This document provides the in-depth background material that supports the Consultant's report on the Feasibility Study for a National Programme to Manage Slope Stability, and the proposed programme that is contained within that report. Most of the material represents a collection of data and analysis of it, in relation to the technical, economic and organisational aspects of slope management in the Lao road sector.
The first part provides the technical assessment of slope instability. This puts it into the context of the patterns of mountainous terrain and rainfall found in Laos, which account for the fact that most landslides occur in the north of the country. The common types of slope failure are described, along with details as to how these affect roads in the Lao PDR. Rainfall data are limited in scope, but a certain amount of analysis has been possible, to demonstrate how landslides can be triggered by severe storms arriving in cyclonic weather systems or from the south-west monsoon, during the long wet season. The effects of these can be detected on emergency road maintenance spending, with variations between years.
The economic appraisal examines the implications of various types of costs associated with slope instability. It shows that the clearance and repair costs for landslides runs into millions of US dollars per year, mainly through the MPWT's emergency maintenance budget. The costs of blockages can amount to significant sums, depending on the length of time that traffic is disrupted; but if it is more than three hours, the cost becomes large, especially for roads with traffic levels of 300 AADT or above. Environment costs are also noticeable. The economic implications of large scale engineering works to improve the stability of hazardous slopes is marginal, but well worthwhile if a failure were to occur within a few years. The implications for improved engineering management also seem to be marginal, though worth investing in if the potential costs of traffic disruption are taken into account.
The institutional assessment suggests that the current structure and working arrangements of the road sector are good, though still undergoing re-structuring. The document describes in some detail the organisation and capacity of the Ministry of Public Works and Transport, and its various central and provincial units. It also examines the road management systems, particularly in relation to off-road maintenance. There is no reason why the current arrangement should not be able to support a programme of slope stabilisation, except that technical skills are lacking in engineering geology, in geotechnical and bio-engineering, and in river engineering. This part of the assessment underlies the capacity development described in the proposed programme for slope stability management.
The final part of this Background Paper provides a number of technical items. These include a substantial inventory of current slope instability on National Roads. The study has also produced a summary of the preferred engineering response to slope instability, unit costs and standard design drawings for slope stabilisation engineering works. Further technical materials are due to be completed later in 2008 under the SEACAP 21 slope stabilisation trials programme.