LANDSLIDES IN THE PIERRE SHALE IN CENTRAL SOUTH DAKOTA

Landslides in the Pierre shale close to the Missouri River in central South Dakota have become more important as the size and number of individual engineering projects have increased. This research was initiated to determine the factors that control landslides in order to explain differences in the stability of adjacent slopes, to develop methods for locating areas of high landslide potential (areas where slides might occur as a result of construction activity), and to propose methods for construction in areas with high landslide potential. The factors that control sliding in the Pierre shale include shale layers and mineral discontinuities, physical discontinuities and local discontinuities. The shale is interbedded reflecting the different sources of the minerals in the layers within the eight geologic members. The thickness of the individual layers controls the spacing and orientation of the joints formed during rebound which in turn control the vertical flow of water through the shale at depth. Water flow into the shale is controlled by surficial non-shale deposits and the physical discontinuities that extend to the surface. Horizontal flow within the shale is controlled primarily by the mineral discontinuities. Water is essential for landslides thus the interrelationships between the discontinuites and flow must be understood. As an example the largest slides in the shale occur where extensive layers of uniform nonswelling shale overlie interbedded layers of bentonitic shale and bentonite. Areas with high landslide potential can be divided into two groups, areas where sliding will occur during construction and areas where slides will develop after construction. Slides during construction occur in areas that have already been disturbed by landslides and areas where the shale has been deteriorated by weathering and has high natural water contents. Areas where slides are likely to develop after construction are those where the amount of water entering the shale increases as a result of construction activity or areas where natural flow within the shale has been inhibited by the construction of a fill or an embankment. There is no single method that will insure the location of every area with high landslide potential but there are several methods which used concurrently will delineate these areas. These are: air photo interpretation and field reconnaissance; resistivity, self potential and seismic surveys; drilling, sampling and penetration testing; the results of simple laboratory tests, and the interpretation of the stress deformation behavior of samples tested in undrained compression. In addition it is possible to determine the location of slip surfaces and to locate areas of active weathering using one or more of the above methods. Landslides during construction can be prevented if the shale in landslide masses and the shale that is highly weathered or has high in-situ moisture contents is removed from the fill areas prior to the construction of a fill and removed from cuts during construction. Landslides after construction can be prevented in fill areas if the water flowing through the shale is intercepted below the fill and increased water entry into the shale above the fill is avoided. Landslides in cuts after construction can be prevented by eliminating water entry into the cut areas.

Media Info

  • Features: Appendices; Figures; Tables;
  • Pagination: p. 707

Subject/Index Terms

Filing Info

  • Accession Number: 00082886
  • Record Type: Publication
  • Report/Paper Numbers: No. 635(67) State Stud
  • Files: TRIS, STATEDOT
  • Created Date: Mar 26 1975 12:00AM