Ranjan Low-cost Road

Geologically Active – Williams et al. (eds) © 2010 Taylor & Francis Group, London, ISBN 978-0-415-60034-7

Low-cost road for the development of Nepal and its engineering geological consequences R.K. Dahal

Department of Geology, Tribhuvan University, Tri-Chandra Campus, Ghantaghar, Kathmandu, Nepal

S. Hasegawa

Department of Safety System Construction Engineering, Kagawa University, Takamatsu, Japan

N.P. Bhandary & R. Yatabe

Department of Civil & Environmental Engineering, Ehime University, Matsuyama, Japan

ABSTRACT:  Construction of roads in the mountains of Nepal is quite complicated because of steep slopes, thick soil profiles, weak rockmass and the extreme rainfall of the monsoon season. In the name of “low cost”, many roads of Nepal do not have any standard engineering structures. As a result, low cost road construction and maintenance programs are widely affected by landslide and debris flow triggered by monsoon rainfall. Generally, shallow failure occurred along the roadside, both in uphill as well as downhill slopes, are major geological problems of roads of Nepal. Although, cost effective techniques are very important for a developing country like Nepal, experience of Nepal reveals that low cost roads are not the best solution for sustainable development of underdeveloped countries. 1  Introduction Nepal is a mountainous country situated in the heart of the Himalaya. This young mountain chain is also famous worldwide for its very active tectonics. Furthermore, it lies in an area of strong monsoon precipitation, with the rainfall distribution being such that over 90 percent occurs within a short three months. Extreme rainfall events are very common which can bring over 400 mm of rain within 24 hours. Thus, these geological and climatic factors make the mountain slopes of Nepal highly vulnerable for to rainfall triggered landslides. Construction of roads in the mountains of Nepal is complicated because of steep slopes, thick soil profiles, weak rock mass and torrential rainfall due to the monsoon. This paper is intended to describe the engineering geological issues of low cost roads in Nepal with some illustrations. Later in the paper, some mitigation measures used to stabilize the slopes are also evaluated with some illustrations. 2  Road construction practice in Nepal A significant factor in the development of a country is the provision of improved access to physical facilities and social services. Nepal’s total road network and density are low and only 43% of the population has access to all-weather roads. In the last ten years, road construction projects in Nepal have been considered a major part of infrastructure development. The growth in roads shows an exponential increase from 376 km in 1950 to 20,600 km (including usable rural roads) by 2007 (a period of 58 years). Even now the road density is low, about 6 km/100 sq km. Most of the roads (either rural roads or national highways) in Nepal are low cost roads, not built to international standard. Nowadays, there are many projects of district 4085

