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3. Badie Ahmad “Stability of Spread Footing Supported by Clay With an Underground Void ” thesis presented to The Pennsylvania State University at University Park Pa. in 1983 in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
4. Baus R. L. “The Stability of Shallow Continuous Footings Located Above a Void ” thesis presented to The Pennsylvania State University at University Park Pa. in 1978 in partial fulfillment of the requirements for the degree of Doctor of Philosophy.