MOORE & TABER                     

 

 

Soil Grouting and Ground Improvement Specialists

 

         

Permeation grouting techniques were used to stabilize a Southern California ocean bluff, following a localized slope failure.  Over one week of constant watering from an unattended irrigation system led to failure of a 12-m thick sandy marine terrace deposit. The failure undermined a large portion of a residential back yard, threatening the adjacent home.

Mitigation measures involved stabilization of running sands with permeation grouting techniques, to allow for the steep near-vertical backcuts required for remedial grading.

Two distinct grout mixtures were used, including sodium silicate and ultrafine cement. The ultrafine cement developed much greater strengths, whereas the sodium silicate was used within the outermost portion of the slope face.

More than 600 sleeve-port grout injection pipes were installed on the slope face and in the rear yard. Limited access techniques were used, and all work was performed by hand. Total permeation grout quantities were in excess of 1,000,000 liters.

Grouted terrace sands performed very well during excavation of the backcut and in-grading benching. The otherwise “running” sands adopted the character of sandstone. Air-powered digging spades were required to excavate the grouted material.

The failure scar was mitigated by reconstruction of the slope face with cement-treated soil fill. Seepage was addressed by drilling a horizontal drain from the heel of the backcut through the grouted terrace. Typical “burrito” backdrains were also installed as grading progressed.

Tree wells were installed periodically as the slope was reconstructed. Each well was fitted with its own drain. These planters were stocked with native, drought-resistant scrub in order to alleviate the need for an irrigation system, and to maintain coastal aesthetics.

The combined remedial system resulted in an overall factor of safety of greater than 1.5.

Reference:  Geraci, McLarty, Dahncke and Hourihan (2004)

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