CASE HISTORY No. 1
|PROJECT||A 166,000-sf dock-high warehouse with real 900 psf floor loads.|
|SITE||The proposed warehouse was located on the site of an old sawmill and sawmill pond. The site is underlain by up to 16 feet of sawdust, wood chips, logs, and milled lumber with pockets of very soft clay.|
|PROBLEM||This situation would normally require a pile foundation beneath foundations and slabs. The high floor loads would require hundreds of closely spaced piles, making the project uneconomical. The presence of large trees and debris in the pond would also make pile-driving difficult. The warehouse had to be supported on a shallow foundation system to be viable.|
|SOLUTION|| To reduce post-construction settlements, a 16 foot high surcharge was placed on one half of the building. After the settlements leveled out, the surcharge was placed on the other half of the building,along with additional fill, to accelerate the settlement. As soon as the second half attained the same amount of settlement as the first half, the surcharge was removed and construction commenced on schedule.|
The foundations were designed to tolerate a higher amount of settlement than would normally be expected. All foundations had to be supported on four feet of structural fill which required removal of old foundation elements and debris.
The pavements close to existing fill materials required sensitive control of the subgrade and pavement operations as well as the use of lightweight materials to reduce settlements.
|RESULTS|| The client was able to build the building within budget and on time. After 15 years, the building slab is still in excellent condition even though the design floor loads have been exceeded. The pavements did not experience any failures and are still in excellent condition.|
Because of the successful results with this building, the client was able to successfully build several other on-site structures with similar subsurface conditions.
CASE HISTORY No. 2
|PROJECT||A two-story wood frame office building with a building footprint of about 14,000 square feet.|
|SITE||The proposed office building was located in the downtown area of a valley city. The site is under laid by approximately 100 feet of loose silt and sands and occasional seams of peat with a high water table.|
|PROBLEM||The subsurface conditions would normally require driven piles extending to depths greater than 100 feet. The costs for this deep foundation would exceed the economic viability of this project. Due to the urban nature of the site, a surcharge was not feasible.|
|SOLUTION||The geotechnical engineers on this project had considerable experience with compensating foundations where a sufficient weight of soil is excavated out to compensate for the weight of the building. In this case, an excavation of two-and-one-half feet was required. The building was supported on a grid foundation where all footings were continuous and structurally tied together in a continuous grid. Footings were supported on at least two feet of structural fill. Due to the granular nature of the subsurface soils, settlements were realized during construction.|
|RESULTS||The owner was able to build his project feasibly. The building which is now over ten years old, has functioned excellently. A recent examination of the building with a tile floor revealed a crack-free environment.|
CASE HISTORY No. 3
|PROJECT||A four-unit townhouse development on a hillside.|
|SITE||A hillside with potentially unstable soils requiring cuts on the order of 20 to 30 feet in depth.|
|PROBLEM||A previous geotechnical engineer had recommended an expensive tieback shoring system to support the excavations and pin piles to support the structure.|
|SOLUTION|| Utilizing an open cut benched excavation with vertical stabilization elements (small, driven, wide-flange members) were used to support the bench cuts. The vertical elements were surveyed for potential movement during construction.|
The pin piles were eliminated by both compacting the footing subgrades and installing a continuous grid foundation system for the buildings.
|RESULTS||By eliminating the shoring and pile foundations, the client was able to build the buildings with significant savings of costs and time. The site and buildings are functioning well after many years.|
CASE HISTORY No. 4
|PROJECT||Numerous single-family residences.|
|SITE||An 8-foot-thick delta deposit formed from stream deposits of coal mining operations from 80 to 100 years ago. The delta was deposited atop 60 to 80 feet of very soft organic deposits.|
|PROBLEM||Previous residences were built on long, driven wood piles extending to below the soft deposits.|
|SOLUTION|| The delta deposits were in place long for a sufficient period of time to consolidate the soft deposits due to the weight of the delta soils. An excavation of about two feet of soil would equal the weight of the new building and not cause any additional weight on the underlying soft soils. |
All footing and foundation walls were then tied together in a continuous grid, forming a rigid foundation able to withstand minor settlements.
|RESULTS||Many residences have been successfully built on the delta using this compensating method, thereby significantly reducing building costs for dozens of owners.|
CASE HISTORY No. 5
|PROJECT||A 33-acre retail development.|
|SITE||The site was previously a sand and gravel pit, with a 90 foot deep pit and stockpiles of tailings material on site. The stockpiles contained about 100,000 yards of material.|
|PROBLEM||site challenges included filing of the pit, use of the stockpiled materials, and the disposal of site runoff. Import material was originally planned to fill the pit, and a large vault was planned to store runoff. Would it be possible to use the screenings to fill the pit?|
|SOLUTION|| The screenings were used to fill most of the pit, allowing a lesser amount of compaction. The upper 20 feet of the pit was filled with compacted granular material. Settlement monitors were then placed on top to measure potential settlement. Settlements were minimal. |
One side wall of the pit consisted entirely of gravel. Four large-size pipes, 90 feet in length, were placed near this gravel wall and surrounded with gravel as the pit was fill. After the pit was filled, infiltration testing was performed. Approximately 475,000 gallons of water was introduced into the infiltration pipes. The test results showed the pipes could handle a flow rate of 3,200 gpm. This resulted in the need for a much smaller stormwater retention vault.
|RESULTS||The client was able to utilize material already on site at a considerable cost savings. A portion of the site's runoff was directed to the vertical infiltration system allowing for a smaller retention vault.|