Guidelines for Managing Geotechnical Risks in Design–Build Projects (2018)

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18 This chapter focuses on the identification of geotechnical risk for the typical DB project. It will cover the project development process and highlight those points where geotechnical risk should be evaluated. The chapter will provide a list of inputs and outputs to the geotechnical risk identification process as well as tools that emerged out of the analysis of the survey and case studies that have been found to be commonly used. 2.1 Geotechnical Risk Identification Throughout Project Development Similar to the generic risk assessment cycle of managing all types of risks on a project, the geotechnical risk management process proposed starts with the risk identification process. Risk identification is the process of finding, recognizing, and describing risks. There are multiple ways in which project risks can be divided based on their types. For example, they can be divided into (1) external, (2) organizational, (3) project specific, (4) legal and contractual, and so on. The complete risk assessment will cover all these areas in order to assess the project’s risk profile and arrive at reasonable mitigation measures. In this research, however, the emphasis is much more limited and focused on geotechnical risks that can be identified through site investigation and testing. As such, most of the types of risks that are of interest in this work fall under the category of project-specific design-related technical risks. The geotechnical risks should be identified at an early stage of the project, that is, commonly after conceptual design, and again reviewed after preliminary design (Figure 2.1). Early identifi- cation of major project risks will help in avoiding the selection of problematic project solutions and costly remedial action in later phases. It is a well-established fact that as the project design gets further along, changes to project scope will become costlier. As discussed in Chapter 1, geo- technical risks are typically the first types of risks encountered in projects and may constitute the highest level of uncertainty during the pre-award phase of a project. In fact, as discussed later in Chapter 6, risks list should be dynamic and updated at different stages of the project, especially to retire risks that never materialized. 2.2 Geotechnical Risk Identification: Strategies, Methods, and Tools Risk identification is the process of identifying risks that can adversely affect the project cost and schedule along with opportunities that can reduce project costs or result in a reduction in project duration. Most agencies have their own risk management policies and standard operat- ing procedures for conducting formal risk analyses on DB projects, including risk identification. C H A P T E R 2 Geotechnical Risk Identification

Geotechnical Risk Identification 19 However, this guidebook presents some of the common types of risks that were highlighted by both the survey and case study results. For geotechnical risk assessment, the attention is focused on relevant risk factors. One of the tools used for risk identification is the use of a risk catalog. Developing a catalog of geotechnical risks can facilitate the process of risk identification. The catalog developed in this project was organized according to the geoconstructability guidelines of the American Society of Civil Engineers (American Society of Civil Engineers 2011): dewatering, deep foundations, mass excavation, and tunneling. As more risks were identified by using the surveys and the case studies, a more comprehensive list pertinent to the scope of this project was developed. This list was added to a template for geotechnical risk register that is shown in Chapter 4. These risks can act as a checklist for agencies to consider what is applicable to their projects, in addition to offering a suggested categorization of the respective risk level, based on the results of the research. Table 2.1 shows a list of 27 DB geotechnical risk factors that were identified by the analysis of the literature review, case studies, and expert geotechnical engineers. The ten most common geotechnical risks encountered in DB projects are shown in Table 2.2. The guidebook provides techniques for the agencies to prioritize their identified risks, prior to even commencing risk analysis, which emerged out of the input from both DOT employees and the industry and generated 27 geotechnical risk factors. Importance Index Prioritization Technique. Risks were ranked on the basis of the responses from both the DOT employees and contractors assessed by an importance index. For further Conceptual Design Preliminary Design Design Development Working Drawings Construction Extensive Contractor Input Figure 2.1. Generic DB timeline. Number Factor/Risk Number Factor/Risk 1 Caverns/voids 15 Subsidence (subsurface voids) 2 Chemically reactive ground 16 Existing structures likely to be affected by the work (other than utilities) 3 Liquefaction 17 Contaminated material 4 Karst formations 18 Landslides 5 Rock faults/fragmentation 19 Settlement of adjacent structure 6 Lateral spreading 20 Sensitiveness of public consideration (parks, historic buildings, etc.) 7 Seismic risk 21 Soft compressible soil 8 Underground manmade debris 22 Groundwater/water table 9 Groundwater infiltration 23 Settlement in general 10 Presence of rock/boulders 24 Soft clays, organic silts, or peat 11 Settlement of bridge approaches 25 Highly compressive soils 12 Eroding/mobile ground conditions 26 Scour of bridge piers 13 Replace in situ material with borrowed material 27 Slope instability 14 Unsuitable material Note: Prediction of subsurface condition due to inaccessible drilling locations and utility conflicts were not included in the analysis due to inconsistencies in the data (i.e., high number of missing responses for those risks). Table 2.1. List of geotechnical risk factors.

