COMPLIANCE INFO_1968-2006 - Laserfiche WebLink

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110 February, 1968 SA 1 1 SA k the bearing capacity of the fill will be limited only by the shear strength of fill is :r the new fill. Unfortunately, the addition of'new fill has a serious side effect: area (. 6 the addition of load creates substantial settlements. If the structure is relatively light, such as a one-story building, the load- a dishe ` bearing capacity can be circumvented by continuous foundations which have of the 1 sufficiently low bearing pressure that they will not shear the major part of as shov the underlying sanitary fill, and which are structurally reinforced to bridge went W over the occasional soft spots that inevitably occur. Continuous floor slabs, nonunif( reinforced as mats beneath single-story buildings, or continuous strip or in rel strap foundations have been used successfully. When neither added fill nor x ll the continuous foundations can provide adequate support, the structure must f be supported by piles or by piers which extend through the fill to firm virgin ?, strata below. These, of course, will provide a foundation that is independent of the characteristics of the fill. However, there are certain serious con- struction difficulties which will be considered later. Settlement.—Old fills settle and sanitary land fills are usually the worst of all. There are a number of mechanisms acting simultaneously which contribute to,the settlement, Fig. 4(b). First, the loose resilient materials which make +; up much of the fill consolidate under load. The void spaces between and within the solids are compressed and the settlement corresponds to volume %change. Three components of load contribute to the settlement: (1) There is continuing settlement under the weight of the sanitary fill itself, including ` its cover; (2) any new leveling or bearing fill will contribute an additional and usually substantial increment of settlement; and (3) the structure and its dead load (transient live load is not likely to contribute) will add further to ,the consolidation settlement. A second mechanism of settlement is less obvious. When the fill consists of large bolids with open spaces between and finer materials adjacent or above, there is sporadic movement of these fines into the open voids. The movement may be induced by water seepage through the fill, by vibration, or J by changes induced by chemical or biological decomposition. The third mechanism is decomposition both by chemical and biological means. This decomposition is accompanied by the production of gas and a ? substantial reduction in solid volume. All three mechanisms are essentially processes with the settlement continuing but at varying rates. The settlement caused by consolidation com- mences immediately upon loading. Depending on the degree of saturation on the fill, a substantial part occurs immediately, followed by settlement that is s initially rapid but which continues at a decreasing rate with increasing time. Theoretically, consolidation settlement never ceases. The 'rate of settlement caused by decay and decomposition depends on temperature, moisture, air, and other local conditions including the percolation of ground water. In gen- eral, it takes place most rapidly immediately after completion of fill and decreases with increasing time and with increasing depth below the ground cumulatfc surface. Significant changes in the environment, however, can cause either an discontini increase or decrease in the rate of decay and decomposition. Settlement trated in caused by ravelling occurs sporadically during and immediately following the There mechanism which triggers it: intense rainfall, sudden fluctuations in ground fills. Lin water, or severe shock such as that associated with nearby blasting or typically earthquakes. The settlements which are observed may exhibit a definite pattern. If the 4"soil Education, 1 k