PROJ00180 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I A.2. GEOTECHNICAL INVESTIGATIONS The geotechnical investigations are described in Appendix E. These investigations were conducted in March 1993 by SMITH GEOTECHNICAL/Engineering Consultants. The plan of development of a new structure is based on this data. If, in the final analysis, the Owner decides to repair the structure, additional subsurface drilling, coring, and testing the concrete in the structure will be required. This investigation was limited to a visual inspection of the structure and drilling two (2) test borings at each end of the structure. Strength testing was not conducted on the existing structure concrete or the soils and rock encountered in the borings. A.3. SOIL AND ROCK DESCRIPTION 1. Subsurface Soils. The overburden soils at the dam sites consist of sands, gravels, and some cobbles. Shale was encountered in the borings at a depth of eleven feet (11') to thirteen feet (13') below grade. The predominant soil type encountered in the overburden was fme to medium silty sand. This material ranged from loose to medium dense with SPT blow counts from 3 to 13 blows per foot, and the moisture ranged from damp to saturated. Some cobbles were encountered in the overburden but did not appear to be predominant and were estimated to be in the three inch (3") to six inch (6") size. This would not expect to be typical along the Poudre River. To the contrary, it is typical to fmd cobbles of this size and larger more predominantly. This lack of cobble in the abutment fIll may be due to the possibility that imported fill may have been placed when the structure was constructed. 2. Rock. Shale bedrock underlies the overburden soils. The rock is weathered for the fIrst few feet and becomes less weathered with depth. The bedding varies from no noticeable bedding structure to being fissile with easily distinguishable bedding planes. The bond between the bedding planes is not highly cemented, and excavation of the material should be able to be accomplished without blasting. 3. Groundwater. The groundwater depths were measured in the boreholes immediately after drilling and found to be at depths from eight feet (8') to nine and one half feet (9.5') below grade. This depth is approximately two feet (2') above the river water level at the time of measuring. 4. Borrow Materials. There are no sources of borrow materials at the immediate structure site. All earth borrow materials and all rip rap and bedding materials will be hauled to the site from other sources. No large quantities of earth fill materials are required for the project as the only need will be to rebuild and expand the abutment areas. PAGE4 . CbaptcrV