Experimental investigation of rainfall criteria for shallow slope failures

A theory of the internal-response-based rainfall criterion for predicting slope failure is proposed based on artificial rainfall tests for a sandy slope. Key elements in a generic model describing shallow slope failure are identified from the tests with extensive soil moisture and piezometric measurements. The observed retrogressive slope failure was triggered by a toe failure, followed by an abrupt increase in debris discharge. The onset of the failure was preceded by a clear transition point on the soil moisture vs. time curve at the soil–bedrock interface. Both external and internal responses of slopes to rainfall can be expressed using widely adopted I–D (rainfall intensity–duration) plots. Experimental results from the tests indicate close relationships between the internal-based and external-based I–D envelopes for critical slope states. The theory of the internal-based I–D criterion proposed here will be useful for more accurate slope failure predictions.