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). H. KLEINFELDER & ASSOCIATES File No. S-2599-1 <br /> March 3, 1983 <br /> Page 5 <br /> The lack of consistency of the soil and debris mixture is the main item that <br /> creates the potential for differential settlement of structures. Differential settlement <br /> could occur in localized areas with a high percentage of organic debris or none <br /> compacted construction debris. As a result, it is possible that additional maintenance, <br /> above and beyond the normal, could be expected when buildings are designed with <br /> conventional spread-footing-type foundations. Placing a few feet of engineered fill <br /> below foundations would help minimize this potential. This alternative is discussed <br /> further in the section entitled "Conventional Shallow Foundations". An alternate to <br /> this, which is also discussed below, would be to support the structure by a rigid <br /> foundation and slab-on-grade system. This could be considered a raft-type foundation <br /> reinforced by post-tensioning technique. This alternative could be designed so that any <br /> effect from potential differential settlement could be minimized. <br /> The high percentage of organic content placed in the fill on the northerly portion <br /> of Lot 1, is such that it is still generating gasses. This material was near saturation <br /> at the time of our exploration, and did exhibit odors. These items indicate that <br /> decomposition is currently taking place. The by-product of this process is a generation <br /> of various gasses; specifically, methane gas. Methane gas can be explosive at the <br /> right concentrations when trapped in a non-vented, confined area, and mitigating <br /> measures to minimize the opportunity for lateral flow are recommended in the section <br /> entitled "Gas Control Systems". <br /> Conventioanl Shallow Foundations <br /> Our exploratory backhoe pits indicate that the higher concentrations of debris <br /> and soil mixtures exist at levels below 10 feet. Shallow meterials were relatively <br /> loose and normally had less than 10 percent of debris mixture. It is our conclusion <br /> that the proposed residential buildings can be supported by conventional spread footings <br /> where they are supported by at least 3 feet of engineered fill. This material could <br /> o <br />