PROJECT: WEST AFRICA PIPELINE AND GAS FACILITY LANDSLIDES, West Africa

Flowslide affecting a jetty pad and pipeline routes
Flowslide affecting a jetty pad and pipeline routes

Natural gas development is occurring off the West Coast of Africa. The facility owner was expanding the plant when reactivated ancient landslides affected construction of the primary gas delivery system between the offshore gas field and the fractionation plant on the island.  The plant is situated on a volcanic terrace and dense jungle masked ancient landslides that formed the bluff above the island’s shoreline.

Landslide Technology was retained to provide landslide stabilization expertise.  Fast-track geotechnical services to mitigate slope stability concerns included investigation, mitigation design, and construction.  Investigation at the remote jungle site included land and aerial reconnaissance, evaluation of existing and new geotechnical data, ring-shear strength testing, planning supplemental explorations, instrumentation monitoring, landslide modeling, and stability analyses. 

Landslide Technology quickly recognized the geologic origin and mechanics of the landslides, which allowed mitigation design to be conceptualized quickly and confidently.  Multi-discipline group sessions were held at company headquarters and onsite to address mitigation options and select those that helped keep overall plant construction on schedule.  The alignment of the primary pipelines was modified to fit the landslide mitigation measures and to reduce the length of pipeline on the active landslide.  While modified pipeline components were being manufactured and shipped from the U.S., the onsite earthwork team faced significant challenges to regrade the slope and stop movements within the two months available.  Most of the mitigations utilized materials and equipment available onsite and locally.  Retaining wall construction was accelerated using prefabricated wire mats shipped from the U.S.  An international dewatering firm installed horizontal drains and vertical pumped wells.  Landslide Technology provided construction management of mitigation measures and prepared a manual for operation and maintenance.  The construction of the gas delivery/reinjection pipeline was successfully completed and placed into service.