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By I Chan

The Wambo Rail Spur located near Singleton, New South Wales, Australia, runs for 14 km linking the Mt Thorley rail loop and running north-west alongside Jerrys Plain Road to the Wambo Coal Mine at Warkworth. A portion of the project is a 260 m long tunnel located where the rail line passes under Jerrys Plain Road. The tunnel has a low cover and is mostly within highly weathered to fresh laminated siltstone interbedded with coal seams, sandstone and conglomerate. This paper presents the design basis and construction methods used to achieve the 100 year design life of the tunnel required by Wambo Coal while also satisfying settlement and vibration limits imposed on Jerrys Plain Road. 

Jan 1, 2008

By Johns A. L

The concept of the Melbourne Underground Rail Loop and the organ- isation to achieve its construction are covered in the companion papers (Reference 1, 2) and will not be repeated here. The Victorian Railways, as well as being the eventual operator of the Loop when it is completed by MURLA, have also been responsible as "Contractors" to MURLA for the construction of the "cut and cover" or "box" tunnels and related approach works located on existing Railway property. These tunnel connections link the existing suburban system to the new underground works. The following tabulation indicates the significant work volume involved in this cut and cover tunnelling exercise and which is covered in some detail by this paper.

Jan 1, 1981

By M Norbert, P Mok

The mainline running tunnels for Legacy Way comprise of two-lane tunnel boring machines (TBM) driven tunnels. The length of the TBM tunnel section is approximately 4.2 km. The TBMs employed are double shield TBMs. Typical support to the segment ring while advancing a double shield TBM comprises of filling the excavated annulus between the ground and the segmental lining by injecting pea gravel, followed with primary grouting to fill between the pea gravel some distance behind the excavated face. The methodology adopted for the Legacy Way project, however, did not follow this typical approach, instead, two component grouting of the annulus was carried out.Where the annulus is typically filled with pea gravel, support is provided to the segment ring very close to the end of the tail shield, whereas in the case of two component grout this is not practical as the risk of grouting in the tail shield is high. The staging of the two component grout injection, the grout early age strength properties become key issues in ensuring that the segment ring leaving the TBM tail shield is stable and can support the necessary external loads.Two-component grout is a grout with two components, cementitious grout (component A) and accelerator (component B), commonly adopted for earth pressure balance (EPB) TBM. The grout reaches its thixotropic state in a matter of seconds providing initial support for the segment rings. Manual injection of two component grout to fill the bore annulus was carried out in stages leaving a portion of the segment rings unsupported. Ring stability during TBM advance was provided by a combination of ram thrust and the segment circumferential joint shear connectors.This paper outlines the design considerations such as rock load derivation by probabilistic analysis carried out utilising the software JBlock, 3D finite element analyses using the software Strand7 for ring stability and the testing and back analysis of the shear connector load bearing behaviour. In particular, the actual available capacity of the shear connectors against their published capacity by supplier was discussed.CITATION:Mok, P and Norbert, M, 2014. Tunnel boring machine excavation stability – double shield tunnel boring machine advance with partially grouted annulus, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 51–62 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

According to the Australian Bureau of Statistics, fatalities from road transport accidents represented an average of over 97 per cent of all transport related accidents between 1997 and 2002. With increasing traffic density, tunnels are becoming a more viable means of providing alternative travel routes to ease areas of congestion in the road transport network. However, unlike open road conditions, a fire incident in the confined space of a tunnel environment may impact upon many users that are remote from the incident location. In this context, designing for an appropriate level of safety in tunnels is therefore an important consideration for achieving consistency in the life safety measures for users of the road transport network. Unfortunately, like fire safety engineering design for buildings, there are presently no clear measures in the design processes to assess the adequacy of the design in terms of attaining the level of safety implicated in the design objectives. This is partly due to the indeterminate nature in which the design objective or the level of performance measure is stated û the intent of the objective is relatively clear but the measure of it is not. Another reason is the lack of a standardised procedure for determining the critical design variables affecting life safety. This is important to ascertain consistency in the use or adoption of the important parameters for design. This paper looks at the processes involved in the fire engineering design of road tunnels that are currently practised. A review of the design processes for fire safety in road tunnels is provided, which includes the range of fire scenarios in a tunnel environment, the traffic flow and composition, the relevant fire protection systems, the ventilation and smoke control system, the egress provisions and the benefits of incorporating fire brigade intervention. A simplified risk assessment approach is developed for a typical road tunnel to assess and evaluate the impact of a range of design parameters on life safety. Using a sensitivity technique, the important variables are then identified and means of reducing design variations associated with them are recommended. The technique may be further refined for use in the development of codes or guidelines in order to develop a suitable means of deriving more consistent design values, and hence achieve better consistency in the overall level of safety in the design.

