As a part of the Railway Electrification series, I will explain the railway line survey with interesting examples.
Now, as you are aware of some basic terms railway construction. After reading some prerequisite information, you will be able to perform a survey of the track.
We have already learned the terms in railway surveying and foundation types.
Railway Line Survey with an Example
Railway surveying is usually done in two steps/stages.
Survey Step 1: Marking of chainage for LOP and CSD
First is done for making layout plan (LOP) and cross-sectional drawing (CSD), (the first step is again
repeated, if there is a climatic change or there is a gap of 5-6 months due to certain reason like lockdown before initiating the foundation excavation work, then it is again done for verification of the site conditions as per the recorded data obtained during the first step. If there is any change, which may affect the type of foundation assigned by the designer then LOP is again corrected and then handover to the site engineer for further excavation work).
Note: Before the first step, the local civil team from the soil investigation department, used to provide the soil pressure, wind pressure to the designer as it is also taken into consideration before assigning the foundation type.
The designer after considering all the factors, assigned every foundation a three-digit code which implies soil bearing capacity and the vertical load the mast can bear. On that basis, if in the future there is a difference in the site conditions then the designer can change it by checking the volume chart.
Let’s move to the first step done by the surveyor using an example:
The project is started and the person is assigned to survey from 0km of the region. So, the engineer must carry, 30m measuring tape, thread, pen, and notebook.
If he is at 0/0, he needs to measure the clear span as per the site condition for instance. If the clear span is 45m (usually in multiples of 4.5), so after 45m, he must ensure there is no signal mast, bridge, platform, rob, culvert.
If there is any type of construction, he must have to change the span in the multiple of 4.5 to avoid the construction as due to that construction site engineer is not able to excavate the foundation.
And also rules do not allow to excavate the site, this is the first and most challenging task in the project.
1km = 1000m
1000/45 = 22.2 foundation (will be 22 after changes due to avoidance of so rules).
During the survey, he needs to observe and write the details of the bridge starting chainage and ending.
So that, it could be depicted in a LOP. Similarly, with the ROB, LC Gates, CULVERT, he needs to note every detail before planning for the LOP as the site engineer would just rely on the data given in LOP.
If there is an error, the company executing the work would face heavy loss. (The labour employed for excavation need to be paid as they have done as per told by the engineer.)
(He also needs to give the details of the types of mast used in 0 km, if this is yard then types of portal quantity, types of boom required for the assembly).
So, in conclusion, layout planning and cross-sectional drawing is the most crucial step in the project.
All these details are used to draw the layout plan of the location, which needs to be signed by the higher authorities to ensure its authenticity.
So here, the first step of the survey is completed.
Survey Step 2: Assigning the Foundation
In this survey, we will study the factors which the survey observes for finalizing the foundations at the particular location.
Let’s take an example to make it more clear.
Abhimanyu who is the designer executive in the company was assigned the task to survey 33km, so with all the equipment.
Abhimanyu travelled to the site location and from 33/0 marking stone started his survey. With the pen and paper, his hand he noted down all the locations.
Generally, there are approximately 23 foundations in 1Km, so he noted location wise sequence in the form if 33/1;33/2;33/3…..in the another column.
He was observing the cess level and shoulder width of the particular location.
For example- If 33/2 is the location, then from the center of the track measure the distance required.
You must have 30cm gap left after your foundation marking is done, than on that basis type of foundation is decided.
If implantation at a certain location is 2.80m, so it must have some space after 3.45m.
In case of signal approaching the implantation need to be increased so that the loco pilot must be able to see the signal from a distance. There is a sequence of increasing the implantation of 5 poles in such a manner that the loco pilot is able to see from a distance.
In case of shoulder width of less than 30cm then one needs to change the foundation from b-type to Bg-type foundation.
Surveyor must ensure that during the marking the supervisor does not provide it below the transmission line, on the culvert, or the rob.
If done the excavation would not be possible and it may result in complete cancellation.
All of these records are noted and layout planning and cross-sectional drawing are made.
In the upcoming article, we will learn more about Indian railway foundation and quality checks.
I completed my BTech in electrical engineering in 2020, believe in the philosophy of ‘FIRST YOU LEARN THEN YOU EARN’. I am currently working as a GET in the ‘Railway Electrification’ project.