LOWER NORTH OUTFALL SEWER AND NORTH OUTFALL SEWER REHABILITATION USING AMERON S T HAB METHOD

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1 LOWER NORTH OUTFALL SEWER AND NORTH OUTFALL SEWER REHABILITATION USING AMERON S T HAB METHOD Bob Fisher and Lance Stracner Ameron Protective Lining J.R. Pipeline Co Inc. Abstract: The City of Los Angeles sewer tunnel infrastructure is in need of major repairs. The NOS was constructed in the early 1900 s. At that time, the newest materials to combat sewer gases and corrosion was a ceramic tile lining. However, the sewer gases were still able to penetrate and degrade the grout in between the tiles causing them to fail. The tile and sections of the concrete of the tunnel are now failing and collapsing to the tunnel floor. The method that was selected for the project had to structurally rehabilitate the tunnel and protect the new concrete from future corrosion. The City of Los Angeles awarded two contracts to complete the sewer tunnel rehabilitation. Phase I rehabilitated 30,512 LF of the Lower North Outfall Sewer (LNOS) and Phase II rehabilitated 16,876 LF of the North Outfall Sewer (NOS). Colich/J.R. Pipeline Joint Venture (JV) was the low bidder on each project and selected Amerons T Hab method for rehabilitating the sewer tunnel. The concrete used in the process was a 4000psi self consolidating concrete designed by J.R. Pipeline, Cemex, and Grace Materials. Introduction: The City of Los Angeles North Outfall Sewer (NOS) and the Lower North Outfall Sewer (LNOS) were constructed in the 1900 s. The NOS begins as a 48 concrete pipe and increases in size up to a 10 6 tunnel as it passes through the downtown area. The NOS was the first large diameter sewer tunnel completed in the City of Los Angeles. It collects the wastewater from all the downtown sewer systems, transporting it to the Hyperion Sewer Treatment Plant. Rehabilitating the LNOS Phase I was the first phase of the City s master plan to rehabilitate the large sections of the NOS wastewater system. The sewer was originally constructed with ceramic tiles to protect the concrete from sewer gases. However, the mortar used to install the tiles corroded and failed causing the tiles to fall off of the tunnel exposing the concrete beneath. This concrete over the next 70 years eroded to a point of failure. In 1992 the City of Los Angeles constructed the North Outfall Relief Sewer (NORS) to divert the wastewater from the NOS. This allowed Figure 1 Original NOS Construction in 1920's 1

2 time for the City of Los Angeles Engineers to design an appropriate rehabilitation method with the lasted in rehabilitation technologies. Design Requirement: In designing the rehabilitation for the LNOS Phase I the City of Los Angeles designers disregarded the integrity of the existing concrete due to its level of unknown corrosion. The rehabilitation involved casting a new PVC liner inside the existing sewer tunnel. The City had approved three PVC liners for the rehabilitation, Ameron T Lock, Agru CIP Liner, and Anjac Doran Conplast. The Concrete specified was 4000psi, self consolidating, and shrinkage reduced. The new cast in place concrete section had a minimum thickness of 9 at the invert and 12 at the soffit. The NOS Phase II rehabilitation design accepted the structural integrity of the existing sewer tunnel. This allowed the City to reduce the new cast in place concrete section. The City required hydro demolition to remove all the corrosion and expose sound grey concrete to prepare the existing surface of the tunnel. Local sewer flows had to be bypassed and a new 72 sewer diversion constructed. Two brick siphon structures were rehabilitated, three 78 concrete siphon barrels were rehabilitated, 13 maintenance holes were rehabilitated, and 5 new maintenance hole were constructed. Figure 2 Cross Section of New CIP Liner 2

3 Project Construction Phase The first phase was the LNOS Phase I Rehabilitation which began in July of 2004 and finished in April of The LNOS was 30,512 lineal feet of 10 6 clay tile lined tunnel. The rehabilitation consisted of 12 inches of new self consolidating concrete and Amerons T Hab PVC liner. The rehabilitation required cleaning of the exiting sewer tunnel, surface preparation, and sewer bypassing. The second phase was the NOS Phase II Rehabilitation. This phase began in March of 2007 and will finish in February The NOS Phase II was 10,929 Lineal feet of 10 6 semi elliptical clay tile lined tunnel and 5,945 lineal feet of 7 9 semi elliptical clay tile lined tunnel. The rehabilitation consisted of 6 to 9 inches of new self consolidating concrete and Amerons T Hab PVC liner. Debris Removal Access pits were constructed at City designated locations. These were spaced approximately 10,000 lineal feet apart. The initial cleaning removed all the debris that had built up within the sewer tunnel. The debris ranged in depth from 6 to 24 in some areas. The LNOS Phase I had 4 steel ribs installed on a previous contract to shore up the collapsing sewer tunnel. The ribs were very corroded and degraded. The debris consisted of clay tile, degraded concrete, steel ribs, and sewer sludge. The debris was collected within the tunnel with a skidsteer loader and transported to the access point where it was removed and placed into covered 20yd roll off containers. The containers were staged and allowed to dewater prior to disposal. All of the debris was recycled at a local material recycle facility. Figure 3 Existing steel ribs in LNOS 3