Jan 1, 2008

By D Mather

Fibre reinforced shotcrete has long been accepted as temporary ground support in both mining and civil tunnel linings. Greater knowledge and understanding of shotcrete as an engineering material and advances in its quality have enabled designers to eliminate the requirement of a second pass lining. The initial shotcrete can be used as the permanent tunnel lining or be incorporated into the final lining design, rather than ignored and considered as sacrificial.For the initial shotcrete lining to become a suitable permanent tunnel lining it must be able to establish and maintain stability over time when subjected to all possible loads. To ensure this, best engineering practices are required during the design phase of the project to analyse; ground conditions including rock mass properties, ground and ground water quality, rock mass loadings, excavation sequencing, and construction methodologies.The increased durability of steel fibre reinforced shotcrete over traditional tunnel support, in the right ground conditions, makes it possible to achieve a serviceability design life of greater than 100 years (as required in most infrastructure projects). By specifying a good quality shotcrete mix and ensuring adequate quality control for batching, fibre dosing, preproduction testing, excavation sequencing, and application control, it is possible to eliminate the requirement of a secondary lining. The properties of a suitable permanent lining must be well established using suffi cient preproduction testing in combination with post application monitoring.A major benefit of steel fibre reinforced shotcrete in ground support applications is the removal of any requirement for workers to work under unsupported ground. Its use can also significantly reduce, if not eliminate, the manual handling associated with placing traditional reinforcement such as lattice girders and mesh. Both of these benefi ts are significant with the ever increasing focus on health and safety.This paper highlights factors that must be considered in the design and specifications to enable an initial shotcrete tunnel lining to become the permanent shotcrete tunnel lining.

Mar 8, 2011

By W Mahoney, F Clement, E Saraiva

Prefabricated waterproofing sheet membranes are extremely complicated to install in underground sections with complex geometries and, despite being already subjected to quality tests in the factory, the installed membrane often exhibits leakages due to different reasons. Main sources of leaks are the required high amount of welding seams and damages caused during installation of reinforcement, as well as overstretching and poorly installed secondary concrete linings. Also the design of the tunnel lining is strongly influenced and limited by the use of prefabricated waterproofing sheet membranes. The use of sprayed waterproofing membranes for more than a decade has contributed to durability and serviceability, as well as to increasing sustainability of tunnel linings. The presented sprayed waterproofing membrane MasterSeal 345 is an advantageous alternative to prefabricated waterproofing sheet membranes under typical tunnelling conditions, especially in geometrically complex areas, such as in lay-by niches, cross passages and crossover caverns, where installation of conventional waterproofing membranes is inherently difficult, and locating leaks is challenging. This membrane has been successfully used in underground projects with different waterproofing design concepts and under diverse hydro-geological and environmental conditions for over a decade. It provides tunnel designers with different options and optimisation for the design of the tunnel concrete lining. Additional advantages to owners, contractors and designers from the use of the sprayed membrane include flexibility in the design, increased productivity and flexibility in working programming, as well as improved logistics, resulting in significant program and cost savings and reduced long-term maintenance costs. This paper describes the key features of this sprayed waterproofing membrane, its application range and limitations, the waterproofing concept, design options and related benefits. Further, guidance for membrane application and quality control and a summary of two recent project references in the United Kingdom and in Switzerland are provided.CITATION:Saraiva, E, Clement, F and Mahoney, W, 2014. The use of sprayable waterproofing membranes in underground structures – concept, design options, benefits and limitations, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 323–332 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By P Bartlett, K Naidoo

