Case History: Complex Design and Construction of Tunnel and SOE to Accommodate Challenging Site Conditions

Transcription

1 Case History: Complex Design and Construction of Tunnel and SOE to Accommodate Challenging Site Conditions John Yao, P.E. (Jacobs Associates) Emad Farouz, P.E. (CH2M HILL) 9/27/2010

2 Project Background

3 Project Overview Narragansett Bay Commission (NBC) developed a comprehensive program to abate CSO pollution in the Narragansett Bay. This was the largest civil works project in the history of Rhode Island. Phase 1 of the program was completed for a total cost of $350 million. NBC received the Project of the Year Award from the Underground Construction Association of SME.

4 Project Overview Phase 1 of the CSO Abatement Program includes a deep storage tunnel, shafts, adits, a CSO pump station, and several near- surface interceptors and facilities. Construction for Phase 1 began in 2001 and was completed near the

5 Project Components

6 OF-067 Near-surface Facilities

7 Subsurface Conditions Sands with various amounts of silt (SM and SP-SM) SM) and nonplastic silts (ML) Soils are typically medium dense, but range from loose to very dense Groundwater levels measured from boreholes are typically 4.6 m (15 ft) or less below the ground surface

8 Site Constraints

9 Diversion Structure SOE Concepts 1)Temporary excavation support using reinforced soilcrete walls consisting of soldier beams encased within soilcrete (i.e., jet grout), with multiple levels of bracing. 2)Permanent secant pile walls, with multiple levels of temporary bracing.

10 Diversion Structure SOE

11 Diversion Structure SOE

12 Diversion Structure SOE

13 Diversion Structure

14 Diversion Structure

15 Consolidation Conduit 124-foot foot-long, 108-inch inch-id reinforced concrete pipe

16 Ground Improvement

17 Construction Overview Diversion Structure Gates & Screening Structure Approach Channel

18 Construction Diversion Structure

19 Construction G & S Structure

20 Construction Tunnel

21 Construction Tunnel

22 Construction Tunnel

23 Conclusions The use of jet grouting was quite successful in lowering the risk of damaging the existing box conduits and other facilities from ground movements due to tunnel and shaft excavations. A combination of secant piles, soilcrete elements, and localized dewatering were used to complete the tunnel and shaft excavations on this project.

24 Conclusions (authors opinions) Leaving SOE design to the contractor for similarly complex projects may unfairly burden the contractor and increase the overall project risk in the traditional low-bid environment. Design by a qualified design team with adequate time and resources is recommended for complex projects. Designers should strive to present one constructable method, with adequate details to convey the intent of design to the contractor.

25 References 1. Castro, R., Vincent, F., Hughes, G., and Albert, P Drop Shafts for Narragansett Bay Commission CSO Abatement Program. Proc. of the Rapid Excavation and Tunneling Conf. (RETC),, ed. M.T. Taylor and J.W. Townsend. Society for Mining, Metallurgy, and Exploration (SME). 2. Farouz, E., and Yao, J Case History: Complex Design and Construction of Tunnel and SOE to Accommodate Challenging Site Conditions. Proc. of the North American Tunneling (NAT) Conf.,, ed. L.R. Eckert, M.E. Fowler, M.F. Smithson, Jr., B.F. Townsend. SME. 3. Hughes, G., Kaplin., Halim, I., Albert, P Design and Construction of the Fields Point Tunnel Pump Station for the Narragansett Bay Commission CSO Abatement Program, Providence, Rhode Island. Proc. of the NAT Conf.,, ed. M.T.

26 References 4.Kaplin, J., Peterson, J., and Albert, P Underground Construction for a Combined Sewer Overflow System in Providence, Rhode Island. Proc. of the RETC,, ed. G. Almeraris and B. Mariucci. SME. 5.Schmall, P., Corwin, A., Spiteri, L Ground Freezing Under the Most Adverse Conditions: Moving Groundwater. Proc. of RETC,, ed. M.F. Roach, M.R. Kritzer, D. Ofiara, and B.F. Townsend. SME.

27 Questions/Comments