LANDSLIDES ON THE PANAMA CANAL -- RECENT ACTIVITY IN THE GAILLARD CUT

During construction of the Panama Canal’s 12.6-km-long Gaillard Cut at the beginning of the 20th century, landslides caused extremely serious construction problems. Most of these slides occurred in soft rocks, mainly Tertiary volcanic tuffs, clay shales, and mudstones. Landslide activity resulted in additional excavation that more than doubled original volume estimates for the cut.

After completion of construction, landslide activity in the Gaillard Cut reduced as a result of reduction of excavation works. In spite of this, landslides in the cut between 1914 and 1930 resulted in 40 million m3 of additional excavation. A resurgence of landslide activity occurred as a result of the first widening of the cut in the 1960s. During the following period (1960-1990), at least three major landslides occurred: Cartagena Extension Slide (1964), Hodges Hill Movement (1968), and West Empire Active Area (1973). In addition, other slides were related to maintenance of or deepening of the navigation channel and/or to periods of heavy precipitation; examples were the East 1925Sta Culebra Slide (1974) and the East Cucaracha Landslide (1986). Of these events, only the East Cucaracha Landslide caused serious disruption to Canal operations. As a consequence of these major movements, considerable improvements in landslide control/remediation were implemented by means of the Landslide Control program (LCP), which was instituted to reduce the risk and effects of landslide activity in the Gaillard Cut.

In 1991, the Panama Canal Commission (now the Panama Canal Authority) embarked on the US$1 billion Canal Improvement Program, which included the second widening of the Gaillard Cut to permit two-way passage of Panamax-size ships. Excavation works for the Cut Widening Program (CWP) were completed in December 2001. As in the first widening, this second widening effort also brought a resurgence of landslide activity: several landslides occurred, both first-time slides and reactivations. These slides were triggered by various factors, such as improper excavation sequences, unpredictably high groundwater levels, and previously undetected geologic conditions.

This increase in landslide activity is still in progress and is expected to continue as a result of the new Channel Deepening Program for the Gaillard Cut that began in January 2002.