Saturday, May 25, 2019

Professional Bridge Site Survey: Technical Norms and Specifications

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Bridge Site Survey:

1. Carry out reconnaissance survey of the bridge site area. Establish necessary triangulation stations to determine Bridge Axis Length, as well as horizontal and vertical control of the area. Well condition triangles should be formed while selecting the triangulation stations.

2. In triangulation, distance of Base Line must be measured in an accuracy of 
1: 2000.

3: Observed two sets of horizontal circle reading by the theodolite to measure the angle of base triangles. Note that the difference between the mean angles of two sets should be within a minute. Angular misclosure for base triangle should be
±30" (N^0.5) and other triangle ±1'(N^0.5)

4. Compute the length of proposed bridge axis by triangulation survey from two adjacent base triangles by using sine law and determine the length of bridge axis by taking average length. Computed mean length of bridge axis from two base triangles should be >=1:2000.

5. Conduct fly levelling to transfer the R.L. from given BM to the nearest triangulation station of the bridge axis and make circuit close for checking error of closure.

6. Carry out reciprocal levelling to transfer level from one bank to other bank of the river / stream within a precision of ±25(K^0.5) mm. Determine the RL of the other triangulation stations by fly levelling from the end point of bridge axis.

7. Plot a topographic map indicating contour lines at suitable interval (contour interval =1m). Interpolate the Index Contour lines precisely by arithmetic calculation method with the help of the guide points and then interpolate remaining contour lines either by graphical method on by estimation method. Do not erase RL of guide points in the original sheet even after plotting of contours.
Note: Value of Index Contour Multiple of (5* Contour interval)
8. Draw longitudinal section along the river bed up to 150m up-stream and 50m down-stream. Assuming 0.00 at centre of bridge axis. Draw cross section at 25m interval from topographic map and one at the bridge axis.

Scale for plotting
a. Topographic map: 1:500
b. L-section: Horizontal Scale 1:500 and Vertical scale 1:50
c. Cross section: Horizontal scale 1:50 and Vertical scale 1:50

9. Carry out hydrological survey of river/stream. Collect hydraulic data such as velocity of flow, high flood level, normal water level and low water level. All these should be shown in map and cross section of river. All these should be shown in map and cross section of river.

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1. Professional Topographic Survey

2.Professional Road Alignment Survey
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