Construction
Supervision
Summary
As
of April 25, 2002, total length of main tunnel excavation
has reached to Sta. 2+582.50 or 929.50 meters from the tunnel
portal.
Seventeenth
(17) niches (4 Emergency & Call Niche and 13 Firefighting
Niches) and two lay-by (1 left side and 1 right side) have
already been excavated inside the main tunnel
Concrete
work of the Foundation Beam and Concrete Lining Works has
been continued. As of April 25, 2002, concrete lining construction
has reached to 252 meters at the main tunnel.
As
of April 25, 2002, total length of Evacuation Tunnel Excavation
has reached to Sta. 2+577.70 or 924.70meters from the tunnel
portal.
Two
(2) cross passageways have been excavated across the Evacuation
and Main Tunnel.
As
of April 25, 2002, total length of Ventilation Adit Tunnel
Excavation has reached to Sta 0+959.50 or 790.01 meters from
the Tunnel Portal.
Excavation
In
the month of April, the rock encountered in the Main Tunnel
was classified as Class B to A until middle of this month.
On April 16, 2002, a small fracture zone appeared from right
side of the tunnel face and gradually moving towards the left
side until 23rd of this month. Fracture zones and
some joints, almost parallel to tunnel axis, with small water
inflow on the right side of the tunnel face were continuing
until the end this month and based on the rock condition,
the rocks were classified as class C1 to B.
Because
of the condition of the rock encountered, the Tunnel Engineer
gave instruction to install random rock bolts and to increase
the shotcrete thickness from 50 mm to 100 mm.
A
total length of 159.20m (station 2+603.9 ~ 2+444.7) was excavated
in the Main Tunnel this month, giving a total length of 951m
(Progress: 24.65%) from the tunnel portal.
Niche
Excavation:
Eighteen
(18) Niches – Four (4) Emergency Call Niches and Fourteen
(14) Firefighting Niches – in the Main Tunnel were already
excavated. Excavation of niches continued according to the
design niche distribution plan.
Layby
The
Layby-Left No.1 and Layby-Right No.1 had been completed since
last month.
Behind
Works (Behind Tunnel Excavation)
The
pouring of Class D concrete for the Foundation Beams of the
Lining Concrete continued this month. The placing of concrete
continued from Station 1+917 to 2+015 on both sides with a
total length of 98m each side. The foundation beams on both
sides of the Pedestrian Cross Passage No.1 were completed
this month.
Installation
of Mole Drain Pipes, with filter cement aggregate, on both
sides of the tunnel continued simultaneous with the foundation
beams.
Cutting
of Rock bolt heads and installation of geo-textile covers
continued up to Sta. 1+983m.
Installation
of EVA Waterproofing Membrane also continued following the
covering of rock bolt heads. The Engineer continued to require
testing of the welded joint sheets using air pressure test,
as per procedure stated on method statement, prior to continuation
of the installation.
Pouring
of Lining Concrete also continued as per design segment approved.
The Engineer carefully checked, during the joint survey with
the contractor, the setting of the form for both bulkhead
sides and the thickness as per design requirements.
The
concreting works started with the first block (L/C No. 2)
located from Sta. 1+665 to Sta. 1+677. Twenty-three blocks
(L/C No.24) up to Station 1+941m, totaling to 276 meters,
including five (5) Fire Fighting Niche, one (1) Emergency
call, and one (1) Notch box out with vertical groove for electric
cable for Jet Fan were already completed.
In
the Evacuation Tunnel, the condition of the rock encountered
was generally good, although at some times we had experienced
water seepage on the excavation face. Geologically, the rock
condition was stable on class B. On some portions, it was
almost classified as class A this month.
The
excavated tunnel length for the month of April was 170m (station
2+607 ~ 2+437), giving a total length of 954m (Progress: 24.73%)
from the tunnel portal.
The
Temporary Transformer Niches No.1, 2 and the enlarged Transformer
Niches No. 3 and 4 were also completely excavated as per approved
plan submitted by the contractor.
The
Enlarged Pedestrian Cross Passageway Nos. 1 and 2 has been
completed since last month.
The
ventilation system made for Evacuation Tunnel through Pedestrian
Cross Passage No. 2 has a good result and improved the ventilation.
Wasted air coming from the Main tunnel was still eliminated
out through Pedestrian Cross Passage No. 2 and then through
the Evacuation Tunnel.
For
Ventilation Adit Tunnel, the anomalous water seepage spouted
again on April 4, 2002 at the excavation face station 1+029.4
with a discharge of more than 1.0m3/min. Moreover, on the
said station, crashed rock and fracture zone with soft filling
was encountered so the support type III remained effective
until the Engineer issued an instruction to change the type
of the supporting system from III to II starting Sta. 1+024.90.
The
rock encountered was observed to have some fractures and some
joint planes parallel to tunnel face and water inflow on almost
every round, which hindered the activities of the contractor.
On
several happens, the type of the supporting system was changed
from II to I but because of the condition of the rock encountered,
the support type was returned to type II until the end of
this month. The Engineer instructed to continue type II support
with the installation of swellex-type rock bolts and increased
on the thickness of shotcrete from 50mm to 100mm.
The
excavation continued under rock class C1 with water seepage
for every round.
Geologically,
on the average, the rock condition is classified as C1 and
90 percent of blasting rounds have water inflow continuing
the end this month.
The
contractor maintained enough capacity of water pump to avoid
any delay on the excavation works that might be caused by
water seepage. However, they still could not achieved the
normal cycle time for each round because of the unavoidable
ponding of water on the excavation face.
The
excavated length for the month of April is 92.2m (station
1+035.0 ~ 0+942.8), totaling to 806.71m (Progress: 46.03%)
from the tunnel portal.
Assembling
of Layby Sliding Form was completed on the month of April
2002 and was started to shift towards the Portal of the Main
tunnel.
The
shotcreting works under Gabion was completed on 7th of April
2002.
The
shotcrete trial spray demonstration on the surface of the
Gabions was done on April 01, 2002 in the presence of the
Vice Project Manager of PMU85. This presentation was approved.
However, the contractor proposed to continue the observation
on the sprayed surface and to execute shotcreting works once
the gabion has finally settled and has become stable. This
matter already approved by the Engineer.
In
addition, the grading, re-compaction and surveying works on
the base coarse of the Access road asphalt pavement had commenced
in this month.
Progress To Date
