Bore
Sr.
No.
10.5
Minimum N - (SPT)
Minimum N - (SPT)
hole
value to be achieved
value to be achieved
value to be achieved
75+800
76+050
76+400
76+650
76+900
76+950
77+200
77+450
77+600
77+750
78+030
78+180
78+330
78+450
78+700
14
14
16
8
15
14
14
14
14
16
14
14
14
14
14
14
14
16
11
16
14
14
14
14
16
14
14
14
14
14
14
14
16
12
16
14
14
14
14
16
14
14
14
14
14
Chainage
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Minimum N - (SPT)
at 0.5m depth
at 1.0m depth
at 1.5m depth
Process of Ground Improvement with compaction
To achieve the required minimum N values at site following steps are proposed,
I.
It is proposed to compact Original Ground level to 97 % of proctor density with sheep foot roller at the
above mentioned chainage locations. Thereafter, N Value shall be verified at 0.5 m, 1.0m & at 1.5m
depth, if desired N value is achieved as mentioned in above Table-1 then construction of embankment
II.
III.
will be carried out. If it does not achieve required minimum SPT N value then follow step no 2.
It is proposed to excavate the top soil upto 0.5m and then compact it with sheep foot roller at the above
mentioned chainage locations. Validate the assumed N values as mentioned in table no.1 to ensure
safety of embankments against liquefaction.
If N
value can not be ensured with the above mentioned procedure, in such case it is proposed to
excavate more may be 1.0m or 1.5m (depending on existing soil condition and requirement of target
minimum N values), prepare a compacted bed on which the excavated soil to be refilled and
compacted. This procedure should be repeated till the proposed bottom level of embankment is
achieved. Once, it reaches to the proposed bottom level of embankments, N
IV.
V.
at depths corresponding to chainages mentioned in above table no. 10.1.
value shall be verified
As per the liquefaction calculations existing soil at ch.77+000 location not found to be liquefiable.
Hence, considering an influence zone of 100m (50m on either side) no special compaction is proposed
to mitigate liquefaction.
As a trial basis and validation compaction using sheefs foot roller with 10 nos of passes at CH 78+180
has been carried and results shows that improvement in SPT values. Results of Post and Pre SPT
values are presented in Annexure 6.