Career Episode 1
Detailed engineering survey and design for expansion of a hill road.
 
1.INTRODUCTION
CE 1.1  
During my seventh semester at Kantipur Engineering College, Dhapakhel, Lalitpur, I
had to carry out detailed engineering survey and design for expansion of road section
as part of a practical assignment in Transportation engineering II. I worked on
expansion of Arughat-Arkhet road section located at Gorkha District of Nepal. The
survey works required five days, dating from 12th Jan 2012 to 16th Jan 201 and the
design part took almost a month.
2.BACKGROUND
CE 1.2
Ability to work in team is vital in engineering and for this reason we were required to
work in a group of three, under extensive guidance and supervision of Er. Sudeep
Thapa. In addition to our supervisor’s instructions, we referred online resources,
several books on transportation Engineering and surveying, Nepal Road standard
(NRS) 2070, road note 31 and past reports for thorough understanding of the survey
and design procedures. We needed to prepare a final report of all our works, which, in
fact, was used by our teachers for final evaluation.  
CE 1.3
We were required to carry out detailed engineering survey and design for upgrading
an existing 2999.48 m earthen roadway of one lane to two lanes road with gravel
finish. The roadway designed to link Soti village and Arughat bazaar was located in
Gorkha district of western development region and served as the trekking route to
Mount Manaslu. Majority of the road section passed through the mountainous terrain
and was dominated by the presence of sedimentary rocks along with sand deposits.
The road was classified as a feeder road with gravel finishing having a total road
width of 7.5m with a carriage width of 5.5m.
CE 1.4
In addition to the design of horizontal curves, vertical curves and pavement, I made
necessary provision for adequate drainage and slope protection through the design of
the side drains, cross drainage, subsoil drainage and retaining structures. Furthermore,
 I investigated the impact of the project on the environment identified some pragmatic
approaches to alleviate those ramifications.
CE 1.5
Our objectives required us to carry out following activities:
1. Desk study and Reconnaissance survey
2. Technical, Environmental and Economic feasibility study of the expansion project
3. Geometric design of road
4. Design of retaining structures, side drains and cross drainage structures
5. Design of pavement
6. Estimation of Cost
7. Preparation of final report including conclusion and recommendations
 
3.PERSONAL ENGINEERING ACTIVITY
CE 1.6
Initially, I with my group members, studied topographical and geological maps of the
area and gathered relevant information about existing road, existing structures, natural
features such as river, hills etc. and made plans for the detailed field study. In the
field, we adopted open traverse method for surveying. My team first fixed traverse
points and established a reference station near the starting station. My group partners
and I then took turns to set up total station in the traverse points and observe all data
necessary for plotting contour.  My team studied drainage requirements, nearby
structures, construction material and traffic volume manually. Using the data obtained
from field survey, I calculated coordinates of all the points recorded by total station.
For this, I used various principles of surveying. I then plotted a contour map using
AutoCAD and civil 3D.
 
CE 1.7
Using the contour map, I chose a suitable centreline for the upgraded road from
technical and economic considerations. Then I opted for geometric design of the road.
I used Nepal Road Standard (NRS) 2070 as input document for selecting the
centreline alignment and for the geometric design of road.  For design of road, class
of road acts as basic determining factor, which is ascertained from traffic volume.
Therefore, I first classified the road as Class IV Nepalese Standard Road. The
proposed road passed through hilly terrain. Therefore, following the design standards
for Class IV road in hilly terrain I adopted design speed of 30 km/hr and maximum
gradient of 10 %.
 
CE 1.8
 Then, I designed horizontal curves and their elements to provide smooth deflection
from one straight to another, to avoid obstacles and to include positive obligatory
points. While designing horizontal circular curves I tried to keep the radius as large
as possible for comfortable riding. I adapted a minimum radius of 100 m at points
where large radius was not possible (as per NRS minimum radius for comfortable
riding is 50m).  To counteract the effect of centrifugal force in horizontal curves I
raised the outer edge of the pavement with respect to inner edge in curves (super
elevation) using the equation suggested by NRS. After horizontal curves, I designed
vertical curves (summit/valley) at the intersection of two longitudinal grade lines in
vertical plane for safe and smooth flow of traffic. I calculated the lengths of summit
curves using stopping sight distance criteria and valley curves using night visibility
criteria.

CE 1.9

However, some of the locations had a very steep slope with gradient up to 45%
characterised by extremely sharp curves. Under those circumstances, I designed
hairpin bend using the design criteria from NRS 2070 with a minimum design speed
of 20mph having radius of curvature of at least 15m and transition curve of at least
15m with minimum gradient of 4% and maximum superelevation of 10%, preferably
located on the section with minimum cross section and maximum stability.

CE 1.10

Then I calculated volume of earthwork in cut and fill. I had selected gradients such
that amount of earthwork would be minimized. I adopted the formation slope of 1:1
for cuts and 1:2 for fill. I used following dimensions for cross sectional elements after
referring the NRS.

a. Right of way : 20.0m (10m on each side of Centre Line)

b. Road width : 7.5 m

               c. Carriage width : 5.5 m

d. Shoulder width : 2.0 m (1m on each side)

 
CE 1.11
The next step was to determine the pavement thickness that would provide smooth,
safe and efficient movement of vehicles on the road. I used the CBR method of
design, which first involved the determination of soaked CBR value of the subgrade
soil. I anticipated traffic flow at the end of expected life of the road using an
appropriate traffic growth rate as 7.5%. I selected the appropriate design curve as per
 the traffic classification based on number of commercial vehicles per day. Using the
graph plot of thickness versus subgrade CBR value for the curve, I obtained the
required thickness of pavement.
 
