Ash Basin Excavation Under Strict Orders – A Measured Approach.pdf

Mark Taylor, WSP USA, Inc.
EVAN ANDREWS, Sequoia Services
Longde Jin, WSP USA, Inc.
Naveen Ganji, WSP USA, Inc.

Description

Ash Basin Excavation Under Strict Orders – A Measured Approach Authors Mr. Mark Taylor - United States - WSP USA, Inc. Mr. EVAN ANDREWS - United States - Sequoia Services Mr. Longde Jin - United States - WSP USA, Inc. Mr. Naveen Ganji - United States - WSP USA, Inc. Abstract A heavy civil contractor in the Southeast US was hired by a major electric utility to restore two retired ash basins to their original condition using the closure-by-removal approach, a 46-acre basin and an 86-acre basin containing about 2.5 and 5 million tons of CCR, respectively. Both basins had a varied history of use and reconfiguration, and the larger one experienced an unwitnessed progressive landslide in 2021 during free water decanting. Access to the larger was highly restricted due to post-slide safety concerns, forcing the contractor to take a limited incremental approach to early phases of construction under intense scrutiny from the owner’s engineering and management teams. Working with a geotechnical consultant, the team relied on their experience and intuition from similar projects and on the consultant’s proprietary application of CPT data to CCR strength interpretation under various states. A theoretical approach to equipment loading was applied to stability evaluations along with modeling of layered ash stratigraphy under variable hydrogeologic conditions. Working from high to low topography and strong to weak presumed CCR strength, the team empirically and analytically developed strategies to approach areas of uncertainty. This measured approach led to increased owner confidence and larger increments of work being approved to achieve the excavation production required to meet the strict project schedule. In this presentation, the following topics are discussed: • Using basin history, geomorphology, and hydrogeology to predict responses to excavation of highly variable CCR. • Balancing contractor experience, intuition and diligence with engineering analysis and hard numbers to mitigate risk from challenging site conditions. • Deconstruction of a dry stack with a post-failure (landslide) highwall. • Applying a state-of-the-art CCR technical knowledge base and proven low-tech excavation methods to practical construction strategies in a high-risk basin. • Data-driven approach to safe CCR excavation during construction using CPT data.

 
May 15th, 10:30 AM May 15th, 11:00 AM

Ash Basin Excavation Under Strict Orders – A Measured Approach.pdf

Grand Rapids, Michigan

Ash Basin Excavation Under Strict Orders – A Measured Approach Authors Mr. Mark Taylor - United States - WSP USA, Inc. Mr. EVAN ANDREWS - United States - Sequoia Services Mr. Longde Jin - United States - WSP USA, Inc. Mr. Naveen Ganji - United States - WSP USA, Inc. Abstract A heavy civil contractor in the Southeast US was hired by a major electric utility to restore two retired ash basins to their original condition using the closure-by-removal approach, a 46-acre basin and an 86-acre basin containing about 2.5 and 5 million tons of CCR, respectively. Both basins had a varied history of use and reconfiguration, and the larger one experienced an unwitnessed progressive landslide in 2021 during free water decanting. Access to the larger was highly restricted due to post-slide safety concerns, forcing the contractor to take a limited incremental approach to early phases of construction under intense scrutiny from the owner’s engineering and management teams. Working with a geotechnical consultant, the team relied on their experience and intuition from similar projects and on the consultant’s proprietary application of CPT data to CCR strength interpretation under various states. A theoretical approach to equipment loading was applied to stability evaluations along with modeling of layered ash stratigraphy under variable hydrogeologic conditions. Working from high to low topography and strong to weak presumed CCR strength, the team empirically and analytically developed strategies to approach areas of uncertainty. This measured approach led to increased owner confidence and larger increments of work being approved to achieve the excavation production required to meet the strict project schedule. In this presentation, the following topics are discussed: • Using basin history, geomorphology, and hydrogeology to predict responses to excavation of highly variable CCR. • Balancing contractor experience, intuition and diligence with engineering analysis and hard numbers to mitigate risk from challenging site conditions. • Deconstruction of a dry stack with a post-failure (landslide) highwall. • Applying a state-of-the-art CCR technical knowledge base and proven low-tech excavation methods to practical construction strategies in a high-risk basin. • Data-driven approach to safe CCR excavation during construction using CPT data.