State of Road Disasters and Experiences from the Current Road Building Practices in Nepal

Netra Prakash Bhandary

Graduate School of Science and Engineering, Ehime University 3 Bunkyo, Matsuyama 7908577, Japan

1. INTRODUCTION Topographically, Nepal is divided into southern plains (Terai), mid-hills and the mountains. The plains cover about 17% of the total national territory while the mid-hills and mountains together cover the rest (i.e., 83%). The hilly and mountainous areas are geologically young and active, and affected by a constant tectonics uplifting accompanied by down-cutting of the river systems. The consequences on the predominately soft and deeply weathered rock-mass have produced an extremely rugged topography with local differences in elevation varying from 70 meters to 8,848 meters above the mean seal level. In addition, the annual rainfall in Nepal is highly heterogeneous, temporally as well as spatiality, which severely affects the stability of mountain slopes. Annual rainfall amount varies from less than 250 mm in the areas of Himalayas to around 5,000 mm in central Nepal. The rainfall regime of the Low and Middle Himalayas is controlled by the Southeast Asian monsoon. The resulting steep, unstable and highly erosion-prone slopes are divided into many gullies and small valleys. For this very reason, the construction and maintenance of infrastructure, particularly the roads, in such a rugged topography is both difficult and costly.

Nepal is one of the least developed countries with a GDP (Gross Domestic Product) per capita income of 383 US dollars. Over 31% of Nepal’s population still remains below the international poverty line. Even today more than 86% people still live in rural areas where minimum physical infrastructures are still lacking. The major challenge of the Nepalese Government is to provide an appropriate level of infrastructure to those remote and scattered settlements to support developmental activities and thereby reduce the level of poverty.

Plans do exist for the development of road network, but due to a number of reasons including the natural difficulties, many people are still deprived of the use of roadway transport facilities. On top of that the exiting road network greatly suffers natural disasters, particularly landslides and erosion related problems every year diverting the road network development budget to maintenance and repair. All this has repeated for several years in the recent past, and the most affected roads in this category are the highways connecting the capital city of Kathmandu and the rest of the country. These highways include Prithvi Highway, Narayanghat-Mugling Highway, Tribhuvan Highway, and Araniko Highway, as indicated in Fig. 1. Apart from losing a large amount of national budget in reconstruction work, the frequent closure of traffic through these highways greatly affects the national economy. This paper deals with the state of roadside disasters in the recent past and discusses the experience from current road building practice in Nepal at a time when there are great expectations that Nepal will soon have a fast-track road connecting the capital city of Kathmandu and a Terai town of Hetauda, which has been planned to reduce the travel time from Kathmandu to Terai by two to three hours. 2. ROAD NETWORK IN NEPAL 2.1 An overview of national road system and current status According to official road development plan, the roads in Nepal are categorized in four groups: national highways, feeder roads, urban roads and district roads. National highways are the main highways extending in east- west and north-south direction, which directly serve the greater portion of the longer distance travel, provide consistently higher level of service in terms of travel speeds, and bear the inter community mobility (regional interest). These roads are the main arterial routes passing through the length and breadth of the country as a whole. The feeder roads, on the other hand, serve as the routes connecting the district headquarters as well as the national highways.

In the last four decades, a total of 17,281 km of road network has been developed in Nepal. Out of this, there are 5,273 km (31%) of black-topped (i.e., surfaced) roads, 4,613 km (27%) of graveled roads, and 7,394 km (42%) of earthen/dirt roads. Similarly, in terms of the road category, there are

3,339 km (19%) national highways (five national highways are currently under construction), 4,196 km (24%) feeder roads, 2,362 km (14%) urban roads and 7,390 km (43%) district roads, as shown in Fig. 1. As the development of railways, waterways and ropeways is negligible and the feasibility of its expansion has also been found negligible, Nepalese have to depend on the road and air transportation. The present average road density in Nepal is 11.74km per 100sq.km. In terms of population, the average road density is 1,412 persons per km (population census 2002). These data indicate that among the South Asian nations, Nepal has a very low road density not only in terms of serving the population but also in providing accessibility to the various parts of the country. The existing and proposed strategic road network is shown in Fig. 2.

