| Mudrocks are problematic rock materials because of their characteristic low strength, low durability, and high swell potential. Unconfined compressive strength is a widely used rock property in rock engineering and is important in the design of civil engineering structures founded on rock. This property is used in evaluations of foundation bearing capacity as well as for sliding stability analyses. Values of unconfined compressive strength of mudrocks are required for design but, because of the low durability and fragility of these materials, it is often difficult to obtain appropriate samples for testing. Thus, a need for obtaining a reliable estimate of mudrock unconfined compressive strength from common engineering index properties was identified. The purpose of this research was to examine three index properties (point load strength index, slake durability index, and dry density) to determine if they could be utilized as predictors of unconfined compressive strength. Further, an examination was made of the type of mudrock present in the foundation of eight concrete structures and measurements made from settlement surveys taken at each of the project sites.; Results of laboratory tests were compiled for eighty samples of mudrocks from the central Appalachians, an area known for its abundance and diversity of mudrocks. The laboratory investigations that were performed on these samples included unconfined compressive strength, point load strength index, slake durability index, and dry density. Settlement measurements taken over varying periods at eight navigation locks and flood control dams founded on mudrocks were evaluated.; Bivariate and stepwise regression analyses were applied to unconfined compressive strength and three index properties for six types of mudrocks to determine if one or more of these index properties would be a useful predictor of compressive strength. The index properties selected were point load strength index, slake durability index, and dry density. Results of the stepwise regression analyses indicate that there are statistically significant relationships between unconfined compressive strength and point load strength index for certain types of mudrock, in particular siltshales, mudshales, clayshales, and siltstones. No useful relationships between point load strength index and unconfined compressive strength were found for mudstones and claystones. When considering all mudrocks as a group, the primary independent variable found to be significant in the prediction of unconfined compressive strength was the point load strength index. Predictive equations were developed for siltshales, mudshales, clayshales, and siltstones.; At the eight sites where settlement surveys had been conducted, it was found that the time at which the elevation change measurements began varied by project and was often well after the project had been built. At each of the eight projects examined, much of the early settlement history was unrecorded. In general, the movement records indicated low magnitudes of settlement at most of the projects. In most cases, the measured elevation changes did not exceed the accuracy of the survey method. |