or rural road construction. These roads are being constructed with the participation of the people but very littletechnical supervision. Many international donor agencies are providing funds for local governments to construct roads. Some of the major donor agencies for low cost road projects in Nepal are the Asian Development Bank (ADB), World Bank (WB), UK Department of International Development (DFID), the Swiss Agency for Development and Cooperation (SDC), Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ, an international cooperation enterprise from Germany), Japan International Cooperation Agency (JICA), and the United Nations World Food Program (WFP). High-paid short term consultants from developed countries work on these road construction projects and provide engineering as well as socioeconomic consulting service for low cost road construction. But, most of the time, international consultants only suggest economical road construction practices rather than sustainable road construction methods suited to the highly dynamic Himalayan environment. It is not unusual for the total cost of a rural low cost road project to be lower than one day’s travel and daily allowance for an international consultant. For example, for 2009/10, the District Development Committee of Dolakha district has approved 100 low cost rural road projects and most of the rural roads are 10 to 15 km long whereas the budget sanctioned for each road project is only about US$270!! (District Technical Officer, Dolakha district, pers. comm.). In fact, road construction practices in Nepal are mostly guided by the desire of the donor agencies and the interests of local political leaders. This is partly attributable to the lack of uniform and mandatory national standards and guidelines. Many stretches of road do not have any standard engineering structures and the roads are usually constructed on side slopes requiring cut and fill. Locally available materials are used to protect the cut slope, usually dry stone retaining walls or bioengineering are used for protecting slopes. In recent years, district or rural road construction projects have already grown by 11% annually. A related fact is that more than 50% of the Village Development Committees (VDCs) from all over Nepal have a User Committee for rural road construction. Nowadays, many slopes in the mid-hills are dissected by earthen roads and, due to the lack of engineering standards; these roads are almost unusable for vehicle movement. As a result, low cost roads are prone to shallow and deep seated landslides during the monsoon. The poor engineering conditions of the roads hampers the delivery of social services in the remote hill and mountainous districts and directly or indirectly affects the country’s economic development. Lack of connectivity in presence of low cost road projects are major impediments to the development of Nepal. In Nepal, about one third of the total road length is earthen roads (33%), with the remainder of the network comprising gravel roads (22%) and bitumen sealed roads (45%). The Nepal Road Standards classifies roads as follows: • National Highways connecting the length and width of the country (Figure 1) • Feeder Roads providing access to important trade centres and district headquarters from the national highways • District Roads providing access between a district’s headquarters and its trade centres. • Urban Roads within the city area • Rural Roads to provide access to rural settlements and agricultural centres National highways and feeder roads are included in the Strategic Road Network (SRN) under the jurisdiction of the Department of Roads (DoR); the SRN comprises nearly one third of the total road length. The remaining two thirds are considered as district roads, rural roads, urban roads, agricultural roads and capillary roads which are under the jurisdiction of Department of Local Infrastructure Development and Agricultural Roads (DoLIDAR) and local bodies (District Development Committees, Village Development Committees and Municipalities). Major highways like Prithivi Highway, Tribhuvan Highway, Siddhartha Highway, and East-West Highway are continuously in the maintenance phase. New highways like Dhulikhel-Sindhuli Road, Chhinchu-Jajarkot Road, Surkhet-Jumla Road, Katari-Okhaldhunga Road, Mid-Hills Roads and Beni-Jomsom are in the construction phase. Likewise, 4086

Figure 1.  Strategic road network of Nepal.

there are many more road projects running at a local level with the financial aid of many international donor agencies. Low cost road construction and maintenance programmes are widely affected by landslide and debris flows triggered by monsoon rainfall. The failures also vary in severity and losses. Roadside slope failures have not commonly resulted in major loss of life, because most catastrophic failures have occurred in less populated areas. Economic and financial losses are, however, substantial. Generally shallow failures occurring along the roadside, both on the uphill as well as the downhill slopes, are major problems for Nepalese roads. These problems are excessive in both major highways and rural roads. Through enforcement of the Public Works Directives (PWD) in 2001some degree of uniformity has been achieved in the project implementation practices. Table 1 lists existing road construction practices adopted for the construction of roads in Nepal. 3  Geological issues OF roads IN Nepal 3.1  Geology and geomorphology of Nepal in brief Having emerged as a result of tectonic uplift of sedimentary deposits, the rock-mass in the Himalaya has a high degree of fragility and a greater tendency to undergo accelerated decomposition under the influence of climatic factors. With 83% low to high mountainous areas, Nepal covers approximately one third of the Himalayan mountain ranges in the central Himalaya. The Nepal Himalaya has eight well-defined regional geomorphologic zones in a north–south direction and each of these zones has a unique altitudinal variation, slope and relief characteristics, and climatic pattern. Figure 2 provides the structural framework and geological map of Nepal. Controlled by the monsoonal winds and regional geomorphology, the climate of Nepal is extremely varied. It ranges from seasonally humid subtropics to semiarid alpine, but in a more global sense, the climate of Nepal is tropical monsoon, except for parts of the northern area, which lie in the rain shadow of the Himalaya and have a cold semi-desert climate. It is often said that the wet monsoon over the Himalaya provides almost 90% of South Asian water resources. Orographic effects are the main cause of extreme monsoonal rainfall in Nepal, which usually begins in June and ends in September. 3.2  Landslides as major geological issues of roadside slopes Factors such as excessive rainfall and human intervention are the main triggers of landslides along the roadside slopes of Nepal. Factors such as groundwater conditions, river under 4087

Table 1.  Existing road construction practices in Nepal (modified after Dahal et al. 2006). Landslide occurrence

