Opening of Quotes - Laurel Woods Drainage Improvements Proj No. 121-007 - Selge Construction Co., Inc.

Home Browse Search

Weaver Consultants Group 6 4.3 Structure Foundation Considerations In general, the soil conditions, as previously described, appear to be adequate for the support of manhole or outlet structures. An exception to this is in the vicinity of Boring B-1 where the granular soils beneath a depth of about 5 feet are very loose. For structures in this area, we recommend the very loose soil be removed to a depth of 2 feet below the structure bottom and replace with compacted coarse aggregate meeting the general gradation requirements for Indiana Department of Transportation (INDOT) No. 8 coarse aggregate. Based on these conditions, we recommend that the base be proportioned using a net allowable soil bearing pressure of 2,000 psf. In our opinion, the subgrade should be compacted to densify the soils loosened by the excavation process to minimize the risk of excessive settlement. Since groundwater is likely to be below the base of the structures, the effects of buoyancy are not likely to be a consideration. 4.4 Dry Wells We understand that dry wells are being considered to provide infiltration of the collected runoff into the below grade stratum. Groundwater was generally encountered at a depth of about 5 feet below the ground surface. The soil profile above the groundwater was somewhat mixed with fine to coarse sand and fine to coarse sand with silt. These soils are generally conducive to infiltration of water. Below the water table the soil profile was even more mixed with some locations having sand (SP), silty sand (SM) and clayey sand (SC) underlain by silt (ML). The silty sand, clayey sand, and silt are far less permeable than the sand soils and infiltration will within these zones will be slow and limited. In addition to the infiltration issue, excavation below the groundwater level will require dewatering and shoring to prevent soil collapse of the excavation sidewalls. Two soil particle size distribution tests were performed on representative samples of the sand (SP) type soil. Results of these test were used to estimate the soil infiltration rate. The estimated infiltration rates based on the Hazen Formula are presented in Table 1. Table 1 – Summary of Infiltration Estimates Location Depth (ft.) Infiltration Rate (in./hr.) Correction Factor Design Rate (in./hr.) Soil Classification (USCS) B-1 8½ - 10 100 3 33 SAND with SILT, some gravel (SP-SM) B-4 3½ - 5 44 3 15 SAND with SILT, little gravel (SP-SM) Based on the results of our laboratory analysis, the soils classified as sand can be considered to have a design infiltration in excess of 10 inches/hour or the maximum limit provided by local code.