Fig. 1: Existing and Proposed Strategic Road Network (Source: DoR, Nepal)

Type of Road(Total 17,281 km as of April 2006)

4613 km(27%)

5273 km(31%)

7394 km(42%)

Black TopGravel RoadEarthen Road

Road Category(Total 17,281 km as of April 2006)

2362 km(14%)

3339 km(19%)

4196 km(24%)

7390 km(43%)

National Highway

Feeder Road

Urban Road

District Road

Fig.2: Road Type and Road Category (Source: DoR, Nepal)

2.2 General trend of road network development As rods serve the basic infrastructural need, a huge amount of national budget has been spent in developing the road networks in Nepal. A massive amount of international support both as grant and loan has been utilized to achieve the current size of road network. The trend of total road network development during the last 50 years is shown in Fig. 3, which indicates that the development of road

Pokhara

Kathmandu

Narayanghat

Hetauda

Mugling

network in Nepal is exponentially increasing.

Development of Road Network in Nepal

y = 4E-55e0.0674x

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1940 1950 1960 1970 1980 1990 2000 2010

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Fig. 3: Development of Road Network in Nepal (Source: DoR, Nepal)

Department of Roads, the sole government authority to look after road development and maintenance in Nepal, has prepared a long term road development plan−20-year Road Sector Plan in 2002, which is being implemented from the fiscal year 2002/2003. According to this, the strategic network expansion is around 5,000 km within the next 20 years. Within the current 10th five-year plan there is a provision for strategic road network extension by about 1,000 km. 2.3 Network planning at national and departmental level The history of development of roads in Nepal is comparatively short. The first motorable road was constructed in the Kathmandu valley in 1924 when the first road development program was initiated in the country. The first long distance road to link Kathmandu with the southern plains was taken up in 1953 with the Indian assistance. Since then, the development of road sector got higher priority and the nation started to build roads from the first five year plan. The road development strategies between the period between 1950 and 1970 were mainly focused on:

• To facilitate the movement of goods and services within the country without the use of transport network of the neighboring country India

• To strengthen administrative, social and political linkages with the zonal and headquarters • To facilitate external trade and commerce

In the early seventies, the road development priorities were revised and focused at strengthening the identified corridor of movement between the Terai (southern plains) and Hills by developing the north-south link roads. After 1990, the objectives of the road program were further defined in terms of maintaining economic growth rate, supporting the reduction of poverty and the reduction of regional imbalances.

The Department of Roads has prepared many different types of planning documents both for long term and short term. It has prepared a 20-year (2002 – 2022) master plan for strategic road network in 2002, which was formally published in June 2004. Beside the National highways, district road networks are being developed under the Department of Local Infrastructure and Agricultural Road (DoLIDAR). A separate District Transport Master Plan (DTMP) for each district is being prepared on the basis of available and expected resources. 2.4 Network capacity and traffic growth Design capacity of two lane black-topped roads is 7,500, 5,000 and 3,500 vehicles per day on plain, rolling, and mountainous terrain respectively. Based on a traffic survey (2001), 45% of the network

has traffic less than 250 vehicles per day while only 3% of the network has a traffic volume exceeding 3,000 vehicles per day. The maximum traffic of 8,032 vehicles a day has been recorded in the urban section (Koteshwor–Bhaktapur) of Araniko Highway. Because of the poor road condition and low reliability of services only the limited highways have high traffic volume such as Prithvi Highway which passes the traffic more than 3,500 vehicles per day.

Based on traffic demand assessment and factoring/projecting the future planned GDP growth, a study carried out by Nepal Engineering Consultancy (NEPECON) has forecasted that the national average of annual traffic growth rate of 5.5% for the period of 2003 – 2007 period and 6% for 2007 – 2017 period and 6.5% for 2017 – 2022 period. The projected traffic for the existing network indicate the drop of percentage of network having a traffic level of less than 100 vehicles a day from 30 percent in 2001 to 26 percent in 2012 and 19 percent in the year 2022. The percentage of network having traffic levels more than 250 vehicles a day subsequently increases from 55 percent in the year 2001 to 64 percent in 2012 and 73 percent in 2022.