Methods

Generic guidelines

Labour intensive   method

Applied for construction of early roads   in Nepal, labour groups employed as   labour contract, no work contracts, no   heavy equipment used except   work tools, mostly full cut roads,   structures and embankments   minimized, side casting of surplus   material permitted,   blasting for rock breaking,   Embankment and fills compacted   with light equipment, equipment   used for pavement construction Applied in highways, feeder roads and urban roads, earthwork equipment used for cut, slope trimming and embankment construction, mechanized compaction of backfill and embankments, labourers used for minor works—drainage, slope finishing, subgrade preparation etc., full range of equipment used for pavement construction, blasting for rock breaking permitted, large contractors employed for construction Mostly used for district roads and feeder roads, only light equipment used, no heavy equipment used, small local contractors used for civil work contracts, maximum use of local labourers for works, limited blasting permitted for rock breaking, large scale and long distance haulage not practical Stage construction of road formation (1.5 m, 2.5 m, 4.0 m) in combination with bioengineering, only local labourers used through community based organizations, wages equally distributed, no profit retained by community based organizations, no contractors may participate, balanced cut and fill principle—no haulage of surplus material, bioengineering measures as an integral part in each stage, natural compaction principle—no artificial compaction, only local material used except some gabion wires, use of cement discouraged, blasting for rock breaking not permitted, road formation out cambered for sheet flow—no side drains, equipment may be used only for gravelling and pavement, prevailing method for rural and agricultural roads, also applicable for construction of highways and feeder roads, method is inherently poverty focused and uses poorest people

Conventional   Mechanized Road Construction   Practice

Labour-Based   Road Construction   Method

Low-cost   Environment-friendly   and Participatory   (LEP) Method

4088

High Risk of Landslides Need extensive costly mitiga­ tion measure

High Risk of Landslides Need extensive costly mitiga­ tion measure

Medium Risk of Landslides Need extensive mitigation measure

Generally destroyed by monsoon rainfall so seasonal road Shallow failures are prominent Needs routine care by community

Figure  2.  Simplified Geology and physiogeography of Nepal (modified after Dahal & Hasegawa 2008).

cutting and deforestation of slopes are also facilitating landslides on roads. In this context, it is easy to accept that landslides are the major engineering geological issues in low cost roads of Nepal. Brief scenarios for landslide occurrences in the main physiographic provinces of Nepal are given in Table 2. 3.3  Roadside slope failures For the prediction of rainfall triggered landslides, the concept of hydrological landslidetriggering thresholds has been already developed to some extent. Similarly, a correlation between rainfall intensity, rainfall duration and landslide events are also already established (Dahal & Hasegawa, 2008). Moreover, the influence of rainfall on landslides usually depends on landslide dimensions, kinematics, material involved, etc. Experiences show that shallow failures are usually triggered by comparatively short intense storms (Campbell, 1975; Wieczorek et al., 2000; Kim et al., 2004) whereas most of the deep-seated landslides are affected by long-term variation of annual rainfall as well as daily rainfall which has to last at least some couple of years. In the Himalayan context, shallow landslides are associated with torrential rainfall brought by the monsoon (Dahal & Hasegawa, 2008). Not only shallow landslides, but also deep-seated landslides are usually associated with the monsoon rainfall. Many roadside slopes along the highways consist of considerable numbers of deep-seated landslides which undergo prolonged creep during torrential rainfall. For example, a large and well known landslide of the Prithivi Highway, named the Krishnabhir landslide (Figure 3), occurred after some days of intense precipitation, in the Trishuli River valley (Lesser Himalaya) at the beginning of mid of August 2000 and blocked the Prithivi Highway, the main entry route of Kathmandu, for 11 days. Because of low cost mitigation measures and “wait and see” principles, the highway was blocked many times since 2000 and it was stabilized in 2005. Shallow landslides that generally flow downslope at a very high velocity are found to be the most devastating. In various parts of Nepal extreme rainfall can reach up to 200  mm in 24 hours and studies shows that this value is enough for triggering landslides on steep slope (>30°) in the Lesser Himalaya (Dahal & Hasegawa 2008). The intense rainfall that occurred in Chitawan (central Nepal) on July 2003 resulted in a series of landslides affecting steep roadside slopes of the Mugling-Narayangadh Road, all having similar characteristics. 4089

Table 2.  Landslide problems in various physiographic provinces of Nepal. Physiographic provinces Siwaliks (Churia) Range

