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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

MICRO TUNNELLING – METHODS AND DEVELOPMENTS PAUL NICHOLAS Wirth Soltau Micro tunnelling ABSTRACT Micro tunnelling is a mature method of construction using pipe jacking, developed in Japan in the 70's and in Europe in the 80's and into the USA in the 90's. At the start the method was used for the installation of jacking pipes of less than DN800 and for lengths not exceeding 60m. Today we are able to use the method for diameters of up to DN3000 and for drive lengths of over 2000m using sophisticated computer controlled slurry micro tunnelling. At the other extreme for small diameter pipes there is extensive development in the use of pilot tube micro tunnelling which can now be used to install pipes from DN100 to DN800 for drive length of 125m at a greatly reduced cost. This paper will discuss some examples and look into the future of micro tunnelling. INTRODUCTION Firstly we should try and define micro tunnelling terminology as accepted by various guidelines and specifications worldwide. The following definition is not accepted by all but is used by the author. In the USA the new ASCE Standard Construction Guideline for Micro tunnelling defines it as a 'Trenchless Construction Method' and does not impose size limitations. A tunnel may be considered a micro tunnel if all the following features are utilized during construction. Remote Controlled Personnel entry is not required for operation Guide Normally references a laser beam, capable of installing gravity sewers to the required tolerance for line and grade. Pipe Jacked The pipeline is constructed by consecutively pushing pipes using a jacking system. The pipe is installed as spoil is continuously excavated and removed.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Continuous Support Continuous pressure is provided to the face of the excavation to balance between groundwater and the earth pressures. There are several tunnels being installed under the name of micro tunnelling by methods that do not comply strictly to the above definitions, for the purpose of this paper all these trenchless methods may be referenced and they include the pilot tube method and small diameter systems with vacuum spoil removal. PROJECT CONSIDERATIONS It is a fact that failures are better remembered than successes and in micro tunnelling this is particularly true. Recent developments in technology that have been fully incorporated into the equipment have allowed the envelope in project design for micro tunnelling to be pushed even further, it is inevitable that some of these projects will have problems but without these testing projects the speed of development would be slowed down considerably. Many of the problems on a given project can be avoided by proper site investigation, design and understanding of construction parameters. Some of the key parameters to be considered are: Length and Diameter of Drive Typical drive lengths are in the 100 m to 170m (300 ft to 500 ft) range but drives of over 1000 m (3,000 ft) are possible in the larger man-entry diameters. Length of drive is determined by expected jacking forces, where axial pipe load capacities are large the use of intermediate jacking stations will be required, potential wear on cutters, guidance system, and cost/ability to place intermediate shafts. Long drives with small diameter micro tunnelling machines are riskier than shorter drives. Straight Versus Curved Alignments Straight alignments are recommended because of easier guidance, lower concentrations of jacking stresses in the pipe string, and simpler future maintenance. Curved alignments are unusual in the U.S. but are more common in Europe and Asia. Curved alignments allow longer drives with fewer shafts when following curved alignments of public rights-of-way. Depth of Drive and Water Table Depth The depth of drive and its relationship to the water table can determine whether micro tunnelling is the preferred method versus open cut and other trenchless methods. It also determines the hydrostatic pressure that must be balanced at the machine face. High hydrostatic pressures require additional jacking forces to advance the machine against the pressure. In addition, if the water pressure is very high, precautionary measures may be needed to avoid the pipe string from moving back into the jacking pit whilst the new pipe sections are being added. The main impact on cost of micro tunnelling due to depth is the increased cost of the shafts required. Shafts are a major cost item in a micro tunnelling project. Shaft dimensions typically range from 2.4 to 6 m (8 to 20 ft) in length or diameter for