Premier Diamond Mine is planning a new, mechanised, block cave, with a production level approximately 1000 m below surface. A high degree of tunnel damage is expected, due to stress and the relatively low in situ strength of kimberlite. An evaluation of the timing of tunnel excavation, tunnel size and spacing has been carried out to define critical parameters for planning layouts and development schedules. Extensive use has been made of three-dimensional FLAC3D numerical models, calibrated against known rock mass behaviour at 650 m depth, to examine the influence of undercut advance on production level excavations. These were able to represent the effect of stress rotation on tunnels during undercut advance and the effect of an inclined undercut. The analysis has provided guidelines that are possibly applicable to any deep block cave layout. The choice of drawpoint layout is of considerably less significance than the proportion of ground extracted on the production level elevation prior to advancing the undercut. The analysis shows that damage to production development will be potentially severe if it is all excavated prior to advancing the undercut, or is mined directly beneath the undercut face. The development of the main production tunnels alone ahead of the undercut may be feasible, but no breakaways should be put in as they appear to trigger a rapid increase in the severity of damage. The optimal sequence is when all production tunnels are developed at least 10 m in plan behind the undercut, where the induced peak field stress is less than 20 MPa and a maximum support pressure of 100 to 500 kN/m2 is require to contain movement. The assessment showed that the conditions are not significantly improved by increasing drawpoint spacing from 15 m to 18 m. The vertical spacing between the undercut and production level beneath is investigated. Provided production level development is carried out beneath the undercut, there would appear to be little benefit in increasing the vertical spacing between the undercut and production level beyond the current 15 m to 18 m.

Jan 1, 2000

By N Taylor, P Hewitt

The Northern Beaches Storage Project (NBSP) is part of Sydney Water’s SewerFix™ Program to improve the wastewater system and protect public health and the environment. It was built by the SewerFix Wet Weather Alliance (the Alliance), a partnership between Sydney Water, RPS, MWH, Parsons Brinckerhoff and United Group Infrastructure.The project temporarily stores excess wastewater diverted from the Narrabeen Submain during wet weather. The project considered a below-ground storage facility, which involved constructing a deep tunnel from Brookvale to Fairlight, connecting into the Northside Storage Tunnel and a storage tank, which was subsequently adopted and constructed.The storage tank scheme included a pumping station and inlet and outlet pipes installed by microtunnelling. The storage tank site is in the Brookvale industrial area situated in an area of deep marine sediments overlying Hawkesbury Sandstone at about 30?m below ground. Microtunnelling for the inlet pipe was conducted from a 12?m deep jacking shaft. The jacking shaft and 14?m deep pumping station excavations were carried out from within secant pile earth retaining structures adjacent to existing buildings.Construction activities had the potential to cause settlement of the adjacent buildings. During excavation and microtunnelling the water ingress, adjacent groundwater level and settlement of the adjacent buildings were monitored. The monitoring data was assessed against an action plan, which modified construction activities as required to minimise the risk of damage to buildings from settlements caused by lowering of the groundwater table outside the excavations. The secant pile construction, excavation, microtunnelling and pumping station construction proceeded without incident or damage to adjacent buildings.This paper highlights that tunnel/underground options should be considered during options development, describes the original storage tunnel scheme and presents details of the successful microtunnelling and deep shaft construction adopted on the NBSP.CITATION:Taylor, N and Hewitt, P, 2014. Tunnelling on Northern Beaches Storage Project, Sydney, to improve water quality, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 451–458 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