CE 1.12
It is imperative to analyse the characteristics of the subgrade as the designed
pavement had to be constructed over the subgrade. The performance of the subgrade
is usually governed by its load bearing capacity, moisture content and the strength and
stiffness of the subgrade soil. Therefore, I recommended to use the subgrade material
of adequate strength and stiffness to be applied over the properly consolidated and
compacted foundation layer. Furthermore, to eradicate the problem with subgrade
saturation, I provided the cut-off subsoil drainage in the form of a perforated pipe
covered with a geotextile material.
 
CE 1.13

The road was river route type following Budi Gandaki River, which is the major river
of the area. I used the data provided by Department of Hydrology and Meteorology
(DHM) to study maximum discharge of different return periods for this river and
other significant watersheds crossing the alignment. These data also provided general
understanding about the climactic conditions and rainfall pattern of the area, based on
which I scheduled my work plan.

CE 1.14

Functionality of a road greatly depends on the drainage facilities provided. If water

CE 1.15
For design of the side drain, I obtained design discharge following rational method
equation using the catchment area, runoff coefficient and the rainfall intensity
obtained from the gauge station located in the area. Based on the hydraulic properties
of the desired drain, I determined its cross-sectional area using Manning's equation for
the given discharge. I referred to NRS to fix the longitudinal slope of the side drain
and used riprap as material for lining to dissipate the energy from the discharge. I
 provided trapezoidal area and increased the area obtained by about 30 % so that the
water could also serve for the irrigation of the nearby agricultural land.
                                                                                                                                                       
          

CE 1.16

There were some distinct locations where it was mandatory to provide the cross
drains for the safe passage of natural drainage and stream crossing under the road.
Therefore, depending upon the economics, site condition and the environmental
consideration, I selected reinforced concrete(RC) pipe culvert as the stream crossing
carried low discharge. I designed the culvert to satisfy the passage requirement as
well as hydraulic requirements and selected the slope of the culvert as specified in
NRS 2070. In addition, I incorporated some special design considerations for the safe
passage of the fish and protection against scouring and other potential environmental
damages downstream in the design of the culvert.

CE 1.17
Slope stability was the major problem for the given road. In addition to providing
drainage facilities, I provided retaining structures wherever there is abrupt change in
the ground levels. I designed a stone masonry gravity wall of adequate thickness able
to resist both sliding and overturning. Furthermore, to avoid the submerged earth
condition, I provided weep holes in the retaining walls, which otherwise would result
in enormous earth pressures causing serious structural failures.
 
CE 1.18
Road construction is associated with several direct ramifications to the environment
which include wide ranging impacts to ecosystem, soil stability, water resources,
wildlife and so on. I tried to alleviate these ramifications by balancing the earthwork
in cutting and filling, using the locally available to minimise imports, subtle
adjustment in the design alignment to enhance the vehicle efficiency and appropriate
selection of the wearing course to increase the surface smoothness which reduce the
emission and fuel consumption of the vehicle. In addition, to address the potential
problem of erosion, sediment control and slope instability of the hillslopes, I applied
bio-engineering techniques by utilising vegetation in conjunction with the engineering
structures.
 
CE 1.19
 The final part was to estimate overall cost of the project. I estimated final cost of the
project by considering rate of materials and services based on norms of District
Development Committee, Gorkha. Our supervisor had asked us to prepare individual
reports. Therefore, I finally prepared a report of all my works.
 
4. SUMMARY
CE 1.20
Through the diligent efforts of me and my group, we were successful in completing
the project within the time frame. Although I had a strong theoretical base for the
surveying, transportation and soil engineering, it was only after the project, I
understood the essence and the functionalism of those theories. Moreover, it made me
competent in the various surveying techniques, design of the road pavement, soil-
water interactions, design of road side drain and retaining structures. In addition, it
made me understand the impact of engineering project on the environment and
incorporate various environmental considerations during the design of the structures.
The project allowed to apply my engineering knowledge to redefine the physical
environment that really benefits the society and literally improve millions of lives. To
sum up, the project had a significant impact in supplementing my technical ability and
problem-solving skills.
 
 
5. ANNEX
1. Formulas for setting out horizontal curves

Tangent length,

Length of curve,

Apex distance,

Distance between tangent length and length of curve = 2T - L

           Where,

R = Radius of the curve

∆ = Deflection angle

e = Apex distance
2. Formulas for setting out vertical curves

Summit Curve:

L= , when S<L

L= ,when S>L

Valley Curve:

, when S<L

, when S>L

Stopping sight distance (S) is considered for design of vertical curves.

Elements of the Vertical Curves:

Tangent length,

Length of curve, L = A*R

Apex distance, e =

The formula for setting the offset of the curve, Y

Algebraic difference between the gradients (A) = Total change in grade = g1- g2

Length of vertical curve = A/r

3. Manning’s formula

V=
𝑛

Q=AV