Chain Surveying or Linear Surveying | ______7_8_a_7_2_6_0_b_7_d_5_b_d_5_a_5_5_5_7_b_6_3_f_a_8_5_8_4_b_1_b_b______
It is the method of land surveying in which only linear measurements are made.
Chain surveying requires chain, tape and ranging rods.
Chain surveying is not suitable for large areas having many details.
(The term “details” means a natural or manmade features at or near the ground surface).
It consists of the following:
Hard details include buildings, roads, walls etc.
Soft details include river, vegetation, trees etc.
Overhead details include power and telephone lines.
Underground details include survey of water mains, sewer etc.
Principles of Chain Survey
A triangle is a simple figure which can be plotted from the lengths of three sides even if the angles are not known.
In chain survey, the area to be surveyed is divided into a framework consisting of triangles.
Selection of survey station and Survey lines
- The main station should be mutually intervisible so that ranging can be done easily.
- Survey lines should be as few as possible so that framework of triangles can be plotted easily.
- Survey lines should pass through a level open ground as far as possible so that chaining can be done easily.
- The frame should have atleast one long baseline that runs through the middle of the area.
- The main survey lines should form well conditioned triangles with no angles less than 30 degrees or more than 120degrees.
- The survey lines should be selected such that there are no obstacles in chaining and ranging.
- The survey lines will be close to the details to avoid long offsets.
- If required, number of subsidiary stations should be selected and subsidiary lines run to avoid long offsets.
- Each triangle should have a check line to detect mistakes in measurements and plotting.
- While selecting main stations and survey lines, the basic principles of surveying of working from whole to the part should be followed.
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