20 Guidelines for Managing Geotechnical Risks in Design–Build Projects details, see Chapter 2 in the NCHRP Project 24-44 final report, available from TRB’s website at www.trb.org by searching on NCHRP Web-Only Document 247: Managing Geotechnical Risks in Design–Build Projects. Table 2.3 shows the ranking of the risks in terms of their importance index. Agencies could use this index as a pre-analysis measure to gauge the riskiness of the geotechnical risks on their projects and guide the preliminary investigations that characterize a project’s underground con- ditions to be addressed in the RFP. Risk Score Technique. Risks were ranked again on the basis of the responses from both the DOT employees and contractors but assessed by using aggregate average risk scores obtained from the survey responses of both DOT employees and industry. Those scores were further categorized into high, medium, and low risks to provide the agency a preliminary assessment prior to its actual project specific assessment of its project specific geotechnical risks. Table 2.4 Number Factor/Risk Number Factor/Risk 1 Slope instability 6 Landslides 2 Soft clays, organic silts, or peat 7 Rock faults/fragmentation 3 Chemically reactive ground 8 Settlement in general 4 Subsidence (subsurface voids) 9 Contaminated material 5 Groundwater/water table 10 Karst formations Table 2.2. Ten most encountered geotechnical risk factors. FACTOR/RISK Importance Index [%] Rank Groundwater/water table 42.64 1 Settlement in general 37.69 2 Contaminated material 37.22 3 Soft compressible soil 36.04 4 Scour of bridge piers 35.37 5 Slope instability 34.87 6 Settlement of bridge approaches 34.87 7 Highly compressive soils 33.77 8 Presence of rock/boulders 32.65 9 Seismic risk 32.42 10 Soft clays, organic silts, or peat 32.10 11 Settlement of adjacent structure 31.82 12 Existing structures likely to be impacted by the work (other than utilities) 31.12 13 Unsuitable material 31.07 14 Landslides 30.75 15 Sensitiveness of public consideration (parks, historic buildings, etc.) 30.35 16 Underground manmade debris 29.07 17 Groundwater infiltration 28.79 18 Replace in situ material with borrowed material 28.16 19 Liquefaction 27.84 20 Lateral spreading 27.01 21 Rock faults/fragmentation 26.17 22 Subsidence (subsurface voids) 26.17 23 Karst formations 24.06 24 Caverns/voids 23.47 25 Eroding/mobile ground conditions 22.36 26 Chemically reactive ground 20.21 27 Table 2.3. Importance index of geotechnical factor risk in DB projects.

Geotechnical Risk Identification 21 shows the risks categorized based on their risk level (high, medium, or low). Table 2.4 can be used as a checklist to inventory those risks that are present in the given project and to record an initial assessment as to their degree of impact. The completed checklist can then be used as input into the more detailed risk analyses described in Chapters 3 and 4. It is important to note that risk identification is pertinent to specific projects. However, these ranked or categorized lists of risk factors can be used as an effective checklist to ensure that project teams do not disregard major common DB project risks. A project risk listing may also have more risks identified depending on the project’s characteristics and interaction between identified risk factors that should be considered and accounted for. Category Identified Risk Factors Present Degree of Impact High [1-10] Landslides Slope instability Contaminated material Highly compressive soils Settlement of adjacent structure Prediction of subsurface conditions due to inaccessible drilling locations Subsidence (subsurface voids) Soft clays, organic silts, or peat Sensitiveness of public consideration (parks, historic buildings, etc.) Scour of bridge piers Medium [11-20] Soft compressible soil Seismic risk Karst formations Caverns/voids Existing structures likely to be impacted by the work (other than utilities) Groundwater/water table Utility conflicts Lateral spreading Liquefaction Rock faults/fragmentation Low [21-29] Settlement in general Underground manmade debris Settlement of bridge approaches Presence of rock/boulders Eroding/mobile ground conditions Chemically reactive ground Unsuitable material Groundwater infiltration Replace in situ material with borrowed material Note: Based on NCHRP Project 24-44 survey. Table 2.4. Ranked geotechnical risks.