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

pipe lengths of 1.2 to 3 m (4 to 10 ft). The goal is usually to use the minimum shaft size that will allow reasonable production rates and thereby minimize the cost associated with this component. SOIL CONDITIONS AND THEIR VARIABILITY Soil or rock type and variability of soil conditions determine the type of cutter head and machine to be used and the expected advance rate. A radical and unexpected change of ground conditions can prevent a drive from being completed and require hand tunnelling or a rescue shaft to permit the job to be completed. Likelihood of obstructions or boulders: boulders or man-made obstructions also can prevent a drive from being completed and it is often difficult to adequately determine the risk of obstructions being in the path of the bore. MACHINE TYPE Newer micro tunnelling machines have additional features that allow increased and/or more reliable performance under a range of ground conditions and the different types of machines available (principally slurry and auger boring) have different characteristics that make them more suitable under different site and job conditions. Use of a machine already owned by a particular contractor is advantageous from a cost point of view but the machine should be suitable for the job conditions. Cutter Head Design The cutter head is usually selected by the contractor but the selection of the cutter head is dependent on expected soil conditions and thus is dependent on the geotechnical report. A cutter head that does not match in suitability for the expected soil conditions will cause slow advance rates at best and be unable to advance at worst. Over cut The amount of over cut also is usually selected by the contractor but the engineer may choose to limit the amount of over cut when very small settlements are required. Major settlement problems usually are related to loss of control at the excavation face rather than too much over cut. Large over cuts coupled with lubrication and high groundwater pressures may give less resistance against the pipe being pushed back into the shaft from the water pressure on the machine face. Pipe Selection The owner may select one particular pipe type or may allow the contractor to choose the pipe according to specified pipe characteristics. If the pipe cracks or fails during installation, repair options are very limited in non-man entry pipes. If the failed pipe is near the beginning of the pipe string, additional sections may be jacked until the failed pipe can be removed from the arrival pit.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Lubrication Selection Lubrication can lower jacking forces and reduce the risk of pipe damage on most micro tunnelling jobs. It can be critical on long micro tunnelling drives. If lubrication is considered critical to the success of a drive then its use may be included in the contract documents and bid items. For long drives with IJS the use of automatic bentonite systems with programmable valves should be considered. Slurry Handling, Separation and Disposal Decisions on these items are typically made by the contractor but it is important that accurate soils information be provided to the contractor to properly design the system. Large amounts of fine material can be difficult to remove from the slurry and may require hydro cyclone or centrifuge separation systems. Removal and dumping of wet material from site is an important consideration. Size of Jacking Pit Versus Length of Pipe Sections The size of the jacking pit determines the length of individual pipe sections that can be used. Larger pipe section lengths increase productivity but increase the shaft size and hence the surface disruption caused by the micro tunnelling operation. If the contractor’s working area is restricted as to location and/or size, then this must be clearly understood. Ability to Sink a Rescue Shaft If rescue shafts are impossible at any point along the drive, this needs to be known in advance and accounted for in the geotechnical investigation, the selection of the size and type of machine. Crew A highly-skilled crew of four to eight men is typically used, and production rates are approximately 10 to 20 m/day( 30 to 60 ft/day) for routine jobs, although rates of 65 m/day (200 ft/day) or higher have been achieved. Mobilization time typically ranges from three to ten days. EQUIPMENT DEVELOPMENTS Engineers have always been looking for solutions to problems and for pipe installation this means using trenchless methods at greater depths for longer drives in difficult ground conditions. It is these requirements that have driven the development of the equipment over the last few years. These developments include: Digital Control and the Use of Computers Curved Micro tunnelling Hydraulic Pump and Motor Developments Water Jets

