STABILITY MODELING OF A DRAINED LANDSLIDE, MEEKER, COLORADO

Remediation of an active landslide was carried out in June of 2001 at a site north of Meeker, CO along a fill embankment on State Highway 13. This remediation was accomplished through the installation of approximately 1900 ft. of horizontal drains into the landslide. The drains were made of geosynthetic wick material and were installed using a new method developed by the authors. Drain lengths, attitude, and placement were carefully documented during installation; this data was used to generate a site map defining the drain field.

The stability of the drained slope was evaluated for numerous recharge and drainage conditions using a two-dimensional slope stability program. Considerable effort was made to define the drained water table surface within the slope, which has an irregular, corrugated shape around the drains. A mathematical model was developed to define the surface using equations originated for agricultural drainage engineering applications. This model compared favorably to our own field data and data from laboratory drainage experiments. The model depends on several parameters that are readily measured in the field, estimated, or taken from site maps, including drainage flow rate, depth to bedrock or impermeable layer, hydraulic conductivity, and drain spacing.

Three important contributions toward landslide stabilization are provided by this research: it verifies the effectiveness of horizontally driven wick drains, it provides a method of accurately predicting the average drained water table surface configuration, and it provides a method of calculating ideal drain spacing during the design phase of the remediation program.