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108 February, 1968 SA 1 SA 1 ' There is little information available regarding the engineering character- the cr istics of sanitary land fills. Since 1947, the writer has investigated approxi- larger f mately 30 such sites to determine their potential behavior for building bearin; construction. Three test boring records selected from two different projects the de are representative. Two, Figs. 1 and 2,are from an uncontrolled sanitary land and be, fill from a.central Georgia city, to be used for an open-shed farmer's mar- over tl ket. The third boring, Fig.3,is from a controlled fill in the Georgia Piedmont, becaus proposed for the construction of a high school. the str The thickness and description of the materials encountered in the boring mass t are shown at the left of each illustration. To the right is a graph that depicts levelin their relative strength or density in terms of the standard penetration re- Part c sistance. (This is the number of blows of a 140-1b hammer falling 30 in. required to drive a 1.4-in. M, 2-in. OD, steel sample tube a distance of 1 ft.) All three borings show a relatively firm crust, undoubtedly the covering or leveling fill, underlain by alternate layers of soil and garbage, debris, or rubbish. In general, the penetration resistances of the fill are low to very 77-7— low, 7---low, seldom' greater than 10 blows per ft and in most cases 2 blows to 4 blows per ft. Fig. 2 shows high penetration resistance in the fill associated with a concentration of concrete and brick building debris. Such hard spotsm7T_ or points of high resistance are deceptive because they lead the uninitiated to believe that the fill is denser than it really is. It is difficult to measure the density of sanitary land fills.,The limited data available from the previously mentioned studies indicates in-place densities of 50 lb to 75 lb per cu ft, which are 40% to 60% of those of the soils in the same area. If there is anything consistent about the sanitary land fills, it is their erratic composition and extremely erratic, but low, densities. ' The ground-water level is often quite variable. Many of the fills were built in low, swampy areas. In such cases, the ground-water levels are close to the fill surface. At most sites, the addition of the sanitary land fill raises the original ground level and so the ground-water level is well below the surface of the fill, as in Figs. 1, 2, and 3. In some cases the thin covering layers of the soil within the fill tend to trap ground water, and therefore the levels of such trapped water fluctuate widely depending on rainfall and the NOR tendency of the thin soil layers' to rupture under significant differential heads. At any rate, the ground-water levels within sanitary land fills tend to vary with the season. They frequently are not related to the ground-water B. S s level in the adjoining virgin ground; instead, they may be substantially higher. FIG.IN SA ENGINEERING PROBLEMS rN UTILIZATION OF SANITARY LAND FILLS foundati and eve. Bearing Capacity.—The bearing capacity of the fill is a major considera- of the 1 { tion in foundation design. Although the term is sometimes applied to the over- our exI { all ability of the soil to support a load, it is used in the more restricted loads w Z sense in foundation engineering to define the ability of a material to withstand Ther the foundation load without shearing. As shown in Fig. 4(a), shear in the sanitar3 sanitary land fill may develop in either or both of two ways. The most sig- blanket { nificant factor is the relatively thin crust of soil overlying the more spongy punchinj and resilient sanitary fill. When the foundation is relatively small compared the new to the thickness of this soil cover or crust, the foundation may punch through mately et , ` k