GEOLOGICAL INVESTIGATION FOR HIGHWAY, RAILWAY, BRIDGE AND TUNNEL-(Part 4)

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•Vanes are pushed completely in the bore-hole and then rotated
•Rotation of the vanes produces the shearing of the soil
•Magnitude of the torque T at the failure of the rotation of vanes i.e. when the vanes are unable to rotate at all. The torque necessary to rotate the vanes is a measure of the shear strength of the soil. Applied torque T is directly proportional to the cohesion C among the soil particles. The relationship is given by:

T = Cp (d2h/2+d3/6), where d and h are the diameter and height of the vanes of the equipment, respectively

•(vi) Bearing Capacity Test: This test is carried out to determine the Load Bearing Capacity (also known as Bearing Capacity) of the ground. It is carried out by the actual loading of either sample taken from the ground-strata or test is carried out in-situ. Loading is carried out over a plate placed on the ground sample in the lab or in-situ, through a jack carrying the sufficient dead load to receive its sufficient reaction. Load settlement curve is plotted and safe load bearing capacity is determined from the plotted graph. This test is mostly carried out in-situ environment

Some important Terms used in these context:
Rock Mass Classification (RMC): Rock mass classification systems are used for various engineering designs and stability analyses. These are based on empirical relationship between Rock Mass Parameters i.e. condition of rock being: Intact, Stratified, Moderately Jointed, Blocky, Swellable, etc and Engineering Applications such as Tunnels, Slopes, Foundations and Excavations. The first Rock Mass Classification System in Geotechnical Engineering was proposed by Terzaghi in the 1940 for the tunnels with steel-set support.

Rock Recovery Ratio (RRR): This is a percentage of the rock cores obtained from the total drilled length in one drilling operation. The good recovery of a rock i.e. good Rock Recovery Ratio expresses the soundness of rock-mass

Rock Quality Designation (RQD): Rock Quality Designation is one of the rock properties used for Rock Mass Classification.

“International Society of Rock Mechanics, USA” describes it as a test on the core samples of at least  ̴ 55 mm (dia) NX drills (solid carbide drills made up of Al Ti N: Aluminium Titanium Nitride).

The drilled core segments even if they get broken, are placed in a series one after the other in a wooden box. Total length of the solid core along the axis is measured for a drilling core run (length) of 150 mm. RQD is calculated with the following relationship:

RQD = [Sum of the length (in mm) of the core recovered of the length not less than 100 mm / Total length of drilling] x 100

 


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MuhammadTayyab

Me from Pakistan and im the student of undergraduate;BS Electronics.

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