The Challenge
Build a large private residence on a waterfront site where the foundation for the basement is to be well below the water table and were the waters of Lake Washington are a few feet to the east. There were existing sensitive structures (an existing retaining wall and sanitary sewer trunk) directly adjacent and running through the area to be excavated. The site was in a noise-sensitive neighborhood with extremely limited construction access.

The Solution
A 4-foot-thick SoilFreeze shoring wall with a perimeter of approximately 370 LF was installed outlining the future foundation. Additional freeze pipes were strategically placed to underpin the retaining wall and sewer trunk main.

The freeze pipes were installed deep enough into the silty sands with gravel to withstand the hydrostatic pressure, which eliminated the need for dewatering. Noise from generator and refrigeration equipment positioned on the lake shore was deflected upward by a simple structure of straw bales and insulation boards. The project was completed successfully with no impact on existing structures and no complaints from neighbors.

The Challenge
The Port of Los Angeles needed to relocate existing utilities to allow for the deepening of the shipping channel between San Pedro and Terminal Island. Microtunneling with receiving and jacking shafts was the chosen method of construction. One shaft was located near the footings of a freeway bridge, another a few feet from a historic maritime museum, and two others were in an active container yard processing millions of square feet of containers per day. All shafts had excavation inverts more than 90 feet below grade. Groundwater within 10 feet of ground surface was salty, warm, and subject to tidal influence. Beach sands with silt layers were the predominate soils.

The Solution
5-foot-thick frozen soil shoring cells with inside diameters ranging from 14 to 22 feet were installed to depths of 140 to 145 feet below grade. A single row of freeze pipes formed the shoring cell with extra vertical freeze pipes installed through the MTBM pathway to provide additional thickness and stability. After excavation, the general contractor’s jacking and receiving rings were poured directly against the exposed frozen soil of the shoring wall. Freeze pipes were modified and relocated to give the microtunneling machine clear access to penetrate the shafts. The frozen shafts remained open and in use for over a year. All existing structures were free from damage.

The Challenge
Install sewer pump station 30-feet deep within several feet of the shore of Lake Tahoe. Noise restrictions and soil conditions consisting of gravels and cobbles with few fines prevented a sheet pile installation. Grouting was prohibited due to environmental concerns. Dewatering had failed to provide adequate groundwater control and caused settlement damage to existing structures and utilities. SoilFreeze was brought to the site after construction had started.

The Solution
A thick frozen-shoring cell around the perimeter was designed and installed to provide excavation support with no interior bracing or tie-backs necessary. Lateral groundwater movement was completely stopped by the frozen shoring. The highly permeable gravel and cobble-filled soils beneath the excavation required “zone freezing” to create a watertight, 15-foot block of frozen soil. This essentially created a “plug” inside the vertical, frozen soil cell perimeter resulting in a completely dry excavation and a successful project.

The Challenge
An active railway refueling facility requires replacement of several hundred feet of utility pipelines and related deep vaults. High groundwater (2 feet below ground surface) and contaminated and unstable soils made dewatering highly problematic from both a cost standpoint and the potential catastrophic damage to live railways. To accommodate the active railway and re-fueling activities, the work was done in two phases. Numerous existing underground utilities ranging in diameter from 8 to 36 feet crossed the pipeline alignment at depths of 5 to 15 feet BGS.

The Solution
The Frozen soil shoring was designed and installed to provide a narrow vertical trench wall profile with “bulges” around the wider deep vaults. This kept contaminated soil excavation to a minimum while providing watertight structural support for excavation and construction. The rail tracks and other structures were monitored twice a day for any settlement or movement. Precise engineering and analysis of the soil conditions prior to installation rendered the shoring wall completely waterproof preventing lateral groundwater movement as well as arresting groundwater “up-lift” from below the base of the excavation.

The railway and fueling facility had no interruptions during construction. Existing utilities and structures remained in service and undamaged. The success of the SoilFreeze system resulted in the owners cost being substantially below the estimated cost for construction.