Viva Q&A Guide

• Narrow width of the river to minimize bridge length and cost.
• Straight reach — avoid meanders/bends to ensure smooth, undisturbed flow.
• Stable, well-defined banks (preferably rocky) for strong abutment foundations.
• Favourable approach roads on both sides to minimize earthwork.
• Square crossing — axis perpendicular to flow to reduce scour and bridge span.
• Good foundation soil at a reasonable depth for pier/abutment stability.

• Economy: Minimize cut and fill — balance earthwork volumes to reduce cost.
• Gradient: Maintain permissible ruling gradient as per road standards.
• Obligatory Points: Connect positive points (towns, bridges) and avoid negative ones (marshy land, heritage sites).
• Geology: Avoid landslide-prone areas, geological faults, and unstable zones.
• Drainage: Ensure adequate drainage to prevent pavement damage and waterlogging.

1. Calculate Tangent Length:
   $T = R \tan(\Delta/2)$
2. Calculate Curve Length:
   $L = \dfrac{\pi \cdot R \cdot \Delta}{180°}$
3. Chainage of PC (Point of Curve / BC):
   Chainage of PC = Chainage of IP $- T$
4. Chainage of PT (Point of Tangency / EC):
   Chainage of PT = Chainage of PC $+ L$

Raw field observations always contain minor errors, resulting in a traverse misclosure. Adjusting the bearings and lengths (using Bowditch or Transit rule) distributes this error proportionally across all legs, ensuring the traverse forms a perfectly closed polygon mathematically — a prerequisite for accurate plotting and area calculation.

Resection determines the instrument station’s coordinates by observing at least three known control points.

1. Set up the instrument at the unknown station (P).
2. Sight at least three visible known control points (A, B, C) and record horizontal angles between consecutive pairs ($\alpha$ = ∠APB, $\beta$ = ∠BPC).
3. Analytically compute P’s coordinates using Collins Point Method or Tienstra’s formula based on the known coordinates of A, B, C and the observed angles.

The major traverse establishes the primary control framework for the entire survey area.

Angular Error:

Angular Correction: Distributed equally to all angles if within permissible limit $c\sqrt{n}$.

Linear (Coordinate) Error:

where $\Sigma L$ = algebraic sum of Latitudes, $\Sigma D$ = algebraic sum of Departures. Both should be zero for a closed traverse.

Correction Method: Bowditch Rule (equal linear and angular precision) or Transit Rule (angles more precise than distances).

A minor traverse is run between major traverse stations to capture interior details. The methodology is identical to the major traverse: angular and linear misclosures are computed and corrected via Bowditch/Transit rule. However, the permissible error limits are generally less strict (higher tolerance) than for the major traverse.

• Syllabus Methods: Tacheometry (Stadia Method), Plane Tabling, and Radiation using a Total Station.
• Method Predominantly Used: Radiation method with a Total Station — angles and distances to detail points are measured directly, with coordinates and elevations calculated automatically.

Observations recorded:

• High Flood Level (HFL) marks on banks/rocks.
• River bed profile along the bridge axis (L-section).
• Cross-sections upstream and downstream at regular intervals.
• Bank stability characteristics and soil/rock type.
• River flow direction and velocity indicators.

Map Symbols used:

• Arrow indicating river flow direction.
• Dotted horizontal line for HFL mark.
• Hachured/dashed lines for bank edges.
• Double line with end bars for the bridge span/axis.

• Finding the narrowest section of the river to minimize span.
• Ensuring the axis was perpendicular to river flow (square crossing).
• Verifying solid rock or stable soil foundation conditions on both banks.
• Checking that approach roads wouldn’t require excessive cut or fill earthwork.
• Observing the HFL evidence (watermarks, debris on trees).

• Topographic Plan showing the road corridor and centerline.
• Longitudinal Section (L-Section / Profile) showing ground level vs formation level.
• Cross-Sections (X-Sections) at regular intervals (15 m or 20 m).
• Mass-Haul Diagram for earthwork volume calculations.
• Curve Data Tables (IP chainage, $\Delta$, $R$, $T$, $L$, BC/EC chainages).

