Mechanism analysis of a landslide in highly weathered volcanic rocks of Niushoushan Hill in Nanjing

Abstract

In this paper, the landslide mechanism in highly weathered volcanic rocks is analyzed in Niushoushan Hill in Nanjing; this hill is mainly composed of volcanic tuff rocks. The gradually weathered rocks reduce the hillslope stability and cause landslides during continuous rainfall. The kaolin and montmorillonite clay minerals were tested using an X-ray diffractometer. The subsequent swelling, disintegration, and permeable tests indicated the location of soft zones and the poor hydraulic conductivity of the highly weathered tuff (HWT). The overflow from boreholes and joints exposes a confined aquifer that is caused by rainfall infiltration in the lower moderately weathered tuff (MWT), which crops out on the top of the hill and is bounded on the interface of the HWT and MWT. The electrical resistivity tomography method was carried out for the considered slope to define the boundaries of the discontinuities as a supplement to drilling. The displacements of the slope surface and the deep rocks were monitored, and the results indicated that sliding had not stopped after a long period of continuous rainfall. Slope stability analysis, considering a water head rise due to rainfall infiltration, was carried out using the Slide v6.0 computer package. The simulation included steady-state flow, transient seepage associated with rainfall and slope stability variation caused by different infiltration conditions. The results indicate that the HWT with low permeability can confine the activity of the lower aquifer and result in a rapid rise of pore pressure in response to rainfall, which can lead to slope failure.