Port Infrastructure for Mine Development in Remote Locations
Stanley R. Cowdell, P.Eng.* and Geoffrey J. Harrison, M.Sc., P.Eng.**
*President, Westmar Consultants Inc., #400 – 233 West 1st Street, North Vancouver,
BC V7M 1B3; PH 604-985-6488; [email protected]; **Manager, Westmar
Consultants Inc., #400 – 233 West 1st Street, North Vancouver, BC V7M 1B3; PH
604-985-6488; [email protected]
Abstract
This paper describes Westmar Consultants involvement in the provision of port
infrastructure for Newmont Gold Company’s Batu Hijau Copper Mine Development
Project on the island of Sumbawa in Indonesia.
Particular challenges on the project included poor geotechnical properties of
soft marine sediments with respect to seismic performance, the presence of coral
limestone intrusions within the soil mass, the random occurrence of long period
waves generated by remote storms in the southern ocean, and the remote location.
Batu Hijau Copper/Gold Project – Sumbawa, Indonesia
The location was remote, the terrain difficult, and even the ocean uncooperative as
Westmar Consultants Inc. tackled a major port infrastructure project in Indonesia.
Acting as specialist consultants to Project Managers Fluor Daniel, of Denver,
Colorado, Westmar of Vancouver, British Columbia, provided expertise on design,
procurement and construction of the port facilities. Our project involvement included
construction of a dedicated berth for the loading of concentrates, a pile-supported
jetty for general cargo handling, and a floating berth for coal barge unloading.
The Challenges
As a project, it was thwart with challenges including:
•
Poor geotechnical properties of soft marine sediments with respect to seismic
performance.
•
The presence of coral limestone intrusions within the soil mass.
•
The random occurrence of long period waves generated by remote ocean
storms.
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•
The extremely isolated location on an island about 600 km east of the
Indonesian capital of Jakarta.
The Batu Hijau project entailed the development of an open pit mine for
recovery of gold and copper, along with associated concentrator, coal-fired thermal
electricity generating plant, port facilities, and construction camp, all situated on the
west end of the island of Sumbawa in the Lesser Sunda Islands chain. Situated east of
the island of Bali, Sumbawa is part of the Indonesian Archipelago between the
islands of Lombok and Flores at 116 degrees east longitude and 9 degrees south of
the equator (Figure 1).
The area is undeveloped with no major infrastructure such as roads, power or
water supply, and the local population of 10,000 relies on subsistence farming and
fishing.
Joint Venture Discovery
The Batu Hijau copper deposit – Batu Hijau is Bahasa Indonesian for Green Rock –
was discovered in 1990 as part of a joint venture exploration between Newmont
Mining Corporation and the Indonesian Government. After pre-feasibility,
optimization and final feasibility studies, Fluor Daniel was retained by Newmont in
August 1996 to perform detailed engineering, procurement and construction for the
project.
After the final feasibility studies, the major project characteristics were
identified as:
•
Average annual production of 715,000 tonnes of copper concentrate per year.
•
Production of 18 tonnes of gold per year.
•
1.9 billion US dollar capital budget.
•
167 MW coal fired thermal power generation facilities.
Figure 1. Project location.
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Benete Bay, a sheltered bay on the southwest coast of Sumbawa opening onto
the Alas Strait between Sumbawa and Lombok was selected as the site of the
concentrator, the thermal generating station, town site and the port facilities.
Westmar Retained
In April 1997 Westmar Consultants Inc. was retained by Fluor International, the
project EPCM contractor, to provide expertise on the design, procurement and
construction of the port facilities. The final feasibility studies had defined the
following requirements for the new port:
•
Concentrate Cargo Berth to accommodate ocean going bulk carriers ranging
in size from 130 metres LOA to over 200 metres LOA, with an annual
throughput of 715,000 tonnes per year and maximum monthly throughput of
100,000 tonnes per month.
•
Shiploader capable of loading concentrate at rates up to 2,000 tonnes per
hour with the material reclaimed from covered storage and delivered to the
shiploader by conveyor.
•
General Cargo Berth to handle deliveries of breakbulk and containerized
cargoes primarily in barges up to 5,500 dwt, but also small ocean going
vessels. Cargo handling to be by crawler mounted mobile crane or ships gear
onto semi-trailers or low boys. The wharf deck to have provision for
temporary storage of empty containers stacked up to three high. The berth is
to also incorporate a fixed ramp for roll-on/roll-off transfer of cargo and
equipment.
