Pipejacking for Pantai Sewer Network in Kuala LumpurPhase 1, Package 1 of a major sewerage project is currently being undertaken by Shimizu-Road Builder-Hitachi Plant JV in Kuala Lumpur (KL), Malaysia for the government. Phase 1 is divided into several sub-projects. The Pantai trunk sewer (click here) is a sub-project consisting of a new 5.4 km-long segmental tunnel sewer, 2.5 m diameter and 2.8 m diameter internally, which will carry sewage to the Pantai sewage treatment plant, the upgrading and expansion of which forms another sub-project. The Pantai sewer network sub-project, totalling around 13 km in length, consists of the following five sections: Dang Wangi sewer diversion, Brickfields sewer diversion, Petaling Jaya trunk sewer, Damansara sewer diversion, and Old Klang Road trunk sewer (see Figure 1 here). Visit www.shimz.co.jp/english/index.html, www.rb.com.my and www.hitachi-pt.comWith the exception of Damansara, all the above sewers connect into the new Pantai trunk sewer. The sewer diversions will intercept the existing sewer branches before they reach the existing 1.5 m-diameter trunk and divert the flow into the new trunk sewer. The main purpose of the Petaling Jaya and Old Klang Road sewers is to provide a point to which future diversion projects in those areas will be directed. The Puchong sewer network sub-project includes around 2 km of pipejacking and will divert the existing flows at several small local sewage treatment plants into an existing pumping station.Due to a combination of space constraints, heavy traffic conditions and an increasing awareness of the social costs of more traditional methods, the pipejacking method has been specified to install most of the sewers. This is the biggest and most complex pipejacking project ever undertaken in Malaysia, and expertise has been pooled from Japan and Europe to assist local contractors, who have limited experience.Eleven remote-control slurry TBMs and three open-face manual excavation shields have been used to install HDPE-lined reinforced concrete pipes, from 300 mm to 1,800 mm internal diameter. This is the biggest and most complex pipejacking project ever undertaken in Malaysia. Following six months of planning and investigations, pipejacking started in July 2004. One river crossing about 80 m long is starting now, with a Rasa TBM. Then in around May, there will be a final 60 m river crossing. Then 100% of the pipejacking will be finished.Utility diversionsIn many cases, utility diversions had to be carried out before shaft construction could commence. Due to the lack of availability of accurate records and the relative unreliability of surface-based detection it became apparent that trial trenching should be carried out at each shaft location to determine the exact location of utilities. In Dang Wangi, oil-filled 33 kV electricity cables had to be diverted. As these cables are no longer commonly used, custom-made joints had to be fabricated in Holland to join the existing cable to the modern XLPE type. This work delayed shaft construction by many months.Shaft construction110 launch and receiving shafts were required. Three different shaft construction methods were adopted to allow for varying soil conditions, site physical constraints, environmental considerations and availability of materials. They are steel sheet piled (rectangular), cast in-situ reinforced concrete caissons (circular) and finally a composite of the former two methods. See Figure 2 here.Initially, two main shaft methods were selected, i.e. steel sheet piles for shallow shafts (up to 9 m deep typically), and cast in-situ concrete caissons for deep shafts (typically 9 m to 25 m). However, during the construction of the first few caissons in the Petaling Jaya area, difficulties were encountered at depths of around 5-7 metres with the relatively soft ground collapsing into the excavation. In one case, as the excavated face could not remain stable in the time between excavation and the placement of reinforcing mesh, formwork and concrete, casting could not proceed. Grouting was carried out to stabilise the soil and the shaft was completed successfully.In the next two shafts, groundwater flow behind rings cast at a higher level created voids behind the shaft. The reduction in friction caused one of the shafts to settle approximately 200 mm. Again grouting was carried out, and ring height reduced from 900 mm to 500 mm. The shaft was completed but not before losing valuable time. Shimizu therefore