Survey Camp Viva Questions and Answers

Answer:

The main and specific objectives of the survey camp are as follows:

• Main Objective: To consolidate and update the students’ practical as well as theoretical knowledge of Civil Engineering Survey.
• Specific Objective: To enhance their skill and knowledge in planning, designing, and implementing survey procedures and equipment for various engineering tasks in an integrated way.

The specific objectives listed are:

• Control Surveying: To practice horizontal and vertical control survey with respect to the National grid system and produce a topographic map in the coordinate system.
• Coordinate Transfer: To perform analytical resection and intersection for the transfer of coordinates through the National grid system.
• Road Survey: To practice linear segment survey through Road Alignment Survey.
• Bridge Site Survey: To practice horizontal and vertical control survey surrounding a cross-drainage area (Bridge Site).
• Professional Development: To build confidence in conducting any type of civil engineering survey as per required accuracy and within a given time frame under individual leadership and teamwork.

Answer:

Based on the survey camp standards, the responsibilities include:

• Instrument Verification: Receive all necessary surveying instruments (Theodolite, Total Station, Level, etc.) from the store and thoroughly check them for any defects or maladjustments.
• Accessories Check: Ensure all accessories like tripods, ranging rods, staves, tapes, arrows, and pegs are available and in good working condition.
• Stationery Collection: Collect all necessary field books, level books, graph papers, drawing sheets, and other stationery items required.
• Team Coordination: Brief the team members about the schedule, specific tasks, and gathering point. Ensure all members are present and ready.
• Logistics Preparation: Ensure that personal gears and any camp-specific requirements (like first aid, tents) are arranged.
• Understanding Requirements: Review the “General Instructions” and project objectives to understand the scope of work.

Answer:

The “planning and designing” is a critical phase involving strategic preparation:

1. Reconnaissance (Recce): The first step. The team inspects the assigned area to understand the terrain (topography, slopes, obstacles).
2. Design of Control Network: Based on the Recce, design the network of Major and Minor traverses. This involves selecting suitable station points that are inter-visible and form well-conditioned figures.
3. Selection of Methodology: Deciding on methods for horizontal control (e.g., Closed Traverse) and vertical control (e.g., Fly leveling).
4. Accuracy and Specifications: Planning work to meet accuracy standards (e.g., closing error limits) and determining the scale of plotting (e.g., 1:500).
5. Resource and Time Management: Allocating tasks among team members and scheduling days for specific projects (Traverse, Leveling, Detailing).
6. Equipment Selection: Choosing the appropriate instruments based on the task design.

Answer:

Answer:

The main objectives of traversing are:

• Establish Horizontal Control: To determine the accurate coordinates (N, E) of a series of control points (stations) that form the framework for the survey.
• Fix Boundaries: To determine the lengths and directions of boundary lines of a property or area.
• Detail Surveying: To provide a reference framework from which details of ground features (like buildings, roads, trees) can be located.
• Route Alignment: To survey the alignment for linear projects like roads, railways, canals, and pipelines (typically using open traverse).

Answer:

Traverses are classified into three types:

• Closed Traverse (Loop Traverse):
  • Definition: A traverse that starts from a known point and terminates at the same point.
  • Use: Area control, boundary surveys, and detailed surveys of a specific region.
  • Check: Complete geometrical and mathematical checks are possible (e.g., Σ Interior Angles = (2n-4) × 90°).
• Link Traverse (Connecting Traverse):
  • Definition: A traverse that starts from a known coordinate point (and bearing) and terminates at another different known coordinate point (and bearing).
  • Nature: It is geometrically open but mathematically closed.
  • Use: Used for long strip surveys (highways, railways) where control points are available at both ends to check accuracy.
• Open Traverse:
  • Definition: A traverse that starts from a known point but terminates at an unknown point (does not return to the start or close on a known point).
  • Nature: No direct geometrical or mathematical checks are available.
  • Use: Exploratory surveys, linear works like roads or pipelines where high accuracy is less critical or control points are unavailable.

Answer:

The procedure for traverse surveying involves the following steps:

1. Reconnaissance (Recce): Visit the site to inspect the terrain, identify suitable locations for traverse stations ensuring inter-visibility, and plan the layout (Open or Closed).
2. Selection and Marking of Stations: Select final station positions based on criteria (firm ground, inter-visible). Mark stations permanently using pegs, nails in concrete, or paint marks. Reference the stations so they can be restored if lost.
3. Linear Measurement (Distances): Measure the lengths of traverse legs. Use a tape (chaining) or Electronic Distance Measurement (EDM)/Total Station. Apply necessary corrections (slope, temperature, pull) if using tape.
4. Angular Measurement: Set up the instrument at each station. Measure horizontal angles (interior or exterior) between adjacent legs and the magnetic bearing of the starting line.
5. Computation and Plotting: Check angular misclosure and apply corrections. Compute Latitudes and Departures (L = l cos θ, D = l sin θ). Check linear misclosure, balance the traverse (e.g., Bowditch method), calculate coordinates, and plot.

Answer:

Answer:

When selecting traverse stations, the following criteria should be followed:

• Inter-visibility: Adjacent stations must be clearly visible from each other to allow sighting.
• Firm Ground: The ground should be stable and flat to set up the instrument (tripod) securely.
• Leg Length: Survey lines should be as long as possible to minimize the number of stations and accumulated angular errors.
• Well-Conditioned: Avoid very short legs or extremely acute angles between lines.
• Accessibility: Stations should be easily accessible for the surveyor and equipment.
• Obstacles: Select stations to minimize line-of-sight obstructions (trees, traffic).
• Permanence: Avoid placing stations in areas liable to disturbance, such as the middle of a busy road.

