Documents from the Engineer
Here are more of the documents from the engineer.
BLE inc. Bunnell-Lammons Engineering, Inc.
Geotechnical, Environmental and Construction Materials Consultants
Upont client’s request, staff professional K. Williams visited site to observe the foundation excavations of the proposed home. The excavations were extended to -5 feet below existing grade until alluvial (cobble) layer was encountered. Groundwater was observed to be seeping into the footing area through the footing sidewalls.
We understand that the proposed home will be supported on a crawl space foundation. We understand that a bearing pressure of 2500 psi is required. We recommend removing soft wet soils until suitable material is encountered (in this location the cobble layer was considered competent bearing material).
We recommend that the entire foundation system be undercut to expose the cobble layer, which was encountered at depths ranging from 4 to 5 feet below the existing grade or 3.5 to 4.5 feet below the bottom of foundation. We recommend making the footing excavation 3 feet wide. Prior to the placement of stone in the excavation, a separation fabric, such as Mirafi 140N or equivalent, should be placed in the excavation. The footing excavations should be advanced 8 to 10 feet in length, lined with fabric and backfilled with #57 stone before making additional excavations to minimize caving of the excavation.
We also recommend over-excavating the interior pier footings so that the pier footings are continuous and are inter-connected with the perimeter wall footing. The inter-connected footings will convey groundwater to a sump area located outside of the building footprint. We understand that the groundwater will be drained by gravity or pumped away from the building footprint.
Once stone backfilling is complete, the fabric should be overlapped over the stone. During the placement, it is recommended that the stone and fabric be placed in quick succession, as groundwater will quickly de-stabilize the excavation. Mechanically densify the stone in 12-inch thick lifts by pounding the surface of the stone with the flat part of the backhoe bucket. Given the shallow groundwater, it is recommended that temporary pumps be used to remove water from the foundation excavations.
We recommend that the BLE representatives be on-site to observe the foundation excavation and backfilling.