Strength and creep properties of a frozen coastal sand in saltwater

In 1998, the Port of Los Angeles contracted to have a force main under their primary shipping channel relocated from a depth of 13 m to 26 m. Access shafts were excavated using frozen ground technology to a depth of 26 m, with the frozen ground used for support of the excavation. When the shaft was within 1 m of the required depth, water started to enter into the excavation. Six hours later, the shaft collapsed. An investigation was conducted into the strength of the frozen soil. Unconfined compression strength tests were conducted at strain rates of 0.1% and 1%. The samples were saturated with water from the shaft, which had a salt concentration measured as equal to that of seawater. Short-term compressive strength was measured between 1300 and 1900kPa. Constant stress creep tests were also conducted, indicating a strength of about 760 kPa. All testing was conducted at a temperature of -10°C.