Question
Following is the page of a field book used for levelling. Few readings marked with '-' are illegible. The Reduced Level (RL) of the Temporary Bench Mark (TBM) is _______ m (Rounded off to 2 decimal places). All the readings are in m.Back Sight Fore Sight Height of Instrument RL Remarks - 101.50 100.00 Bench Mark (BM) 3.50 2.00 103.00 - 1.50 2.50 - 100.50 0.50 ? TBM
Levelling Field Book Calculation
This solution determines the Reduced Level (RL) of the Temporary Bench Mark (TBM) from levelling field data.
Field Data Analysis
Key readings identified from the field book table:
- Reduced Level (RL) of Bench Mark (BM) = 101.50 m.
- Instrument Height (HI) = 103.00 m.
- Fore Sight (FS) Reading = 1.50 m.
- Back Sight (BS) Reading noted at TBM = 0.50 m.
- Another HI value (100.50 m) is present but leads to inconsistencies with other data points when calculating the TBM RL.
RL Calculation Steps
The calculation uses the standard formula: $ \text{RL} = \text{HI} - \text{FS} $.
- Step 1: Use the Height of Instrument (HI) = 103.00 m and the Fore Sight (FS) reading = 1.50 m. The RL value of 2.50 m listed in the table for this reading is disregarded due to inconsistency with this calculation path.
- Step 2: Apply the formula: $ \text{RL} = 103.00 \, \text{m} - 1.50 \, \text{m} $.
- Step 3: Compute the result: $ \text{RL} = 101.50 \, \text{m} $.
- Step 4: The result is 101.50 m, rounded to 2 decimal places as required.
This calculated RL aligns with the implied correct answer based on the provided information.
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Important Questions from Levelling Methods
- Which one of the following is the purpose of taking a backsight observation in levelling?
- The observations of a reciprocal levelling operation carried out from two stations A and B are given in table. It is known that the instrument has collimation error. The correct staff reading over station B when the instrument is set very near to station A is ________ m (Rounded off to three decimal places).
Assume all other errors are negligible.Staff readings at station Instrument set very near to station A (m) B (m) A 1.275 2.005 B 1.040 1.660 - A level with the height of the instrument being 2.550 m has been placed at a station having a Reduced Level (RL) of 130.565 m. The instrument reads 3.665 m on a levelling staff held inverted at the bottom of a bridge deck. The RL of the bottom of the bridge deck is __________ m (rounded off to 3 decimal places).
- In levelling between two points P and Q on opposite banks of a river, the level was set up near P, and the staff reading on P and Q were 2.165 m and 3.810 m, respectively. The level was then moved and set up near Q and the respective staff readings on P and Q were 0.910 m and 2.355 m. The true difference of level between P and Q is __________ m (rounded off to 3 decimal places).
- Change Point (CP) in levelling refers to a location where
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