A LARGE SCALE MODEL TEST ON DETECTION OF POTENTIAL RISK OF SLOPE FAILURE BY MONITORING OF SHEAR STRAIN IN SHALLOW SECTION

A large scale model test was carried out in this study to investigate relationship between an increase of the potential risk of slope failure and the shear strain in the shallow section. A simplified shear strainmeter (MPS) was developed to measure the shear strain. MPS comprises a screw at the lower end of the compact body of 0.6m in length and 10mm in diameter so that easy installation without pre-borings. Moreover, lateral compression by installation in the surrounding soil makes strong contact, thereby resulting in high sensitivity. A model slope was composed of soft deposit by Kanto-loam and 45 degrees of inclination and 3.5m of height. Several sets of MPS and conventional sensors of inclinometers and displacement transducers were set to compare the reactions in the test. Seven steps of cuttings were carried out from the toe of slopes to make unstable. The model slope did not fail immediately after a completion of final cut, and 7 minutes of a time lag existed prior to the failure. Clear increases in the responses of shear strains (θ) were measured with the progress of slope cuttings in the tests. The relationship between θ and the displacement shows good agreement in the reactions. Similar reactions to the creep strain curve were observed in θ. A couple of minutes' time could be provided for escape by identifying either a 2nd creep or a 3rd creep. Accordingly, the relationship between the increase of the potential risk of slope failure and the increment of shear strain in the shallow section of slope was confirmed. It was clarified that this simplified monitoring can save worker's lives by escape prior to failure.