高原冻土地区公路路基回填材料优选及施工技术

Optimization of backfill materials and construction technology for subgrade of highway in plateau frozen soil region

以中国一带一路重点项目西藏羊大公路(羊八井至大竹卡公路)改建工程为依托,研究了高原冻土地区公路路基施工优化设计,提出了拟采用的4种公路路基回填材料方案,分别为原土基层、天然级配砂砾+水泥稳定砂砾基层、粉质黏土+气泡混凝土基层、人工级配砂砾+宕渣基层,面层均采用中粒式沥青。利用有限元分析软件MIDAS-GTS NX建立路基模型,对比,分析了经历冻融循环前后4种路基回填材料方案内力变化、结构变化。研究及施工结果表明:采用天然级配沙砾底基层+水泥稳定砂砾基层+中粒式沥青混凝土面层的2号施工方案在模拟监测点处的竖向应力值变化率最小为6.04%、水平应力值变化率最小为4.23%,冻融循环后变化率不大,竖向沉降和水平位移更快趋于稳定,分别为30.10 mm和35.16 mm。结合现场施工条件进行2号方案施工优化,降低材料冻融循环对路基稳定性的影响,减少了土体结构变形。而且,将建模理论计算值与工程监测值进行对比,分析验证了该方法的正确性。

Relying on the reconstruction project of Yambajan—Dazhuka Highway in Tibet—a key project of China′s Belt and Road Initiative,the optimal design of the highway subgrade construction in plateau frozen soil region is studied herein,from which four schemes of the backfill materials those are planned to be used for the highway subgrade are proposed,i.e.undisturbed soil base,naturally graded gravel+cement-stabilized gravel base,silty clay+foamed concrete base and artificially graded gravel+slag base respectively,while the medium granular asphalt is adopted for all the surface courses.A subgrade model is established with the finite element analysis software--MIDAS-GTS NX,and then the internal force changes and structural changes of the four schemes of the subgrades backfill materials before and after the freeze-thawing cycle are comparatively analyzed.The results from both the study and the construction show that the minimum changing rate of the vertical stress value is 6.04%with the changing ate of the horizontal stress value of 4.23%at the simulated monitoring points for the No.2 construction scheme of the backfill materials of naturally graded gravel base+cement-stabilized gravel base+medium granular asphalt surface course,for which the changing rate is not so large,while both the vertical settlement and the horizontal displacement more quickly tend to be stable and are 30.10 mm and 35.16 mm respectively.Combined with the in situ construction condition,the No.2 construction scheme is optimized,and then the impact from the material freeze-thawing cycle on the stability of the subgrade is lowered and the structural deformation of the soil mass is decreased as well.Furthermore,the correctness of this method is verified through the comparative analysis made between the modeling theoretical calculation value and the engineering monitoring value.