decided to construct some shafts using a combination of sheet-piles at shallow depths, and cast in-situ rings thereafter. To minimise the consumption of sheet piles another method was adopted. This involved driving a ring of sheet piles around the external diameter of the caisson, and then constructing the in-situ caisson within the protective piled “curtain”. Once hard ground was encountered, the piles were removed and made available for other shafts. This development led to the caisson method also being adopted for some shallow shafts.AlignmentInitial soil investigations were carried out in 2001. This information helped the designers determine suitable manhole locations, and therefore pipejacking lengths. The sewer alignment includes several curved drives, and passes through widely-varying soil conditions, under and through river wall structures, and close to many existing underground structures, making construction particularly challenging. The sewer route includes at least six river crossings. Pipejacking was specified for the majority of the sewer networks. In any case, the depth of the sewers (up to 21 m, but typically 5-13 m) and the congested nature of the urban environment would make open cut methods impractical and/or prohibitively expensive.Several curved alignments with radii as low as 200 m were required to thread past a variety of subsurface structures supporting elevated road, rail and light transit systems. The total network length is 13 km. There are several drives 250-340 m long. The longest is a 371 m-long 1,800 mm-diameter curved drive in Dang Wangi. This will be the longest pipejack ever to have been carried out in Malaysia.Soil investigationThe KL area in general consists of Kenny Hill formation sedimentary deposits. This is mudstone, shale, phyllite and sandstone, usually weathered into silt, sand and clay residual soils of a varying depth and mixture. This is overlaid by relatively thick alluvial deposits composed of soft clay, silt, loose to medium dense sand and gravel. Fill exposed to the ground surface overlays these deposits. Groundwater levels are typically 2-4 metres below ground but this varies according to rainfall.The initial soil investigation boreholes were carried out using multi-speed rotary boring machines. Standard Penetration Tests to BS1377 were done at 1 to 1.5 m intervals, using split-barrel samplers. A wide variety of soil conditions were discovered, including sand, silt, clay, gravels, limestone, sandstone, quartzite, shale and granite. To verify these conditions and to obtain further data Shimizu chose to carry out 35 further boreholes. Jacking pipe designPipe diameters on the project vary from 225 mm to 1,800 mm. Vitrified clay and reinforced concrete jacking pipes were specified for small and large diameters respectively. However, due to concerns regarding quality and handling and the number of relatively long drives (up to 122 m) it was agreed to use reinforced concrete for all diameters. All pipes are designed and manufactured to BS5911 and are being supplied by manufacturers in Johor Bahru and Ipoh, Malaysia. (see Figure 3 here).Maximum expected jacking loads were calculated using the method from the 2000 edition of the Japan Sewage Works Association Standard. The maximum allowable jacking load of the largest 1,800 mm pipes, with a barrel thickness of 160 mm, is 1,600 t. Concrete grade is 50 or 60 N/sq mm.The pipes are typically 3 m long. However, for curved drives, shorter pipes have been used to maintain a maximum angular deflection of 0.5° at each joint in accordance with the Pipejacking Association guidelines. This is to prevent an excessive concentration of jacking load on the pipe joint face. The flexible pipe joints consist of a cast-in grade-316 stainless steel external collar. Finned natural rubber ring seals provide water tightness and are applied to the spigot end of the pipes before the pipes are joined in the jacking shaft.Pipes over 900 mm in diameter have a 1.5 mm-thick HDPE lining bonded to the concrete using an anchor knob system. The HDPE is applied to 330° of the pipe internal circumference, with the invert (30°) unlined. Pipes below 900 mm diameter have a 38 mm sacrificial concrete lining. This is because man-entry into pipes of this size, for plastic welding at the joints, is not allowed. All pipes greater than 900 mm diameter also included three lubrication and grouting ports. Both vertical wet-casting and pipe spinning methods were used for manufacture.Pipejacking