Answer:

• Definition: The leg ratio refers to the ratio of the lengths of adjacent traverse legs (sides).
• Ideal Ratio: Ideally, adjacent legs should be of comparable length (ratio 1:1).
• Limit: In practice, the ratio between the shortest and longest adjacent legs should generally not exceed 1:2 or 1:3. This ensures that the focusing of the telescope remains consistent and centering errors are minimized.

Answer:

If the leg ratio is not maintained (i.e., a very short line is followed by a very long line or vice versa):

• Focusing Errors: The observer has to frequently change the focus of the telescope from infinity (long leg) to near (short leg), which can introduce parallax errors or Line of Collimation errors if the instrument is not perfectly adjusted.
• Sighting Difficulty: It becomes difficult to bisect the target accurately on a very short line compared to a long line.
• Error Propagation: The angular error caused by imperfect centering or bisection is significantly magnified on the shorter leg, reducing the overall accuracy of the traverse.

Answer:

The Short Leg.

Reason: Angular errors due to centering (instrument or signal) are inversely proportional to the length of the sight.

(where α is the angular error, e is the centering error, and D is the distance).

If D (length of leg) is small, the resulting angular error α is large. Therefore, centering and bisection errors on a short leg produce a much larger angular error than the same magnitude of error on a long leg.

Answer:

Answer:

In a closed loop traverse, the angular error is computed by comparing the sum of the measured angles with the theoretical geometric sum of the polygon.

• Sum of Measured Angles: Add all observed interior (or exterior) angles.
• Theoretical Sum: Apply the geometric condition:
  • For Interior Angles: Σθ = (n – 2) × 180°
  • For Exterior Angles: Σθ = (n + 2) × 180°
  • (Where n is the number of sides/stations)
• Determine Error (e): Error = Sum of Observed Angles – Theoretical Sum.
• Check Permissible Limits: The error is compared against the allowable limit (e.g., k√n).

Answer:

The bearing of a traverse leg is calculated using the known bearing of the preceding line and the included angle measured at the station.

Formula (using Back Bearing):

• Sign Convention: Use (+) if the angle is measured clockwise (right) and (-) if measured counter-clockwise (left).
• Check: If the result is > 360°, subtract 360°. If the result is < 0°, add 360°.
• Note: Back Bearing (BB) = Forward Bearing (FB) ± 180°.

Answer:

Consecutive coordinates (also called Dependent Coordinates) are the coordinates of a station defined relative to the preceding station rather than a global origin.

• Latitude (L): Distance measured parallel to the North-South meridian.
  L = l × cos θ
• Departure (D): Distance measured parallel to the East-West line.
  D = l × sin θ

Where l is the length of the traverse leg and θ is its reduced bearing.

Answer:

For a mathematically closed loop traverse, the algebraic sum of all latitudes and departures should equal zero. The closing error is determined by summing them:

• Sum Latitudes: ΣL = L₁ + L₂ + … + L_n
• Sum Departures: ΣD = D₁ + D₂ + … + D_n

If ΣL ≠ 0 or ΣD ≠ 0, a closing error exists.

Answer:

Closing error is the cumulative effect of various errors in the survey work:

• Linear Measurement Errors: Inaccuracies in chaining/taping (incorrect length, sag, temperature, slope).
• Angular Measurement Errors: Inaccuracies in theodolite readings, centering, or leveling.
• Plotting Errors: Inaccuracies in drafting (if graphical).
• Blunders: Mistakes in reading or recording data (e.g., transposing numbers).
• Natural Factors: Refraction, curvature (if ignored), or local attraction affecting compass bearings.

Answer:

Once the total errors in latitude (ΣL) and departure (ΣD) are known:

• Magnitude of Linear Closing Error (e):
  e = √[(ΣL)² + (ΣD)²]
• Direction (Reduced Bearing) of Closing Error (θ):
  θ = tan^-1 | ΣD / ΣL |

The quadrant is determined by the signs of ΣL and ΣD.

Answer:

If the relative precision (closing error / perimeter) exceeds the permissible limit (e.g., 1:2000 for rough surveys):

1. Verify Calculations: Re-check all mathematical computations for latitudes, departures, and bearings.
2. Field Re-survey: If calculations are correct, the error stems from fieldwork. The survey must be repeated to find the source of the error.
3. Reject Data: Large errors usually indicate blunders (gross errors) rather than random errors, so the data cannot simply be adjusted mathematically.

Answer:

Answer:

Independent coordinates (Total Coordinates) are the coordinates of traverse stations defined with respect to a common, fixed origin (0, 0).

• They are calculated by cumulatively adding the adjusted consecutive coordinates (Latitudes and Departures) starting from the known coordinates of the first station.
• They allow any point’s position to be defined uniquely on a grid (Northing, Easting).

Answer:

In Nepal, independent coordinates are used as Northing and Easting to align with the National Grid System based on the Modified Universal Transverse Mercator (MUTM) projection.

• Standardization: It ensures consistency across all national cadastral and topographical maps.
• Positive Values: The system uses a “False Easting” (500,000 m) and “False Northing” (0 m) to ensure all coordinates within the country are positive, avoiding calculation errors associated with negative signs.

Answer:

• Adjustment Requirement: Consecutive coordinates (ΔN, ΔE) must be calculated first to determine the closing error of the traverse.
• Mathematical Integrity: The traverse must be mathematically closed (balanced) by distributing the error into the consecutive coordinates before computing final positions.
• Propagation Prevention: Computing independent coordinates directly from unadjusted consecutive coordinates would result in an “open” figure for a closed loop and propagate errors cumulatively to every subsequent station.

Answer:

After determining the final independent coordinates (N, E) for two stations (e.g., A and B):

• Adjusted Length (L):
  L = √[(N_B – N_A)² + (E_B – E_A)²]
• Adjusted Bearing (θ):
  θ = tan^-1 [ (E_B – E_A) / (N_B – N_A) ]
• The specific quadrant of the bearing is determined by the signs of the numerator (Departure difference) and denominator (Latitude difference).

