Geotechnical uncertainty may be the most difficult risk to manage in construction. In Design- Build (DB), where the project’s price is fixed before design and in many cases the subsurface investigation is complete, the risk profile is fundamentally changed and the owner must address it. This paper assesses the potential of DB as a tool for addressing geotechnical uncertainty in public transportation projects by comparatively evaluating three successful approaches.
The first case study involves the use of a Geotechnical Baseline Report as a subsurface condition risk allocation tool. The second uses unit price pay items inside the larger lump sum contract to share the geotechnical risk with the design-builder. Finally, a “nested DB” landslide repair clause inside a design-bid-build interstate highway contract successfully addressed the post-award potential landslide risk. The paper concludes that each of the contractual management approaches provided an effective means for addressing geotechnical uncertainty in DB public transportation projects.
Case study research is best used to conduct an in-depth look at promising procurement processes such as DB (Eisenhardt 1991). Case studies help find the details of the “how and why” aspects for the project of interest. This is especially true for studies that examine a number of different cases (Yin 2008). The research team developed a defensible, repeatable methodology to direct the case study process.
A variety of research methods were used, including multiple sources of information, maintaining a chain of evidence, and searching for patterns among the data through data coding (Taylor et al. 2009, Yin 2008). In-depth case study research was essential in this study to obtain the details of how different public agencies used DB project delivery as a risk management tool to address geotechnical uncertainty.
In others words, the three selected cases represent an agency that recognized the geotechnical risk potential in each project and then selected a carefully crafted tool to manage the risk using DB project delivery, presenting a proactive rather than reactive solution. The Table 1 is a summary of the salient characteristics of three case study projects analyzed in the paper.
CASE STUDY DETAILS AND ANALYSIS
The objective of this section is to portray the breadth and depth of the case study project population and analyze how DB project delivery was an effective means to provide geotechnical solutions and manage risk for transportation agencies. The format has been standardized for each project to enable each project to be compared with all other projects in the sample (Taylor et al. 2009).
The owner’s geotechnical consultant chose to establish the baselines for each soil type. This was developed using preliminary geotechnical data obtained from a boring program with a spacing of roughly one boring every 1,000 ft. Because the design-builder had authority to vary the alignment, this particular data set could easily be off the final alignment. Table 2 provides a summary of the GBR used to quantify the subsurface material properties risk.
SUMMARY AND RECOMMENDATIONS
Two primary conclusions are supported by the case study analysis and the approaches may be generalized to other contracts or circumstances. First, the decision to use DB project delivery for a project with greater than normal geotechnical uncertainty, like the Honolulu Guideway, cannot be made arbitrarily.
The accelerated nature of DB not only shifts the geotechnical design responsibility to the DB contractor but it also greatly heightens the pressure to complete the geotechnical investigation and design tasks as quickly as practical to permit the start of early construction activities. The second conclusion is that DB project delivery can actually be used as a tool to mitigate the risk and facilitate the speedy resolution of geotechnical issues as was shown in the Missouri landslide.
The rest of the conclusions are project specific conclusions, highlighting how DB project delivery was used to resolve specific geotechnical challenges and general conclusions that focus on the effectiveness of using DB project delivery as a means to resolve geotechnical issues.
The following project specific conclusions can be drawn from the case study analyses:
- Investing the resources to prepare a GBR for a projects with a known high level of geotechnical variation provides a means to not only reduce the contingencies that must be included in a DB procurement but also provides an effective means to quantify differing site conditions if they are encountered.
- The use of selective unit pricing provides an effective means for managing geotechnical quantity risk.
- The use of a “nested” DB provision that requires a prequalified geotechnical specialty subcontractor to be a member of the team on a project with known geotechnical issues provides an innovative solution to reduce response time to geotechnical issues unexpectedly arising during DBB project execution.
- O’ahu Elevated Guideway Project: The use of a GBR as a means to allocate subsurface condition risk appeared to result in cost savings for CCH.
- US 2 Rockfall Mitigation Project: The use of unit price pay items for the uncertain features of the scope allowed MDT to get as much rockfall mitigation completed as possible for the available funding. This was particularly significant because this project had a fixed price and had to be delivered without a contingency for differing site conditions.
- I-270 Slide Repair Project: DB project delivery permitted MoDOT to complete an emergency slide repair on the I-275 project in significantly less time than two previous DBB slide repair projects.
Source: Iowa State University
Authors: Carla Lopez del Puerto | Douglas D. Gransberg | Michael C. Loulakis