Hard rock TBMs are very often open machine layouts, with just a part roof shield over the front of the machine. The whole system is designed for fast face advance and the economy of the project often depends entirely on the rate of advance. Typically, hard rock conditions will demonstrate stable and good ground for a major part of the tunnel. However, short sections of crushed shear zones with clay and gouge material may cause serious time delays. Spiling rock bolting has been proven to be very efficient under such circumstances, provided the fully grouted rebar bolts can be placed in a controlled and practical manner.Environmental restrictions are becoming more and more a part of tunnel excavation projects. Even hard rock TBM tunnelling may require a strict ground water control, because of consequences on the ground surface from lowering the ground water level. Such consequences may be surface settlement, negative influence on ground water resources or damage to vegetation.Pressure injection ahead of the advancing tunnel face (in this paper named pre-injection), using microfine cement and chemical grouts, is today a proven technology. As examples can be mentioned (Garshol, 1997) about 100 km of pre-injected tunnels below Oslo City and about the same length of subsea tunnelling elsewhere in Norway. Examples from other parts of the world are also available, like below Stockholm, Sweden, the Inland Feeder project and Hollywood Metro both in Southern California.To take advantage of spiling rockbolts and pre-injection, it is an obvious prerequisite to be able to drill the necessary boreholes in the right positions and at the correct angle. In drill and blast excavation this is simple, but in TBM projects it has repeatedly turned out to be difficult. More than once owners have accepted bids containing reassurance from the contractor that the drilling method will be sorted out later. Experience shows that if ælaterÆ means after start of the TBM operation, it is often too late.

Jan 1, 1999

By A De, B Palmer, rade, P Stowasser, A Fanning

Mining and tunnelling share many commonalities (eg confined working environments, excavation equipment and processes), but of significance is an overarching commitment to provide safe work conditions and environments. This includes reducing exposure to hazardous airborne contaminants such as dust and fumes, in particular Respirable Crystalline Silica (RCS) and Diesel Particulate Matter (DPM), with methods that are environmentally sustainable. In mining, wet methods are common to suppress airborne contaminants, however these methods are reliant on water availability, can be less effective for respirable dust, can have implications for environmental water contamination and can increase maintenance on mining equipment. In contrast, the use of dust scrubbers that provide filtration of airborne contaminants are well established in the tunnelling industry and frequently used to provide spot extraction (dust control at the source) and act often as a complement to the main ventilation system. This paper sought to learn more about the advancements in tunnelling that could be readily applied to mining to improve health outcomes. The paper includes a review of literature and legislation related to health and sustainability and interviews with three respected, and experienced managers from the global tunnel construction industry. It is from these interviews that the focus of the paper turns to Sydney’s WestConnex underground tunnel network and the success of stage 3A M4-M5 construction link. The findings position dust scrubbers as integral to the overall project success as they enabled a Tunnel Production Line (TPL), where multiple stages of construction could take place simultaneously by controlling high volumes of dust at the source. The findings also suggest efficiencies of using mobile scrubbers, both track mounted and hydraulic stepping systems, to accompany road headers and other equipment throughout the excavation process. The findings have transferable applications to underground mining processes in which workers are exposed to high volumes of dust (eg drill and blast) or situations in which dust control at the source, mobility and flexibility offer value (eg room and pillar mining).

Apr 16, 2024

By H Asche

The Melbourne Metro project has evolved from the Victorian Transport Plan. MM1 is the second major phase of the proposed separation of Melbourne’s radial railway system, creating a line that will operate independently across the metropolitan region. The central section will run beneath the inner suburbs and the central city. The initial project comprises nearly 8 km of twin bore tunnels, three cavern stations and two cut and cover stations, as well as a dive structure and connections with the existing rail system. This paper describes the development of the geological model, a modification of the rock mass classification system derived during the EastLink project and the influence of the geology on the design of the tunnels and stations for the Department of Transport’s business case.The majority of the tunnelling will be in the siltstone and sandstone bedrock. This material has been extensively folded, sheared and intersected by igneous intrusions. A revised rock mass classification system has been developed for the Melbourne Formation to assist in identifying the important engineering properties of the rock and to rationalise the support types required.The Metro’s tunnel alignment crosses the Yarra Delta deposits in the lower reaches of the Moonee Ponds Creek and again at the Yarra itself near Princes Bridge. These deposits vary in extent and thickness over very short distances. The investigation of these materials has been carried out using conventional drilling techniques in conjunction with sonic drilling methods.Over the central section of the Metro, the positions of the new station are determined largely by transport planning requirements and urban development opportunities. However, the stations, and the tunnels, have been the subject of studies, optimising exercises, and selection processes to arrive at the concept design. This paper describes the influence of the varied geology on the development of the design, and the identification and management of the risks in tunnelling under the centre of Melbourne.