Answer:

A linked traverse connects two points of known coordinates and bearings. The procedure is as follows:

1. Angular Computation: Calculate bearings of all lines starting from the known initial bearing.
2. Angular Error Check: Calculate the bearing of the final known line using your data. Compare this computed bearing with the actual known bearing of that line. The difference is the angular closing error.
3. Angular Adjustment: Distribute the angular error to all legs (equally or weighted) to correct the bearings.
4. Coordinate Computation: Calculate the consecutive coordinates (Latitudes and Departures) using the adjusted bearings and measured lengths.
5. Linear Error Check: Sum the calculated coordinates to find the position of the closing station. Compare this with the known independent coordinates of the closing station to determine the linear error.
6. Final Adjustment: Apply Bowditch’s or Transit rule to balance the consecutive coordinates and then compute the final independent coordinates.

Answer:

In topographic surveying, details are categorized based on their nature and purpose in map preparation:

Answer:

To generate an accurate contour map, soft detail points must be selected at “controlling points” where the terrain behavior changes. The selection criteria include:

• Change of Slope: Points must be taken at every point where the slope of the ground changes (e.g., from flat to steep, or convex to concave). This ensures that the interpolation between points assumes a uniform slope.
• Ridge and Valley Lines:
  • Ridges: Points must be taken along ridge lines (water dividing lines) to define the outward pointing “U” or “V” shape of contours.
  • Valleys: Points must be taken along valley lines (drainage lines) to define the inward pointing “V” shape of contours.
• Break Lines: Points should be located at the top and bottom of distinct breaks in the terrain, such as embankments, cuttings, retaining walls, or terrace edges.
• Summits and Depressions: Spot levels are required at the highest points (summits) and lowest points (depressions/ponds) to accurately close the innermost contour lines.
• Area Coverage (Grid/Random): On flat or uniformly sloping ground with no distinct features, points should be taken at regular intervals (e.g., 10m to 20m spacing) to ensure full coverage.

Answer:

When using a Tacheometer or Total Station for detailing, the following data is observed and recorded:

1. Station Data (At Instrument Station):
   • Station Name: The identifier of the station occupied.
   • Height of Instrument (HI): Vertical distance from the station peg to the instrument’s trunnion axis.
2. Orientation Data:
   • Back Sight Station: The reference station used for orientation.
   • Back Sight Reading: The horizontal circle reading set at the reference station (usually 0°00’00”).
3. Observation Data (For each Detail Point):
   • Point ID: Sequential number for the detail.
   • Horizontal Angle (θ) / Bearing: Angle measured clockwise from the reference direction.
   • Vertical Angle (α): Angle of elevation (+ve) or depression (-ve) to the point on the staff.
   • Stadia Readings: Top Hair ($S_1$), Middle/Axial Hair ($S_2$), and Bottom Hair ($S_3$). From these, the Staff Intercept ($s = S_1 – S_3$) is derived.
4. Description/Remarks: A clear description is essential for plotting (e.g., “SE corner of House”, “Road Center”, “Change of Slope”).

Answer:

In tacheometric detailing, the Stadia Method is generally used with the staff held vertically. The distances are computed using the following formulas:

Answer:

The primary objectives of the Two-Peg Test are:

• Check for Collimation Error: To determine if the line of sight (line of collimation) of the level is strictly horizontal when the bubble tube is centered.
• Verify Permanent Adjustment: To ensure that the axis of the telescope is parallel to the axis of the bubble tube.
• Quantify Error: To measure the magnitude of the inclination error in the line of sight so that it can be corrected mathematically or mechanically.

Answer:

Procedure:

1. Select Two Points: Choose two firm points (pegs), say A and B, located on fairly level ground, approximately 60 to 100 meters apart.
2. First Setup (Mid-Point):
   • Set up the level exactly at the mid-point C between A and B (AC = CB).
   • Take staff readings on A (h_a1) and B (h_b1).
   • Since distances are equal, errors cancel out. Calculate True Difference (H):
     H = h_a1 – h_b1
3. Second Setup (Near One Peg):
   • Move the instrument to point D, very close to one peg (e.g., close to A).
   • Take readings on A (h_a2) and B (h_b2).
   • Calculate Apparent Difference (H’):
     H’ = h_a2 – h_b2
4. Comparison:
   • If H = H’, the instrument is correct.
   • If H ≠ H’, the line of collimation is inclined and requires adjustment.

Answer:

Yes, the instrument can still be used for leveling.

How to use it:

• Method of Balancing Sights: The surveyor must strictly maintain the Back Sight (B.S.) distance equal to the Fore Sight (F.S.) distance for every setup.
• Reasoning: Collimation error is directly proportional to distance. If the horizontal distances to the Back Sight and Fore Sight are equal, the error in both readings will be identical.
• Cancellation: When calculating the difference in elevation, the errors cancel out:
  dH = (B.S._obs + e) – (F.S._obs + e) = B.S. – F.S.

Answer:

• Connecting Benchmarks: To connect a newly established Benchmark (BM) to the starting point or a National Grid Benchmark.
• Checking Accuracy: To run a line of levels from the end of a survey back to the starting Benchmark (Check Leveling).
• Rough Determination: To determine the approximate reduced levels (R.L.) of points rapidly.
• Long Distance Transfer: To transfer a level over a long distance where intermediate precision is not the primary concern.

Answer:

• Equalize Distances: Keep Back Sight and Fore Sight distances approximately equal to eliminate collimation and earth curvature errors.
• Stable Change Points: Select firm, stable ground for Turning Points to prevent staff sinking.
• Vertical Staff: Ensure the leveling staff is held strictly vertical using a bubble level.
• Avoid Long Sights: Limit sight length (generally under 100m) to minimize reading and refraction errors.
• Check Loop: Close the level circuit back to a known benchmark to detect errors.

