The GLF/SELi’s joint venture performance on the Umiray-Angat Transbasin Tunnel – in some of the most difficult terrain in the world – was outstanding, and one of their most challenging projects, taxing their logistical and engineering skills to the full.
The challenge
This one had it all:
What’s more, this project is considered to be the first successful TBM project in the Philippines. Hence the client body, The Metropolitan Waterworks and Sewerage System (MWSS), should be proud of SELI’s remarkable tunnelling achievement averaging over 540m/month for this fully lined tunnel.
The people
Mr Armando Tamai, SELI’s overseas project manager summed up his company’s modest reaction to the successful completion of the TBM drive on 18 February 2000.
“Actually we’re quite disappointed that we couldn’t match our tendered advance rate . We were severely hampered by major changes in the original access arrangement due to ‘El Niño’ and our crews having to cope with everything these rugged mountains could throw at us.”
“Yes, conditions on site were quite severe at times,” pointed out Franco Fabricio, the JV’S project manager. “In fact we drove the first 4km in about five months and, in June 1998 excavated and lined 1km of tunnel, with over 60m in one particular day. So despite our delayed start, we were optimistic that we could achieve our expected average rate of advance of 886m/month.”
“However at the end of July we experienced our first collapse at the TBM cutterhead and excavated only 47m the entire month of August.”
“Soon after that we encountered the first of a series of major water inflows that, by the end of the drive, had risen to 810litre/s. This is resulted in difficult working conditions, downtime for the rail spoil disposal system and long term wear and tear of components such as the locomotive traction system. At times our ‘uphill’ drive was awash in water, due to silting and ponding in the tunnel and some of our miners had to swim to work.”
“We also experienced a maximum rate of tunnel closure of 0.2m/h in the hardest rock types where the overburden was greatest, at about 1000 – 1200m cover to the tunnel,” commented Andrea Ciamei, Chief Engineer. “Three times our Columbian and Filipino miners had to drill and blast or hand excavate hard rock outside the TBM shield when the tunnel converged. It was very dangerous work for the men to dig the machine out. Then in November this year, with only 300m to go before our breakthrough at the Umiray portal, we hit yet another major fault zone and an 8m-high collapse at the TBM cutterhead buried the machine. Finally we broke through on 18 February this year
“So I’m sure that you’ll understand how proud we are of the remarkable results achieved on this job,”concluded Mr Tomai.
The Works
The Umiray – Angat Transbasin Project (UATP) is the second development phase of the Angat Water Supply Optimization Project which aims to increase the supply of raw water from the Angat Reservoir to Metropolitan Manila by drawing upon reserves from the Umiray River. The latter, located in Central Luzon Island between the Bulacan and Quezon Provinces, runs northwards along the Sierra Madre mountain range and discharges into the Pacific Ocean at Dinglan Bay.
The catchment areas of these two water sources is located in rugged mountainous terrain with forest clad slopes and a sparse indigenous population of Negrito forest people. No roads or tracks exist close to the tunnel and construction of access roads linking the existing regional road network to the works site is expressly prohibited by local environmental protection legislation.
Thus the permitted access route to the site for the contract was by paved road from Manila to Angat, then by barge for some 23km along the Angat Reservoir between landing Site Nos.1 and 2, and by road for 4-5km to the Macua tunnel outlet and main job site. Here substantial river training works, land reclamation works, and an 11.3km long, 35kV power transmission line had to be in place prior to commencement of tunnelling works.
When the water failed
As rainfall on the western side of the Sierra Madre is erratic at the best of times, the water level in the Angat Reservoir often falls to a point during ‘El Niño’ when navigation between the landing sites by barge is no longer possible.
Nevertheless in November 1995 the MWSS tendered and awarded the Asian Development Bank Funded contract for the UATP for P1.409 B to the Italian GLF-SELI JV consisting of Grandi Lavori Fincosit, Societa’ Esecuzione Lavori Idraulici and J.V. Angeles Construction Corporation. The Notice to Proceed was issued in January 1996 for the 1,154 day contract that included the following works:
a) diversion works on the Umiray River to convey in total water inflows varying from 2.5m³/s in dry periods (El Niño) to a maximum of 30m³/s during the wet season (La Niña);
b) transbasin tunnelling works which included 13.1km of main tunnel, branch tunnels to diversion weir sites and a ventilation shaft;
c) suspended rail-car system to the crown of the main tunnel located at the Umiray Basin for operation and maintenance purposes;
d) mini hydro electric plant at the Macua outlet of the main tunnel;
e) logistics support infrastructures including a camp for the MWSS Staff for maintenance and operation of the project facilities ; and
f) power transmission line to Macua for power supply during construction and connection of a mini – hydroelectric plant to the local power network during operation.
Administrative and weather hiccups
From day one the works were doomed to delay due to adminstrative reasons beyond the contractor’s control. Hence no substantial site preparatory works could be undertaken during this first period.
By 16 September 1996, all approvals were in place and by April 1997 the Italian JV had completed their original 16 months tasks in just seven months.
Unfortunately ‘El Niño’ persisted for many months rendering the reservoir partially then totally unavigable from April 11, 1997 until late October 1998. This left the JV ‘high and dry’ and desperately needing to develop alternative means of gaining access to transport all equipment, bulldozers, its heavy TBM and back-up plant to the remote site.
Tunnelling by helicopter
In order to minimise further delays the JV decided to transport all equipment to site by air. An 11-tonne helicopter, the heaviest available, was located and the TBM, locomotives, lining moulds, fabrication plant, trucks etc. were all broken down into manageable components and flown to site.
By February 1,1998 the site was prepared and the TBM established on site ready to commence serious tunnelling some six to seven months behind the original programme. However, as transportation by barge was not yet possible supply of all back up materials including spare parts, cutters, cement, reinforcement etc. had to be continuously flown to site using three 1-tonne helicopters. In spite of this very high progress rate was achieved on the initial 4km drive.
The TBM
The particular specification for the tunnelling works required a TBM with a minimum cutterhead drive power of 1200 kW. However the JV decided to use a sophisticated double shielded TBM with 1890 kW cutterhead power as illustrated in the General Specification on Table 1. This 4.88m diameter machine has been substantially redesigned and developed from the first generation of hard rock, double shielded TBMs and includes the following:
Other advantages of the TBM and back up becomes from the use of a special designed back up sytem accommodating spoil disposal for two complete trains (equivalent to 5. 2m of tunnel advance), hence minimizing trains delays, with a variety of other state of the art facilities.
Tunnel Lining System
The tunnel lining consists of four, 1.3m wide, 0.2m- thick hexagonal segments as shown in Fig 2. These were fabricated on site and each included 55kg of steel cage reinforcement for normal rock loads with 110kg/segment where high loads were anticipated.
Gaps between the segment and rock were filled by blowing in pea gravel through two annular holes in each segment. Grouting of the gravel takes place immediately behind the TBM back-up.
Each cycle of advance of 2.6m is geared to complete filling of one train and includes: 4 x 0.65m machine strokes; 4 alternative regrips of the main TBM grippers.
With the help of a mechanised segment erector and hard rock grippers the arrangement allows very high speeds of advance to be achieved in good quality rock, with a steady of advance in poorer ground using a combination of thrust on the TBM grippers and thrust against the lining segments.
Related Files
Map of the overall project site
Assembly of hexagonal segmental lining
