宽围压加卸荷条件下特高坝填筑料强度变形研究

开展大型三轴试验,系统研究了特高坝堆石料和砂砾石填筑料在宽围压加卸荷条件下的强度变形特性。结果表明:相比堆石料,砂砾石料在低应力条件下的强度低,采用砂砾石填筑的大坝应防止坝坡浅层失稳。围压对强度指标和邓肯模型变形参数均具有重要影响,对于特高土石坝,宜根据应力分布情况分段采用不同的强度指标和变形参数,以提升坝体结构应力变形计算精度和提高工程安全性。卸荷—再加载循环内,均产生了正值的轴向变形和体积变形,循环结束后,应力-应变、体变-应变曲线均回归至原有的正常加载形态;在卸载段,低围压、低应力水平条件下往往表现为体胀,随围压和应力水平的提高,主要表现为卸荷体缩;在再加载段,无论围压大小还是应力水平高低,均主要表现为体缩。随围压的提高,回弹模量与初始切线模量之比增大;同一围压下,随应力水平的提高,回弹模量变化不大,略有降低的趋势;大石峡工程高填筑标准砂砾石料和堆石料K_ur/K约1.98~2.22,但指数n_ur要远大于n;对于那些特高坝和高坝而言,有限元计算时假定n_ur=n是不太适宜的,应开展回弹模量试验研究。

Experimental study on strength and deformation of filling materials of super-high dams with wide confining pressures under loading and unloading conditions

The triaxial tests with wide confining pressures under loading and unloading conditions are carried out to study the strength and deformation of filling materials of super-high dams.It is found that the strength under low confining pressure of sand gravel is lower than that of rockfill materials,so the slope of dams filled with sand gravel should be gentler to prevent instability.The range of confining pressure has great effects on the strength indexes and deformation parameters.The change of nonlinear strength index is not as significant as that of linear strength index,and the change of nonlinear strength index of sand gravel is not as significant as that of rockfill.For a super-high dam,different strength indexes and deformation parameters should be adopted according to the stress distribution of dam crest,dam slope and dam body.The axial and volume deformations occur during unloading-reloading cycle,and after the cycle the curves of stress-strain and volumetric strain-axial deformation return to normal shape.During unloading,the volume of samples mainly seems to expand under low confining pressures and stress level,and contracts under high confining pressures.During the reloading stage,the volume deformation mainly shows shear shrinkage regardless of the confining pressure or stress level.The ratio of resilient modulus to initial tangent modulus increases with the confining pressure,and the resilient modulus seems to decrease with the stress level.The the ratio of K_ur/K is about 1.98~2.22,but the resilient modulus index nur is larger than the initial tangent one n.