Answer:

Meaning: Balancing of sights refers to the practice of keeping the horizontal distance between the instrument and the Back Sight station equal to the distance between the instrument and the Fore Sight station (D_BS = D_FS).

Why it is required:

• Elimination of Collimation Error: Ensures the vertical error is the same for both readings and cancels out during subtraction.
• Elimination of Curvature Error: Cancels the error caused by earth’s curvature, which depends on distance (0.0785 D²).
• Minimization of Refraction Error: Helps minimize atmospheric refraction errors, which are roughly proportional to distance squared.

Answer:

• Lower Limit (0.6 m):
  • Minimize Refraction: The air layers closest to the ground (bottom 0.5m) are affected by heat radiation, causing “shimmer” and erratic refraction.
  • Visibility: Grass or small obstacles often obstruct views near the ground.
• Upper Limit (2.0 m):
  • Verticality Error: Reading higher on the staff magnifies errors caused if the staff is not perfectly vertical.
  • Stability: The top of an extended staff is more prone to swaying in the wind, making accurate reading difficult.

Answer:

The error of closure is the difference between the theoretically known elevation and the computed elevation.

• For a Closed Loop: (Start and end at same point)
  Error = Σ B.S. – Σ F.S.
  (Ideally, this sum should be zero).
• For Connecting Two Benchmarks:
  Error = (Σ B.S. – Σ F.S.) – (R.L._Last – R.L._First)

Answer:

The permissible error of closure (E) is calculated using the formula:

E = ±C√K

• E: Error in millimeters.
• K: Distance leveled in kilometers.
• C: A constant depending on precision.

For Fly Leveling (rough leveling), the constant C is typically between 24 and 100 (Commonly ±24√K mm).

Answer:

• Equalize Sights: Keep Back Sight and Fore Sight distances equal.
• Short Sights: Limit sight lengths (e.g., < 60-80 meters) to minimize curvature of the ray.
• Avoid Ground Heat: Take readings at least 0.5m – 1.0m above ground to avoid refractive air layers.
• Timing: Avoid leveling during hot midday hours when air “shimmering” is maximum. Work in early morning or late afternoon.

Answer:

To eliminate collimation error, the surveyor must ensure Balancing of Sights.

• The instrument is set up such that the distance to the Back Sight is equal to the distance to the Fore Sight.
• By making D_BS = D_FS, the error e becomes identical for both readings.
• When calculating rise or fall, the error cancels completely:
  (BS + e) – (FS + e) = BS – FS

Answer:

• Circular Bubble: Attach a small circular spirit level (bull’s eye bubble) to the staff to ensure it is plumb.
• Plumb Bob: The staff holder uses a plumb bob to check verticality.
• “Wave” the Staff: The staff holder slowly rocks the staff towards and away from the instrument. The surveyor records the minimum reading, which corresponds to the true vertical position.

Answer:

• Definition: A turning plate (change plate) is a heavy metal plate with sharp claws and a raised central stud.
• Purpose: Used on soft, sandy, or unstable ground to provide a stable base.
• Function: It prevents the staff from sinking into the soil while the instrument is moved from one setup to the next, ensuring the elevation of the Change Point remains constant.

Answer:

Three-wire readings (Top, Middle, Bottom hairs) are required for:

• Accuracy Check: Provides an arithmetic check. Middle reading should equal approximately (Top + Bottom) / 2.
• Distance Measurement: Allows calculation of distance using stadia principles:
  Distance = 100 × (Top – Bottom)
• Balancing Sights: Enables immediate distance calculation to ensure Back Sight and Fore Sight distances are equal.

Answer:

The error is distributed cumulatively and proportionally to the station number (assuming equal distances).

Correction Formula: For the n^th station out of N total stations:

Correction_n = -e × (n / N)

Application:

• Correction per station factor (k) = -e / 15
• Station 1 Correction: 1 × k
• Station 2 Correction: 2 × k
• Station 15 Correction: 15 × k (equals -e)

Answer:

Definition: A precise method used to determine the elevation difference between two points separated by an obstacle (like a wide river) where setting the instrument midway is impossible.

Objective:

• To accurately transfer a Reduced Level (RL) across a wide gap.
• To eliminate systematic errors caused by Collimation, Earth’s Curvature, and Refraction, which cannot be eliminated by standard balancing of sights in this scenario.

Answer:

Procedure: Let A and B be points on opposite banks.

1. Setup 1 (Near A): Set level near A. Read staff on A (h_a) and B (h_b).
   Diff = h_a – h_b.
2. Setup 2 (Near B): Shift level to near B. Read staff on A (h’_a) and B (h’_b).
   Diff = h’_a – h’_b.
3. Calculation: The True Difference (H) is the mean of the two apparent differences:
   H = [(h_a – h_b) + (h’_a – h’_b)] / 2

Answer:

Accurate vertical control is critical for bridge alignment, necessitating reciprocal leveling because:

• Impossible to Balance Sights: The instrument cannot be placed midway over the water, violating the primary rule of leveling.
• Large Errors: Long sights across water amplify curvature errors (0.0785 D²) and collimation errors.
• Variable Refraction: Air over water bodies has different densities, causing significant refraction issues. Reciprocal leveling mathematically neutralizes these combined errors.

Answer:

Principle: The principle of a road survey is to locate the best feasible route between two terminal points that is short, safe, easy, and economical, satisfying social and engineering requirements. It involves working from the whole to the part, starting with a broad study of the area and narrowing down to the final specific alignment.

