Deep Mix Method Columns for Storm Water Detention Pond Stability and Constructability-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the design and construction of deep-mix-method (DMM) soil-cement retaining structures and sheet-pile groundwater cutoff walls for three stormwater detention ponds: the 17-foot-deep Administration Pond and the 15-foot-deep North and South Ponds.<br /><br />Soft soils made the unreinforced slopes unstable. Stability analyses compared conditions without ground improvement, with DMM alone, and with DMM plus sheet piling. For example, the Administration Pond’s short-term factor of safety increased from 1.18 without DMM to 1.38 with DMM and 1.44 with the sheet-pile wall; long-term values were 1.51 and 1.55, respectively. The design also considered settlement, constructability, seepage, and conflicts with existing structures. A pre-construction slope failure highlighted the risks of placing stockpiles beside excavations.<br /><br />The selected system used 10-foot-diameter DMM columns, generally 30–35 feet deep, together with sheet piles extending about 50 feet and keyed into an underlying impervious clay layer. Smaller columns were used at clashes. Alternatives such as tiebacks, internal bracing, soil nails, and soldier piles were rejected due to soft fill and space constraints.<br /><br />Construction involved 2,894 DMM columns, approximately 274,758 cubic yards of treated soil, and 269,864 square feet of sheet piling. Two grout plants, two high-torque DMM rigs, and two sheet-pile rigs supported the work. Quality control included pre-construction mix designs, daily strength testing, and field-vane testing. The project team reported completing the work in a record eight months and described it as the largest U.S. application of DMM with sheet piling for this purpose.

Keywords

deep-mix-method

DMM soil-cement

retaining structures

sheet-pile walls

groundwater cutoff

stormwater detention ponds

slope stability

soil improvement

settlement control

construction quality control