Mahabharat Range

Midlands

Fore Himalaya

Higher Himalaya

Trans Himalaya

Major issues Made up of geologically very young unconsolidated and easily disintegrated sedimentary rocks such as mudstones, shale, sandstones, siltstones and conglomerates. Rainfall is normally in the range of 2000 to 2500 mm per year. The combination of geology and rainfall makes the Siwaliks highly susceptible to landslide processes. The Upper Siwaliks contain thick beds of loose and fragile conglomerates. The Lower and Middle Siwaliks have problems caused by alternating beds of mudstones and sandstone. Mudstones can flow when saturated with water, which results in overhanging sandstone beds; when such sandstone beds are well jointed they easily disintegrate into blocks. The Mahabharat Range is the most important barrier to the monsoon clouds and therefore it greatly influences the rainfall distribution pattern in Nepal. The southern face of the range receives extensive rainfall in comparison to the Midlands with a very high frequency of high intensity rainfall. Those areas made up of rocks such as limestone, dolomite, marble and granites have the more stable slopes whereas those underlain by rocks such as phyllite, slate, intercalations of phyllite and quartzite, depict the terrain most prone to landslides. A gentle topography compared to the Siwaliks and Mahabharat ranges. Thick soil formations are found on slopes because of deeply weathered rocks. Usually considered as a rain shadow of the Mahabharat with 1000–2000 mm annual precipitation but some areas also record incidences of high rainfall. Slopes are very prone to landslides after intense rainfall. Most of the population of Nepal lives in the Midlands which is intensively cultivated. Irrigation systems can be found in every terrace on the slopes as well as on old landslide debris; mismanagement of irrigation canals can be noticed everywhere. These improper agriculture practices generally create landslides or reactivate old landslides and usually damage whole villages on the slopes. The frontal portion of the Higher Himalaya. Main rock types being phyllite, schist, marble, quartzite, and gneiss. Tectonically very active and uplifting at a high rate. The topography is steep and rugged. High rainfall; 2000 to 3500 mm, so another vulnerable area for landslide occurrence. Some landslide dams are also noticed in narrow river valleys of this province. The highest area of Himalaya, including all elevated peaks and their slopes above 5000 m. Main rock types are gneiss, schist, marble and quartzite. Vertical or steep rocky slopes are very common. There is little or no soil cover on slopes; rock related failure phenomena are very common, Because of very low population and nil infrastructure development, the degradations of the Higher Himalaya do not draw the attention of planners and researchers. Situated in the rain shadow zone of the greater Himalayan Range, this zone has very low average annual rainfall, so soil related landslides are less frequent but debris flows in snow fed streams are quite common. Riverbanks composed of alluvial and glacial moraine possesses bank failure problem.

4090

Figure 3.  Krishnabhir landslide along the Prithivi highway, a major route connecting the capital city with the rest of the country.

These gravitational mass movements occurred suddenly, generally extending for tens or even hundreds of metres and damaged almost 80% of a total 36 km highway stretch. Based on classifications proposed by Varnes in 1978 and Cruden et al. (1996), most of the landslides on roadside slopes can be classified as translational landslides, rotational landslides, followed in many cases by debris flow. Nevertheless, some highway landslides are very large landslides of a complex nature. The failure surface of translational landslides on slopes is generally at a depth of 2–4 m and appears to affect the whole hill slope. In fact, such small scale landslides are noticed in large scale landslide mass as seen in the Mugling-Narayangadh road (Hasegawa et al. 2009). Rotational slides are generally seen on thick colluvial deposit as well as residual soil where water was not properly managed on cut slopes. Debris flows are even observed in the Jomsom area (Jomsom-Kagbeni-Muktinath road) where annual rainfall is only 250 mm. Many parts of the Mugling-Narayangadh road were damaged due to debris flows and debris slides. These landslides are generally initiated at small areas at the tops of hills or heads of gullies and they flow with extremely high velocity and erode a path damaging everything in the way, finally leaving a deposit rich with high debris load. These debris flows generally have very a shallow depth and most of the debris flows triggered by rainfall appear on roadside slopes with slope angles mainly between 30° and 40°. Failures are rarely recorded on slopes of