper part and straight line at the lower part.The shear outlet of sliding surface appears at the foot of slope,the bottom surface of sliding zone is tangent to the foundation surface,and the shear entrance is always located at the top of slope.With the increase of filling height,the average slope ratio increases,the safety factor decreases gradually,and the change rate of the safety factor also decreases gradually.The multistage slope is in a stable state and meets the requirements of the code.The design scheme of the filled slope is reasonable.