SITE SURVEY
The surveying points should be chosen where
there is a change in slope. The distance between
the two consecutive surveying points should not
be more than 30 metres unless there is an abrupt
change in slope. In case of vertical drop, it is
mandatory that the readings of top and bottom of
the drop be taken. All the readings should be taken
for the same face left or right, more conveniently
on face left position. To minimise the error, take
two way readings and plot the profile in graph
simultaneously.
The distance and elevation of the surveying points
at each station are calculated using the formula
shown in Table 1. Summing up all the data, the
elevation and distance of the surveying points
along the axis and the permanent peg point at
upper or bottom station are obtained. These are
then plotted in the graph to get the profile of the
ropeway alignment along the centre line.
2.3 Soil Investigation
Soil investigation is very important for foundation
design of ropeway. For foundation design, soil
parameters like the specific weight of soil (γ),
angle of internal friction (Ф) and cohesion (c) of
the base soil and back filling material are needed.
For evaluating these parameters, it is necessary
to have the following information:
Soil type, origin and particle size
Approximate particle grading
Plasticity of soil
Compactness
Grain shape
Rough estimate about the moisture
content in soil
Percentage of boulders > 60 mm and
rock types of boulders
2.3.1 Common methods of soil investigation
a) Exploratory pit method
The simplest method for subsoil investigation is
by trial pitting. This method involves manually
excavating trial holes at identified test points. The
subsoil will then be investigated by carrying out
field strength tests as well as by visual assessments
of the trial holes. Number of trial holes that needs
to be dug depend on the variability of the subsoil
around the site and the experience and judgment
of the investigating engineer.
Field investigation procedures:
The position of each trial hole should be
confirmed before commencing excavations.
The trial holes will be excavated using hand-
picks and shovels. The local community can
be mobilised to carry out this work.
Each trial hole should be at least 80 x 150
cm vertically excavated. The soil profile
should be visually assessed and logged by
the engineer during the course of excavation.
These visual assessments will determine the
need for further tests on the soil samples in
the laboratory.
The Dynamic Cone Penetrometer (DCP) test
is carried out at one metre depth intervals
from ground level until a point of required
strength is recorded or until the danger
of sides collapsing makes the excavations
unsafe for those people digging. The ground
strength should be deemed adequate if the
required DCP penetration rate is achieved for
at least three sets of 10 blows before each
reading. The required soil strength should be
determined from the adopted standard charts.
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