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SA 1 SA 1 SANITARY LAND FILLS 109 :haracter- the crust and intoe sanitary fill below. Where the t dation is somewhat d approxi- larger and the sanitary fill not greatly weaker than the soil crust above, the j )r building bearing failure may take place by rotation of a segment of the soil cover and it projects the deeper fill, acting as a unit, as shown in Fig. 4. Because of desiccation iitary land and because it may have been compacted by the weight of equipment operating ! er's mar- over the top, the crust may be relatively strong. This is deceptive, however, ' Piedmont, because the fill underneath is both resilient and weak. In either form of shear, the strength of the soil cover is seldom a major factor in the ability of the 1 the boring mass to withstand shear. The crust may be only 1 ft to 2 ft thick if additional lat depicts leveling has not been. provided. It is seldom more than 5 ft to 10 ft,thick. ; ration re- Part of this crust is ordinarily excavated for constructing the individual ling 30 in. ,.e of 1 ft.) )vering or debris, or - �'' :)w to very :'< '••:SOIL COVER :_;;:_, ;,;..;•: . . blows to 4 :::: �,`+: :.,..i:.•.e.)u '.: .t• �: t �•� . .. �• + t `~ SANITARiSSOClated . ' ^ +•� .a. • , ~•• ® -• � �• C ' , lard spots - t ininitiated PUNCHING SHEAR ROTATIONAL SHEAR he limited i in-place A. BEARING CAPACITY OF FOUNDATIONS ON SOIL COVER OVER SANITARY LAND FILL Lose of the itary land densities. fills were \ I' are close �•. . . • v `. .., , ® . fill raises a , •'$ ' . o, p �.. �o.. •® - '� , below the .. t v B o, 8 0. a a o . ®: : ® • 1 � i covering refore the NORMAL DISHED-IN SETTLEMENT IRREGULAR SETTLEMENT FROM Lll and the HARD ZONES IN THE FILL " a; fferential ' fills tend Ind-water B. SETTLEMENT OF BUILDING SUPPORTED ON SOIL COVER UNDERLAIN BY SANITARY LAND FILL 6 )stantially FIG. 4.—BEARING CAPACITY FAILURE AND SETTLEMENT OF FOUNDATIONS I.. IN SANITARY LAND FILLS WITH THIN SOIL COVERS �v FILLS foundation leaving a much thinner crust, if any, below. Surface inspection and even load tests with small plates may give falsely optimistic impressions :)nsidera- of the bearing of the fill. In spite of optimistic published reports, it has been . the over- our experience that the ability of a sanitary land fill to resist foundationt •estricted loads without failure is seldom greater than 500 lb to 800 lb per sq ft. withstand There are a number of ways the inherently low bearing capacity of the ear in the sanitary fill can be circumvented in foundation design. One is to place a most sig- blanket of new fill above the old_ fill-a blanket that is sufficiently at ' •e spongy punching shear cannot•develop and any rotational shear will be entirely within .ompared the new fill. This means that the new fill must have a thickness of approxi- I through mately 1.5 times the width of the footings placed'upon it. When this is done I