According to traffic survey carried out in the year 2004, the annual traffic growth rate was found 12%. Because of rapid modernization and urbanization of municipalities, motorization is increasing rapidly, and consequently the traffic growth is also increasing rapidly. The current traffic over the long route is dominated by commercial vehicles as buses (27%), trucks (60%) and car/utility (13%). Buses and trucks constitute more than 50 percent of the total traffic. Thus, the current network capacity is not only inadequate to traffic volume but also to provide the basic services to people and to achieve the government poverty reduction strategy (Millennium Development Goals). 3. ROAD BUILDING PRACTICE Road construction technology in Nepal has not been fully mechanized even for national highways. The involvement of labor in road building process is still significant, mainly due to low-cost priorities. Department of Roads has established heavy equipment divisions for managing all the heavy equipments which are used for both road construction and maintenance. There is debate among the transport planners in Nepal whether to adopt fully mechanized construction approach or both labor intensive and equipment-based construction approach because of high unemployment rate and low wage rate. Generally, the labor intensive approach has relatively long construction period and low standard with compared to equipment based construction approach. Construction cost depends on site condition. For example, building of road in rocky area is very costly by labor intensive approach.

Road projects under the foreign grant or assistance with their own technical team are adopting equipment based construction technology except some operators and their assistance required to operate and assist them such as Banepa–Bardibas Road, a Japan funded road project. Road projects with government’s own resources and Nepalese technical team are adopting both equipment and labor-based technology. Up until now, there are no roadway tunnels, which are necessary to enhance the serviceability and accessibility of road network throughout the country. The efforts towards stabilization of slope are negligible. As a result, traffic is usually disrupted in rainy season. Low cost structures such as gabion walls, dry stone retaining wall etc. are used to stabilize the slopes.

Most roads in mountainous terrain in Nepal can be found to have been aligned through the river valley cuts. There may be a number of reasons for this trend in road alignment, but costlier tunnel technology might be one reason that has forced Nepalese engineers to build roads through mountain slopes. All roads through mountains have been built on cut slopes, which greatly disturbs the slope stability leading to frequent roadside slope failures, as has been experienced hundreds of times in the recent decades. In terms of reducing roadside disasters, tunnels (at least in manageable size) may be more appropriate than the cut slopes along roads in Nepal. 4. NETWORK CONDITION AND MAINTENANCE PRIORITIES The expansion of the road network in the late eighties took a new undesired turn in the history of road management and development. With growing people’s aspiration and demand to build more roads, it ushered in an era of just building roads without giving proper attention to its upkeep. As a result, substantial resources started to get tied up with new construction programs and very little money was set aside for maintenance. During that decade maintenance gradually lost its priority resulting in heavy depreciating at a loss rate of 5 km for every 100 km of road built during the decade of the eighties. Donor supported construction of higher standard roads as discrete projects without giving much

attention to its follow up care has also contributed to the poor state of road condition at the time. The earlier attempts to expand the road network without giving considerable attention to its

maintenance resulted in a serious crisis in road management in the late eighties. A larger portion of important road network was found not to be in an acceptable condition to provide effective service to users. The country was continuously losing its road assets due to inadequate attention given to their maintenance. A major shift on policy to effectively address the issue related to road maintenance was taken up in the early nineties. Acknowledgment and acceptance of the concept of minimizing the total transport cost (comprising construction, maintenance and road user cost) for the management of road network in the eighth plan is considered to be a major step in the right direction.

Maintenance of the strategic road network is carried out to serve two basic functions of road management. The first one is to preserve road assets over time, and the second one is to avail required level of services to the users. By realizing the importance of road maintenance, Department of Roads had started the Strengthen Maintenance Divisions Program (SMDP) in 1994 with the objective of building the capacity in the Department of Roads to under take the planned maintenance of the strategic road network. At present the planned maintenance process had been introduced in all 25 divisions. The government has accorded the highest priority to the maintenance of road network. In order to build reliability in financing the maintenance activities, the government has enacted the Road Fund Board Act 2002. The Board is authorized to collect services charges as well as fuel levy independent of the Government revenue basket. While the Board has been already constituted with effective participation of private stakeholders including the representation of Civic Society, it is in fully operation from 2003. Performance Based Maintenance Contract (PBMC) had been introduced in some sections of strategic road network, efforts towards making maintenance activities more efficient and effective.

