Shells are usually used as structural elements in buildings. In Germany they showed remarkable resistance to the effects of bombing during World War II. About 1 decade later, the possibility of employing shells in foundation engineering was explored. Surveys of the literature indicate that shell foundations have been employed effectively in different parts of the world and were proven to provide an overall economical alternative to the conventional flat foundations. However, the geotechnical design of these footings remained the same as for their respective flat ones. Accordingly, the advantages of shell geometry in foundation engineering has not yet been explored in the design of these footings. The objective of the present study is to examine the overall geotechnical behavior of three types of shell foundations resting on sand under axial loading conditions, namely, triangular, conical, and pyramidal shells. Furthermore, the resulting bearing capacities and settlements will be compared with conventional strip, circular, and square flat foundations. The present paper presents an experimental study on nine foundation models tested on loose, medium, and dense sand states. The influence of shell configuration and embedment depth on the ultimate bearing capacity and settlement will be presented. The results of the present experimental investigation have shown the admirable performance of shell foundations with respect to ultimate bearing capacity and settlement characteristics. Shell foundations provide higher resistance to lateral loading as compared with flat ones, and thus they will perform better in earthquake regions.Key words: shell foundation, experimental investigation, bearing capacity, settlement, sand, geotechnical engineering.

Shell foundations, or geometrically shaped footings, were first used as a substitute for the conventional flat shallow foundations in the nineteen fifties in Mexico, West Germany, India, China and the Soviet Union. It is not known whether their use was developed independently or was incorporated after observing their use elsewhere. However, it is certain that their use was not based on any research data that has been reported at that time. Since then, the use of shell foundations has drawn considerable interest around the world. Experimental and theoretical investigations by the author on 'shell type' foundations have shown significant increases in bearing capacity, better settlement characteristics, and ability to resist higher lateral forces which might be induced due to wind loads or earthquakes as compared to the conventional flat foundations. This is primarily due to partial absorption of the vertical load through lateral compression of the soil particles under the shell. Given these attributes, the practical implications could make shell foundations ideally suited for foundations subjected to lateral loadings. It is also known that shell foundations require less construction materials, which could benefit its use in developing countries where materials are scarce and expensive while labor is abundant and inexpensive. This paper presents analytical analysis of shell and flat foundations subjected to lateral loading. The results of this study will be presented in the form of a comparative study and numerical example, which will demonstrate that shell foundations are superior to resist lateral loading.

Abstract. Shell foundations are increasingly adopted around the world as an economic alternative to traditional flat foundations. Evidence of increased bearing capacity and reduction in settlement behavior exhibited by shell footings, coupled with their high potential resistance to seismic loading and sustained lateral earth pressure is valuable in terms of their geotechnical response. Nevertheless, practical use of shell footings is trailing behind conventional foundation structures due to lagging research on the performance and application of these foundations.The objective of this paper is to present the results of experimental modeling on bearing capacity and settlement of shell foundations. Scaled prototypes footing models were developed and tested to evaluate the geotechnical behavior of the shell footing. The study focused on the effect of the parameters govern the performance of this foundations. Contact pressure was measured at several loading conditions namely; working load and ultimate state. Moreover, shell footing and flat models were casted employing high-strength polymeric concrete (UHPFRC). Experimental investigation tests show on average 40-45% higher load-carrying capacity than its flat counterparts.

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