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

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B-1 This appendix contains the templates of the forms and spreadsheets described in the guidelines. The blank spreadsheets are also available for download from TRB’s website at www.trb.org by searching on NCHRP Research Report 884. The process for using these templates was described in Chapter 7. To summarize briefly, the process follows four steps: 1. Table B.1 is intended as a checklist for identifying and qualitatively assessing those geotechni- cal risks that might be present in a given DB project. 2. The risks listed in Table B.1 are input into Table B.2 to conduct the quantitative analysis of risk. 3. Table B.3 is used to correlate Table B.2 output with the DB design process and schedule risk- related geotechnical design decisions for those risks that can be managed in design. Addition- ally, Table B.3 output may also be used to modify the risk exposure dates in Table B.2. 4. The results of Tables B.1 through B.3 are then used to populate Table B.4. The geotechnical risk register has been compiled to show the degree of risk attached to various ground-related aspects of the proposed development. The purpose of the register is to provide an assessment of the risk to the project posed by common ground-related problems and to iden- tify suitable mitigation measures to the control the risk to an acceptable level. The risk register should be developed and refined as the geotechnical design and assessment progresses such that the register will allow the management of the geotechnical risks. The inclusion of a risk in the register does not constitute confirmation that the problem actu- ally exists at the site. A probability of “very unlikely” is indicative of a condition that the available data suggest should not be present. The calculated risk is not the risk that the impact will occur but the risk that the mitigation will be required to enable the project to progress. For the purposes of this risk register the magnitude of each impact and the resulting severity of risk are measured against what could normally be expected for each element. Before incorporation into a project risk register the impacts and risks for each element should be moderated by an assessment of the cost and time implication of individual mitigation measures. The degree of risk (R) is determined by combining an assessment of the likelihood (L) of the hazard occurring with an assessment of the Impact (I) the hazard and associated mitigation will cause if it occurs (R = L × I). The Likert scale against which the likelihood and impact are measured and the resulting degree of risk determined are presented as follows (see also Figure 3.3). A P P E N D I X B Geotechnical Risk Management Workshop Templates

B-2 Guidelines for Managing Geotechnical Risks in Design–Build Projects Very High 5 (I) (R) Risk High Risk Low Risk Medium Risk 4 3 2 1 Impact High Medium Low Very Low Very Likely 5 (L) 4 3 2 1 Likelihood Likely Plausible Unlikely Very Unlikely x = 15 – 255 – 14 1 – 4 Likelihood 5 4 3 2 1 1 2 3 4 5 Impact High Risk Medium Risk Low Risk 5 10 15 20 25 4 8 12 16 20 3 6 9 12 15 2 4 6 8 10 1 2 3 4 5

Site / Ground Hazard Potential Impact Before Control Comments and Proposed Mitigation Risk RatingConditions L I R Co nt am in ati on U nd er gr ou nd V oi ds Previous site use Contaminated materials and groundwater Health and safety, environmental damage, pollution requiring remediation Mine shafts Shaft collapse Surface deformation, structural damage; health and safety Shallow mining Working tunnel collapse, sink holes, subsidence Surface deformation, structural damage Deep mining Tunnel consolidation, subsidence Surface deformation Natural cavities; solution features Unstable natural ground; sink holes Surface deformation, structural damage; health and safety Other voids; basements, sumps, tanks, wells, and adits, etc. Collapse, subsidence Surface deformation, structural damage; health and safety Sl op es a nd E ar th w or ks Existing steep slopes on site Slope failure Site stability; surface deformation at crest, structural damage to services, highways and property Gradient on site Earthworks or retaining walls required to accommodate layout Increased cost As-dug cut material unsuitable as fill Unstable earthworks Surface deformation, structural damage Embankment stability Slope failure Site stability; surface deformation at crest, structural damage to utility services, highways and adjoining property Cut stability Slope failure Health and safety Insufficient suitable fill Import required to achieve design levels Increased cost of development Fo un da ti on s & Su bs tr uc tu re s Loose or soft, compressible soils at shallow depth Ground unsuitable for conventional shallow footings or supporting embankments and structures Excess settlement or alternative foundations Adjacent structures Works on site affecting stability of adjacent structures Alternative design or altered development layout Differential settlement Differential settlements beneath embankments could affect design geometry Damage to the track resulting in remedial works being necessary Aggressive ground chemistry Attack of buried concrete Protection required Table B.1. Initial geotechnical risk identification and assessment register. (continued on next page)

Condition Hazard Impact L I R Comment / Mitigation RR Sl ab s an d Pa ve m en ts Soft and compressible near surface soil Ground unsuitable for conventional ground- bearing slab Alternative slab design Soft and compressible near surface soil Low California bearing ratio due to soft formation Surface damage or alternative design Frost susceptible soils Frost heave Surface damage or alternative design D ra in ag e & F lo od in g High permeability strata Ineffective storm water attenuation ponds/water and environmental Ponds need lining if required to retain water Low permeability strata Ineffective permeability Alternative drainage required High groundwater Effects planned works construction and final levels. Alternative vertical alignment/plateau levels required affecting cut fill balance feasibility Embankment earthworks and cutting slopes will require drainage Insufficient attenuation permeability and retention ponds to accommodate earthworks drainage Flooding Local watercourse Flooding Flood protection required Loose or unstable Excavation instability Collapse or support required; health and safetystrata at shallow depth Hard strata/ Hard digging/hard Increased cost and delay obstructions at driving shallow depth Presence of unrecorded sensitive underground services. Damage during works, posing risk to health and safety of personnel and public Increased cost and delay for unplanned diversions and protection or repair Shallow Inundation of Increased cost and delay; health and safety groundwater excavations Contaminated Precautions for workers Increased cost and delay; health and safetyground Contaminated Increased disposal costs Increased cost and delay; health and safetyground Te m po ra ry W or ks & C on st ru cti on Is su es Table B.1. (Continued).

GEOTECHNICAL RISK REGISTER PROJECT # AFTER APPLIED STRATEGY RISK PROGRESS Date APPROACH TO RISK RESIDUAL RISK ASSESSMENT RISK EXPOSURE (Milestones) No. Risk Factor RISK ASSESSMENT RISK RESPONSE Prob- ability Impact Prob- ability ë Impact Responsible Team Member Method Time/ Budget Impact Comments/ Notes Mitigation Strategy Prob- ability Impact Prob- ability ë Impact Date Exposed to Risk Date Risk Exposure is Passed Date Risk Retired TOTAL Table B.2. Geotechnical risk register.

Geotechnical Design Decision Register Decision Milestones Category No. Design Package Key Decision Associated Risk Alternatives Considered Activity Early Start Date Activity Late Finish Date Decision Milestone Date Remarks General Concern Utility Environmental Geotechnical Construction Table B.3. Geotechnical design decision register.

Geotechnical Risk Management Plan Project Phase Strategy Risk # Geotechnical/ Subsurface Risk Risk Exposure Date Exposure Passed Date Expected Retired Date Pre-advertising Procurement Pre-construction Construction Geotechnical Risk Mitigation Tool Assigned to Risk 1 Early Contractor Involvement 2 Early Third Party Involvement 3 Increase Visibility of Geo- technical Issues 4 Enhanced Contract Mechanisms 5 Life Cycle Decision Making Table B.4. Geotechnical risk management plan.