Financing of all maintenance activities (routine, recurrent, emergency and periodic) is arranging through the Road Fund Board. DoR is the implementing agency for implementing the maintenance activities for SRN. The allocation of maintenance budget for last five year is presented in Fig. 4.

0

200000000

400000000

600000000

800000000

1000000000

1200000000

FY 98/99 FY 99/00 FY 0０/01 FY 01/02 FY 02/03 FY 03/04 FY 04/05 FY 05/06

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nten

ance

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ge

Total maintenance budget (NRs)

Periodic maintenance budget

Fig. 4: Road Maintenance Budget (Source: Road Board Nepal)

5. TYPICAL EXAMPLES OF ROADSIDE DISASTERS The main failure types along the Nepalese highways, especially the Prithvi Highway, Tribhuvan Highway, and Narayanghat-Mugling Highway can be recognized as being surface failures triggered mainly by gully erosion, debris falls triggered probably by mass movement, rock falls caused by joint failure, creep slides triggered by subsurface mineral decomposition, etc. A two-day observational survey conducted by the authors in July 2003 revealed that there were more than 20 noticeable unprotected or poorly protected landslide sites along the Prithvi Highway. A similar survey was conducted along the Narayanghat-Mugling Highway in November 2003, which revealed that no proper measures have been taken to protect the highway from landslide disasters, and that the most of the recent failures that turned into debris and mud flows were triggered by pore-water pressure

generation in the decomposed debris mass near the failure source.

The observational survey was particularly focused on five failure sites, which include one debris fall/slide (Krishnabhir site), one debris flow (near Marsyangdi Powerhouse), and two creep movements (Mugling site and Damauli site) on the Prithvi Highway and one debris flow on the Narayanghat-Mugling Highway, as indicated in Fig. 5. 5.1 Krishnabhir site Krishnabhir site roughly measuring 400m long and 150m wide near the road is located at 84km west of Kathmandu alongside the Prithvi Highway. It showed traces of failure somewhere in 1999, which was triggered by gully erosion of the colluvial deposit on the top of the slope. With the beginning of monsoon of the year 2000, a massive failure of the weathered rock mass in the slope took place resulting in the deposition of the slid mass on the highway and blocked the traffic for two weeks. Reoccurrence took place in the year 2001, and slowly turned into a stabilized deposition of slid mass in the year 2002. Although the efforts have been made by the Department of Roads to stabilize the slid mass by applying gabion retaining walls and bio-engineering techniques, the landslide seems to have stabilized naturally due to reduction in slope gradient rather than due to the efforts made by the department of roads (Fig. 6).

According to Humagain (2001), the major rock types in the Krishnabhir area are phyllite, quartzite, schist, and slate with some calcareous bands. Intercalation of the quartzite and calcareous band in phyllite may be considered to have given rise to instability of the slope. In addition, presence of talc and graphite along the foliation planes seems to have further decreased the shear strength of the rock mass.

Based on topographical observations and exposure of the rock mass near the slope surface, the landslide is seen to have been induced by not only excessive rainfalls but also the inherent geological factors such as development of fractures on the slope rock mass due to imperceptible movement of the huge mass that failed in the long past (as

① Krishnabhir site② Mugling site③ Debris flow near the powerhouse④ Damauli site⑤ Debris flow on N-M Highway

Kathmandu

Pokhara Prithvi Highway

Narayanghat-MuglingHighway

TribhuvanHighway

NarayanghatMugling

Damauli

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① Krishnabhir site② Mugling site③ Debris flow near the powerhouse④ Damauli site⑤ Debris flow on N-M Highway

Kathmandu

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Narayanghat-MuglingHighway

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Damauli

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Fig. 5: Locations of landslide sites along the Prithvi Highway and Narayanghat-Mugling Highway.

