Maud Farm Road Investigation

摘要

This paper presents the findings of an extensive site investigation into the causes of embankment settlement over five flexible pipe culverts ranging respectively in 36,24, 36, 36, and twin 48 inch diameter. The site location is on an east-west County Road 131 near Maud, Oklahoma. The project was developed and designed by the Bureau of Indian Affairs (BIA). The issue here concerned a lawsuit brought by the BIA against the contractor in which the BIA wanted to know if the contractor could be held libel for the embankment settlement. At stake was contact retainer held by the BIA in the sum of $358,000 against the contactor. The site geology consists of very shallow alluvial soils and/ or residual soil underlain predominately sandstone and sandstone and interbedded shale in the narrow drainways. The embankment was constructed from roadway cut sections containing residual sandy and clayey soils underlain by sandstones and sandstone interbedded with shale. The site landscape is one of shallow rolling hills. The field investigation consisted of a total of 15 piezocone soundings at the site. Soil properties of the embankment material, the underlying shallow alluvial and/or residual soil, and underlying geology were inferred from the piezocone tip resistance (q_c) and friction ratio (R_f). Three piezocone soundings were made in a staggered pattern at each of the five pipe locations in as close a proximity to the pipe centerline as possible. The analysis used software for the analysis of buried structures, Cande-2007 Update Release 7/31/2011, Version 1.0.0.7. This software uses a finite element mesh analysis. A detailed analysis revealed that the settlement at each pipe location was due to deformation below the pipe grades. The piezocone tip resistances in the embankment indicated a very stiff material and did not support the BIA claim that the contractor was responsible for the subsidence above the pipe culverts. The analysis showed that the settlements were the result of vertical pressure against a yielding base, a concept borrowed from theoretical soil mechanics.