Field Testing of Earth Pressures in a Large-scale Natural Loess Slope

Abstract

An in-situ large-scale earth pressure test was undertaken in a natural loess slope in Lanzhou, China. A 14.5-m-high natural slope was gradually cut into a vertical slope through a series of eight slope cutting work conditions. By pre-installing re-bar meters and cutting slope unloading, the real earth pressure distribution law and potential slip surface development mechanism, along with the variation of the Slope Cutting Depth (SCD), were obtained under the condition that each point in the free surface can move independently and freely. Earth pressure increases slowly at first and then decreases sharply along the Slope Excavating Depth (SED). The increase rate for 9.0 to 10.4 m is 3 to 4 times as much as the former conditions, so the self-stability height of the slope is 9.0 to 10.4 m. The unsaturated natural loess shear outlet of the slope is always located at the H/3 (where H is the natural slope height) position, so the slip surface does not pass through the bottom of the slope. The measured values of unsaturated vertical slope earth pressures are far less than the values calculated by Rankine’s earth pressure theory–especially the size and position of the maximum earth pressure.