HOW APPLIED GEOLOGY SOLVED PROBLEMS ON SELECTED HIGHWAY ENGINEERING PROJECTS IN NEW HAMPSHIRE

A study determined that twenty-five percent of the concrete aggregates utilized in New Hampshire may potentially cause deleterious alkali-silica reactivity (ASR) expansion in concrete and adversely affect the long-term durability of concrete structures. ASR gel was confirmed in a number of existing concrete bridges through uranyl acetate UV-light testing as well as core sampling and petrographic thin section analysis. ASR induced distress has resulted in costly repairs for some structures and has significantly reduced the service life of others. There are admixture(s) that can reduce ASR expansion in new concrete made with reactive aggregates.

A two phased study to estimate the remaining service-life and to assess the condition of thirty-year old rock reinforcements was conducted at the Barron Mountain rock cut along Interstate 93 in Woodstock, NH. Two types of rock reinforcement are installed at the site including: (1) partially bonded, resin grouted, prestressed rock bolts, and (2) fully bonded, Portland cement grouted, passive tendons. Phase 1 of the condition assessment included an evaluation of site conditions, a review of installation details, an estimation of remaining service-life and assessment of the rock reinforcement utilizing a combination of four nondestructive geophysical tests. Phase 2 consisted of invasive testing of selected rock reinforcement to verify the results from the first phase.

During 1988, the NHDOT remediated a one hundred foot high rock slope located on Interstate 89 in New London, NH. The rock excavation work consisted of removing 100,000 cubic yards of potentially unstable rock, which was dangerously close to the highway. This site was unique in that the granite rock contained anomalous concentrations of uranium and thorium. Due to the naturally occurring radioactive minerals in the rock, a Health and Safety Plan was implemented to protect construction workers and the general public. Extensive sampling, testing, on-site monitoring and training of personnel took place during the construction phase. A rock disposal site was selected due to ability of nearby organic bogs to absorb dissolved uranium minerals.