Road Debris removed from the road

Photo: 2003.11

Stabilized deposit

Fig. 6: An oblique view of Krishnabhir Landslide

Fig. 7: An oblique aerial picture of Krishnabhir Landslide and assumed block of massive failure

indicated in Fig. 7). Speculations can be made of movement of an old deposit in creeping manner causing upper part of the fractured mass to take a form of debris fall. Although borehole investigation needs to support this speculation, the depth of mass movement, based on the size of the failure, can be estimated at 30 to 40 meters, and the depth of the debris fall on the top is 8 to 10 meters. 5.2 Mugling site About 106 km west of Kathmandu, this landslide site is situated on side of the Prithvi Highway near Mugling. The only traces of the landslide movement at this site are subsidence of about 150m length of the road (Fig. 8) and visible scarps near the crown. Seeing the amount of subsidence that has been observed for more than four years, this failure can be categorized as creeping movement of the mass that might have failed a long time ago. A maximum of about 1.5m subsidence can be seen near the midpoint and 30-50cm depressions can be seen near the edges. The gabion retaining walls along the road edge constructed by the Department of Roads for protecting the road from failure show that this area was recognized as a landslide site at least five years ago (estimated).

Observation of the topography as sagging of the slope surface shows that this landslide site is an old deposit of previous failure and subsequent subsurface weathering of rock minerals through the existing plane of failure might be considered to have triggered the creeping landslide, which remains comparatively active during monsoon periods. Based on the subsided length of the road, the depth of the landslide can be estimated at 15-20m. 5.3 Debris flow near Marsyangdi

Powerhouse This site is located near the Marsyangdi Hydropower House on Prithvi Highway about 114km west of Kathmandu. The debris flow event took place in late July 2003 and disrupted the traffic between Kathmandu and Pokhara for two days as the bridge over a tributary of the Marsyangdi River was swept away by the debris. The size of the largest boulder in the debris is about 5m (Fig. 9) and the reason for the flow of bridge may be supposed to be the box culvert just upstream

Original level

Subsidence

Present level

30-40 cm

Fig. 8: Creeping landslide near Mugling and the road subsidence

5m rock

Swept away Bridge

Fig. 9: The vicinity of the Marsyangdi Powerhouse damaged by the debris flow

Diversion road

Debris flow

Bridge upstream

Bridge downstream

Fig. 10: Upstream and downstream from the swept-away bridge and the remains of the box culvert

from the bridge. It is considered that the culvert caused a damming effect during the flow of debris (Fig. 10). 5.4 Damauli site The creeping movement near Damauli on the Prithvi Highway (about 155km west of Kathmandu) can be identified from road subsidence with a maximum depression of 1.5-2.0m in the middle and 50-60cm near the edges (Fig. 11). The length of depression along the road, which seems to be quite close to the crown of the slide, is about 60m. Collapse of surface soil and decomposed rock mass can also be observed with frequent outcrop of clayey soil. Some of the exposure reveals that the slope material is composed of previously failed deposit, as shown in Fig. 12. This landslide is quite similar in nature with the one near Mugling. 5.5 Debris flow on Narayanghat- Mugling

Highway The debris flow on the Narayanghat- Mugling Highway (about 125 km west of Kathmandu) has a run-out length of about 650m and had spread on about 100m length of road. This is the second largest debris flow alongside the Narayanghat-Mugling Highway that took place in 2003 monsoon and killed four people. The highway was blocked for nearly two weeks due to a huge amount of debris deposited over the road (Fig. 13). An estimated 25000-30000 cu.m. of debris was generated resulting in the formation of a steep channel with an average gradient of 1:10 in the lower portion and 1:5 in the upper portion (Fig. 14).

The observation of the failure source reveals that it was triggered by a local failure at an altitude about 150m from the road level (Fig. 15). The failure might have taken place due to generation of pore-water pressure in the decomposed clayey mass near the source point. 6. GEOTECHNICAL ASPECTS OF THE

INVESTIGATED FAILURE TYPES 6.1 Overall features The major types of landslides and slope failures observed or identified during this survey can be classified as being debris fall under the influence of probable mass movement, creeping landslides, and debris flows. The following paragraphs explain the geotechnical features of the investigated failure sites.

Subsidence (1.5-2m)

Original road level

Fig. 11: Creeping landslide near Damauli showing the road subsidence

Previous deposit

Fig. 12: Traces of deposited material as a result of previous massive failure (Damauli site)

Road

Deposit

Fig. 13: Debris deposit on the sides of Narayanghat-Mugling Highway

Krishnabhir landslide can be categorized as being a massive debris fall site, which might have occurred primarily due to possible development of cracks in the upper layer of rock mass near the slope surface. Such failures are quite frequent in places where the rock mass is relatively stratified, dipping, and weakly jointed. In particular, when the slope material is detached from the bedrock, such as due to widening of fissures, the chances of such failures are higher. The loss of cementation between the stratified layers due to chemical weathering or formation of clayey material through the fissures may also cause such slope failures.

