金沙江某水电站上下坝址岩体卸荷差异研究

UNLOADING OF THE ROCKMASS AT THE UP AND DOWNTREAM DAMS OF HYDROPOWER STATION IN JINSHA RIVER

在河流下切、斜坡成坡过程中，斜坡应力场不断调整和适应坡体的变化，表浅部岩体在应力变化过程中往坡外发生卸荷，在同一地区岩体卸荷深度应当相差不大。而在西南某水电站相隔仅1.4km上下坝址勘察过程中发现，两坝址岩体卸荷深度却存在较大差异，上坝址岩体卸荷深度在20m以上，最大深度达到90m；下坝址岩体卸荷深度仅为5-20m。通过现场调查及数值模拟成果表明，上下坝址岩层方位是两坝址岩体卸荷差异的决定性因素，上坝址为顺向坡，岩层走向与边坡走向平行，倾角较陡的岩层形成拉裂面，易于风化营力的侵入，岩体卸荷深度大；下坝址为横向坡，岩层走向与边坡走向近于垂直，岩体强度远大于岩层面的强度，且平行坡向的结构面数量少，岩体卸荷深度在20m以内。

The process fiver bank slopes. The of stream trenching and slope formation cause a continuous change in the stress field of the superficial rockmass is unloaded in the change of stress field. The depth of unloading should be indifferent in the same area. An investigation is carried on the stress field at a hydropower station in southwest China. The station has two dams. The up and downtream dams have a distance of 1.4km. The investigation detected that unloading depths of the rockmasses at the two dam sites have wider differences. At the upstream dam site, the unloadin depth is more than 20m, and its extreme depth can reach to 90 m. At the downstream dam site, the unloading depthis only 5-20m. Field survey and numerical simulation indicate that orientation of the rock formation is the key factor for the difference in the unloading depths at the up and downstream dams. Trends of rock formation and fiver bank slopes at the upstream dam are paralleled. The roekmass of steep dip angle is easy to be cracked. The weathering is invaded. The depth of the rockmass unloading is deep. At the downstram dam, the trends of the rock formation and fiver bank slopes are nearly are perpendicular. The strength of the rockmass is greater than the bedding planes. The structural surfaces that parallel to the river bank slopes are less. Therefore, the unloading depth of rockmass is within 2Om.