Even small landslides can cause considerable disruption, injury or fatalities. It is frequently forgotten that landslides often affect project infrastructure, rather than the project site itself, causing disruption, economic losses, and sometimes loss of life.
Landslides are particularly common on new roads or railway lines on steep slopes. Thus, take great care when cutting slopes to create a road bench to ensure that the newly created slope is stable. Simple mitigation measures, such as gabian baskets, can greatly increase the stability of a cut slope.
In many cases the road bench is created by cutting or blasting a rockslope. In this case, be careful to ensure that rock blocks have not been left in a state that could allow instability to develop. After blasting or cutting, inspect the slope for signs of instability, and remove blocks that may fall.
Be very careful to manage water appropriately as in many cases, instability arises from poor management of surface water. Ensure that drains and culverts are continuous - i.e. that they:
Do not end without a suitable discharge point;
Do not feed water into, or concentrate water on, the slope (which can greatly reduce stability);
Discharge into a channel that is both secure from erosion and has the capacity to cope with the additional flow, even in heavy rainfall.
Where drainage lines cross the line of the road or railway, ensure that there is a culvert in place that can cope with the flow.
Sometimes it is necessary to create a road or railway line through use of cut and fill measures. Such fill slopes can be very prone to failure if inappropriately designed. Ensure that the fill:
Has proper levels of compaction;
Is appropriately retained;
Has drainage to prevent high water pressures from developing.
After construction, regularly inspect completed roads and railway lines, and take prompt action if distress is developing.
Other infrastructure can be affected by landslides, with serious consequences. Thus, for example, water or gas pipelines are easily damaged by landslides. Ensure that appropriate measures are in place to guarantee their security, and monitor them for signs of landslides. Electricity infrastructure can also be affected. Examples include small scale project hydroelectric plants, which are often affected by debris flows, and pylons that may be struck by, or built upon moving, landslides. Plan the location of such infrastructure carefully.
In some areas, early warning of heavy rainfall can be available that may help to identify if a potentially hazardous event may occur. Monitor local and national weather forecasts for periods of heavy rainfall.
Where landslides do pose a risk, put in place a contingency plan to deal with the consequences of an event, and ensure that all staff are aware of its implementation.
Carefully consider the consequences of a landslide for local people and properties. Ensure that the likelihood that the project could trigger landslides with high consequences for local stakeholders is acceptably low.
An example of a landslide early warning system: http://hkss.cedd.gov.hk/hkss/eng/landslip_top.aspx