Estimating and Contracting Rock Slope Scaling Adjacent to Highways (2020)

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1 The nation’s transportation system has tens of thousands of natural and constructed rock slopes adjacent to roadways. Over time, these rock slopes deteriorate because of weathering, freeze/thaw, and other natural processes. These processes loosen rock that can fall onto the roadway, posing a hazard to its users and increasing risks for transportation agencies. Roads and highways are frequently closed by rockfall events, inhibiting the free flow of traffic and commerce. Agencies reduce rockfall hazards and risk in a number of ways. An effective measure is intentionally removing loose rocks from slopes, or “scaling.” This reduces future rockfall potential and risk. Despite scaling’s effectiveness and its widely accepted applica- tion, especially in mountainous areas, there are no standardized guidelines to assist agencies with planning, estimating, and administering scaling projects. The objective of this study is to document current rock slope scaling practices adjacent to highways, as performed by state departments of transportation (DOTs). The informa- tion was gathered through a literature review and a detailed questionnaire sent to state DOT geotechnical leads and to the three regional offices of the Federal Lands Highway division of the Federal Highway Administration. Responses were provided by 42 DOTs and two Federal Lands Highway division offices; an 81% DOT response rate. Follow-up interviews with six DOTs provided additional insight regarding scaling practice within their departments. Not all DOTs regularly perform scaling or have many rock slopes, therefore filter questions were formulated to permit responding without requiring a full questionnaire response. Of the 44 respondents, 24 performed enough scaling to respond to the more detailed questions. These 24 responding DOTs and Federal Lands Highway division offices are termed “scaling states” in the body of this synthesis. The survey questionnaire was subdivided into six categories, focusing on: (1) project administration, (2) design efforts, (3) plans and specifications, (4) administering construc- tion activities, (5) scaled slope performance, and (6) lessons learned. Each category had several questions asked, for a total of 31 scaling-specific questions. The major findings of the survey are categorized as follows. Project Administration. In general, most scaling projects either are carried out as pro- grammed construction projects or are emergency responses to rockfall events. Scaling states reported that a minority of projects are carried out as part of routine maintenance or as part of other preservation work. Nearly 75% of scaling projects are contracted to scalers meeting specified minimum qualifications, contracted either directly or through a general contractor. On-call lists are also used, particularly for emergency response. Only a very small proportion of scaling projects are awarded to contractors solely on a low-bid basis, a noteworthy departure from most highway construction projects. S U M M A R Y Estimating and Contracting Rock Slope Scaling Adjacent to Highways

2 Estimating and Contracting Rock Slope Scaling Adjacent to Highways Design Efforts. Most designers employ combinations of, in decreasing frequency of use, visual roadside review, maintenance activity and observations, up-close observation (via climbing ropes and boom lifts) of slope features, and newer survey technologies such as unmanned aerial vehicles or laser scanning. To estimate both scaling debris quantities and the production rate of scalers, scaling states rely heavily on expert judgment. Many combine expert judgment with other estimated measures for the unit of measure (e.g., volume or weight per unit area) for scaling debris. A wide range of “reasonable” produc- tion rates were indicated, from 50 to 800 square feet per hour, though the most common response indicated that production rates were too variable to specify. Plans and Specifications. Most scaling states employed a unit of time (hours) as the pay item for scaling, either for each individual or for the entire crew. Few scaling states report use of unit volume or area as the unit of payment; none used a lump-sum basis or unit length. When the time measurement “starts” responses indicate a mix of the scalers ascend- ing the slope, the beginning of the shift, or when the scaler is in position and ready to scale. About half of scaling states use separate bid items for various scaling techniques, typically differentiated by the use of hand techniques versus efforts assisted by heavy equipment. A number of ancillary support activities are often paid as “scaling,” including labor to sup- port scaling operations, vegetation removal, bench cleaning, or safety spotting, among other items. Scaling efforts performed at the request of the contractor (typically for worker safety), rather than those required in the plans, are most frequently handled on a case-by-case basis. Plan drawings typically use oblique photographs with scaling extents noted or plan view drawings with scaling extents shown. Many use a combination of the above, with only a few indicating scaling extents tabulated by station. A minority of scaling states do not require any scaler qualifications. Most scaling states require qualifications for all personnel, the foreman only, or the whole company. Some include a training/journeyman provision to help with resupplying the workforce. Most states measure experience by time spent scaling (hours or years) or by a combination of criteria that includes time spent. Half of the scaling states do not specify completion require- ments for scaling, while the other half indicated scaling is performed to the satisfaction of the engineer or until specified performance criteria are met. Most scaling states rely on contractor-designed temporary roadway protection, which helps prevent damage to the roadway or ancillary structures that may be struck by falling rocks. Scaling states also rely heavily on contractor-designed temporary rockfall protec- tion, which is intended to reduce rockfall-related injury risk. However, most scaling states provide rockfall protection by temporarily closing the road during scaling activities. Nearly all scaling states use common concrete barriers, with the most effective protection achieved using moveable rockfall barriers. Administrating Scaling During Construction. Inspecting work products during construc- tion is a common part of highway construction projects, and scaling is not an exception, despite the typical experience qualifications of the contractor. Most scaling states use a combination of inspecting staff at ground level without special training, specially trained staff on-slope using slope access techniques (ropes, boom lift), and specially trained staff inspecting from the ground surface. Personnel who verify scaling completion are typically experienced with slope scaling projects, either with or without on-slope verification. About a third of the scaling states have had completed scaling efforts approved by construction engineers without scaling experience. Nearly half of scaling states have used or plan to use new technologies such as laser scanning, photogrammetry, and unmanned aerial vehicles (UAVs) for uses related to

Summary 3 scaling, such as measuring scaling completion and coverage, with two DOTs responding that they are planning to use the technologies for pay-item measurement. Scaled Slope Performance. Literature suggests a wide range of scaled slope “life spans,” based largely on professional experience. About half of the scaling states indicated they maintain information informally or through job experience. About a third of the scaling states keep records through maintenance management systems, rockfall management sys- tems, or state police callout records. This synthesis identified knowledge gaps in current practices that could be addressed with research that: • Gathers key information to supplement experienced-based estimation approaches. • Prepares decision support tools to help DOTs with selecting which slopes may be eligible for scaling and subsequent prioritization criteria. • Identifies methods to manage and document scaler production and performance. • Establishes criteria for creation of a scaling database to collect data on production rates, rock quality, slope condition, and challenges overcome.