Austin Builds Three Water Tunnels and Has Four More in ProjectThere are three in-use wastewater tunnels in Austin: Crosstown (1973), Onion (1978) and Govalle (1988). Crosstown delivers flow to the Walnut Creek wastewater treatment plant. Onion and Govalle deliver flow to the South Austin wastewater treatment plant. There are two new wastewater tunnels that have just been completed: Little Walnut South (2006) and Shoal Creek (2006). There is one wastewater tunnel that is currently being constructed and will have a lift station at lower end: Barton Creek.The Shoal Creek, Little Walnut Creek and Barton Creek tunnels are detailed below. The final touches are being given to the Shoal Creek and Little Walnut Creek tunnels, respectively in Central and East Austin. The Barton Creek tunnel is about six months from completion in March 2007. When complete, the tunnels will provide a modern infrastructure that responds to the Environmental Protection Agency's mandate to prevent sewer overflows that damage public health and the environment. Shoal Creek TunnelThe USD8.9 million project is the first step in constructing an upgraded underground sewage system for Austin. Weston Solutions performed preliminary engineering, design and construction services. The project design included the following features: 1,037 linear metres of 1.68 m fibre glass wastewater interceptor installed inside of a 2.74 m-diameter tunnel; three tunnel construction access shafts built out to provide permanent access for operations and maintenance; three lateral connections to join the existing collection system to the tunnel installed by horizontal directional drilling (HDD) technology; almost 610 metres of 20 and 30 cm wastewater mains installed by open cut construction; 196 linear metres of jack and bore construction; 192 linear metres of cured-in-place pipe (CIPP) for 61 cm wastewater line; 76 linear metres of 20 cm CIPP; and connection to the Shoal Creek inlet structure on the 2.44 m-diameter Crosstown tunnel which included gravity bypass to divert flows directly into the tunnel shaft. Visit www.westonsolutions.com Dosco shield TBM being lowered into the shaft Scotty TBM without the finger shield apron The new line extends from a shaft north of 34th Street along an alignment under the creek down to the shaft located south of the 29th Street bridge. The tunnel has been drilled by a double-shielded soft ground Lovat TBM, boring through clay compact shale/sandstone at 12 to 18 metres below the surface. The contractor is W.L. Hailey of Nashville. Tunnelling began in February 2005 at the entrance shaft at West 29th and Lamar Boulevard. Tunnel excavation is complete since the summer of 2005 with hole through by the TBM into the 34th Street shaft. Visit www.lovat.comGround did not necessitate the use of the PRGs. Majority of excavation (820 to 975 linear metres) was in Del Rio clay. Clay had compressive strength of up to 6.2 MPa but 3.45 MPa was more common. Impermeable material yielded zero groundwater concerns. Enough inherent moisture that dust suppresion was not an issue either. Remainder of excavation was in the Georgetown limestone formation. The compressive strengths ranged from 13.8 MPa to 62 MPa. With the higher compressive strengths, the contractor reconfigured the head with mini-discs (16.5 cm) to complete the drive. Fortunately water was not an issue in the limestone either. The support and lining consisted of ribs (3 pieces - W4 x 13) and boards (90 cm to 1.5 m lengths) supplied by American Commercial (ACI). Plymouth 6-tonne locos (2 in-house, 1 backup) from Mining Equipment were used for mucking-out. Visit www.americancommercial.com and www.miningequipmentltd.comThe next steps included excavation of a third shaft (adjacent to the 29th Street shaft) where the connection to the Crosstown wastewater tunnel will be constructed; excavation by bore for the three connections into the tunnel to connect existing wastewater collection systems; and excavation and construction of the junction box at the 34th Street shaft to connect the 1.37 m and 61 cm wastewater lines to a vortex drop in the shaft. The current final tasks involve installation of replacement vortex units (IPEX), final system tie-in and restoration. Planetary Subsurface Utility of Dallas was subcontracted by W.L. Hailey to perform three challenging directional drilling installations and install three 60 cm casings for new laterals to a 2.54 m tunnel from 29th to 34th Street. The laterals serving the large tunnel required installation at severe grades (88 m at a 13.5% grade, 15 m at a 47% grade, and 23 m at a 125% grade). All three installations were made with a compact Ditch Witch JT2720 All Terrain directional drilling unit. Visit www.ditchwitch.comLittle Walnut Creek TunnelThe KM&M joint venture of Cleveland's The Kassouf Company, Murray Hill Construction and Mole Construction based in Solon, Ohio was the contractor for the USD12.7 Little Walnut south tunnel project. The Little Walnut south tunnel project involved the construction of 4,017.57 metres of a 152.4 cm and 