Modelling discontinuity control on the development of Hell\u2019s Mouth landslide

Lingfeng He,Doug Stead,John Coggan,Matthew Eyre,Mirko Francioni

doi:10.1007/s10346-021-01813-3

Lingfeng He, Doug Stead + Show 3 more

Open Access

https://doi.org/10.1007/s10346-021-01813-3

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Abstract

This paper focuses on numerical modelling and back analysis of the Hell’s Mouth landslide to provide improved understanding of the evolution of a section of the north coast of Cornwall, UK. Discontinuity control is highlighted through the formation of a ‘zawn’ or inlet, the occurrence of two successive landslides and evidence of ongoing instability through opening of tension cracks behind the cliff top. Several integrated remote sensing (RS) techniques have been utilised for data acquisition to characterise the slope geometry, landslide features and tension crack extent and development. In view of the structural control on the rock slope failures, a 3D distinct element method (DEM) code incorporating a discrete fracture network and rigid blocks has been adopted for the stability analysis. The onset and opening of tension cracks behind the modelled slope failure zones has also been studied by analysing the displacements of two adjoining landslide blocks, between which, a joint-related tension crack developed. In addition, a sensitivity analysis has been undertaken to provide further insight into the influence of key discontinuity parameters (i.e. dip, dip direction, persistence and friction angle) on the stability of this section of the coastline. Numerical modelling and field observations indicate that block removal and preferential erosion along a fault resulted in the formation of the inlet. The development of the inlet provides daylighting conditions for discontinuities exposed on the inlet slope wall, triggering the initial landslide which occurred on 23rd September 2011. Numerical modelling, and evidence from a video of the initial landslide, suggests that the cliff instability is characterised by a combination of planar sliding, wedge sliding and toppling modes of failure controlled by the discrete fracture network geometry.

Highlights

Discontinuities produce weak planes in a rock mass that may contribute to the occurrence of landslides under unfavourable conditions associated with orientation, size, intensity and strength of discontinuities (Hutchinson 1989)
Regarding modelling method 2, for understanding influences of the progressive inlet formation on proximal slopes, the results presented in Fig. 11 indicate that the removal of the three blocks leads to progressive displacement of the proximal blocks in zone A-3, directly adjacent to the inlet sidewalls
A good agreement can be observed between the modelled results and field observations.Vectors of block resultant displacement are presented in Fig. 12b, which confirms that displacements in zones A-3 and A-4 are greater than that in zone A-5, with all three regions showing a general displacement trend towards the northwest

Summary

Introduction

Discontinuities (such as joints, cleavages, bedding, foliation, faults and folds) produce weak planes in a rock mass that may contribute to the occurrence of landslides under unfavourable conditions associated with orientation, size, intensity and strength of discontinuities (Hutchinson 1989). To simulate the impact of block removal through toe erosion on the inlet formation and investigate the influence of the Landslide development and tension crack formation The formation of the inlet provided daylighting conditions for discontinuities exposed on the inlet sidewalls.

Results

Conclusion