Well-preserved historic structures and cultural charm make Charleston, S.C., one of the top U.S. tourist destinations. The oldest public market in the nation ? the Charleston City Market ? is one of the most popular attractions in the city. But the real story is underground.
Market Street Drainage Improvements
Downtown Charleston is on a peninsula constructed on old tidal creek beds. A coastal location, minimal topographic relief, antiquated stormwater drainage structures, potential for intense storms, and rising tides have contributed to frequent flooding of the historic downtown market. Fortunately, relief is underway as the second phase of a three-phase initiative was completed earlier this year.
For about 200 years, the main drainage feature in the basin has been the historic brick arch that runs the length of the market underneath the buildings to an outfall just beyond Concord Street. Flooding issues have persisted over the years as the peninsula settled, the sea level rose, and the conveyance system filled with sediment.
Construction of the second phase of the Market Street Drainage Improvement Project consisted of 4,000 ft of 9-ft-diameter stormwater tunnels under the Charleston City Market. In addition to the tunnel, three 54-in. drilled drop shafts were constructed between buildings in the market area.
The Value of Construction Management
Although the success of a project of this magnitude depends on the performance and collaboration of all participants, especially the core project team ? the owner, designer, contractor, and construction manager ? this article focuses on construction management (CM). The role of the construction manager typically entails helping the owner (the City of Charleston in this case) during claim negotiations, ensuring construction activities are in compliance with the contract documents, keeping local-government officials apprised of project progress, liaising with the general public (e.g., ensuring consistent project messaging), coordinating materials testing, and maintaining proper project documentation.
It?s best for an owner or designer to engage a construction manager prior to advertising projects of this complexity and high profile. Because the designer, Davis & Floyd/URS, engaged Black & Veatch to provide construction management for the Market Street project prior to completion of the bid documents, and the CM team was able to participate in constructability reviews. The resulting CM review yielded a recommendation for an alternative bid with the option to use a tunnel boring machine (TBM) excavation method instead of the sequential excavation method (SEM) included with the base bid. The recommendation was ultimately accepted and incorporated into the bid documents. Of the eight bids received, the four contractors with the lowest bids all selected the bid alternative recommended by the CM team. Inclusion of the alternative approach saved the city approximately $6 million out the $20 million budget originally established for the project.?
Once construction began, the construction management team provided guidance to the city. Tunneling is not new to the city, but the specialized construction of sinking caisson through low-strength soils, tunneling beneath abandoned structures and connecting to an existing live stormwater tunnel was not standard practice. The city relied on the CM team to confirm adherence to the city?s standard construction requirements, standard industry practices for tunneling and special requirements of this project.
Cost-reduction proposal evaluation: The contractor for the Market Street project, a joint venture of Triad and Midwest Mole, submitted a cost-reduction proposal early in the project to better align with proposed means and methods and reduce construction costs. The proposal involved raising the elevation of one segment of the tunnel alignment and modifying the connection to the existing tunnel in an effort to reduce the slope of the alignment. The construction management team assisted the city in evaluating the proposal and weighing the initial cost reduction against the increased future maintenance requirements associated with the change. Ultimately the change was rejected after careful review by all parties and additional analysis by the CM team.
Project documentation maintenance: One of the construction manager?s primary roles is ensuring that sufficient construction documentation is maintained. This documentation comes in handy for evaluating changes to the contract that may arise during construction as well as analyzing and predicting trends. The CM team maintained daily reports including shaft sinking and tunnel excavation progress, contractor personnel onsite, stored materials, photographs, weather and rainfall data, hours worked, subcontractors onsite, and other such pertinent construction documentation. Upon completion of the project all this information was transmitted to the City of Charleston and archived electronically for future reference.
Change order evaluation: The Market Street contract documents required the completion of several cone penetration tests (CPTs) to determine the location of an abandoned sewer tunnel that crossed paths with the Market Street Stormwater Tunnel. During this early investigation, the contractor discovered that possible voids between the two tunnels existed much closer to the alignment of the Market Street Tunnel than originally thought. The voids were likely the result of continued deterioration of the abandoned sewer tunnel.? The core project team worked together to evaluate options and address the problem. A quick response was necessary to avoid costly project delays as the contractor was unable to proceed with construction until a resolution was reached. The construction documentation already developed by the CM team helped expedite evaluation of the cost proposal for the contract changes.