Mar 8, 2011

By E S. Bernard

Toughness testing of fibre reinforced concrete (FRC) at 28 days age is typically undertaken as part of quality control for the many applications where fibres are used in concrete, including shotcrete, tunnel segments, and cast-in-place tunnel linings. The performance achieved at 28 days is usually assumed to be retained with increasing age. However, as the average strength grade of concrete used in most tunnelling applications, including tunnel segments, has steadily increased over the last 20 years, this assumption is becoming increasingly unviable. This is because for some types of fibre the mode of post-crack fibre behaviour depends on the strength of the concrete and can change from a desirable high-energy pull-out mode to a low-energy rupture mode as the strength and age of concrete increases. This paper describes a series of trials performed over two years in which the American Society for Testing and Materials (ASTM) C1609/C1609M beam tests were used to assess the performance of FRC reinforced with two widely used brands of steel and macro-synthetic fibre. The hooked-end steel fibres used for half the beams exhibited a dramatic fall in performance beyond 56 days age as the mode of failure changed from pull-out to rupture. The other fibre did not exhibit a fall in performance with age. This phenomenon highlights the need to quantify performance of FRC at much later ages when long-term performance is required, for example, to resist seismic events or changes in ground stress due to nearby excavations. As an alternative, a reduction factor may be applied to the performance of FRC mixes for which evidence of satisfactory long-term performance is not?available.CITATION:Bernard, E S, 2014. Age-dependent changes in post-cracking performance of fibre-reinforced concrete for tunnel?segments, in Proceedings 15th Australasian Tunnelling Conference 2014, pp 229–236 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By T J. Sullivan, H Pinkster, G Swarbrick

From 2002 to 2006, longwall mining was undertaken directly beneath the Cataract Tunnel, which is a 100-year-old, heritage-listed tunnel in Hawkesbury Sandstone responsible for delivering 20 per cent of Sydney’s annual water supply. At one location, undermining resulted in movement of at least 350 mm along a known fault that transects the tunnel. During this movement, the continued operation of the tunnel was ensured through a careful system of planning, monitoring and management.Of key importance to the success of the operation was the use of advanced numerical modelling to guide operations at all levels, including feasibility assessment, pre-mine mitigation works, monitoring design, operation performance and post-mining condition. This allowed many aspects of the potential impacts to be explored, including joint movements, rock mass deformations and changes in permeability. A key challenge was to successfully model near-field influences on adverse geological structure due to very far-field effects. This paper explains the model’s conceptual development, calibration, performance and limitations.Modelling provided the confidence to manage the impacts of large mining-induced movement on key infrastructure and ultimately predicted fault movement accurately. The fault movement remains one of the highest ever recorded due to mine subsidence.CITATION:Swarbrick, G, Sullivan, T J and Pinkster, H, 2014. Longwall mining beneath critical infrastructure – prediction versus performance of the Cataract Tunnel, New South Wales, Australia, in Proceedings AusRock 2014: Third Australasian Ground Control in Mining Conference , pp 157–166 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 5, 2014

By D R. Wines

The design of near-surface civil infrastructure requires detailed consideration of the geological/ geotechnical conditions, excavation geometry and sequence and ground support measures to ensure stability of the underground openings and minimal impact on overlying or adjacent infrastructure. Twin parallel road tunnels have been designed and built with connecting cross passages and a piggyback busway tunnel as part of a large infrastructure project in Australia. The tunnels were excavated in poor to fair quality rocks using road headers. Temporary ground support includes shotcrete, rock bolts and canopy tubes. Extensive numerical analyses have been performed to analyse the expected behaviour of the tunnels during excavation, including two-dimensional analyses using UDEC and three-dimensional analyses using FLAC3D. Structural defects in the rock are explicitly included in the 2D analyses to examine the potential for localised ground instability. The stress redistribution is captured by the 3D modelling with an accurate representation of the complex excavation geometry and the detailed excavation and support sequence. This paper presents the modelling methodology, numerical results and discussions on integrating both 2D and 3D analyses to achieve reasonable design.

