ABSTRACT
To assist in the design of the Middle Route of the South-to-North Water Transfer Project (SNWTP) in China, two areas, each 16m wide and 31m long, along an 11m high 22 cut slope in a typical medium-plastic expansive clay were extensively instrumented and their engineering performance was monitored. The 1200 km Middle Route of the SNWTP is to carry potable water from the Yangtze River region in the south to many arid and semiarid areas in the northern regions of China, including Beijing. One of the major geotechnical problems is to design safe and economical dimensions for cut slopes that form an open channel with a trapezoidal cross-section in unsaturated expansive soils which possess high swelling and shrinkage potential. The unique instrumentation package was designed to consider the influ-
ence of both the independent stress state variables: soil suction and net normal stress. The instrumentation package included tensiometers, thermal conductivity suction sensors, moisture probes, earth pressure cells,
inclinometers, a tipping bucket rain gauge, a vee-notch flowmeter and an evaporimeter. The fundamental mechanisms of rainfall infiltration into the unsaturated expansive soil during two artificial rainfall events and the complex interaction among changes of soil suction (or water content), in situ stress state and soil deformation leading to slope failure were studied. Not only are the monitoring data useful for engineering designs of slopes in expansive unsaturated clays, but they are also invaluable for calibrating constitutive models and numerical simulation procedures. This case study is thus an invaluable resource both for the practising civil engineer as well as the numerical modeller.