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Rock Cutters Slurry and Lubrication Slurry Pumps Laser Development Pipe Improvements Digital Control and the Use of Computers The industry standard has moved away from analog systems to fully integrated digital ones as can be seen in modern large diameter TBM control systems. Automatic fault warning and redundancy is incorporated and the number of functions is not limited and new functions such as gas detection may also be added easily. The new guidance systems such as those from TACS (Wirth Soltau) and VMT (Herrenknecht) have three-dimensional graphical representation of the MTBM showing the roll and future position of the MTBM with reference to the laser. This is achieved by double plate targets and the latest digital cameras and processing systems. The digital control systems (PLC) are generally linked to a central computer and display allowing for accurate recall and record keeping of all data and functions for future reference. These systems also allow for manuals and drawings used for maintenance and repair to be immediately available stored on the computer. A modem link may allow for software downloads and for technical assistance on fault finding without a site visit from a technician. One of the results of all these new systems is operators can be trained more easily and they are able to install pipes accurately to line and grade in difficult conditions with less overall experience. Curved Micro Tunnelling Drives The new guidance systems incorporated also allow for the installation of curved drives either by the use of laser technology with the use of reference prisms and total survey stations which is generally the system used in diameters of 2m and larger. In smaller diameters the use of Gyro compasses (Schwarzer) with hydrostatic grade correction are becoming popular and have provided very accurate curved drives for small DN600 pipes. Generally, the minimum curvature is 100m with standard equipment and pipes but smaller radiuses (6m) have been completed recently with special micro tunnelling equipment and pipes developed in Japan. Hydraulic Pump and Electric Motor Developments With the need for MTBM’s (Micro Tunnelling Boring Machine) to work in variable grounds conditions and deal with rock and obstructions there has been one main answer "POWER". The amount of power now available to the cutter in new equipment in particular hydraulic driven systems has increased by 50%. Today a 1350mm OD MTBM could have a 132KW power pack installed in the MTBM giving over 200,000Nm of torque and up to 18RPM on the cutter. This has only been made possible due to electric motors becoming smaller and improvements in hydraulic pumps and motors. This added power at high cutter RPM with improved cutter technology has made rock micro tunnelling practical and successful.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Water Jets The problems of slurry machines in plastic clays are well documented typically older machines suffer from low production and sometimes high wear in these ground conditions. In 1997, high-pressure water jets were added for the first time by Soltau to the front of an MTBM. These jets were set to wash the face of the cutter and to rotate with the cutter, the jets are pointing backwards to clear the crusher, which typically becomes blocked in clay. The jets are typically running at a pressure of 200 to 250 bar and they add about 40litres per min of water to the discharge slurry system. Production through clay typically doubles when the jets are used. Rock Cutters Experiments with rock cutters on the face of MTBM’s started in the 80’s but the success was limited to shorter drives in moderately soft rock. One of the problems was the pressure seal on the discs required to work in a pressurized slurry environment. Typically, seals washed out and the bearings failed. In the mid 90’s the development and use of rock disc’s diverged. New cantilevered "mini disc" technology was introduced and these discs were about 150mm diameter and in the laboratory provided high cutting rates. As an alternative, the traditional rock disc cutter was made smaller at 200mm diameter. As these technologies evolved the use of cutters with two or three disc edges with tungsten inserts became popular as they allowed large bearings and consequently a longer life. It took time for the manufacturers of cutters to understand that on slurry MTBM the cutters could not be changed during a drive and that the life of the cutter disc was more important than production. Today on heads of 900mm and up a mixed face, cutter with picks and roller cutters is common and these cutters have been successfully used in mixed ground with large boulders. For solid rock cutter heads some of the raised bore, disc technology is utilized, as the RPM and torque of the MTBM’s has increased allowing higher disc loadings to be used, production in rock has improved considerably. For hard rock stronger than 100mpa generally the MTBM needs to be 1320mm OD or larger. Small diameter rock (DN400 - 600mm) heads have been utilised but there is no guarantee of their success in any given type of rock, generally, these small rock heads should only be used in sedimentary rock with rock strengths of less than 80mpa. As longer drives were required, it was recognized that the ability of changing cutters would be required; this has been achieved in MTBM’s over 1500mm outside diameter. These machines typically have a central access of about 550mm and are likely to have the ability to pressurize the cutter face with compressed air to allow disc changes below the water table in unstable ground conditions. These machines have been developed for use in very mixed ground conditions including solid rock. Slurry & Lubrication The use of Bentonite and polymer as pipe lubrication has been routine for a long time to reduce jacking loads. In micro tunnelling the circulating slurry has generally been water as high flow rates kept the material moving and in suspension. Today there is experimentation with polymers in the slurry system to breakdown sticky clays in the cutter and then additional polymers added to the discharge slurry to improve the separation on the shakers. This area requires further research.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Slurry Pumps With the addition of slurry jets (additional to High pressure water jets) the power of slurry systems has increased dramatically to make these jets very effective. Older DN800mm systems may have had a 12kw charge pump and 18kw discharge pumps with no flow control apart from diverting valves working with 75mm slurry lines. Today a typical system for DN800 pipes will have 37kw pumps both with variable frequency control and charge and discharge flow meters with 100mm slurry lines. The new pumps can pass 75mm solids and due to the special steel used in the body and impellor, very little maintenance is required. Laser Development Lasers have continued to develop, the latest models are effective to 600m and achieve a usable "spot" at this distance by having the ability to focus the spot electronically as the distance increases. Pipe Improvements The original pipe jacking pipes used for micro tunnelling were reinforced concrete and these have steadily improved with spun concrete and steel banded bell and spigot joints. The development of jacking pipes from other materials has really helped the spread of micro tunnelling. To some the development by the clay pipe industry to make a jacking pipe was a surprise but today the majority of pipe used in micro tunnelling in the 200mm to 600mm inside diameter range are made of vitrified clay pipe. Centrifugally spun Fiberglas reinforced polymer mortar pipe was developed in Europe primarily as an open cut water pipe it was used on some occasions for pipe jacking but in the late 80’s in the USA the pipe became the dominant pipe used in all sizes in micro tunnelling. In the early 90’s from Germany polymer concrete pipe was developed this was an ideal solution for a jacking pipe with the strength and wall of concrete and the chemical stability of Vitrified clay and glass fibre pipe. The use was limited to Germany with a small percentage being imported into the USA. New factories have been set up in USA, Malaysia, Taiwan and Middle East Steel pipe was only used for special casing applications; the time to weld made the productivity very low. In the mid 90s Permalok was developed this is a bell and spigot in wall joint for steel pipe which pushes together and welding is not required. This joint is only available in the USA and some 15% of the total installed micro tunnelling pipe is steel with Permalok ends. It is a good product for use in very difficult ground conditions where the ability to "pull back" is important. These developments have allowed projects to be completed that we would not have thought possible a few years ago. We are seeing projects being completed at one end of the spectrum in large diameters up to 3.6m outside diameter for long drives of over 1000m in mixed ground conditions and at the other end small diameter of 150mm in rock.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