Procedure: The road survey is generally carried out in the following four stages:

• Map Study: Topographical maps (contours, natural features) are studied to identify possible routes. Tentative alignments are marked avoiding obstructions like steep hills or ponds, and gradients/obligatory points are checked roughly.
• Reconnaissance Survey: A field inspection is done along the tentative routes. Instruments like a compass, Abney level, or pedometer are used to collect details of terrain, soil conditions, and river crossings. The most feasible route is selected.
• Preliminary Survey: A detailed survey of the selected route to finalize geometric features. A traverse (P-line) is run using a theodolite and tape/EDM. Levelling (L-section and X-section) is performed to estimate earthwork, and the alignment is refined on paper.
• Final Location Survey: The centerline of the final approved alignment is transferred from the map to the ground. Intersection Points (IPs) are established, curves are set out, and detailed geometric design is implemented.

Answer:

The outputs typically include:

• Route Plan / Map: A topographic map showing the road corridor, centerline, physical features, and property lines.
• Longitudinal Section (L-Section): A profile showing the ground level and the proposed formation level along the centerline, determining cuts and fills.
• Cross-Sections (X-Sections): Profiles perpendicular to the centerline at regular intervals (e.g., 15m or 20m), used to calculate earthwork volume.
• Quantity Estimates: Calculations of cut and fill volumes.
• Project Report: A detailed document containing design criteria, cost estimates, soil reports, and specifications.

Answer:

• Short: The route should be as direct and straight as possible between terminal stations to minimize travel time and cost.
• Easy: The alignment should follow the natural terrain to provide easy gradients and curves.
• Safe: The road must provide adequate sight distance and stability, avoiding hazards like landslides.
• Economical: The total cost (construction, maintenance, and vehicle operation) should be minimized by balancing cut and fill.

Answer:

• Obligatory Points: Must pass through positive points (bridges, towns) and avoid negative ones (landslides, religious sites).
• Geometry: IPs should allow for suitable curve radii and easy gradients, avoiding sharp deflection angles.
• Intervisibility: Adjacent IPs must be intervisible to facilitate surveying.
• Terrain: The line should generally follow contours to minimize earthwork.
• River Crossings: Crossings should be at right angles (90°) for the shortest bridge span.
• Sustainability: Avoid unstable slopes and marshy lands.

Answer:

Chainage increases continuously from the starting point. When a curve is introduced, adjustments are made along the curve path.

1. Chainage of IP: Add distance from previous station to the IP.
   $$\text{Chainage of IP} = \text{Chainage of Previous Station} + \text{Distance (Station to IP)}$$
2. Calculate Tangent Length (T):
   $$T = R \tan(\frac{\Delta}{2})$$
3. Beginning of Curve (BC): Subtract tangent length from IP chainage.
   $$\text{Chainage of BC} = \text{Chainage of IP} – T$$
4. Length of Curve (L):
   $$L = \frac{\pi R \Delta}{180^\circ}$$
5. End of Curve (EC): Add curve length to BC chainage.
   $$\text{Chainage of EC} = \text{Chainage of BC} + L$$

Note: You cannot calculate EC by adding T to IP, as the arc length is shorter than the sum of the two tangents.

Answer:

Given $R$ = Radius and $\Delta$ = Deflection angle:

• Tangent Length ($T$): Distance from IP to tangent points.
  $$T = R \tan\left(\frac{\Delta}{2}\right)$$
• Length of Curve ($L$): Length of arc from BC to EC.
  $$L = \frac{\pi R \Delta}{180^\circ}$$
• Apex/External Distance ($E$): Distance from Mid Point of Curve (MC) to IP.
  $$E = R (\sec\left(\frac{\Delta}{2}\right) – 1)$$

Answer:

• Positive Obligatory Points: Control points through which the road alignment must pass due to strategic, commercial, or technical reasons.
• Negative Obligatory Points: Control points or areas that the road alignment must not pass through due to safety, cost, or social restrictions.

Answer:

Positive: Bridge sites (stable banks), intermediate towns/villages (connectivity), mountain passes (lowest crossing point).

Negative: Religious sites (temples, graveyards), unstable terrain (landslides, marshy land), costly structures, and protected wildlife areas.

Answer:

The deflection angle ($\Delta$) is the angle between the prolongation of the preceding survey line (back tangent) and the forward survey line. It indicates how much the route deviates from a straight line. It ranges from $0^\circ$ to $180^\circ$ and can be Right (+ve) or Left (-ve).

Answer:

1. Set up the theodolite at the IP and level it. Set Vernier A to $0^\circ00’00″$.
2. Sight the Back Station using the lower clamp.
3. Transit (plunge) the telescope so it points along the prolongation of the back line.
4. Release the upper clamp and turn the telescope to bisect the Forward Station.
5. Read the angle on Vernier A. This is the Deflection Angle ($\Delta$).
6. Note if the turn was to the Right ($R$) or Left ($L$).

Answer:

• Right-Hand Deflection (+ve): The forward survey line deviates to the right (clockwise) of the prolongation of the previous line.
• Left-Hand Deflection (-ve): The forward survey line deviates to the left (anti-clockwise) of the prolongation of the previous line.

Answer:

To establish the MC, we bisect the internal angle ($I$) at the IP. When $0^\circ$ is set on the Back Station:

• The internal angle lies on the “inside” of the traverse bend.
• For a Left deflection, the formula typically used is: Angle to set = $90^\circ + \frac{\Delta}{2}$.
• This sets the line of sight along the bisector of the internal angle relative to the back station line.

Answer:

For a Right-Hand deflection, with $0^\circ$ set on the Back Station:

• The internal angle is on the right side.
• The formula typically used is: Angle to set = $90^\circ – \frac{\Delta}{2}$.
• This points the telescope along the apex line to the MC.

Answer:

The 15m multiple peg (chainage peg) is skipped. The BC and EC are critical geometric points that must be surveyed and plotted. If a regular chainage peg falls very close (e.g., within 3m) to the BC or EC, the regular peg is omitted to avoid congestion and redundancy in the data.

