Prediction of Future Settlement of Backfill at an Aggregate Mining Quarry Site in Irwindale, CA Using Numerical Method and Settlement Monitoring Data

Abstract

Future static settlement of a former aggregate mining quarry site in Irwindale, California is predicted based on the monitoring data and using numerical analyses that consider the total settlement of the deepest portion of the rockfill. The portion of quarry analyzed was backfilled with approximately 61 to 67 meters, has a volume of 2.6 million m3, and covers an area of 114,900 m2. The backfill material ranges from silty sand (SM) to silty gravel (GM) and was compacted to achieve an average relative compaction (RC) of 96%. The deepest fill area is currently being monitored with survey data to predict future 50-year settlement due to secondary compression. Settlement monument data from three different locations has been collected and made available starting from May 2009 up to now. A 3-dimensional model of the rockfill was used to determine an appropriate upper and lower bound of predicted future 50-year settlement from today in 13 stages and scenarios. The modified secondary compression index was estimated along with the modified compression index that was back calculated to match the field monitoring data. We could find good agreement between the field monitoring data and our numerical model when considering total settlement of the rockfill.

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