Comparison of Extended Column Test and Propagation Saw Test
Comparison of Extended Column Test (ECT) and Propagation Saw Test (PST)
Introduction: Stability or “Instability” Tests are an important tool for determining the likelihood of a slope to produce an avalanche. Many different tests have been developed over the years – each with their own strengths and weaknesses. These tests provide a way to safely apply stress and deformation to a slope that is steep enough to slide (usually 250 or steeper) and observe and quantify the results. These results can then be interpreted to make larger inferences about the overall stability of a snowpack and the propensity for it to fail and produce an avalanche. It is important to note that stability tests only provide information limited to small area and, unless instabilities are revealed, do not provide conclusive evidence of stability (Mc,Clung and Schaerer, 2006). One major shortcoming of many stability tests such as the Compression Test (CT) and Loaded Column Test is that while they are effective at locating the weakest layers in a snowpack, they fail to demonstrate the propensity of a fracture within the weak layer to propagate. Research has shown that in order for an avalanche to occur there must initiation of a weak layer fracture and the fracture must propagate within a slab and weak layer (Ross and Jamieson, 2008). Two tests were independently developed to account for propagation propensity: The Extended Column Test (ECT) and the Propagation Saw Test (PST). The purpose of this lab was to learn the proper technique for conducting each of the two tests and comparing the results of the tests. Since stability tests were to be performed, site location required a slope of at least 250. The site chosen is just east of US Highway 550 on the road to the Little Molas Lake Park and Campground approximately six miles south of the town of Silverton. The slope was east facing at 800 had a 260 angle.
-Pit Location
Figure 1: Map of site location.
Introduction: Stability or “Instability” Tests are an important tool for determining the likelihood of a slope to produce an avalanche. Many different tests have been developed over the years – each with their own strengths and weaknesses. These tests provide a way to safely apply stress and deformation to a slope that is steep enough to slide (usually 250 or steeper) and observe and quantify the results. These results can then be interpreted to make larger inferences about the overall stability of a snowpack and the propensity for it to fail and produce an avalanche. It is important to note that stability tests only provide information limited to small area and, unless instabilities are revealed, do not provide conclusive evidence of stability (Mc,Clung and Schaerer, 2006). One major shortcoming of many stability tests such as the Compression Test (CT) and Loaded Column Test is that while they are effective at locating the weakest layers in a snowpack, they fail to demonstrate the propensity of a fracture within the weak layer to propagate. Research has shown that in order for an avalanche to occur there must initiation of a weak layer fracture and the fracture must propagate within a slab and weak layer (Ross and Jamieson, 2008). Two tests were independently developed to account for propagation propensity: The Extended Column Test (ECT) and the Propagation Saw Test (PST). The purpose of this lab was to learn the proper technique for conducting each of the two tests and comparing the results of the tests. Since stability tests were to be performed, site location required a slope of at least 250. The site chosen is just east of US Highway 550 on the road to the Little Molas Lake Park and Campground approximately six miles south of the town of Silverton. The slope was east facing at 800 had a 260 angle.
-Pit Location
Figure 1: Map of site location.
Cited: McClung, David, and Peter Schaerer. The Avalanche Handbook. 3rd ed. Seattle, WA: Mountaineers, 2006