•
Small craft berths for pilot boats and tugs.
•
Construction Dock for off-loading equipment, materials and heavy loads
during construction and for receiving coal shipments for the thermal
generating facility during normal operation.
Figure 2 shows the layout of the port site facilities in Benete Bay.
Figure 2. Port site – Benete Bay.
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Procurement
Fluor determined that the shiploader would be procured on the basis of a design
supply contract, while, the concentrate berth, the general cargo berth and the small
craft facilities would be procured on the basis of design-build contract. The
construction berth which was required well in advance was to be designed in-house.
Westmar, working in conjunction with the Fluor and Newmont team, was
retained to: complete concept/preliminary designs for each of the required facilities;
develop design criteria and technical specifications; assist in preparing tender
documents; review tenders received; performance design audits; and to provide some
on site construction inspection assistance. All detailed design and construction was to
be by either Fluor or third party contractors.
Geotechnical and Seismic Considerations
Geotechnical, topographic and hydrographic surveys, wave climate data, and seismic
criteria were provided to Westmar from studies and investigations commissioned by
Fluor Daniel.
Geotechnical engineering was provided by Golder Associates. A program of
field investigations included boreholes, cone penetration tests and seismic profiling,
was undertaken. It was found that bedrock, consisting of epiplastic volcanics over
sandstone, was overlain by very soft silt, clay and sand. The thickness of the soft
marine sediments varied from zero at some points along the shore where rock
outcrops occurred, to more than 20 metres offshore in water depths of 10 to
15 metres. The upper surface of the epiplastic volcanics exhibited varying degrees of
weathering.
Based on the results of material sample testing, it was concluded that during a
seismic event the soft marine sediments could undergo simultaneous liquefaction and
lateral displacement, sliding in the direction of the down slope. This down slope
movement of the soft sediments would result in lateral loads on piles or caissons
which would be in addition to seismic loads from ground accelerations.
The feasibility studies had assumed that the foundations for the marine
structures would consist of large diameter, thick wall steel piles drilled and socketed
into the underlying bedrock. The pile size and wall thickness established to withstand
the lateral forces generated during a seismic event by the down slope movement of
the soils. The costs for the proposed structures was very large and the project budget
was at risk.
Westmar, using experience gained on its projects on the west coast of North
America recommended, an alternative design which would consist of locally
strengthening the soils around each of the structures using stone columns to reduce
the risk of liquefaction and the corresponding down slope movement. Once the soils
were strengthened, conventional driven piles of significantly reduced wall thickness
could be used. Golder Associates of Vancouver were retained to assist in confirming
the feasibility of the proposed solution. The net result was a dramatic reduction in the
estimated project cost.
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Shiploader
The feasibility study identified a fixed shuttling/luffing shiploader requiring extensive
vessel warping to allow access to all holds. Westmar’s review modified this concept
to delete the luffing function and add slewing capability to achieve the following
advantages:
•
Simplified shiploader design.
•
Reduced vessel warping required to give access to all holds.
•
Reduced number of berthing and mooring dolphins required.
The performance and design criteria plus the technical specifications were
prepared on this basis.
Concentrate Berth
The location of the Concentrate Berth was approximately 250 metres from a small
headland adjacent to the concentrate storage area where the foreshore was sufficiently
shallow to allow economic construction of a rock fill causeway using surplus material
from excavation for onshore construction and mine development. Westmar developed
detail design for the causeway including gradation of core fill, filter layers and
armour stone, and slope profiles, to protect against the 100 year return period wave.
The design accommodated the gradation of the material available from excavation on
site.
Configuration of the berth was developed to meet the following criteria:
•
The reach and range of the slewing shuttling shiploader must allow access to
all holds of the design vessel with the vessel warped into position using spring
lines connected to berthing dolphins.
•
Maximum clear space between berthing dolphins of 0.55 x smallest vessel
length.
•
Maximum vessel overhang beyond outer dolphins 0.375 x overall vessel
length.
•
Minimum vessel overhang beyond outer dolphin 0.225 x overall vessel length.