Examples of Large Diameter Projects. SAMUT PRAKAN WASTE WATER TREATMENT PROJECT – THAILAND The complete project covers an extensive area, some 127 sq.km, just south of Bangkok with a population of 765,000. The complete project that includes the collectors, treatment plant and outfall was awarded to the VSK a Thai joint venture. Collecting both industrial and house hold waste, via some 120km of sewer lines, from both banks of the Cheo Phraya river, most will be installed by micro tunnelling pipe jacking methods. The diameters vary from DN300 to 3000 pipes; collection is via gravity flow to a treatment plant at Bang Khlong Dan, some 50kms out of Bangkok City centre. For the river crossings, twin 800mm lines, were installed by directional drilling methods, and the 3.5km long out fall, into the Gulf of Thailand, by segmental tunnelling. The works, outlined here, are the main trunk sewer, running parallel to Sukhumvit road, from the Khlong Dan treatment plant to Samut Prakarn itself, via an intermediate pumping station. The main line, 3m dia. runs for some 30km and was installed by micro tunnelling pipe jacking methods in 61 drives. The drives, at depths of 8 to 18m, were at a maximum length, in several cases, of 600m from the drive to the reception shaft. Ground Conditions The water content of the soft clay, on the tunnel horizon, can vary between 40% and 140%. In addition, in these deposits of soft to medium marine clays and alluvial soils it is not unusual to find shells and sand lenses. The clay is not homogenous, and as well as varying in water content, the shear strength, and density, can vary considerably over a very short distance. Shear strength generally increases with depth, but site investigations have shown that the shear strength can increase suddenly by up to 5 times from a low 7.0 kN/sqm to 35.0 kN/sqm within one or two meters. Jacking Pipe The pipe was manufactured at a purpose built factory adjacent to the site. It is a dry cast, reinforced concrete pipe, with an ID of 3000mm and an OD of 3600mm, in 3m lengths. To ensure adequate corrosion protection it is equipped with an internal, in-situ, HDPE liner, which is site welded, at the pipe joints, after installation, to give a continuous liner. Individual pipes weigh in at approximately 22.5 tonne, and are produced and tested to meet with the necessary BS. Requirements. Micro tunnelling Equipment The equipment consisted of five complete micro tunnelling systems supplied to the VSK Joint venture by Soltau Micro tunnelling of Germany. Apart from the shields, the equipment was standard for an EPB micro tunnelling system with a control booth and power pack located on the surface. The jacking system consisted of 4 x 300ton telescopic cylinders.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

