瀑布沟大坝心墙拱效应分析

在总结前人提出的拱效应系数基础上，对拱效应系数的公式进行了改进，认为拱效应系数应该是实测土压力与上覆土压力和孔隙水压力之和的比值。结合瀑布沟大坝监测资料，用改进的拱效应系数计算公式对大坝心墙拱效应进行计算，并对心墙内拱效应进行动态分析。在施工期，施工工艺是影响大坝心墙拱效应系数的主要因素，填土在仪器埋设以上0～20 m时，拱效应系数较大，随着填土的增加拱效应系数减小，施工期坝体内应力分布在蓄水初期起决定性作用。在蓄水期，心墙上游侧拱效应系数与水位变化呈反相关联，拱效应系数比下游同高程和0+001 m处大；0+001 m处拱效应系数与水位变化呈正相关联，且此处拱效应系数最小；心墙下游处拱效应系数与水位变化呈正关联的关系，在心墙与基岩接触处拱效应系数大于100%。产生这种规律的原因主要有湿化、渗流、水力劈裂作用，三者共同影响，从而导致心墙内应力发生变化。

Arching effect analysis of core wall in Pubugou dam

Based on the previous definitions of arching effect coefficient, the formula of arching effect coefficient is improved. It is suggested that the arching effect coefficient should be the ratio of measured soil pressure and the sum of overlaying soil pressure and pore water pressure. Combining with the monitoring data of Pubugou dam, the arching effect of core wall is calculated by the improved formula of arch effect coefficient; and dynamical analysis of arching effect is made. Construction technology is the main factor affecting the arching effect coefficient of core wall during the construction. The arching effect coefficient is larger when the filled soil is 0-20 m above the instruments; and decreases with the rising of filled soil. The stress distribution of dam during construction plays an important role in initial water storage. During the impoundment, the arching effect coefficient of upstream side of the core wall shows inverse correlation with water level variation. The arching effect coefficient of upstream side is larger than that of downstream side at the same elevation and 0+001 m. The arching effect coefficient at 0+001 m shows positive correlation with water level variation, where gets the smallest arching effect coefficient. The arching effect coefficient of downstream side of core wall shows positive correlation with water level variation. The arching effect coefficient is larger than 100% on the contact surface between core wall and bed rock. There are three reasons for the above laws, such as wetting, seepage and hydraulic fracture; and the combined effect of the three results in stress variation in core wall.