CORRELATION OF BACKSWAMP SEDIMENTS ATCHAFALAYA TEST. SECTION VI. ATCHAFALAYA LEVEE SYSTEM, LOUISIANA.

Atchafalaya Test Section VI is a 2000-ft-long portion of the Atchafalaya Basin Protection Levee System in south-central Louisiana. The soil in the area comprises fine-grained sediments laid down under shallow freshwater conditions. These backswamp deposits are underlain by a thick substratum of sands and gravels. The backswamp at Test Section VI is 100 to 110 ft thick where not consolidated by levee loading and 88 to 91 ft thick under the center line of the levee. Nine borings were made in Test Section VI for the purpose of interpreting the various depositional layers which compose the foundations soils and determining the effect of the levee fill upon the underlying soils at the site. An attempt was also made to define the extent and patterns of subsurface deformation which accompanied settlement of the levee. Samples from all nine borings were tested for engineering properties. In addition, undisturbed samples suitable for radiographic analysis were obtained from one of the borings. The backswamp deposit at Test Section VI was subdivided into layers A through H on the basis of sedimentary features revealed by radiography. Correlation sections were made between the nine borings at Test Section VI. Structure and isopach maps were constructed on the basis of these correlations. It was revealed that the structure of the levee had a pronounced effect on the pattern of settlement in the underlying soils.