This paper presents an equipment to perform shear tests under low constant normal stresses. This equipment maintains a normal stress during the whole joint sliding by means of a lever arm and dead weights. For common joint samples (around 100 to 150 cm), the applied normal stresses can range from 20 to 200 kPa. The results of some sets of joint tests are presented. The joints came from road cuts in the central part of Portugal. One of the sets is from quartzite discontinuities and the remaining are from schistous discontinuities. A description of the geological characteristics of the joints and the analysis of the results of the tests are presented.
Rock slope stability analyses require the knowledge of the shear strength of the most relevant discontinuities. The determination of the strength parameters should be evaluated by shear tests. These tests should reproduce as close as possible the features that occur in the field. In this case, normal stresses are low, typically smaller than 0.2 MPa, and should be kept constant during the sliding. In the proposed paper, a new equipment to perform shear tests under low constant normal stresses is presented. This equipment maintains a normal stress during the whole joint sliding by means of a lever arm and dead weights. For common joint samples (around 100 to 150 cm), the stresses used can range from 20 to 200 kPa. These values of normal stress cover the range of stresses that can commonly be found in road cuts. The height of this kind of slopes, which are particularly frequent in mountain roads, can go from 10m to around 40 m. This paper presents the results of some sets of joints. The joints came from road cut slopes in the central part of Portugal. One of the discontinuity sets is from jointed quartzite discontinuities and the remaining sets are from schistous discontinuities. A description of the geological characteristics of the joints is presented and an analysis of the results of the tests is also put forward.
The shear tests were performed on joints prepared from rock material collected in 4 rock slopes from road cuts in the central part of Portugal. The roads are the IP3 (Itinerario Principal n°3) and the EN 234 (Estrada Nacional n° 234), near Coimbra. In both cases, they are located in the Buçaco Ordovician-Silurian Syncline and in the Schist-Greywacke pre-Ordovician Complex (Beiras Group). Slope 1 is located at km 55 of the IP3. It develops along 150 m and is placed close to the central zone of the Buçaco Palaeozoic Syncline. This slope is composed mainly by impure quartzites, though schists and carbonaceous schists are also present. The latter display a dark colour and are very weathered (W5). The impure quartzites are set in persistent benches with a weathering degree ranging from W2 to W4. They present purplish, greyish and whitish colours and are composed primarily by quartz (more than 75%) and white mica and ferrous oxides.
