非饱和土诱导减载涵洞的竖向土压力研究

为准确计算诱导减载涵洞的主要荷载，采用圆弧小主应力轨迹描述诱导减载涵洞上方回填土拱效应，以推导考虑土拱效应的滑移面土压力系数表达式，继而基于非饱和土的双应力状态变量强度理论确定滑移面摩擦切应力，建立诱导减载涵洞顶部的竖向土压力解析解，结合等沉面高度求解给出应用步骤，最后对比文献现场实测进行正确性和适用性验证，并定义减载率分析基质吸力及分布形式、吸力角、减载材料厚度和变形模量等因素的影响特性。结果表明：所得涵顶竖向土压力解析解可合理反映基质吸力及分布形式、土拱效应、减载材料性能和等沉面高度的综合影响，完善了诱导减载涵洞设计理论；非饱和土强度提升使摩擦作用增强与等沉面下降同时发生，基质吸力和吸力角对减载率具有双重影响，表现为减载率均先增大后减小，且均布吸力下双重影响更为明显；减载率随减载材料厚度增加而非线性增大并趋于稳定，但随减载材料变形模量增加非线性减小。

Vertical earth pressure against an induced trench installation culvert in unsaturated soils

To accurately calculate primary loads for an induced trench installation culvert, the study first described the soil arching effect of unsaturated backfills above an induced trench installation culvert by using the circular-arc trajectory of minor principal stress, so as to derive a theoretical formulation of the earth pressure coefficient at a sliding surface. Then, the frictional shear stress at a sliding surface was determined based on the strength equation of two stress state variables for unsaturated soils, and an analytical solution of vertical earth pressure at the culvert top in unsaturated soils was presented. Application steps of the proposed solution were provided along with height calculation of an equal settlement plane, and comparing validations against field measurements reported in the literature were performed. Finally, load reduction rate was defined to analyze the influences of different factors including matric suction and its distributions, suction angle, compressible material thickness, and deformation modulus of compressible materials. Results show that the obtained analytical solution of vertical earth pressure could reasonably account for the comprehensive influences of matric suction and its distributions, the soil arching effect, the performance of compressible materials, and the height of equal settlement planes. Consequently, the proposed solution could improve the structural design theory of an induced trench installation culvert. The frictional effect increased and the equal settlement plane decreased simultaneously with increasing unsaturated soil strength. Both matric suction and suction angle had dual-effects on the load reduction rate, reflected by the fact that the load reduction rate increased at the beginning and decreased afterwards, and the dual-effect was more obvious for uniform suction. With the increase in compressible material thickness, the load reduction rate increased nonlinearly and tended to be stable, whereas it decreased nonlinearly with increasing deformation modulus of compressible materials.