2021-03-05_REVISION - M1977141 - Laserfiche WebLink

Home Browse Search

F)� By ATL Date 10/11/2020 Client Aggregate Industries Sheet 5 of 7 Updated Rockfall Evaluation—Lyons Quarry:Technical Review Chkd.By NA Date 10/21/2020 Description Update Job# 10246984-002 Table •n A Berm Height Evaluation Rock Type Rock Size % Caught by Berm Height(ft) (ft) 7 8 9 1x4 100 100 10n 2x4 100 100 100 Dacite 2x6 qq.q inn 10n 3x6 qq.q 100 inn 6x12 WR inn 100 2 qq.q 100 100 4 100 100 100 Sandstone 6 qR.6 qq.q 100 8 q7.9 W7 inn 12 W6 100 100 Northwest Facing Dacite Wall At the toe of the northwest-facing wall is backfill from previous reclamation work that creates a flat runout area ranging from about 80 feet wide in the north to about 30 feet wide at the south end. A catchment berm along the north side of this flat area would be required to catch the rockfall from the northwest-facing dacite wall. Section B, shown in Figure 3, was selected as the critical section for this slope because of the slope height and steepness. A catchment berm with a 1 H:1 V slope was added 30 feet from the toe of the slope to represent the shortest runout area available at the south end of the highwall. Placing the berm 30 feet from the toe provides a factor of safety, because at Section B (which is the highest slope), a longer runout area is available and at the south end where the runout area is only 30 feet the actual quarry slope height is much lower. The results are shown in Table 5 and indicate that an 8 feet high catchment berm would catch 100% of all rock sizes simulated. In addition to the inherent factor of safety built into the evaluation as stated above a berm height of 12 feet high would provide an additional factor of safety of 1.5 relative to berm height. 4.0 LIMITATIONS The rockfall evaluation presented herein, while useful, has some limitations in practical application. Site-specific field data was not taken to determine the input coefficients to CRSP such as surface roughness, amount of vegetation (tangential coefficient), elastic properties of the highwall (normal coefficient), or rock densities. These parameters were conservatively assigned based on judgment and previous project experience and analyses. Additional field data would improve the accuracy and confidence of the evaluation. The physics of a rock falling down an irregular natural slope are complicated and are subject to multiple interactive factors. The CRSP program is an attempt to provide statistical analysis based on empirical relations and an algorithm which has been field calibrated. The CRSP program is not intended to be an exact predictor of rock behavior, therefore a factor of safety should be included in the mitigation design to account for model uncertainties. Additionally, the program utilizes a two-dimensional analysis whereas rockfall behavior is actually a three-dimensional phenomenon.