1. Bearing of the initial and subsequent tangent lines.
2. Distance between Intersection Points (IP to IP).
3. Deflection angles at the Intersection Points.
4. Profile levelling readings (BS, IS, FS) along the center line.
5. Cross-sectional levelling readings perpendicular to the center line.

A field test performed on a dumpy or auto-level to verify that the line of sight is perfectly horizontal when the bubble is centred (checking for collimation error).

1. Mid-point setup: Place the instrument exactly midway between pegs A and B (equal distances). Collimation error cancels — calculate true height difference $H = h_{a1} – h_{b1}$.
2. Near-one-peg setup: Move the instrument close to peg A. Record readings $h_{a2}$ and $h_{b2}$. Calculate apparent difference $H’ = h_{a2} – h_{b2}$.
3. Compare: If $H = H’$, no collimation error. If $H \neq H’$, the line of sight is inclined and needs adjustment.

A precise method to determine the elevation difference between two points separated by an obstacle (river, ravine) where the instrument cannot be placed midway. The level is set up on both banks alternately, and staff readings are taken from each side.

This completely eliminates errors due to earth’s curvature, atmospheric refraction, and collimation error — as these errors are equal and opposite in the two setups.

Types of levelling done: Fly levelling (BM transfer), Profile levelling (L-section of road), and Cross-sectioning.

Arithmetic Check:

Closing Error:

Correction: Total error is distributed cumulatively and proportionally to distance:

When conducting a Total Station traverse, trigonometric levelling provides the Z-coordinates for each station. The vertical closure error is the difference between the starting known elevation and the final calculated elevation of that same point after closing the loop. This misclosure is then distributed proportionally to the lengths of the individual traverse legs.

Set up at PC, zero the instrument toward the IP, then turn successive deflection angles $\delta, 2\delta, 3\delta\ldots$ to set each peg along the curve.

Horizontal distances in road projects span kilometres, while elevation changes are typically only a few metres. Using the same scale would make all terrain appear completely flat — cuts and fills would be invisible on paper. The vertical scale is exaggerated (typically 10× the horizontal scale) to make slopes, cuts, and fills clearly visible for design and earthwork estimation.

• L-Section: Horizontal 1:1000 / Vertical 1:100
• X-Section: 1:100 both axes (natural scale to preserve channel shape)

We determined the HFL by:

• Observing watermarks and staining on rocks and bridge piers.
• Identifying debris/branches caught high up in trees along the banks.
• Noting scour marks and erosion lines on the bank face.
• Conducting local inquiries with older residents and farmers who witnessed past floods.
• Cross-referencing with any available historical gauge records from the nearest hydrological station.

1. Find the Fore Bearing of AB from coordinates:
   $\theta_{AB} = \tan^{-1} \dfrac{x_B – x_A}{y_B – y_A}$ (determine quadrant by signs)
2. Calculate Back Bearing of AB (= Fore Bearing of BA):
   $FB_{BA} = FB_{AB} \pm 180°$
3. Calculate Fore Bearing of BC:
   $FB_{BC} = FB_{BA} + \text{Clockwise included angle at B}$
   (If $> 360°$, subtract $360°$)

Examine the sequence of contour RL values (e.g., 100, 105, 110…). The constant difference between consecutive lines is the Contour Interval (CI) — in this case, 5 m.

An Index Contour is every 5th contour line, drawn thicker for easy map reading. If CI = 5 m, then every 25 m contour (100, 125, 150…) would be an index contour. The elevation value is typically labelled on it.

