强震过程滑带超间隙水压力效应研究:大光包滑坡启动机制

大光包滑坡是汶川地震触发的最大规模滑坡,其滑带地质背景为埋深400 m的饱水层间构造破碎带。为研究强震过程该带间隙水压力(孔隙和裂隙水压力)响应特征,设计夹饱水软弱层地质体单元模型,并开展系列振动台试验,结果表明:振动过程软弱层超间隙水压力显著大于上下硬层,且具有瞬态生成和逐渐累积特性,进一步揭示依赖模型非协调变形的"振动冲压-拉张"和"振动剪切"是瞬态超间隙水压力成因、依赖软弱层非协调变形的动力损伤是超间隙水压力累积成因,从而建立了垂直和水平振动耦合作用下包含间隙水压力系数r_w和间隙水压力作用的有效面积系数h的地震滑坡滑带有效应力模型。对于大光包滑坡,滑带h估测范围为0.7~0.9,当r_w为0.73~1.04时滑带抗剪强度可降为0;振动台试验表明,汶川强震过程大光包滑坡区地震动参数可使r_w达到这一水平。最后,提出大光包滑坡启动的"强震作用-层间错动带控滑-动力非协调变形致损、扩容-超间隙水压力激发-滑坡启动"演化过程机制。

Excess interstitial water pressure within sliding zone induced by strong seismic shaking:An initiation model of the Daguangbao landslide

Daguangbao(DGB)landslide,formed within a saturated bedding fault 400 m in depth,is the largest landslide triggered by the 2008 Wenchuan earthquake.To study pore and crack water pressures(i.e.,interstice water pressure)responses within weak layers,a series of shaking table tests were conducted on a geological model with a saturated weak interlayer.The results show that the excess interstice water pressure within the weak layer is much larger than that in both the upper and lower layers and that the excess water pressure of the weak layer is characterized by transient generation and gradual accumulation.It was proposed that compression-tension and shear behaviors of the model depending on uncoordinated deformation and dynamic damage depending on uncoordinated deformation within the weak layer respectively induce transient excess water pressure and accumulation of the excess water pressure.An effective stress model for earthquake-inducted landslides under both horizontal and vertical shaking conditions,containing the interstice water pressure ration r_w and the effective area index of interstice water pressure h,was developed.For the DGB landslide,site investigations show thatηis in the range of 0.7-0.9 and that the effective stress of the sliding zone decreases to zero while r_w ranges from 0.73 to 1.04.The shaking table tests also show that the seismic parameters in the landslide area during the Wenchuan earthquake can make r_w reach the above range.Finally,the failure mechanism of the DGB landslide mechanism from strong seismic action,damage and expansion of dislocation interface resulted from dynamic uncoordinated deformation,excitation of the excess interstitial water pressure to initiation of landslide was concluded.