Investigation of Khost-Gardez Road Failure at 23.6KM

The investigation aimed to determine the cause of the road failure from an engineering perspective. The assessment revealed that the control of water was less than adequate, contributing to the failure. The road design was adequate, but the failure was exacerbated by the presence of talus deposits, which are unstable soil masses in the presence of water. The investigation found that the emergency repairs undertaken in the fall of 2010 were successful in restoring the road to acceptable levels of use. However, the follow-on visit to the area and subsequent recommendations by LBG (Leighton Asia) were reasonable and followed standard engineering practices. The report emphasizes that water control will be paramount to the successful long-term repairs to this section of roadway. LBG has provided an engineered solution that will provide years of life to this section, but without proper drainage installed and maintained, these problems can re-occur. Field reconnaissance observations were conducted on June 30, 2011, by a team consisting of engineers and technicians. The team observed the ongoing roadway repairs, which included excavations to remove unstable sliding portions of the failure zone. The excavations were designed to allow for the proposed permanent road realignment. The team also observed that the excavation to the east of the road continued to uncover loose material, which was widespread in the area excavated and likely beneath the road, holding moisture and allowing for slippage along the failure plane. A detailed technical review of documentation provided by LBG related to the road construction and their contract was conducted by Tetra Tech. The review included soil/geotechnical reports, materials testing reports, field density reports, contract construction documents, QA/QC & field observation reports, and photos taken during construction. Initial observations from this document review include that the road appears to have been installed in accordance with contract specifications and standard engineering practice. However, there is no record of LBG conducting slope stability surveys per their original Scope of Work, and the drainage system installed for the road did not allow for proper drainage of water on the east side of the road in the failure zone. The investigation found several findings of fact, including that the drainage system installed for the road did not allow for proper drainage of water on the east side of the road in the failure zone, which may have contributed to the road failure. Additionally, LBG indicated that they heard discussions on previous historic road failures from locals after the road failure. The investigation also found that no slope stability review and analysis was performed, and LBG/B&V JV failed to analyze the watershed properly and engineer the culverts, ditches, cross drains, and other drainage structures to appropriately address water in the failure zone.