Pipeline Geohazards Unique to Northern Climates

Abstract

Pipelines in northern climates can be impacted by geohazards that are unique to cold regions. Some of these include frost heave, thaw settlement, solifluction, icings, glaciers, ice-rich slopes, and others. This paper will discuss most of these geohazards as they have been monitored, mitigated, and managed along the Trans Alaska Pipeline (TAPS) and other pipelines in Alaska and Russia. Early analyses of frost heave and thaw settlement of piles concluded that frost heave and thaw settlement would be controlled by installing passive heat removal devices (heat pipes). In permafrost areas heat pipes have generally worked well. In unfrozen terrain or discontinuous permafrost the heat pipes have not been able to maintain stability. Examples of each of these situations will be discussed. Steep rolling terrain makes up a significant part of the TAPS route. Some of the slopes are in permafrost and others are in thawed ground. For the past 15 years, surveillance and monitoring of some of the slopes along the pipeline route has documented the response of slopes in frozen ground. Warmer (that is near 0 degrees C) ice-rich slopes can creep. An example of this is documented on a slope instrumented with inclinometers and thermistors. Other slope movements related to pore pressure increases caused by active layer containment of unfrozen groundwater flows will be discussed. The impact of solifluction zones on pipeline construction and routing will be addressed as it has been managed along the TAPS. Other near surface slope movements that appear to be similar to solifluction have been observed along the pipeline right-of-way on the workpad. This paper will address an interrelationship of these observed slope behaviors. In doing this the interaction of slope seeps and the freeze front as it forms in fall and then recedes in spring and summer is compared to observations of engineered projects. Icings can be observed in several locations along TAPS. In some cases these can be related to slope movements. In other cases the icings have reached the aboveground and caused maintenance issues. TAPS was designed to avoid future surges of several large glaciers. In most years these glaciers have retreated and have not been a significant issue. A recent large earthquake caused a landslide on the largest glacier near TAPS and resulted in some review of the activity on that glacier. In 2002 a large earthquake centered near TAPS caused liquefaction in some areas, breakage of ice in lakes in some locations, and sand boils very close to the pipe. These observations will be related to the thinly frozen active layer over a deep talik during the earthquake.