To meet the above criteria for the design range of vessel sizes the number of
berthing dolphins was set at five, spaced 40 metres apart. Two mooring dolphins for
bow and stern lines were needed to permit secure docking with the proviso that if
wind speeds exceeded working limits (40 knots) the vessel would be centred on the
berth and secured.
Figure 3 shows the general arrangement of the concentrate berth.
The following major components were included in the scope of work for the
design-build contract:
•
Steel pile supported berthing dolphins with energy absorbing fender systems.
•
Steel pipe pile supported mooring dolphins with quick release mooring hooks.
•
Shiploader pivot support structure consisting of steel pile supported concrete
deck.
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•
•
•
Walkways giving access from the shiploader support to berthing and mooring
dolphins.
Rock fill causeway.
Pile supported access trestle and conveyor support between the end of the
causeway and the shiploader pivot support.
Using the foundation concept described above comprised of locally
strengthened soils and driven vertical steel piles, our preliminary design identified
that both the cost, construction schedule, and construction risk for marine
foundations, would be significantly reduced from that originally proposed while
providing improved performance of the structures under both seismic and vessel
berthing loads. The all vertical pile structure also had the added benefit of avoiding
uplift forces in piles with the consequent requirement for heavy caps, batter piles, or
tension anchors into bedrock.
P-y curves were developed for the overburden materials to allow design of
piles against lateral loading. Studies were made on the use of H-pile tips and pile shoes
for penetrating the weathered bedrock interface for provision of a “key” and resistance
for uplift forces.
Figure 3. Concentrate berth.
General Cargo Berth
Westmar reviewed the general arrangement and layout developed in the feasibility
study.
A general arrangement with the following features was provided with the
design-build tender documents:
•
Wharfhead 20 metres wide x 94 metres long.
•
Two mooring dolphins, one off each end of the wharf.
•
Access walkways to mooring dolphins.
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•
•
•
•
•
Ramp 18 metres long by 12 metres wide with 1V:6H slope built into one end
of the wharfhead.
Two berthing dolphins on one end of the wharfhead to allow alignment of
barges at the ro/ro ramp (one dolphin to act as a mooring dolphin for the main
berth face).
Floats and access ramp for small craft and tug moorage.
Access bridges with concrete abutments aligned to accommodate low-boy
turning radii for one-way circulation on and off the wharfhead.
Energy absorbing fender system capable of accommodating barges with
freeboards as low as 0.3 metres throughout the tide range.
Figure 4 shows the general arrangement of the general cargo berth and the
coal berth.
Our preliminary design indicated that a wharfhead structure supported entirely
by vertical steel pipe piles, as at the Concentrate Berth, was feasible. This would offer
advantages such as simplicity of construction, cost, and performance under seismic
and berthing impact loading. Precast or cast-in-place concrete caps and decking was
identified as the most economic and serviceable construction for the superstructure.
Densification of soils around the perimeter of the structure was again required to
overcome the problem of seismic induced soil liquefaction and down slope sliding.
Figure 4. General cargo berth (left) and coal berth (right).
Design-Build Tender
Design criteria and data supplied in the design-build tender package included the
following items:
•
General arrangement and typical section drawings showing the preliminary
design concepts and facilities arrangement.
•
25 year design life.
•
Climatic data.
•
Bathymetric soundings and site plan.
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•
•
•
•
•
•
•
•
•
•
•
•
Tide, wave and current data including 100 year return period wave heights at
berth locations.
Seismic design ground acceleration and design factors and coefficients to
meet AASHTO.
Preliminary shiploader loads to be confirmed later by the shiploader supplier.
Results of geotechnical investigation and copies of subsequent studies
regarding p-y curves, liquefaction, pile tips, and uplift resistance.
Characteristics of largest and smallest design vessels.
Berthing and fendering criteria including approach angle, berthing energies,
and hull contact pressure.
Mooring criteria including line tension and range of direction of pull.
Live load criteria including detail wheel loads for specialized cargo handling
equipment, impact allowance, and uniformly distributed loads.
Load combinations and factors.
Design codes.
Specifications for materials, execution of construction and quality control.
Corrosion protection requirements and thickness allowances (a minimum of
5 mm in combination with protective coatings).
