Wet Mass Soil Stabilization for Excavation Support-PPT Presentation

PPT Presentation

Pdf Summary

The Northwest Drive Grade Separation project at Minneapolis–St. Paul International Airport required new retaining walls between an existing roadway and a new drive. Cohesionless sands with variable silt content, shallow bedrock, and limited working space made conventional excavation and soil-stabilization methods challenging. The design called for improved ground to support excavation, with a minimum specified compressive strength of 2,000 psf.<br /><br />Permeation or chemical grouting and jet grouting were considered, but variable soil conditions raised concerns about uneven grout penetration, large treatment volumes, and maintaining jet-grout geometry near the surface. The project instead used shallow, mechanical mass mixing to create a cemented soil matrix, or soilcrete, that functioned as a gravity structure. Design checks addressed overturning, sliding, shear, and bending, with a target design strength of 200 psi.<br /><br />Construction used a 60-inch-wide mixing tool, a leading-edge approach, and contiguous panels. Operations were monitored through data on grout specific gravity and flow, binder content, and tool rotation speed. The confined site also required careful management of batching and material storage.<br /><br />Field samples exceeded the minimum design strengths. The stabilization allowed excavation to proceed rapidly, and the alternative approach proved cost-effective and beneficial to the schedule. The project demonstrated that conventional stabilization methods are not always the best fit; the choice of technique should reflect the site’s soil conditions, access, and construction constraints.

Keywords

Northwest Drive Grade Separation

Minneapolis–St. Paul International Airport

retaining walls

soil stabilization

mechanical mass mixing

soilcrete

cemented soil matrix

ground improvement

jet grouting

chemical grouting