Building a Shoring System for a Cistern in San Diego
Malcolm Drilling was subcontracted to design and build a Secant Pile Shoring System and Dewatering System for the Support of Excavation of a new deep Cistern structure. Their scope also included the CFA foundation piles and the associated in-Situ load test program to verify the piles’ load-carrying capacity.
The excavation depth was significantly reduced through an airport-led redesign effort, which required Ground Improvement of the unstable bay deposits to mitigate liquefaction and provide lateral support to the CFA piles. Malcolm’s Ground Improvement expertise provided necessary design-assist input to guide the owner toward a constructible and economical Deep Soil Mixing solution.
A depressurization system, consisting of 11 deep wells, was installed right next to the cistern ring. Additionally, a recharge system with 15 deep wells was positioned approximately 40 feet away from the cistern ring to reduce the potential settlement impacts on nearby structures.
Both the Soil Mix Columns and CFA piles were designed to be installed from the bottom of the excavation, which required working in very challenging access conditions and necessitating drill rig disassembly, hoisting, and re-assembly in the excavation. To reduce mobilization costs, Malcolm provided one machine that could successfully perform both scopes with minimal cost and downtime for the owner.
This project is one of the many examples of Malcolm’s ability to package multiple complex disciplines with engineering design services for the successful execution of all sizes of projects.