The landslides near Mugling and Damauli were found to have clear signs of creeping displacement. The subsidence of the road is a clear evidence of extremely slow movement of the landslides. Such landslides usually have a well defined slip plane through a layer of soil composed primarily of weak clay material. Other creeping landslides may also include deep-seated gravitational creep of rock mass, whose movement mechanism is governed more by the rheological behavior of rocks. The deep-seated gravitational creeps are usually very large, so the observed landslides may not fall in a category of deep-seated creeping landslides. The movement mechanism of creeping landslides is such that the frictional resistance of the slip layer soil is slightly greater than the shear component of the weight of the sliding mass, which means that the factor of safety is slightly greater than unity.

The failure types near Marsyangdi Power House and along Narayanghat-Mugling Highway were debris flows, which usually take place on slopes covered by thin unconsolidated rock and soil debris, especially where the vegetation cover is insignificant. Of the three main distinctive elements of a debris flow, i.e., the source area, the main track, and the depositional toe, the slope features near the source area play an important role to cause the debris flow, and combined with this, the flow of unconsolidated material in the main track results in a destructive flow of soil, gravels, boulders, and rocks. Debris flows are frequent in topographic concavities or hollows at first-order watersheds (Corominas et al. 1997). Such topography favors the accumulation of colluvium and the convergence of groundwater flow necessary to cause the failure. 6.2 Stability analysis and prevention The stability analysis of natural slopes like Krishnabhir landslide site employing limited investigation data will result in a factor of safety that may be as erroneous as estimated by the rule of thumb. The debris material at the site after failure often seems to deposit with a slope angle of above 30 degrees,

Approx. 3.0~4.0m

(Previous Sediment deposit)

Fig. 14: Depth of debris channel and the previously deposited debris material on the sides of the channel (Narayanghat-Mugling Highway)

Source point

Heavily decomposed soil deposit

Fig. 15: Weathered deposit near the source area (Narayanghat-Mugling Highway)

which may be evident that the angle of internal friction for the slope material may be around 30 degrees. A soil material with such a high angle of internal friction on a natural slope must have greater stability, but as the angle of original slope inclination is around 40 degrees, the deposited debris mass often exhibits instability and starts failing, especially under the influence of developed water table during rainy periods. On top of that is the clay portion mixed with the debris deposit, which might have an internal friction angle of around 20 degrees. During rainfall events, the frictional resistance of the debris deposit is governed more by the strength of clay mixed in the slope material. This is how the soil in Krishnabhir landslide site is supposed to fail during monsoon periods. The prevention of this failure at present conditions of Nepal’s landslide prevention practice may be difficult. However, the risk of further failure and frequent highway closures may be reduced by removing the loose debris deposit and applying appropriate measures to protect the failure of rock mass up the slope.

On the other hand, the stability analysis of creeping landslides becomes comparatively simple because the slip surface in most cases remains well defined. In addition, identification of slip layer soil and determination of its strength parameters together with the slope geometry may reduce the errors involved with the back analysis. However, it is often difficult to evaluate the strength of slip layer clay because testing a couple of slip layer samples may not give a representative mean value of angle of internal friction for the whole soil in the slip layer. It may therefore be appropriate to estimate the strength parameters by back analysis technique and verify their reliability by conducting shear tests on the slip layer samples. The preventive measures for a creeping landslide may include various techniques such as lowering of the groundwater level, anchoring, restraint piles, etc., but in context of Nepal, these techniques may not be affordable. So, what can be done to reduce the risk of further movement or sudden failure are proper investigation and removal of soil near the top and filling near the bottom.

The stability analysis of debris flow like failures is out of the scope of geotechnical approach to slope stability analysis, but it may not be inappropriate to apply available slope stability analysis techniques to assess the stability of natural slopes at probable source points. Experiences have shown that preventive measures taken near the source areas may substantially reduce the chances of debris flow occurrence. In addition, if the possible soil flow through the main track be obstructed by some structural means, the kinetic energy of the flow mass originated from the source area can be significantly reduced, which may result in complete prevention of debris flow disasters. A widely used preventive measure for the debris flows and mud flows is construction of sabo dams (i.e., debris check-dams), which is also in practice in Nepal but at countable locations.

