Current through Register Vol. XLI, No. 37, September 13, 2024
Section 38-4-10 - Geotechnical Considerations10.1. Geotechnical Investigation: A geotechnical investigation shall be performed for each site. The subsurface investigation shall be performed by a registered professional engineer or engineering geologist. The number, location, and depth or borings, test pits, and/or trenches shall be reasonable for the size, purpose, soils present, and foundation type of the structure. The investigation shall consider depth of soil to bedrock, field classification of soils, character of bedrock, in site testing, soil sampling, determination of groundwater flow and location of seeps and springs, and a soil profile for critical locations in the structure, hydraulic structures and after pertinent locations which may affect the safety of the structure. The number, depth and location of boreholes shall be based on the quantity of material to be impounded and subsurface conditions. A geologic study shall be also conducted for impounding structures to evaluate landslides into the impoundment, bedrock discontinuities such as soft seams, joints, joint systems, bedding planes and fault zones which may adversely affect the structure's performance. Past and future mining to include height of seam, depth and cover rock of the seam. Where underground mining has been done in the past and reliable maps are not available, additional investigation including geophysical surveying and mapping techniques including bore scope observations may be required.10.1.a. Laboratory tests shall be conducted on all foundation and embankment materials to include soil classification through grain size analysis hydrometer analysis, Atterberg limits, density, water content, compaction tests, shear strength, consolidation, and permeability unless the scope, characteristics, or design concept of the site make one or more of these requirements unnecessary. Compaction and proctor curves shall be developed for all fill materials as appropriate.10.2. Geotechnical Evaluation: A summary of all geotechnical data determined in the initial site geotechnical investigation and used in the analysis shall be included in table or figure form in the plan package.10.3. Seepage Analysis: An analysis of seepage and its detrimental effects on structural integrity shall be made. The analysis shall include consideration of potential piping in the embankment, foundations, and abutments. Seepage control measures shall be specified as necessary in order to enhance the stability of the embankment and adjacent area. Drainage systems shall be designed and constructed using a material approved by the Secretary and shall be protected by a properly designed filter zone using standard geotechnical engineering design practices. The design shall specify methods for sealing or controlling seepage encountered in foundation zone during construction.10.4. Foundation Treatment: If analysis indicates a highly fractured foundation, the engineer shall specify necessary treatment of the foundation zone including, but not limited to, foundation grout curtains, dental concrete treatment of fractures or overhangs, and detailed methods of foundation zone cleaning.10.5. Foundation Stability: The foundation must be designed to have adequate bearing capacity to support the embankment and any appurtenant works. Potential subsidence and settlement and their consequences shall be considered using standard engineering practices. Special attention shall be given to differential settlement which lead to cracking of the dam. Spillway pipes on compressible foundations shall be protected from damage due to settlement.10.6. Landslides: The potential for landslides, as determined in the initial project area investigation, shall be evaluated by the engineer. If landslides noted in the dam site or reservoir areas will cause instability of the dam or appurtenant structures, blockage of spillways and other critical drainage structures or overtopping of the dam by displacement of water in the reservoir area, such landslides shall be corrected to a minimum static safety factor of 1.5.