Mar 8, 2011

By M Fuchs

Roadheaders were introduced to mining and tunnelling in the early-1960s. Since this period their main field of application has been for roadway drivages in coal mines and for mineral production, for instance in coal, rocksalt, potash and gypsum mines. Their main field of application in tunnelling is in softer and partly friable rock formations, a suitable area for non-blasting excavation. However, in longer tunnel sections excavators with high ripping forces have replaced roadheaders in many situations. The main arguments against roadheaders have been and still are:a sharp increase in excavation cost with increasing rock strength and increasing abrasivity; and greater risks in conditions which have not been, or could not be, investigated to a sufficient extent. These arguments have, to a great extent, restricted practical roadheader application in production mining and in a lot of æstandardÆ tunnel projects. To address these limitations, factors which could make roadheaders attractive for such conditions and could overcome existing technological difficulties have been investigated. Extension of the economic field of application in hard rock was found to be the most important and the most effective step forward.

Jan 1, 2002

By A Dix

Fire suppression systems are but one of the many technologies currently available to manage operational tunnel risks. However, the actual reasons for their use are often shrouded in mischievous discussions of the marketing variety.The international tunnelling community still stands divided on the merits (or otherwise) of fire suppression systems. For some the debate focuses on their cost compared to the theoretical benefits they bring to human safety.Long standing concerns about their potential adverse effects in an emergency are often at odds with the experience from tunnels which use them. High installation and operational costs are cited as reasons not to use them, yet toll road operators and insurers increasingly use them as a risk mitigation strategy for toll revenue protection.Fact or fiction, myth or reality, should such systems be seriously entertained or are they just another expensive gadget in the escalating array of expensive toys for modern tunnels? Ultimately this presentation argues that they have their place as a risk mitigation measure to achieve a range of objectives. The exact circumstances for their use ultimately fashioning their design and operational characteristics. This is an abstract only. No paper was prepared for this abstract.

Mar 8, 2011

By Luck D

Current methods of mucking out small development tunnels are a major limitation to improved efficiency and high rates of advance. This is particularly true in the deep metalliferous mines of South Africa, where the harsh environment, remoteness of operations and the hard abrasive rock conditions mitigate against the use of the tunnel borer type of equipment. The Loader Distributor Train was designed to overcome the special problems of hard rock tunnelling. It combines advanced innovative technology with proven simple methods of operation and maintenance. The system aims at taking advantage of new, efficient and cost effective power sources in South African mines based on replacing compressed air with electro hydraulics and the new concept of hydropower. It also introduces electronics and computer technology, for both automatic control and fault finding, into the production environment. The system is designed to permit sophisticated equipment to be operated and maintained by a semi skilled labour force. Although still undergoing trials it is believed that the Loader Distributor Train will prove highly effective, and that the new concepts offer considerable potential in areas other than flat tunnels, in particular the cleaning of inclined shafts.