Finally, as a large number of people every year suffer from highway closure and unpleasant travel experience, landslides and slope failures have more often been talked of along the highways than in remote mountain settlements where heavy loss of lives and property takes place almost every year. It may therefore be of significant importance to properly and appropriately plan the engineering works, such as highways, dams, bridges, and many other civil facilities near landslide prone areas. Moreover, engineering implications of the landslide sites and slope failures are important for a long term service to be expected from the constructed facilities. 7. TYPICAL CASE OF LANDSLIDE DISTRIBUTION IN EXISTING HIGHWAY CORRIDORS For an overview of the overall scenario of large-scale active and relict landslides, which are the major source of debris flows, surface failures, and small-scale slope collapses, landslide mapping of the highway corridor with an average width of 3.0km (about 2.0km on the roadside and about 1.0km on the riverside for Prithvi Highway and Narayanghat-Mugling Highway, while 1.5km on either side of the road for Tribhuvan Highway) was done. The mapping was based on the conventional method of reading aerial photographs (scale 1:50,000) and topographic maps (scale 1:25,000). An overall view of the landslide distribution, as a result of the landslide mapping, is presented in Fig. 16, which indicates that the distribution of landslides is dense over the Malekhu-Mugling section of Prithvi Highway and over almost the whole length of Narayanghat-Mugling Highway. Tribhuvan Highway, however, is seen to have comparatively less number of large-scale landslides despite having passed through the mountains of Lesser Himalayan Zone and Siwalik Zone.

Fig. 16: Distribution of large-scale landslides along the highways.

8. CHALLENGES AHEAD There are great challenges for the Nepalese road engineers and builders in expanding and maintaining the road network. Not only the natural difficulties but also the construction technology and financial constraints are the major obstacles in building international standards roads in Nepal. The experience from the world and in particular in mountain roads in countries similar to Nepal has shown that the addition of length in network also inevitably invites additional slope failures. This poses as a great challenge for Nepalese road builders to keep the road service available throughout the year, and thus providing the reliable services. As the current density of road network, 1,412 persons/km is very low even with compare to South Asian country, thousands of kilometers of road has to be constructed to make access to whole population by road network which is possible only with right vision and adequate resources. The development, expansion and maintenance of road network in Nepal are lagging because of weak economic condition and dependence on foreign aids, grants and loans. The condition of donor funded road projects are also not satisfactory after handing it over to DoR because of inadequate maintenance attention being paid. DoR has many challenges towards being independent with its own resources (financial as well as human).

It is quite obvious that the length of road increases in absence of tunnel especially in mountainous regions like Nepal. Many short routes have already been identified and reported as feasible. So, it is both opportunity and challenge to Nepali Engineers to build and operate the road tunnel with their own resources. Many innovative technologies are in use in other countries such as in design, construction and maintenance of roads. So, it is essential to adopt those technologies in planning, design, construction and maintenance of roads for rapid development of road network efficiently.

As the proposed Asian highway passes through the land of Nepal, it is another challenge to upgrade the national highway standards to international standards at least in the proposed route section. There are many road intelligence systems that have been installed in other countries. It is also another challenge to Nepalese road builder to introduce the road intelligence system in Nepalese highways. 9. SUMMARY AND CONCLUSIONS Road network is the most important means of transport system in Nepal. Very little can be expected of the railway and waterway development, and air transportation may not be affordable by all categories of people. Despite unfavorable geographical settings, active and young geology and weak economic condition, hundreds of kilometers of roads have been constructed during the last five decades.

However, frequent roadside disasters have unimaginably affected the national economy. Various plans have been put forward for the development and maintenance of roads, but the trend is more towards increasing the road network than to upgrade the road serviceability and standard. It is because the objectives of the road program were further defined in 1990 focusing on maintaining economic growth rate, supporting the reduction of poverty, and the reducing the regional imbalances. Government has set different working modalities for strategic roads and local roads (district and urban). As the current traffic growth rate is more than 12%, the current network size will be insufficient because of rapid motorization and urbanization.