4 Sewer Bypass and Diversions The City of Los Angeles had constructed the North Outfall Relief Sewer (NORS) in 1992 to remove the LNOS Phase I and the NOS Phase II from service. To facilitate the installation of the Ameron T Hab system the local sewer flows had to be contained into a bypass line or diverted to adjacent sewer systems. The LNOS Phase I bypass required two 8 submersible pumps and a 12 internal bypass pipeline to control the main sewer flows. The main flows were diverted up to one mile internally along the tunnel invert to a diversion structure and discharged into an adjacent wastewater system. The local 8 flows were collected and bypass internally along a gravity 6 and 8 bypass pipeline. One 18 force main was re piped to an alternate wastewater system at the upstream project limits. The NOS Phase II project required a large sewer diversion to allow rehabilitation of the uppermost reaches of the sewer tunnel. The sewer diversion consisted of micro tunneling 204 lineal feet of 72 Hobas Pipe USA and the construction of one sewer junction structure over the 11 diameter East Coastal Interceptor Sewer (ECIS) and one sewer diversion structure over the La Cienega San Fernando Valley Relief Sewer (LCSFVRS). The diversion removed approximately 17 MGD from the NOS system. The structures were both 50 deep excavations solid shored with steel beam and plates. The new structures were cast in place concrete with Ameron s T Lock Lining for protection. Nada Pacific performed the 72 micro tunnel. The local sewer flows were collected and bypass internally along gravity 8 bypass line. Surface Preparation Figure 4 Before and After Surface Preparation Once the sewer diversions were operational and the tunnel was cleaned of all debris, the surface of the tunnel had to be prepared to receive the new concrete liner. The LNOS Phase I specified pressure washing with 3000psi water. The JV modified standard diesel powered pressure washing equipment to be used inside the tunnel. Pressure washing removed all the loose and deleterious materials from the surface of the tunnel walls. However, it does not remove the corrosion on the immediate surface of the concrete. This was verified by a low PH test reading on the interior tunnel surface. The NOS Phase II contract required hydro demolition to the existing concrete surface. (Figure4) Because of the thinner concrete section, the design engineer wanted clean sound concrete exposed with a PH of 7 or greater for accurate bonding with the new concrete. This was achieved by hydro blasting the surface with 18,000psi water. The work was subcontracted to National Infrastructure Hydro Demolition from Vancouver Canada. 4

5 Installation of Ameron T Lock PVC Liner The JV in conjunction with Everest Equipment designed and built steel tunnel forms for both projects. The forms included a starter wall section, arch section, and a form carrier. The carrier strips, relocates, and sets up the arch form sections. The starter wall was stripped and relocated by hand. The process begins with the installation of a 14 starter wall section lined with Ameron PVC. (Figure 5) The starter wall allows for vertical room to setup and strip the Figure 5 Starter Wall Forms arch section of formwork. The starter wall was cast 100 lineal feet ahead of the arch section to allow curing time. The connection between the starter wall and the invert of the tunnel was accomplished with #5 316LN stainless steel rebar at 18 O.C. doweled in 5 and affixed with Sika Dur Hi Mod Epoxy. The thickness of the starter wall section varied between 6 to 9 dependent upon the level of corrosion and the accuracy of the original construction in maintaining the designed internal measurements. The arch section of formwork is set up after the starter wall section has 24 hours of cure time. The form carrier mobilizes the arch sections into place. (Figure 6) The Ameron T Lock PVC is applied and secured onto the formwork. The crews then adjust the formwork to finalize the set up and meet the contract dimensions. (Figure 2) Once the forms are in place the carrier is moved out of the way to allow the concrete slick line and grout port connections to be assembled.(figure 7) The form is then filled with 4000psi self consolidating concrete. The concrete mix was designed with the help from Cemex and Grace Materials. The concrete mix includes four additives to meet the specification requirements and allow for the pumping of long distances as well as maintaining its consolidation within the form sections. The quality control for the concrete was measured by weight and a J Ring spread of 21 to 23. (Figure 8) Due to the limited access points the City granted the request to allow the existing and new manhole to be used for concrete pumping operations. The manholes were spaced approximately 1,000 to 2,000 lineal feet apart. Therefore our typical pumping distance was between 500 and 1,000 lineal feet to the formwork. In one case due to the terrain the manholes were 4,000 lineal feet apart. This required a pumping distance of 2,000 lineal feet to the formwork. The concrete then had to flow 100 lineal feet within the formwork. The self consolidating concrete performed as expected with good consolidation and Figure 6 Form Carrier with Arch Forms 5

6 strength. After an eighteen hour cure the forms are stripped and relocated to the next section. The Ameron T Lock installation is completed by welding all the seams with 1 PVC weld strip. (Figure 9) The Ameron T lock PVC is test by the City for any defects using a 10,000 volt holiday detector. The final result is a newly restored sewer ready for service. (Figure 10) The LNOS Phase I was complete on time and NOS Phase II was completed 10 months ahead of schedule. Figure 7 Formwork with Grout Lines Figure 8 J Ring Test 4,000psi SCC with 22" Spread Figure 9 PVC Welding of all Seams 6

7 Figure 5 Complete Rehabilitation with Ameron T Hab The City of Los Angeles considered these projects a great success due to the limited impact on the local residents and neighboring cities. The restoration of the LNOS Phase I and NOS Phase II expanded the City s wastewater capacity to a level that they have never seen. The service life of the newly rehabilitated sewers is estimated to be over 100 years. Description LNOS Phase I NOS Phase II Total Tunnel Lineal Footage 30,512 LF 16,876 LF 47,388 LF Debris Remove 7,000 Tons 5000 Tons 12,000 Tons Concrete Placed 35,000 yds 13,500 yds 48,500 yds Ameron T Lock Installed 854,336 sqft 421,768 sqft 1,276,104 sqft Table 1 The totals of critical points within the projects. 7