Clay falls into this category since it’s cohesive
and has at least 1.5 tons per square foot of
unconfined compressive strength. (Incident Prevention, 2017) Online. Clay
allows for a slope angle with a ratio of 3/4:1. This means that when there is a
foot of depth, the excavation sides will slope back 3/4 of a foot. This also
translates to a 53-degree angle. The equation for determining the proper
opening width of the slope angle is: (depth x 2) x type slope ratio + width of
original excavation = top width. For example, the slope angle of the clay that
is 6 feet deep by 2 feet wide would be: ‘(6 feet x 2) x .75 + 2 feet = 11 feet
wide at the top.’ (Incident Prevention,
2017) Online. On the other hand, when the cutting will reach the chalk
section of the excavation, it should have a slope with a ratio of 1-1/2:1 or a
34-degree angle. This is because chalk is categorised as a type C soil and is
therefore considered the least stable and most hazardous type of soil. This is
since chalk and other similar types of soil are cohesive with an unconfined compressive
strength of less than 0.5 tons per square foot. To determine the slope angle
for chalk that is 6 feet deep by 2 feet wide, the equation will be (6 feet x 2)
x 1.5 + 2 feet = 20 feet wide at the top. This figure is for type C soil in
general. The width of the track will have to be wide enough to contain two
railway lines therefore 40 feet would be sufficient and safe for such. Once
enough soil is removed with explosives, the rest of the cutting will be carried
out with 360-degree excavators. Since the track will be 40 feet wide, the
cutting will have to consider the fact that it will have to take into
consideration the sloping ratio figures given above for each side. Therefore 40
feet plus 2 x (11 feet + 20 feet) = 102 feet. This means that when the 360-degree
excavators are used, the sloping will have to be 102 feet away from both sides.
360-degree excavators are used for digging rocks and soil and have an
operating weight of at least 9,000 kg.