Projects: Geotechnical Engineering
Situation: Build the world’s largest aquarium; one that would hold more aquatic life than any other and accommodate millions of visitors a year. Here would live beluga whales and whale sharks — never before housed in an aquarium beyond Asia. The largest collection of other aquatic species would reside here too, in eight million gallons of water housed in 100,000 cubic yards of concrete infrastructure. The challenge: how to build these hard assets atop 80 feet of soft soils? ATC drilled for answers.
Results: Retained by the aquarium’s developers to conduct geotechnical exploration, develop foundation system recommendations and test construction materials, ATC discovered highly variable subsurface conditions beneath the ten-acre site, including soft soils to depths of more than 80 feet overlying bedrock. We got to work, helping the client increase the load capacity of deep pile foundations by 40% and reduce total construction costs by $1 million. ATC designed a pile load testing program that included state-of-the-art electronic strain gauges in the test piles: a system that reduced the quantity of piles without compromising safety. Construction field testing was conducted within an intensive Special Inspection (IBC 2000) program. ATC also provided recommendations for deficiencies observed during onsite steel erection.
New Faster Approach to Density Testing Methods – Airport Runway
Situation: Faced with placing 18,000,000 cubic yards of soil and rock mixture — enough to fill a football stadium six times — a grading contractor sought an efficient way to test for confirmation that material placed in the runway embankment met compaction requirements and minimized costs.
Results: ATC’s alternative density testing method reduced the construction schedule by six months and convinced both the client and owner to adopt the program. The client was responsible for moving and placing fill material to raise the ground surface to proper elevations. To minimize costs, the owner selected a fill material composed of a soil and rock mixture from large rock quarries and adjoining properties. After reviewing the initial criteria with the contractor, ATC recognized that traditional density testing methods would not always work given rock content in portions of the fill. Further, we discovered that use of large-scale density tests, initially requested by the owner, would create unacceptable delays and render the project far too costly. ATC developed a faster approach – one based on tests ratified by the U.S. Army Corps of Engineers that reduced testing time and cost without compromising results. A series of seven test strips were employed for the rock and soil mixture. Rather than measuring density, the new method identified the number of equipment passes needed to minimize layer compression. Successful fill compaction was confirmed with a proof-roll test using a 50-ton pneumatic roller. Each day, ATC’s field team reviewed, organized, catalogued, and transmitted 40 to 60 pages of test reports to the owner. Upon completion, ATC will have conducted approximately 13,500 proof-roll and density tests.
Geotechnical Exploration, Foundation Design, Construction Inspections
Situation: No sooner had a real estate developer begun erecting a new 35-story high-rise residential tower than he got the bad news: deep foundation costs would exceed estimates by over $1 million dollars and postpone completion by two months. The problem surfaced at the start of construction, when full-scale load tests revealed that available friction would prove insufficient to drill the deep foundations. ATC was contacted and asked to review this geotechnical conclusion and provide alternatives.
Results: ATC reevaluated the entire foundation system and concluded that the design shaft lengths could be reduced, without compromising safety, to save $300,000. Construction time was not lost; in fact, the schedule was reduced by approximately four weeks. Noting that subsurface data was limited, ATC initiated a rapidly executed program of additional soil borings and rock coring to further describe subsurface stratigraphy and obtain additional data for detailed foundation analyses. A three-week program of soil boring and reevaluation prevented delays, as initial foundation elements were installed concurrently.