1. Determine Chainage of $PT_6$ (End of Curve 6) — you must know this first.
2. Calculate Chainage of $IP_7$:
   $\text{Ch}(IP_7) = \text{Ch}(PT_6) + \text{Straight distance from } PT_6 \text{ to } IP_7$
3. Calculate Tangent Length of Curve 7: $T_7 = R_7 \tan(\Delta_7/2)$
4. Calculate Chainage of $PC_7$:
   $\text{Ch}(PC_7) = \text{Ch}(IP_7) – T_7$
5. Calculate Length of Curve 7: $L_7 = \pi R_7 \Delta_7 / 180$
6. Calculate Chainage of $PT_7$ (End of Curve):
   $\text{Ch}(PT_7) = \text{Ch}(PC_7) + L_7$

When the instrument is at the Point of Curve (PC) with zero set toward the IP (the tangent line), the deflection angle to the exact midpoint of the curve equals half of the total tangential angle to the full arc:

where $\Delta$ is the total deflection angle of the curve. Alternatively, the angle to bisect the internal angle at the IP is used to locate MC from that point.

Yes — using Manning’s Equation.

1. Survey the cross-sectional area ($A$) of the dry riverbed.
2. Measure the longitudinal bed slope ($S$) via levelling.
3. Estimate the roughness coefficient ($n$) based on bed material (sand, gravel, rock).
4. Apply Manning’s formula for a given theoretical depth (e.g., at HFL):
   $V = \dfrac{1}{n} R^{2/3} S^{1/2}$
   where $R$ = Hydraulic Radius = $A / P$ ($P$ = wetted perimeter).

• Cross ridges at the lowest saddles (passes) to minimize elevation gain.
• Cross rivers at right angles where the channel is narrowest.
• Run as parallel to contours as possible to minimize earthwork.
• Strictly connect positive obligatory points (towns, bridges).
• Bypass negative obligatory points (heritage sites, unstable slopes, marshy land).
• Avoid gradients steeper than the ruling gradient.

• Placed at the narrowest and straightest section of the river.
• Stable geological banks (rocky or firm soil) capable of bearing abutment loads.
• Axis perpendicular (square) to river flow to minimize scour and simplify design.
• Sufficient distance upstream and downstream free of bends for smooth flow.
• Good approach road conditions on both banks.

Filled (embankment) materials lack the natural compaction and cementation of undisturbed ground. If placed at a steep slope, the soil mass will exceed its natural Angle of Repose — the maximum slope at which friction alone can hold the material in place.

Exceeding this angle causes shear failure along a slip surface, leading to sudden slope collapse and road embankment failure. Gentle slopes (typically 1.5H:1V to 2H:1V for common fill) ensure long-term stability.

Road alignment is done in four phases:

1. Map Study — Identify tentative routes on topographic maps; check gradients and obligatory points roughly.
2. Reconnaissance Survey — Field inspection with compass and Abney level; select the most feasible route.
3. Preliminary Survey — Detailed theodolite traverse (P-line) and levelling (L-section, X-section) to finalize geometry.
4. Detailed/Final Location Survey — Transfer the approved centerline to ground; set out IPs and curves.

Conditions considered: Topographic (gradient, slope), geological (soil stability), environmental, economic (minimize cut/fill), drainage, and obligatory points.

Curves are set out using Rankine’s Method of Tangential (Deflection) Angles:

Procedure: Set up at PC, zero the instrument toward the IP. Rotate to deflection angle $\delta$ and measure chord $c$ to set the first peg. Then turn to $2\delta$ and measure the next chord from the last peg, and so on until EC.

Obligatory points are control points governing the route of a highway alignment.

Yes — for planning a new major highway alignment.

Patan (Lalitpur) is a densely urbanized area containing priceless historical and cultural heritage including UNESCO World Heritage Sites (Patan Durbar Square, ancient temples, bahas). Three key reasons make it a negative obligatory point:

• Astronomically high land acquisition cost in a dense urban core.
• Legal prohibition against destroying registered heritage monuments and their buffer zones.
• Irreversible cultural damage — loss of centuries-old architecture that cannot be compensated.

Therefore, any new highway alignment must bypass Patan entirely.