When implementing a CHASM simulation it is necessary to set up the 2D profile and specify the initial water table. Other boundary conditions are the upslope recharge, detention capacity, maximum soil evaporation and initial surface suction. The only time-dependent input variable is precipitation, which is specified by the length of the storm (hours) and the amount of precipitation each hour. There are a further seven parameters that need to be provided (see Table), including the Suction Moisture Curve, which is input as a series of points to construct a piecewise linear function.
- Table 1. Parameters used in CHASM
Parameter Units Symbol Saturated hydraulic conductivity m s−1 Ks Saturated soil moisture content m3 m−3 θs Saturated bulk density (unit weight) kN m−3 γs Unsaturated bulk density kN m−3 γ Effective cohesion — c′ Effective friction coefficient Angle φ′ Suction–moisture curve — SMC
CHASM has been used in many countries around the world, for a range of different applications and by different organisations and institutions.
The configuration of CHASM allows a number of different process controls on slope stability to be quickly and simply explored. Common applications of the software include:
- determining the role of negative pore pressures in slope stability
- establishing ‘design charts‘ for different combinations of slope profile, soils, initial conditions and triggering rainfall
- establishing the role of hydrological controls on slope stability
- prioritisation of road cut slopes for remedial works
- determination of topographic controls on slope stability