Environmental & Social Management Framework - About ...

Environmental and Social Management Frameworkc. Addressing Destabilisation of SlopesDue to the complex interaction between water, soil, fragile geology, seismicevents and topography, common features particularly in hilly regions of Nepal areslope failures, landslides, and mass wasting. These factors can easily be furtheraggravated by road construction activities such as earth excavation, namely inunstable zones, drainage works, quarrying and spoil disposal. Practical mitigationmeasures are at hand such as:- First, design the road with optimum balance in cut and fill with goodpositioning of road and good construction supervision;- Second, do not undertake road construction during peak rainy season.In mountainous terrain, gradual widening, i.e. construction of narrow track oftypically 2 m width in the first year and widening later, provides opportunity tonatural stabilization of the slopes and growth of vegetation during rainy season.This helps to control slope failure and soil loss in the hills and mountains;The high geometric standard of highways and feeder roads of DoR/GoN isdifficult to achieve in many areas with irregular terrain. Although the main slopesare often massive, there is very often a micro-topography of spurs and reentrantswhich make it difficult to achieve the geometric standard without aconsiderable amount of slope cutting. Older roads such as the Tribhuvan-Rajpathand the Kathmandu – Trishuli road, built to a lower geometric standarddemonstrates how this can be avoided at the expense of travel speed andcomfort.e. Precaution Measures during Slope Cutting ActivitiesSlope cutting should be done based on the natural type of material, and naturalslope should be maintained. Following Table 5.1 presents the general angle ofslope cutting in different types of geological characteristics.6.1 General Guideline for Slope Cutting TableType of Material and Natural ConditionAngle of Cutting(vertical : horizontal)Loose clay and vulnerable geology 2:1Compacted soil with slope towards road 4:1Soft rock 6:1Hard rock 8:1It is mainly the slope of toe that is vulnerable to slides and erosion. Thus,appropriate measure must be adopted while cutting the slope, as pictoriallypresented below.In cut areas, the exposedslope should be protectedusing conventional civilengineering structures inconjunction with bioengineeringtechniques. Itis also advised to dominimum damage tovegetation during construction.Exposed slopesshould be planted withsuitable vegetation assoon as possible usingpreviously stockpiled topsoil.April 2007 Chapter 6-5