Project Description

LFA provided the geotechnical consultation services for a geotechnical subsurface exploration program at the local Spec-Agg Quarry in Golden. LFA has provided services on an annual basis to the Quarry since 1995 and was pleased to be selected as the lead geotechnical consultant for the project. LFA's role for the annual study is to analyze and document the existing conditions within the quarry with respect to collected rock structure data and analysis of existing quarry wall slope stability.

Scope of Services

LFA's role for the geotechnical investigation included the development and implementation of a geotechnical exploration program, field logging of rock boreholes, analysis and interpretation of the data, and slope stability analyses for the highwalls of the quarry. The subsurface exploration program and slope stability analysis was performed as part of an effort to collect engineering data on the rock at the quarry and to develop a mine plan for the expansion of the quarry to the adjacent land parcel to the south.

The exploration program ultimately consisted of three continuously sampled vertical borings cored to a maximum depth of 825 feet. Water level data, which was previously a significant unknown, was collected in each of the boreholes, and monitored during the program. Acoustic and optical image geophysical surveys were performed on each of the boreholes to collect data pertaining to the depth, dip direction, and dip angles of the discontinuities that were intercepted by the borings. Additionally, geotechnical mapping was performed within the quarry and in road cuts, located in close proximity to the quarry, to supplement the exploration data.

Ultimately, the geotechnical data and slope stability analysis provided by LFA was included as part of Lafarge's application package to obtain approval from the State of Colorado for mining the new area to south. In September, the package was accepted by the State providing approval to expand the quarry. As of January of this year, intensive mining of the new area has occurred with rock quality exceeding the owner's expectations.

During the annual review, new exposures were documented in the middle and upper portions of the quarry, and data collected from these areas was used to assess the current stability of the existing quarry walls. All of the walls continue to remain stable, and are being excavated well within a reasonable safety factor.

Client

Lafarge Spec-Agg Quarry, Golden, Colorado