Answer:

• Safety & Visibility: Ensures vehicles enter the bridge straight, maximizing visibility and minimizing collision risk with railings.
• Structural Stability: Avoids centrifugal forces acting on the vehicle/bridge structure at the entry point.
• Ease of Construction: Simplifies the joint construction between the road embankment and the bridge abutment.

Answer:

• Setup: Level theodolite at IP. Verify deflection angle $\Delta$.
• Locating BC: Measure the calculated Tangent Length ($T$) from the IP backwards along the back tangent. Drive a peg.
• Locating EC: Measure the same Tangent Length ($T$) from the IP forward along the forward tangent. Drive a peg.
• Locating MC:
  • Calculate Apex Distance ($E$).
  • Bisect the internal angle at IP.
  • Measure distance $E$ from IP along this bisector. Drive a peg.

Answer:

The Ruling Gradient (Design Gradient) is the maximum gradient allowed on the road alignment for general design conditions (e.g., 7% or 1 in 14.3 for hill roads). It balances vehicle performance with construction economy.

Answer:

• Longitudinal Section (L-Section): Horizontal 1:1000; Vertical 1:100 (Exaggerated).
• Cross-Section (X-Section): 1:100 (Same for horizontal and vertical to preserve land shape).

Answer:

The Stepping Method is used in steep terrain. Horizontal distance is measured in small “steps” using a tape held horizontally, and the vertical difference for each step is measured using a staff or tape drop. The total distances are the sum of the individual steps.

Answer:

• Steep Hill Slopes: Where slopes are too steep to hold a tape along the ground.
• Rough/Broken Ground: Where terrain is irregular.
• Vegetated Areas: Where line of sight is obstructed.

Answer:

1. Select two accessible points $A$ and $B$ on the back and forward tangents respectively. Measure distance $AB$.
2. Measure angles $\angle PAB$ and $\angle PBA$.
3. Calculate deflection angle $\Delta = \angle PAB + \angle PBA$.
4. Solve $\triangle PAB$ using Sine Rule to find $AP$ and $BP$:
   $$AP = \frac{AB \sin(\angle PBA)}{\sin(180^\circ – \Delta)}$$
5. Calculate Tangent Length ($T$).
6. Locate BC by measuring $(T – AP)$ backward from $A$. Locate EC by measuring $(T – BP)$ forward from $B$.

Answer:

Gradient is the rate of rise or fall calculated as:

Obtain ground RLs from leveling data, calculate chainage difference, and apply the formula.

Answer:

• Traverse Data: Lengths and bearings of survey lines.
• Chainage: Of all stations and detail points.
• Side Widths: Left and Right corridor widths.
• Details: Offsets and chainages of features (houses, trees, streams).
• Bearings: Magnetic North orientation.

Answer:

A horizontal curve is provided at every Intersection Point (IP) where the road alignment changes its horizontal direction, ensuring a smooth transition between straight tangents.

Answer:

A vertical curve is provided at points where there is a change in the gradient (vertical alignment).

• Summit Curve: Up-grade meets Down-grade (Convex).
• Valley/Sag Curve: Down-grade meets Up-grade (Concave).

Answer:

Designing the formation level involves drawing the grade line on the L-Section:

• Plot ground profile (L-Section).
• Draw a proposed grade line that balances Cutting and Filling (Equalizing Earthwork) for economy.
• Ensure gradient does not exceed the Ruling Gradient.
• Maintain minimum clearance over High Flood Levels (HFL).

Answer:

The main objectives are:

• Site Selection: To select the most suitable site and alignment (axis) for the proposed bridge based on technical and economic factors.
• Topographic Mapping: To prepare a detailed topographic map of the bridge site, including the river banks and bed, to aid in design.
• Determination of Span: To accurately determine the length of the bridge axis (river width) which defines the required span of the bridge.
• Hydrological Data Collection: To collect essential hydrological data such as the High Flood Level (HFL), Normal Water Level (NWL), discharge, and flow direction.
• River Training: To determine the extent of river training works (like guide bunds) required, based on upstream and downstream river conditions.
• Design Parameters: To provide necessary data regarding the nature of the river bed and banks for the design of the foundation and substructure.

Answer:

The procedure generally involves the following steps:

1. Reconnaissance: A preliminary inspection of the area is conducted to identify tentative suitable sites for the bridge crossing.
2. Site Selection: The best site is chosen based on criteria like stable banks, narrow width, and straight river reach.
3. Fixing Bridge Axis: The centerline of the bridge (Bridge Axis) is marked on the ground using ranging rods. Two stations (e.g., A and B) are fixed on opposite banks along this axis.
4. Horizontal Control (Triangulation):
   • Since direct chaining across the river is often impossible, a triangulation network is established.
   • A Base Line is set out on one or both banks (perpendicular to the axis if possible).
   • Angles are measured carefully using a theodolite to form well-conditioned triangles.
5. Vertical Control (Leveling):
   • Fly Leveling: A Reduced Level (RL) is transferred from the nearest Permanent Bench Mark (BM) to a Temporary Bench Mark (TBM) at the site.
   • Reciprocal Leveling: Levels are transferred across the river to establish a TBM on the opposite bank, eliminating errors due to curvature and refraction.
6. Detailing: A topographic survey is conducted to locate details (banks, vegetation, structures) and take spot levels for contours. This typically covers 150m-200m upstream and 50m-100m downstream.
7. L-Section and X-Section:
   • Longitudinal Section: Levels are taken along the bridge axis and river bed center line.
   • Cross Sections: Levels are taken across the river at regular intervals (e.g., every 25m) upstream and downstream.
8. Data Collection: Recording HFL, nature of soil, and flow velocity.