Many improvements in road construction technology are necessary. Modern and high-tech technology has to be adopted to develop Nepalese highways to the international standard. Vehicles are following unnecessary long route and consequently high road user cost due to lack of road tunnel. So, road tunnel has to be constructed when and where feasible. The road condition is very poor especially in rainy season because of landslide, debris flow and river cutting. Until a few years ago, the road maintenance work was given very low priority, but at present it has been getting higher priority after it was realized that routine maintenance of roads increases the road serviceability. The Department of roads has started SMDP program in all 25 divisions for planned maintenance program. DoR has introduced performance-based maintenance contract (PBMC) in some section of highway as a pilot project which helps to maintain the road up to date. However, the budget allocated for maintenance is insufficient and disbursement of budget also not timely. A well equipped emergency maintenance team has to be standby to clear road obstruction as the earliest.

The state of highways in Nepal, particularly Prithvi Highway and Narayanghat- Mugling Highway in Nepal indicates that no proper and adequate measures have been taken to mitigate or protect the landslides along the major highways that play a significant role in Nepal’s economic development. The above two highways run along and across the Mahabharat Range of high mountains and midlands, often known as Lesser Himalayan Zone, which lies over a tectonic thrust line known as main boundary thrust, making the range highly vulnerable to landslides. Despite this geological setting, no appropriate and adequate investigations have so far been carried out in order to identify the failure prone roadside slopes and mitigate the landslide disasters as well as to prevent the highway closure during heavy monsoonal rainfalls. In-depth geological investigations, landslide site identifications, and landslide mappings along the major highways of Nepal are the important steps to protect the transport infrastructures of the country from frequent landslide disasters. Finally, as most speculations and data in this paper are based only on the observation, misinterpretation of the actual scenario might have taken place. Nevertheless, this paper will work as a basis for the future investigation programs. References 1. Bilham, R., Blume, F., Bendick, R., Gaur, V.K., 1998. Geodetic constraints on the translation and

deformation of India: implications for future Great Himalayan Earthquakes. Current Science, 74(3), pp213-229.

2. Corominas, J. et al. (1997). Debris Flow, Landslide Recognition: Identification, Movement and Causes, Dicau, R., et al. (Eds.), John Wiley & Sons, pp.161-178.

3. Department of Roads, 2004. Master Plan for Strategic Road Networks 2002-2022. 4. Department of Roads, 1995. Departmental Policy Documents, The DoR Strategy. 5. Department of Roads, 2003. Guide to Road Slope Protection Work. 6. Department of Roads, Guideline for Inspection and Maintenance of Bridges, Vol. 1. 7. Department of Roads, 2055. Road Maintenance Manual for Engineer and Overseer. 8. Department of Roads, 1995. Definition of Maintenance and Maintenance Activities 9. Department of Roads, 2006. Standard ARMP guidelines 2006. 10. Department of Roads, 2045. Nepal Road Standards (First revision - 2045). 11. Hearn, G. J. and Lawrance C. J., 1997. Principles of Low Cost Road Engineering in Mountainous

Regions, Transport Research Laboratory, Berkshire. 12. Howell J., Deoja B. B.and Engler M., 2005. Final Mission Report, Review and Strategic

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Symposium on Geotechnical and environmental Challenges in Mountainous Terrain, GNESYM2001, Kathmandu, Nepal, pp61-67.

14. Japan Highway Public Cooperation. Modern Highways Illustrated – Technology -. 15. Lawrance, C. J. and Cook, J. R., 2003. A Strategy for Slope Hazard Assessment in Planning and

Maintenance, Proceeding of the Sustainable Slope Risk Management for Roads, Kathmandu, March 2003.

16. Ministry of Physical Planning and Work, 2002. National Transport Policy. 17. Malekhu, M.G. and Chalise, D.N., 2003. Slope Management in DoR – Retrospect and Prospects,

Proceeding of the Sustainable Slope Risk Management for Roads, Kathmandu, March 2003. 18. Upreti, B.N., 2001. The physiography and geology of Nepal and their bearing on the landslide

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19. Yatabe, R., Bhandary, N. P, and Bhattarai, D., 2005. Landslide hazard mapping along major highways of Nepal. Ehime University, Japan and Nepal Engineering College, Kathmandu, Nepal.