FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Aunst 28, 1991 BALBI&CHANG ASSOCIATES File No. 1525-69 construction equipment, geotextile fabric should be placed over the subgrade prior to the placement of backfill material. Type and strength of the aeotextile should be determined by the geotechnical engineer base on actual subgrade condition. Another alternative is to introduce additives to the on-site soil to reduce the moisture chemically. Additive may be dehydrated lime. The amount of additive mixed into the soil generally ranges from 3% to 6% by weight. However, the actual amount should be determined from laboratory testing. Depth and extent of on-site soil to be treated with additives should be determined by the geotechnical engineer. Thorough processing the soil is essential to achieve uniform mixing of the additives. Also, adequate number of field testing should be performed to verify the end result. Once the proper grading option is implemented and the subgrade moisture is within the specified range, normal site grading (compacting the soil in lifts to within the specified dry density range) may be resumed until design'grade is reached. No matter which method is implemented, one important final task in completing the construction in wet season is to maintain the proper soil moisture following the site grading period. After the subgrade is prepared to the specified moisture and density, the site should be covered by the concrete of the building floor and the asphalt of the pavement as soon as possible to prevent any further surface water percolation. Delay in covering the subgrade after the site grading work is completed may result in the site soil condition reverted back to the soft and saturated state. Performing site grading in wet season or under adverse weather condition requires good judgement and common sense from the grading contractor-. If wet weather construction is unavoidable, we recommend the grading contractor should first verify the site condition prior to commence site work in order to select the most appropriate construction method. Methods of achieving proper soil moisture content should be consulted with and reviewed by the project geotechnical engineer prior to field implementation. C. Trench Excavation and Backfill Excavation for footings and utility trenches can be readily made with either a backhoe or trencher in either native soil or structural fill. We expect the walls of the footing trenches to stand vertically without significant sloughing because most near surface site soils are cohesive in nature. Where trenches are extended deeper than five feet, the excavation may become unstable and should be sloped back or shored to protect personnel and to provide stability. Walls of deep trench should be inspected to verify their stability prior to personnel, entering the trenches. Page 9 of 17 i