Stabilization of High Soil and Rock Cut Slope by Soil Bioengineering and Conventional Engineering

Construction of a 274.5-m-long (900-ft) and 24.4-m-high (80-ft) soil (upper) and rock (lower) cut slope on the eastbound side of the Massachusetts Turnpike at mile mark 94.1 eastbound for the proposed interchange with Route 146 combined conventional engineering and soil bioengineering solutions. Geologic mapping identified three sections (east, middle, and west) that had different patterns of rock discontinuities, which controlled rock cut design. Each required a different slope design for a stable rock cut. The soil cut design was controlled by soil density, groundwater seepage, and erosion potential from seepage and surface runoff. Soil bioengineering was used to control surface drainage and erosion on the cut soil slope above the 12.2-m-high (40-ft) rock cut and rapidly revegetate the disturbed soil slope, which addressed the project's environmental and aesthetic goals. Conventional crushed-stone drains augment the living soil bioengineering drains. Woody vegetation was used to reinforce the cut soil slope surface. Branches from native living woody plants were installed into the slope face, offering surface reinforcement. Root development along branch lengths provided additional reinforcement. The hydrologic regime was modified as growing plants remove moisture through transpiration and embedded bundled branches channel water off the slope. Basic soil bioengineering stabilization principles by using live fascines and brush layers for soil and rock cut slope stabilization are presented. Discussions include preconstruction conditions, environmental benefits, vegetation harvesting and design, installation, and performance as of October 1996. Cut slope stabilization through soil bioengineering produced an environmentally, aesthetically, and mechanically sound solution, illustrating the benefits of combined technologies.