The solution called for increasing the depth of the tunnels and shafts and modifying how the new tunnel would connect with the city?s existing stormwater tunnel and pump station system. Following a couple rounds of negotiations and meetings between the CM, designer and the contractor, a final change order was accepted and incorporated into the contract.
Contract adherence: Building a project in the heart of downtown Charleston is no easy task. Space for a working shaft and contractor site laydown area was at a premium. Prior to awarding the construction contract, the city spent several years negotiating with the South Carolina State Ports Authority (SCSPA) for a working shaft site. The working shaft was located on land used by the SCSPA for parking and for access to the authority?s cruise ship terminal. Consequently, the construction contract restricted some work activities during cruise ship embarkation and debarkation. Restrictions primarily included limitations on work hours, deliveries and muck hauling. In addition, more disruptive activities such as pile driving were not permitted while a cruise ship was at port. The CM was responsible for ensuring contractor adherence to these provisions.
Communication, Communication, Communication
Communication, Communication, CommunicationJust as the realtor mantra is ?location, location, location,? the importance of communication for construction projects can?t be overemphasized. Project success depends on effective communication between all parties. The CM team conducted monthly progress meetings with the entire project team and various stakeholders but also conducted smaller, weekly meetings with representatives from the core project team.
While the monthly meetings provided general project status updates and coordination of key upcoming activities with stakeholders, the weekly meetings primarily focused on coordination of the items to be completed for that week as well as a look ahead at coming weeks. The focus of the weekly meetings encompassed all significant project tasks along with the more mundane weekly activities. These meetings were especially beneficial for coordinating construction activities outside of normal operations (e.g., special deliveries such as the TBM or short-term road closures). The CM team also used information from the weekly meetings to apprise representatives from the SCSPA and Market Street Business Association of work that could potentially impact their respective operations. The weekly meetings were instrumental for coordinating the city?s third-party construction monitoring.
Third-party monitoring included concrete testing, compaction testing, crack monitoring, groundwater-level monitoring and vibration monitoring. This testing was in addition to any testing the contract required the contractor to perform. It provided an added level of credibility in the event issues arose during or following construction. Fortunately, no significant project issues occurred to necessitate use of these test results.?
The most significant impact to the general public on the Market Street project occurred during construction of the three 54-in. drilled drop shafts. Access to the City Market buildings needed to be maintained throughout the installation of each of the drilled drop shafts. The CM team and contractor conducted pre-submittal meetings to review the project requirements and discuss the contractor?s work plan. In these meetings a couple of minor contract restrictions were modified following discussions with the city and various stakeholders.
For example, the original contract limited the total duration of construction activity at each drop shaft site to one month and allowed operations at only one drop shaft at a time. Discussion at these meetings allowed the one-month duration limit to be broken into multiple phases to better suit contractor means and methods and stakeholder needs without increasing the overall duration at each site. Pre-excavation was performed at all the drop shafts a couple months before mobilization of the drilling rig. This modification benefitted the project by allowing the contractor to find any subsurface surprises and, if found, allowing the design team to make the necessary provisions before the potential conflicts would affect the critical path. Although this modification increased the number of times the contractor worked at each drop shaft location, it did not increase the overall duration and reduced the risk of unknown delays.
?The construction management team was instrumental in ensuring that the project was delivered with limited adverse impact to the surrounding community and businesses,? said Laura Cabiness, P.E., Charleston director of public service.? ?When unexpected and unforeseen conditions were presented the CM team was able to respond quickly with minimal impact to the project schedule and cost.?
CM Benefits for the Owner
Qualified construction managers work closely with city staff, allowing staff members to be more efficient by focusing on other responsibilities and key project decisions that require their input. Having someone from the CM team onsite during construction activity helps ensure that contract documentation is complete. Comprehensive contract documentation is of tremendous benefit when changes arise or future construction requires close scrutiny of past activity. No one likes construction-related surprises, and making sure someone on the team is tracking documentation can help cities like Charleston avoid such surprises.
Jason Swartz, P.E., is the east region tunnel practice leader with the water business of Black & Veatch. He was the local project manager during construction of the second phase of the Market Street project and has worked in the planning, design and construction of water and wastewater tunnels for 15 years.
Steven A. Kirk, P.E., is senior engineering project manager with the City of Charleston Department of Public Service, and has managed stormwater pump stations and complex flood-alleviation projects in his current capacity for nearly a decade.
Stephen O?Connell, P.G., is a construction manager/engineering geologist with Black & Veatch. He served as construction manager for the second phase of the Market Street project and has worked in the design and construction management of water and wastewater tunnels for 10 years.
