Project

The project consists of 8.0m deep temporary excavation
for construction of 4 nos. 23m diameter digester ssupported on micropiles.Conforming design is prefabricated vertical draintreatment with surcharge followed by open excavation within circular cofferdam formed by using sheet piles and ring beams. Due to thick soft slime layer and water seepage concerns, another solution has to be sought.

Keller proposed "Design and Build" solution using both dry and wet deep soil mixing (DSM) techniques to improve in-situ slime to accommodate deep excavation for construction of digesters.

Soil Conditions:
The typical soil condition comprised of 6m to 8m thick
of very soft slime overlying 4m of soft to firm sandy clay
underlain by weathered limestone. The moisture content, liquid limit and plastic index of the slime are 88%, 72% and 40%, respectively.

Design Solution:
Dry DSM columns
(600mm dia. with spacing of 600mm triangular grid)
Wet DSM columns (870mm dia. with spacing of 750mm triangular grid) were adopted. Length of DSM columns varies from 6m to 12m. Design shear strength of DSM block is 100 to 150 kPa. Slope stability and basal heave
analyses have been carried out and achieved safety requirement.

Performance:
DSM columns were formed according to design size and length.Excavation was carried out without any stability and water seepage problems.