equipment selectionThe most important consideration when selecting pipejacking equipment is that the TBM must be well-suited to the ground conditions. The choice of methods for spoil transportation and separation is also important. Other considerations include availability, speed, cost and minimum shaft size. With the exception of connections into existing sewer manholes and a small number of drives less than 30 m in length, slurry systems have been used. The systems used on the project were from four different manufacturers from Europe (Herrenknecht and MTS) and Japan (Rasa and Iseki). Visit www.herrenknecht.com, www.mts-p.de, www.rasa.co.jp To complete the entire process, product pipes, lifting equipment and spoil removal trucks are required. The selected TBMs are all characterised by a rotating cutting face forming the front of a cone-shaped slurry chamber, through which excavated material passes into the slurry pipes to be transported to the surface for separation. The face cutting tools can include teeth, scrapers, discs and rollers. Excavated material is crushed as it passes through a gap between the rotating shaft and the cone. In Iseki Unclemole heads, the cutting head travels along a trochoidal path. In the MTS 2000 system used in Dang Wangi, it was possible to move the crusher cone forwards and backwards to adjust the crusher gap size to suit varying ground conditions.The shields were articulated, enabling them to be steered horizontally and vertically. Three or four hydraulic steering jacks are common. The jacks are fixed across the articulation point allowing the operator to control the direction of the shield. The sewer alignment tolerance for the project is 75 mm horizontally and 25 mm vertically and this is achievable under normal circumstances. The outer diameter of the shields is greater than that of the pipes. This is to create an annular space around the pipes, to reduce friction, and on larger diameters, to allow the injection of a lubricant. This “overcut”, typically 10-20 mm, is very important. It is created initially by the perimeter cutting tools of the TBM. It is therefore very important that the over-cutting ability of these teeth is maintained for the entire drive. On one drive in Old Klang Road, the first Rasa TBM 1200 experienced unusually high jacking pressures early on in the drive. It then encountered hard sandstone and at a chainage of 154 m the jacking force became so high that the drive could not continue. The TBM was recovered and it was found that the perimeter teeth had worn away to the extent that no overcut was being created.Stability of the soil face is provided by a system of pressurised slurry. The slurry used can be water but additives such as bentonite or polymer are often added for improved performance. Slurry is circulated to and from the TBM using charge and discharge pipes, typically 7.5-15 cm in diameter. Flow is provided by a charge pump at the surface and a discharge pump in the thrust shaft. A bypass valve in the TBM just behind the face allows the slurry circulation to be maintained whilst excavation has stopped. The pressure of the slurry is maintained at a level to suit the soil conditions and water pressure. The pressure must be high enough to prevent collapse of the face into the face chamber, which might cause surface settlement, or block the slurry pipes, and low enough not to cause heave or excessive loss of slurry. The slurry pressure is measured by gauges in the chamber and displayed in the control cabin.The excavated material is brought to the surface by the discharge slurry lines, and processed in the soil separation plant. The purpose of soil separation is to remove the excavated material from the slurry, so that the slurry can be re-circulated. This reduces water-use and minimises the volume of material to be removed from the site. Separation equipment includes settlement tanks, trommel systems, screens, shakers and hydrocyclones. Control cabins contain consoles from which the systems were operated and monitored. Information from the TBM is relayed via CCTV (Iseki and Rasa) or via computerized systems (MTS and Herrenknecht). Soil stabilisationIn many areas soil stabilisation was required during shaft construction and TBM launch and reception. This sometimes involved physical soil support in the form of sheet piles, for example a secondary ring of sheet piles around a shaft, or a temporary row of sheet piles in front of the TBM before launching, allowing the