Jan 1, 1986

By W Curlewis, D Hake, Z Cuthbert

The South Island Line (East) will be a medium-capacity railway covering approximately 7 km from Admiralty Station to South Horizons Station on the south side of Aberdeen Harbour in Hong Kong, with intermediate stations at Ocean Park, Wong Chuk Hang and Lei Tung.South Island Line (East) Contract 904 project is located on the island of Ap Lei Chau at the southern side of Hong Kong island and requires extensive construction works to be completed in close proximity to the existing residential estates of South Horizons and Lei Tung. The project also has areas of significant cultural heritage, including 18th and 19th century temples and historical gravesites. Owing to the site access constraints and location for the project, detailed planning and methodology innovations have been required to ensure the most effective and responsible means of delivering the project works. To excavate the tunnels using drill-and-blast techniques in these restricted locations, the maximum instantaneous charge weight that could be fired while blasting was severely limited. To overcome these restrictions, the project team developed and pioneered the use of ‘deck loading’ in Hong Kong to minimise the impact of blasting operations and has successfully implemented double- and triple-deck blasting operations during the completion of tunnel excavation works.Upon completion of the drill-and-blast excavation, the tunnel lining works were completed using both in situ concrete lining with travelling forms and permanent shotcrete works.CITATION:Curlewis, W, Cuthbert, Z and Hake, D, 2014. SIL904 Hong Kong – Drill and Blast Tunnels, station blasting innovations (double- and triple-deck blasting) and lining solutions, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 21–28 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By C Harrison, A Bowskill

The Ambuklao hydroelectric dam was originally constructed in the 1950s in the remote and mountainous region of the northern Philippines. Following its construction the dam has suffered heavily due to siltation and a partial collapse of the intake structure due to a 7.8 magnitude earthquake that struck the region in 1990. Between the years 1990 and 1999 the power station progressively lost its capacity to generate power. In 1999 the owner took the power station out of commission. The power station remained idle over the next 12 years. In 2008 the power station was sold to a new owner who commissioned the rehabilitation works.The rehabilitation project restored the operating status of the power station in June 2011 and increased its capacity from 75 MW to 105 MW. The civil contract of the rehabilitation project required the construction of a new intake structure behind an in situ rock coffer dam on the edge of the existing reservoir, new 6.2?m diameter × 124?m deep blind sunk shaft behind the intake structure, which connects to a new 6.8?m horseshoe profile headrace tunnel that ultimately connected onto the existing vertical penstocks which feed three No 35 MW Horizontal Turbines rated at 155?m head.The unique challenge in rehabilitating this existing hydropower station involved finding solutions that would conclusively deal with the challenging geological and hydrogeological conditions associated with excavating new tunnels and a drop shaft beneath a live dam.McConnell Dowell was awarded the civil works package for the rehabilitation works in August 2008. The Ambuklao rehabilitation program took 33 months to complete.Over 600?m of tunnels were excavated in highly weathered and often challenging geotechnical conditions via drill and blast with the extensive use of high-pressure fissure grouting to control groundwater ingress that was surcharged by the dam.This paper focuses on the use of high-pressure fissure grouting that took place to enable the excavation of the new waterway system and intake structure.CITATION:Bowskill, A and Harrison, C, 2014. High-pressure fissure grouting for drill and blast tunnelling, Ambuklao, Philippines, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 141–152 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By J Y. C Lo

The construction of two drainage tunnels and the associated subvertical drain system at the Po Shan area in Hong Kong was completed in December 2009. This project is the first of its kind to utilise drainage tunnels and a network of subvertical drains to regulate the groundwater table to enhance the long-term stability of the hillside of Po Shan area.The groundwater levels, monitored by preinstalled piezometers, once exhibited dramatic drops during drilling of the subvertical drains; however, have recovered from natural replenishment after effectively plugging of the drains. The level of groundwater drawdown is in line with the design function of the subvertical drains. In order to understand the groundwater flow pattern in the Po Shan area during and after construction and to set out operation schemes for the subvertical drain system so as to control the groundwater table in the Po Shan area, a post-construction review has been carried out to examine the behaviour of the drainage system and its impact on the surrounding subsurface groundwater flow.This paper presents a review of the groundwater monitoring data during and after the construction of the drainage tunnel system covering a period of over 3.5 years. A simplified conceptual hydrological model is developed, which has been verified by the monitoring data, to capture the key elements with regard to groundwater variations in different stages of the construction. The performance of the tunnel and subvertical drain system as revealed from these field measurements is discussed.

Mar 8, 2011