沉桩超孔隙水压力对码头边坡稳定的影响

Influence of excess pore water pressure induced by pile driving on stability of warf slopes

沉桩会对码头边坡稳定产生不利影响,一是引起桩周土体超孔隙水压力的急剧上升,导致土体有效应力降低;二是沉桩的振动加速度会产生对边坡稳定不利的瞬时惯性力。对于灵敏度低的土质岸坡来说,前者是影响其稳定性的主要因素。考虑沉桩时初始超孔隙水压力的分布,根据Biot固结方程超孔隙水压力消散解的一般表达式,建立了沉桩引起的超孔隙水压力随时间消散的解析式,在条分法的基础上考虑沉桩产生的超孔隙水压力的不利影响,建立了沉桩时边坡稳定安全系数的计算公式。根据沉桩顺序对某码头进行边坡稳定分析,结果表明:考虑打桩作用的岸坡稳定安全系数明显降低,沉桩产生的超孔隙水压力逐渐消散,边坡稳定安全系数随沉桩工序历时变化,施工中期由于超孔隙水压力叠加,岸坡最危险,沉桩结束3个月以后,超孔隙水压力基本消散,边坡稳定安全系数接近不考虑沉桩时的值。工程中要根据打桩计划进行边坡稳定计算。

Pile driving engenders disadvantage influence to stability of warf slopes,first it brings the excess pore water pressure in the soil around pile to sharp increase;and this leads to decrease of the effective stress;second vibratory acceleration owing to piling brings adverse instantaneous inertial force to stability.The first is primary for stability of insensitive soil slopes.Distribution of the original excess pore water pressure has been studied;and based on popular expression of Biot concretion differential equation,analytical formula for excess pore water pressure resulted from pile driving has been set up.Considering disadvantage influence from piling,formula of safety factor of stability was set up based on strip dispart method.Stability analysis on a wharf slopes has been done considering sequence of driving construction;result shows that safety factor reduces evidently,excess pore water pressure dissipates gradually;and factor varies with working procedure of driving.In period of construction slope is most dangerous because of accumulation of the pressure value;and the excess pore water pressure dissipate mostly after three months since finish piling,safety factor approximates the value that calculated without taking influence of piling into account.So it is important to check stability of slope during driving.