While tenderers were required to perform their own geotechnical and
structural design under the design-build contract format; the selected contractor’s
direct experience with the soil improvement design requirements was limited. As a
result Westmar and Golder Associates provided direction to the design team and
recommendations as to suitable external geotechnical specialists who could provide
expert assistance.
The Contractors were required to perform trial densification to confirm the
effectiveness of the procedure in addition to full scale compression and lateral load
tests on piles.
Tenders were received from four bidders and after negotiation a contract for
detail design was awarded to PT. McConnell Dowell Indonesia using Consulting
Engineers Maunsell Pty. Ltd. of Australia.
Construction/Contract Administration
Work began on site in January 1998 with the performance of geotechnical
investigations.
Westmar reviewed 30%, 50%, 90% and 100% design submissions and
worked closely with the contractor and its designers to ensure a practical design that
met the owner’s functional and quality requirements.
Soil densification was achieved by installation of closely spaced stone
columns using a vibroflot and the effectiveness measured by performance of cone
penetration tests.
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One issue that required considerable input during construction was the
presence of a previously unidentified extensive coral layer embedded in the
overburden beneath part of the General Cargo Berth. This layer prevented the
installation of stone columns in some areas. Alternative locations and structural
concepts were reviewed and costed, and the risks associated with no densification
identified to allow the owner to make an informed choice. The selected solution
consisted of constructing a densified berm around the perimeter of the structure to
retain the non-densified soils within. Construction was completed mid 1999.
Coal Berth Swell Problems
A temporary port facility, consisting of a floating berth consisting of an 80 metre x
25 metre barge connected to the shore by four stiff legs anchored to gravity anchors
(rock boxes), had been installed at the site at the start of upland mine development.
Ramps hinged at the barge and sliding on abutments onshore provided vehicle access.
This concept was originally developed as the berth had to be in operation prior to the
primary marine contractor being on site and therefore prior to pile driving equipment
being mobilized. The entire facility was installed using shore based equipment.
The barge was aligned parallel with the shore and barges and vessels tied up
against the outer face. Initially, the berth was intended to be for temporary use during
construction, but later it was incorporated into the port site as a berth to handle coal
shipments for the thermal power generating facility.
A floating berth had originally been considered feasible based on the early
wave analysis completed by others that determined that the bay was not subject to
significant deep ocean swells. The Indian Ocean did not agree, however, and the
stiffleg to barge connections failed during an event which generated significant swell
within the bay resulted in extreme motions in the floating berth. Temporary repairs,
consisting of cantilever steel pile mooring dolphins, were not the whole answer as
they also experienced severe damage during subsequent swell events.
Westmar was subsequently retained to design a permanent solution which
would allow the barge berth to continue to be used but without the risk of swell
damage. Our team first performed a forensic investigation of the failure including an
analysis of the occurrence of swell waves in Benete Bay. Using available
oceanographic data for deep water swell waves generated from remote storm events
in the southern ocean, swell waves at the mouth of Benete Bay were propagated to
the dock site using the wave refraction/diffraction mathematical model MIKE21.
Long period wave heights and angles of approach for various return periods were
developed (Figure 5).
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Figure 5. Propagation of swell waves in Benete Day.
This data was used in developing a new barge mooring system consisting of
four cantilever steel pipe pile dolphins. Dynamic analysis of the barge/dolphin system
was performed using Westmar’s in-house DYNMOOR software with and without
vessels of various sizes moored to the barge. The size and number of piles in each
dolphin was determined to satisfy the following objectives:
•
Unoccupied berth to be capable of withstanding the 20 year return period
swell event.
•
Occupied berth to be capable of operation under the 20 year return period
local storm event.
Westmar found that mooring system overload could occur under certain
combinations of moored vessel size and long period swells. To solve this dilemma, it
was recommended that operating procedures should ensure vessels would not be left
unattended at the berth and that they would be removed from the berth immediately at
the onset of a swell event.
Conclusion
Despite the harsh conditions encountered on a remote area of an even more remote
island, Westmar was delighted to be part of a global team working together on a
major port infrastructure project that is environmentally sustainable. Because of those
challenges and others encountered along the way, the finished Batu Hijau deep-sea
port was a credit to all involved and a rewarding project for the Westmar team.
References
Hamer, E., Batu Hijau Copper/Gold Project in Indonesia “Bulk Solids Handling
Journal” Vol. 18, No. 1, January/March 1998.
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