167.03 metres of 106.68 cm gravity wastewater pipeline along Walnut Creek and Northeast Drive. The Northeast Drive alignment allows for the diversion of about 80% of the upstream wastewater flow from the older, existing sewer line into the new tunnel. This significantly reduces the possibility of future overflows into Little Walnut Creek. The work encompassed constructing 1,127.76 metres of 152.4 cm via open cut construction, 2,840.13 metres of 2.56 m excavated tunnel in one continuous run with no intermediate shafts through the Taylor group and the Austin group, a cretaceous limestone formation, which will be lined with 152.4 cm fibre glass reinforced polymer mortar (Hobas) pipe and backfilled with cellular grout. The tunnel was driven at 43 m below ground with a 2.56 m Dosco shielded TBM using ribs and boards for support. The supplier of the ribs and boards was ACI. Visit www.dosco.co.ukThe spoil removed from the tunnel was accomplished by the use of two muck trains, consisting of one 4-tonne locomotive and five 1.6 cu m muck cars. The TBM holed through on 1st November, 2005. The project is about 90% complete and the only items remaining to complete are site restoration and an entrance way that is undergoing a design change to be remodified. The project should be completed at the end of October 2006.The tunnel also connects to 164.59 metres of 106.68 cm wastewater line also installed by employing a 2.74 m main beam TBM. The spoil removed from this section of tunnel was accomplished by the use of one 4-tonne locomotive with five muck cars as well. The main beam TBM was an old Scotty machine that was manufactured in the late 60s to mid 70s.There are two 10.67 to 22.86 m shafts with manhole structures and three junction structures that were installed via cast-in-place concrete method. The contractor for the open cut construction was performed by Benitez Construction of Manor, Texas and the design engineer for the project was Brown and Caldwell. Visit www.brownandcaldwell.comBarton Creek TunnelThe existing Barton Creek lift station, located in the parking lot of Barton Springs pool, receives flow from the Barton Creek interceptor serving the Barton Creek watershed. The USD9.2 million Barton Creek tunnel project includes two sections. Section one is a 549 m-long 2.44 m-diameter shallow tunnel designed by PBS&J. It is constructed in Zilker Park in alluvial materials. A 84 cm fibre glass pipe will be extended into the interceptor and the annular space will be filled with grout. Section two is a 488 m-long 2.44 m-diameter deep rock tunnel, designed by Espey Consultants, under Barton Creek to a shaft location near Toomey Road. It is bored in Georgetown limestone. A 84 cm fibre glass pipe will also be installed in the tunnel. Visit www.pbsj.com and www.espeyconsultants.comThe shallow tunnel will be joined by a drop shaft to the deeper tunnel that extends under Barton Creek to the shaft site off Toomey Road. The main shaft at Toomey will be about 21 m deep and will have a temporary lift station built within the shaft at the low end of the deep tunnel to lift the wastewater to the adjacent South Austin outfall. The temporary lift station will be underground and will be operated until mid-2010. The project will allow the decommissioning of the existing Barton Creek lift station. The 30 year-old lift station has been deteriorated by corrosion. The contractor is Dibco Underground of Ontario. This project began on 15th August, 2005 and is scheduled to end in March 2007. Visit http://dibcounderground.comFuture TunnelsAustin has also four more tunnels under planning: the Downtown wastewater tunnel, the Waller Creek stormwater tunnel, the Williamson Creek wastewater tunnel and the Boggy Creek wastewater tunnel. The Downtown wastewater tunnel (see details in E-News Weekly 10/2006) will be designed to address capacity needs from infill and downtown redevelopment. This tunnel, which will be over 4,250 linear metres in length, is expected to cost about USD30 million. It will be constructed between 2008 and 2011. It will connect to the existing Govalle tunnel so that all of the wastewater flow will be conveyed by gravity to the South Austin regional wastewater treatment plant. Initially it will not have a connection to the Barton Creek tunnel, but that will be completed in the future.The conceptual Waller Creek stormwater tunnel is projected to cost USD50 million but there is insufficient funding to begin the design or construction. This is a drainage control tunnel, not a wastewater tunnel (read E-News Weekly 34/2006 & 27/2006 to know more). The Williamson Creek wastewater tunnel and the Boggy Creek wastewater tunnel are expected to be designed and built between 2010 and 2015 depending on the need. Except those two tunnels, all the tunnels, in service, under build or planned, are part of the USD200 million Austin Clean Water Program (ACWP) efforts to eliminate wastewater overflows in the city. Austin's overall programme deadline expires in June 2009. Visit www.cityofaustin.org/ca and www.ci.austin.tx.us/acwp 37/06.