Investigation of a coastal landslip at Charmouth, Dorset

Abstract

Summary The Dorset coast is an area with a long history of landslide activity and coastal erosion. Geologically the area is composed of the clays, mudstones and limestones of several divisions of the Lower Jurassic (Lower Lias) which are overlain unconformably by Cretaceous clays and sands (Gault and Upper Greensand.) Areas of serious instability appear to occur in close association with naturally occurring reservoirs of ground water, of which Black Ven at Char-mouth is a good example. Problems connected with a small coastal landslip near a private housing estate at Char-mouth were studied and shown to be related to a Pleistocene mudflow. The main purpose of the investigation was to suggest remedial works but the subsidiary aim, forming the theme of this paper, was to assess the usefulness of shallow depth geophysical and geotechnical methods not normally used in instability studies.

Data sources for planning: geomorphological mapping of landslides in north-east Derbyshire

“…Various route planning and coastal erosion studies (see Brunsden et al 1975 a & b;Brunsden & Jones 1972;Denness et al 1975) demonstrate how significant features may not have been recognized during investigations confined to particular sites. Geomorphological studies form a framework for placing a small area in a broader landscape development context.…”

Field testing methods for engineering geological investigations

“…In landslip investigations, the observation of variations in soil moisture content may be important and this can be successfully monitored using resistivity measurements. Denness et al (1975) described seasonal fluctuations in moisture content,for a landslip at Charmouth in Dorset. Forster & McCann (in press) have described the use of resistivity and other geophysical methods in reconnaissance investigations for landslides.…”

A test of mobile weight-drop for surface wave seismic data acquisition

“…For example, it uses to describe the subsurface velocity [4][5][6][7][8], and for geotechnical analysis, identify the slip surface of debris by refraction seismic [8,9]. The last author using a 16 lbs hammer for the seismic source.…”