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SPECIAL NOTES ON PLACEMENT OF COMPACTED FILL SOIL GENERAL The placement of compacted fill for support of foundations, floor slabs, paveme�ts, or earth structures should be carried out by an experienced excavator with the proper equipment. The excavator must be prepared to adapt his procedures,equipment,and materials to the type of project,to weather conditions,and the structural requirements of the architect and engineer. Methods and materials used in summer may not be applicable in winter; fill used in dry excavations may not be suitable in wet excavations or during periods of precipitation; proposed fill soil may require wetting or drying for proper placement and compaction.Conditions may also vary during the course of a project or in different areas of the site. These needs should be addressed in the project drawings and specifications. EXCAVATION/BACKFILL BELOW THE WATER TABLE It is common to have to excavate and replace unsuitable soils below the water table for site correction. As a general rule of prudent construction technique,we recommend that excavation/backfill below the water table not be permitted, uniess the excavation is dewatered. Numerous problems can develop when this procedure is attempted without dewatering. — Inability of the equipment operators and soil technicians to �bserve that all unsuitable soii/materials have been removed from the base of the excavation. — Inability to observe and measure that proper lateral oversizing is provided. — Inability to prevent or correct sloughing of excavation sidewalls, which can result in unsuitable soils trapped within the select backfill. — Inability of the contractor to adequately and uniformly compact the backfill. — Possibility of disturbance of the suitable soils at the base of the excavation: The dewatering methods, normally chosen at the contractor's option, should fo�low prudent construction practice. Excavations in clay can often be dewatered with sump pits and pumps; this technique would�not be applicable for excavation extending into permeable granular soil, especially fo�depths significantly below the water table. Dewater- ing granular soils should normally be done with well points or wells. When dewatering is needed, we strongly recommend that the procedures be discussed at pre-bid or pre-construction meetings. The dewatering technique chosen by the contractor should be reviewed by the architect and engineer before construction starts;it should not be left until excavation is under way. The selection of proper backfill materials is important when working in dewatered excavations. Even with dewatering, ihe base is usually wet and the contractor must be careful not to disturb the base.We recommend that the first lifts of backfill be a clean medium to course grain sand with less than 5°/a passing the#200 sieve.The use of silty sand,clayey sand, or cohesiye/semi-cohesive soils is not recommended for such situations.The excavator should be required to submit samples of the proposed material(s)he plans to use as backfill betore the fill is hauled to the site,so that it can be tested for suitability. � WINTER EARTHWORK CONSTRUCTION Winter earthwork presents its own range of problems which must be overcome;the situation may be complicated by the need for dewatering discussed above. During freezing conditions,the fill used must not be frozen when delivered to the site. It also must not be allowed to freeze during or after compaction. Since the ability to work the soil while keeping it from freezing depends in part on the soil type, the specifications should require the contractor to submit a sample of his proposed fill before construc- tion starts,for laboratory testing. If the soil engineer and structural engineer determine that it is not suitable,it should be rejected. In general, silty sand, clayey sand, and cohesive/semi-cohesive soils should not be used as fill under freezing conditions.All frozen soil of any type should be rejected for use as compacted fill. . It is important that compacted fitl be protected from freezing after it is placed.The excavator should be required to submit a plan for protecting the soil. The plan should include details on the type and amount of material (straw, blankets,extra loose fill,topsoil,etc.)proposed for use as frost protection.The need to protect the soil from freezing is ongoing throughout construction and applies both before and after concrete is placed, until backfilling for final frost protection is completed. Foundations placed on frozen soil can experience heaving and significant settlement, rota- tion, or other movement as the soil thaws. Such movement can also occur if the soil is allowed to freeze after the concrete is placed and then allowed to thaw.The higher the percentage of fines(clay and silt,P-200 material)in the fill, the more critical is the need for protection from freezing. GME CONSULTANTS,INC.-