DMT TESTING IN LANDSLIDE AREA. A CASE HISTORY: TODI’S HILL (UMBRIA, ITALY)

Abstract

The paper analyzes the results of the in situ Dilatometer test (DMT) in a representative slide area in OC clays. The method for detecting slip surface in OC clays is based on the DMT – Kd profile, which exhibits Kd drop to the value Kd≃2 in the slip zones . Features of the method, believed of pratical interest, are: - fast response so avoiding the wait required by inclinometer measurements; - the ability to detect quiescent slip surfaces not revealed by inclinometers; - some ability to evaluate the effects of loosening and remoulding due to sliding on mechanical properties of the soil mass above the slip surfaces. To sound the validity of such “method” in practice, a series of 8 DMT soundings, each 45 m long, was performed in a slope of the Todi’s Hill, notorious for recurrent slips. The paper presents the results of DMT tests in this analyzed slope and shows the Kd profiles obtained. Are summarized all the Kd≃ 2 depths an indicated a set of slip surfaces reconstructed passing through these depths. The study of this landslide was concluded with the following steps: - profile of pore pressure u were obtained at numerous depths during the DMT soundings by DMTC tests . They show that the u are markedly non hydrostatic. - Back analyses were carried out for the seat of slip surfaces reconstructed.