Answer:

The site for a bridge axis should satisfy the following criteria:

• Narrow Width: The width of the river should be minimum to reduce the length of the bridge and overall cost.
• Straight Reach: The river reach should be straight for a sufficient distance upstream and downstream to ensure smooth flow.
• Stable Banks: The banks should be firm, permanent, high, and not liable to erosion. Rocky banks are ideal.
• Square Crossing: The bridge axis should preferably cross the river at right angles (90°) to the flow direction to minimize pier width and avoid skew bridge design.
• Good Approaches: The site should allow for easy and economical construction of approach roads on both sides.
• Foundation Conditions: The river bed should offer good soil strata or rock at a reasonable depth for a safe foundation.
• Velocity: The flow velocity should be moderate; it should not be so high as to cause heavy scour, nor so low as to cause silting.

Answer:

Why Triangulation is used: Triangulation is used because direct linear measurement (chaining or taping) of the bridge axis is often impossible or inaccurate due to the water body, difficult terrain, or width of the river. It allows the surveyor to calculate the unknown distance (bridge span) by measuring a base line on firm ground and observing angles.

How to establish the network:

1. Fix Control Points: Establish two stations (A and B) on the bridge axis on opposite banks.
2. Set Base Line: Lay out a base line (e.g., AC or BD) on one or both banks. The base line should be measured with high precision and ideally be perpendicular to the bridge axis.
3. Form Triangles: Connect the base line stations to the bridge axis stations to form triangles (e.g., Triangle ABC).
4. Condition: Ensure the triangles are “well-conditioned” (angles between 30° and 120°) to minimize geometric errors during calculation.
5. Observation: Measure all internal angles of the triangles and the length of the base line to compute the bridge axis length using trigonometric rules.

Answer:

The length is determined computationally using the Sine Rule applied to the triangulation network.

Formula: In a triangle ABC, where side b (Base Line AC) is known and angles A, B, and C are measured:

Calculation Step: To find the side c (Bridge Axis AB):

Note: The specific angles A, B, C depend on how the triangle is labeled. The logic is: Unknown Side = Known Side × (sin(Angle opposite Unknown) / sin(Angle opposite Known)).

Answer:

The precision is determined by comparing values obtained from two independent calculations.

• Two separate base lines are often used (one on each bank), or two different triangles are formed.
• The length of the bridge axis is calculated independently from both sets of data.
• The discrepancy between the two computed lengths must be within the permissible limit (e.g., 1 in 1000 to 1 in 2000).

Answer:

• Definition: A well-conditioned triangle is one in which no angle is less than 30° and no angle is greater than 120°. An equilateral triangle (60° each) is the ideal well-conditioned triangle.
• Requirement: It is required because the accuracy of the computed side lengths depends on the shape of the triangle. In ill-conditioned triangles (very acute or obtuse angles), a small error in measuring the angle causes a large error in the calculated length (due to the rapid change in the sine function near 0° and 180°). Well-conditioned triangles ensure reliable results.

Answer:

The precision of the base line measurement is typically required to be 1 in 2000 or better. The angular measurements in the base triangle must also be highly precise, often with a permissible discrepancy of no more than a few seconds (e.g., ± 20″) depending on the instrument used.

Answer:

For the base triangles (which directly determine the bridge axis length), a higher degree of precision is required. Therefore, generally 2 to 4 sets of horizontal angles (Face Left and Face Right) are measured. In most standards, 2 sets are the minimum requirement, but 4 sets are recommended for higher accuracy.

Answer:

For subsidiary triangles (used for detailing or extending control away from the main axis), 1 to 2 sets of angles are typically sufficient. A single set (one Face Left and one Face Right observation) is the minimum standard.

Answer:

The upstream coverage area (typically 150m – 200m) is longer than the downstream area (typically 50m – 100m) because:

• Flow Characteristics: The nature of the river flow approaching the bridge (velocity, direction, meandering) critically affects the safety of the bridge.
• River Training Works: Engineers need extensive data upstream to design river training works (like guide bunds and spurs) that guide the water smoothly through the bridge vent and prevent outflanking.
• Scour Protection: The potential for scour is heavily influenced by the upstream approach of the water.

Answer:

• Free Board: It is the vertical margin or clearance provided between the High Flood Level (HFL) and the lowest point of the bridge superstructure (soffit). It acts as a safety factor against unforeseen floods, wave action, and floating debris.
• Reasonable Height: A reasonable height for free board is typically 1.2 m to 1.5 m. It generally should not be less than 1.0 m for important bridges.

Answer:

Guide points (interpolated points) are located to trace the path of contour lines between spot levels.

• Grid/Radial Method: Spot levels are taken at regular grid intervals or radial rays.
• Interpolation: The position of a specific contour elevation (e.g., 100m) is located between two spot levels (e.g., 99.5m and 100.5m) using linear interpolation.
• Formula:
  x = [ (Hc – H1) / (H2 – H1) ] × D
  Where x is distance from the first point, Hc is contour level, H1 and H2 are spot levels, and D is horizontal distance.

Answer:

L-Section (Longitudinal Section):

• Data: Elevations of the river bed along the center line (upstream to downstream).
• X-axis: Chainage. Scale usually 1:500 to 1:1000.
• Y-axis: Reduced Levels. Scale usually 1:50 to 1:100 (exaggerated vertical scale).

X-Section (Cross Section):

• Data: Elevations of the river bed across the river at the bridge axis.
• X-axis: Distance from center line (Left Bank to Right Bank).
• Y-axis: Reduced Levels.
• Scale: Usually plotted at a natural scale (Horizontal = Vertical), e.g., 1:100 or 1:200, to accurately represent the channel area for discharge calculations.

Answer:

Cross-drainage structures are constructed when a canal crosses a natural drainage or a road/railway crosses a water body.

Road/Bridge Context:

• Culvert: Span less than 6m.
• Minor Bridge: Span between 6m and 60m.
• Major Bridge: Span greater than 60m.
• Causeway: A submersible road crossing.

