CHAPTER 5.9 SOIL INVESTIGATIONS One of the important objectives of the reconnaissance of Eniwetok Atoll in October 1948 was to obtain visual information and soil samples in order to permit the determination of bearing values for use by Holmes & Narver in the design of foundations and structures, airplane landing strips, and road construction. In addition, on-site studies were to be made and samples obtained to locate sources of aggregate for concrete and pavement. In the accomplishment of these early investigations, the Recomnaissance Party excavated at widely separated points throughout the atoll, and tc:k samples of the cross sections exposed. These samples were brought back to the United States and experts in the field of Soils Mechanics were retained to make a laboratory analysis for mechanical characteristics, The terrain was seen to be formed of ancient and indurated coral masses capped with an overburden of disintegrated coral of sedimentary or wave-deposited origin, The overburden varied in gradation from sand to coarse gravel, was mixed with varying proportions of organic silt, and contained some intrusions of rocky coral extending above the coral shelf and into the sand. Foundation experts, on the basis of laboratory tests, were asked to evaluate as closely as possible the properties of the undisturbed natural deposits and to estimate the support which the undisturbed deposits would offer for foundations of structures, paving of roadways and areas, and cable anchors, Samples were prepared by the Laboratory retained to preform the work to reproduce field conditions as closely as possible, Bearing values for all structures for which H&N had design responsibility were determined to be adequate. From the laboratory samples which simulated field conditions, bearing values for varying widths of spread foundations were established at different depths in the clean, coral sand deposits. Results of these analyses are presented in graphical form in Figure 5.91. Based upon the results of consolidation tests performed, analyses were made to evaluate the settlement of spread foundations and results of such analyses are presented in graphical form in Figure 5.9-2. In connection with the design of paving for airstrips, roads, and areas, standard curves for the design of flexible paving to support various wheel loads for a wide range of subgrade capacities, such as are shown in Figure 5.9~3, were employed. Sheer test data obtained from the reconnaissance samples permitted analysis to be made directed toward the evaluation of the passive resistance which the coral sands would offer to cable anchors, Results thus developed are shown in Figure 5.9-4 which indicates the limits of desirable design. Amchors designed in accordance with the indicated recommendations had a factor of safety of approximately 1.5 against lateral movement. 5-76