The shield itself is in two sections to allow for launch and recovery from minimal sized shafts. The Soltau EPBs are 3.6 m outside diameter “clay intrusion shields” with an excavation system designed specifically for the ground in the region using well-established concepts. Unlike most EPB shields there is no rotating cutter fitted. The 4m long cutter head, at 55 tonne, has a 2.5 m-long articulated steering section, which is floating on a 2-meter long can, up to 5-degree articulation in the steering is controlled by 4 x 100ton steering cylinders. The material to be excavated is "gathered" in the cone section and augered back to be automatically and continuously loaded into the muck pump, which pumps the muck to the surface, a variable speed auger is used to control the system. To assist in transport of the material the cooling water from main motor, located in the trailing can, is injected into the muck line and the work face. Polymer injection was possible but was not necessary. The trailing can, at 3.5m long and some 32 tonne, is bolted on to the cutter head. Inside the trailing can is the power pack for the operation of the muck pump and all other shield functions. It is powered by a water-cooled electric motor fed from the surface. Additionally within the trailing can are two sets of hydraulically controlled anti-roll wings, (ploughs) which are extended or retracted, to control the roll of the shield. The muck is pumped to the surface for disposal either into trucks or skips. Alternatively, as was the case on many sections of the line used for filling of fishponds, as preliminary fill material for future road widening. It was found that is was possible to pump the excavated material up to a 1000m away from the face with nominal pressures in the muck lines, i.e. as little as 40 to 50 bar. Construction Once underway, the shaft sinking progressed initially at a nominal rate and pipe jacking itself was started in late May 1999. The work progressed at a rate acceptable to all parties, peaking at 3000m of pipe installed during the month of July 2000. Substantial completion of 29Km of the pipe jacking was December 2000. Finishing works, such as manholes etc were completed in 2001 ensuring this section of the works was completed on schedule. Most of the early predictions, such as production rates have been achieved or surpassed, to the extent that drive rates of 30m per 12-hour shift were the norm. The above project could have been completed using other methods such as a segmental tunnel, with a standard EPB machine or a slurry system. VSK pipe Jacking own EPB equipment for segmental tunnels and it was a far sighted decision by them to choose remote controlled pipe jacking system (micro tunnelling) with a shield without any form of cutter relying on intrusion of the material and to automatically load and pump that material to the surface. This system was fast with many of the drives being completed in less than 3 weeks. A second example of a project completed successfully shows how only the latest developments in technology allowed it to be completed successfully.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

TOLT PIPELINE NO.2. - SEATTLE USA Crossing of the Snoqualmie River as part of the Tolt Pipeline No. 2 project for Seattle Public Utilities. Tolt Pipeline No. 2, an aqueduct that will extend roughly 40Km, will increase drinking water capacity to Seattle The Snoqualmie River crossing, one of two micro tunnelled crossings on Tolt, was in an area with liquefiable soils and artesian groundwater pressure. The liquefiable soils presented a concern that the pipeline could slide during an earthquake, which led to a deep design, and the artesian conditions and the depth prohibited open-cut as a viable construction option. The original plans were for three separate drives, but were altered due to complications arising from construction of an intermediate shaft using soil mixing technology. The revised plans combined the original 335m crossing with a 100m drive. The two drives were designed separately to accommodate a change in grade, so the revised plan gave a single 435m drive at a steeper angle uphill. In addition, the drive had to cross through the intermediate partially built soil-cement mixed shaft. The project was awarded to Tri State Construction who awarded the tunnelling as a subcontract to Northwest Boring an experienced micro tunnelling and pipe jacking contractor in the Seattle area. Northwest Boring purchased a 2280mm. outside diameter MTBM from Wirth Soltau of Germany the RVS 800 STS/TACS. North West Boring asked the micro tunnelling system to be designed as a state of the art slurry micro tunnelling system for use on this project and future projects in the region. The geological conditions in the NW of USA are very difficult from solid rock to deep soft flowing alluvium deposits with large boulders and tree obstructions, the equipment was designed to deal with as many ground variations as possible. On Tolt the equipment was to install, 2235mm. OD Permalok jointed steel casing. The equipment was the most powerful micro tunnelling system to be used in the USA with 250Kw of power on the cutter and 0 to 12 rpm. The cutter head was of a mixed ground type equipped with disc cutters and carbide teeth. A unique variable adjustable crusher that allowed the crusher opening to be opened and closed whilst tunnelling was being advanced, this was the first of its kind in the World. It was designed to help deal with clay that requires an open crusher, and fine sand and alluvium which requires a closed crusher it also helps clear timber that can plug the crushing and slurry spoil removal system. To assist with the jacking on Tolt three intermediate jacking stations, which provided an additional 800 tons of jacking force each, and an automatic bentonite injection system were used to provide lubrication along the entire pipe string. The bentonite injection system consisted of a piston type pump and 30 valves spaced along the pipe string. The valves were computer-controlled via a touch screen and bentonite could be placed at any point along the tunnel at any time. The result of this bentonite system was that they had very low jacking loads despite the depth the fine sand, length of the drive and the diameter of the pipe. The project was delayed about nine months due to problems with shaft construction. The shafts were being constructed by cement mix vertical piles in concentric overlapping rings. This delay and the problem with the shaft construction was the reason for eliminating an