Irrigation/Canal Context:

• Aqueduct: Canal carried over drainage (HFL of drainage < Bed level of canal).
• Syphon Aqueduct: Canal carried over drainage, but water flows under pressure (HFL of drainage > Bed level of canal).
• Super Passage: Drainage carried over canal (FSL of canal < Bed level of drainage).
• Canal Syphon: Drainage carried over canal, flowing under pressure.
• Level Crossing: Canal and drainage meet at the same level.

Answer:

Objectives of Intersection:

• Mapping Inaccessible Points: To determine the coordinates of points that are difficult or impossible to occupy physically (e.g., mountain peaks, towers, far banks of a river) by observing them from at least two known control stations.
• Densification of Control Points: To increase the number of control points in a survey area without traversing. This is often used to check the accuracy of existing traverse points.
• Detail Surveying: To locate specific details, such as building corners, trees, or landmarks, during a plane table or total station survey.

Objectives of Resection:

• Locating Instrument Station: To determine the coordinates of the current instrument station (which is unknown) by observing at least three known control stations.
• Establishment of New Control: To quickly set up a station at a convenient location (Free Station) and tie it into the existing coordinate system without starting a traverse from a known point.
• Orientation Verification: It serves as a method to verify the orientation and position of the instrument before commencing detail works in construction surveying.

Answer:

Answer:

A local area map must be compatible with national grid coordinates for the following reasons:

• Uniformity and Standardization: It ensures that the local survey fits seamlessly into the national framework, allowing different projects across the country to be referenced to a single common datum.
• Connectivity: It allows the local map to be connected or mosaicked with adjacent maps without gaps or overlaps.
• GPS Integration: Modern surveying relies heavily on GNSS (GPS). National grids are usually tied to global datums (like WGS84), making it easier to utilize satellite positioning data directly.
• Infrastructure Planning: For large-scale linear projects like highways, railways, or transmission lines that span long distances, a unified coordinate system is essential to align local segments.
• Legal Validity: Land ownership and cadastral surveys often require referencing to the national grid for legal dispute resolution and exact boundary definition.

Answer:

A. Field Procedure of Intersection

Intersection involves observing an unknown point P from two known stations A and B.

1. Setup at A: Set up the Theodolite or Total Station at known station A. Level and center it accurately.
2. Orientation: Backsight to another known station to orient the instrument (or measure the angle relative to the line AB).
3. Observation: Sight the unknown point P and measure the horizontal angle α (Angle BAP).
4. Setup at B: Shift the instrument to known station B. Level and center it.
5. Observation: Sight station A and then the unknown point P. Measure the horizontal angle β (Angle ABP).
6. Calculation: Use the Sine Rule in ΔABP with the known length AB (calculated from coordinates) to find lengths AP and BP, and subsequently compute the coordinates of P.

B. Field Procedure of Resection

Resection involves occupying the unknown point P and observing three known stations A, B, and C.

1. Setup at P: Set up the instrument at the unknown point P. Level and center it.
2. Observation A: Sight the first known control point A and set the horizontal circle reading (typically 0° or a known bearing).
3. Observation B: Rotate the telescope to sight the second known point B. Record the horizontal angle α (Angle APB).
4. Observation C: Rotate the telescope to sight the third known point C. Record the horizontal angle β (Angle BPC).
5. Calculation: The coordinates of P are calculated using the “Three-Point Problem” analytical methods (such as Tienstra’s method or Collins’ method) based on the known coordinates of A, B, C and the observed angles α and β.

Answer:

Horizon Close (or “Closing the Horizon”) is a field procedure and error check used when measuring multiple horizontal angles from a single station.

• Procedure: After measuring angles to various target points (A, B, C, D…) sequentially around the circle, the surveyor takes a final sight back to the initial station (A).
• Condition: The sum of all the individual angles measured around the station should theoretically equal exactly 360°.
• Error Check: If the sum is not 360°, the difference is the “horizon closure error.”
• Adjustment: This error is typically distributed equally among all the observed angles to mathematically “close” the horizon before using the data for computations.

Answer:

Yes, it is possible.

If the Total Station lacks a prism (meaning the EDM cannot measure distance to a standard pole) and there is no leveling staff (preventing standard leveling or stadia methods), the job can be performed using Trigonometric Leveling.

There are two cases:

• Reflectorless Total Station: Modern Total Stations can measure distance to any surface directly.
• Standard Total Station (Non-reflectorless): Requires manual distance measurement (this is the challenging scenario assumed for this question).

Assuming the standard scenario where EDM cannot be used, the procedure is as follows:

Field Procedure:

1. Setup: Set up the Total Station at the first point (Instrument Station, $A$). Level and center it accurately over the station peg.
2. Height of Instrument (HI): Measure the vertical height from the ground peg at $A$ to the optical center (axis) of the instrument using a tape measure. Let this be $HI$.
3. Horizontal Distance (D): Since there is no prism to use the EDM, measure the horizontal distance between point $A$ and point $B$ using a measuring tape. Let this distance be $D$.
4. Targeting: Sight the Total Station telescope towards point $B$. Since there is no staff or prism pole, sight the crosshair directly to the ground mark (peg/nail) at point $B$. This implies the Height of Target ($HT$) is $0$.
5. Observation: Read the Vertical Angle from the display. If the instrument gives the Zenith angle ($z$), calculate the vertical angle ($\alpha = 90^\circ – z$).

Calculation:

The difference in elevation ($\Delta V$) is calculated using trigonometry:

$$ \Delta V = D \times \tan(\alpha) $$

The Reduced Level ($RL$) of point $B$ is determined by:

$$ RL_B = RL_A + HI + \Delta V – HT $$

Since we sighted the ground, $HT = 0$, so:

$$ RL_B = RL_A + HI + D \tan(\alpha) $$

Note: For very long distances, corrections for curvature and refraction ($C_{cr}$) should be subtracted from the reading.