piles of the launch eye to be cut away safely. However, in most cases grouting, including jet grouting, was carried out, using cement or cement/bentonite mixes. This was required mainly in sandy soil conditions at depths of 4-7 metres, above the residual soil strata. In Puchong, jet grouting had to be carried out for launch and reception of the 1,500 mm and 750 mm TBMs for most drives. At one sheet piled shaft in particular, Shimizu encountered great difficulty in controlling water-bearing sand from boiling up from underneath the piles. In Dang Wangi, chemical grouting using sodium silicate and aluminium sulphate was used for a shallow (4 m cover) man-shield excavation to an existing manhole, where high groundwater flows were encountered. Similar ground water conditions were experienced at other shafts in this area.PipejackingThe extent of the project is using almost all of the pipejacking systems available in Malaysia, with additional machines being brought from Singapore, Japan and Hong Kong. In line with the soil conditions, a variety of TBM cutter head configurations were required. Due to the size and complexity of the project, Shimizu engaged a number of management and technical staff with extensive pipejacking experience, from Japan and Europe, to assist the local specialist contractors.Initial planning determined that 12 TBMs would be needed to complete the project within the 30-month contract period. This included six TBMs 750 mm and below, one 1,200 mm, two 1,500s and two 1,800s. Later, TBM resources had to be increased to 14 as of November 2005 (see table). What Where 1 Iseki TCC 300 Puchong 1 Iseki TCC 600 Old Klang Road 1 Rasa DH 600 Petaling Jaya 1 Iseki TCS 800 Puchong 1 Rasa DH 1200 Old Klang Road 1 Herrenknecht AVN 1200 Old Klang Road 1 Rasa DH 1350 Old Klang Road 2 Rasa DH 1500 Petaling Jaya and Puchong 1 Herrenknecht AVN 1800 Dang Wangi 1 MTS 2000 Dang Wangi 3 open-face manual excavation shields Petaling Jaya, Dang Wangi, Puchong The three open face manual excavation shields (1,500 mm diameter and 1,800 mm diameter) were used for a handful of short drives (less than 30 m) to allow the slurry TBMs to concentrate on longer drives, where they are more efficient. Pipejacking commenced at the end of July 2004 in Petaling Jaya, where a new Rasa DH1500 TBM was launched (see Figure 4 here) on a 146 m drive. This 2,120 mm OD TBM is suitable for mixed ground conditions (soft ground, gravel, boulders, soft rock). The face originally had an open area of 40% but due to the soft ground conditions this was reduced by the addition of steel face plates. The crusher gap was increased and a water jet added to prevent the chamber and crusher gap becoming clogged with clay. The 3.1 m-long-TBM is powered by three 22kW cutter head drive motors, providing a torque of 334 kNm. Steering capability is provided by four 50 mm stroke 750 kN jacks.This TBM completed a total of 1,583 m at an average jacking rate of almost seven metres per day (single shift). A similar Rasa TBM in Puchong achieved 5 m per day in difficult water-bearing sandy conditions.For long drives, intermediate jacking stations (inter-jacks) were used, to reduce the maximum jacking force applied to the pipes. These consisted of specially-manufactured pairs of pipes, one with what is effectively an over-long steel collar (female pipe), and one with an extended spigot end to accommodate this collar (male pipe). A ring of hydraulic jacks are placed within the collar of the female pipe. Once installed, these jacks are extended to move the pipeline ahead of the jacks forward. Once the stroke is complete, the main jacks then close the gap. Once the TBM has been removed and the pipeline pushed into final position, the inter-jacks are removed and the inter-jack pipes closed. A maximum of two inter-jacks have been installed in a single drive. This was a 338 m drive in Petaling Jaya, where jacking pressures reached 700 t. Only one inter-jack was actually used.There have been cases of TBM progress being halted by obstructions. In Puchong, an area known to include backfilled mine-shafts, an Iseki TCC 300 TBM has twice encountered debris including solid reinforced concrete objects, steel, plastic and rubber. In Old Klang Road, a similar Iseki TCC 600 encountered a series of timber piles and the horizontal alignment of the tunnel could not be controlled. In both cases the TBMs were pulled back into the shafts using the slurry system to grout the resultant void in front of the head. 13/07.