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

intermediate shaft and created the 430m drive which needed to be completed before an October 31st environmental shut down which lasted 6 months. The pipe Invert depth was 25m and the shaft was made available to the tunnelling contractor in mid-August 2000. There was an early set back when the entry seal failed under the hydrostatic head. After relaunching the machine tunnelling proceeded well, the ground was medium to fine sand with some gravel and up to 30m, a day was installed using 4.8m long pipes. When the machine was at about 330m it encounterd the soilmix area of the abandoned intermediate shaft and within 5m of entering this area the MTBM suddenly became stuck. It was clear that the actual MTBM was stuck as the pipe string could be moved along the whole length. To start the machine and pipes moving again extra jacking cylinders were placed in the first intermediate jacking stations to increase the thrust to 1,400 tons .The jacking station had to be reinforced for the additional load but the pipes and machine were moved and the drive was completed without incident after that. There is speculation that the reason for the problem was that the higher density soil mix columns actually might have dropped onto the top of the machine so jamming it into place. Fog and rain also challenged the crew. On one occasion, the rain-swollen river came within inches of flooding out the main shaft. In addition at times the laser could not penetrate to the target due to a build up of mist in the tunnel due to condensation in the cold steel pipes this presented problems for the laser guidance systems. Despite the challenges, Northwest Boring holed out on Oct. 21 and demobilized before the deadline. Although larger pipe has been installed and longer drives completed, this drive is believed to be a micro tunnelling record in the United States for its size and length. The project was then shut down for 6 months and started again in the following spring. A second drive, connecting the crossing to the pipeline, began in April after the environmental shutdown was completed in July. This drive, approximately 220m, went through an area categorized as a prehistoric landslide area, meaning the crews could expect to find anything from sands and silts to boulders and tree trunks. The Contractor used a bentonite slurry to control slurry losses to the coarse material and to help convey the coarse material encountered to the surface the ground was variable but primarily gravel and sand. The machine successfully tunnelled through all the different material including timber and boulders, it was in this section where the use of the variable crusher was most useful. The machine was received in a frozen shaft to complete this very challenging project. SUMMARY The “State of the art” equipment available to the industry today is highlighted by both the examples. The first in Thailand where equipment was specifically made for the known ground conditions to optimize production and reduce equipment costs and the second where equipment was designed to deal with highly variable and difficult ground, to deal with the ‘unknown’ and avoid a change of condition claim.

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International Conference and Exhibition on Tunnelling and Trenchless Technology 7-9 March 2006, Subang, Selangor, MALAYSIA

THE FUTURE In the last few years, the development has been in the larger diameter machines as illustrated above. In the future, we feel development will be in small diameter systems and their capability in rock. Now rock micro tunnelling is generally only successful from 900mm OD. an exception being the air vacuum systems in use in SE Australia which are able to accurately install 150mm pipe in rock. However, we see a future in the development of HDD techniques in the small diameter micro tunnelling pilot bore systems which will give a much lower cost per meter solution for accurate installation of small diameter pipes in hard ground. The latest pilot tube micro tunnelling systems are using air hammer technology to drive small diameter bores in medium hard rock. We also believe that as the length of micro tunnelling drives increases to well over 1km single drives the use of alternative gyro based steering systems will become normal. The differentiation in construction methods between Tunnelling, Micro tunnelling and Horizontal directional drilling will become even more vague and the use of the term construct by “trenchless technology” will be seen in more and more construction specifications where the contractor will have to choose the best method and equipment to install the required line to the required specification. It is not by accident that some of the major TBM manufactures now also build and supply micro tunnelling and horizontal directional drilling equipment.

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