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Subgrade Improvement for Segmental Retaining Walls
At a large development site in Malvern, Pennsylvania, twelve segmental retaining walls were required to achieve the proposed grades. The subgrade investigation in the karst geology underlying the site revealed a pinnacled bedrock surface underlying partially saturated overburden varying from low plasticity silts to silty sands. Blow counts within the overburden were generally less than 10, and many were observed to be weight-of-hammer. As part of the subsurface investigation a substantial laboratory testing was performed on recovered samples. Subsequent design analyses that subgrade improvement was required beneath six of the twelve retaining walls. Subgrade improvements selected included staged construction, subgrade surcharging, and surcharging with vertical strip drains. For staged construction analyses, the maximum height of retaining wall that could be constructed with the initial undrained cohesion value and comply with required total stress safety factors were determined. The undrained shear strength required to adequately support the total height of the retaining wall under total stress conditions was then calculated where needed. The amount of strength gain and duration needed to develop the strength gain is a function of the distribution of the applied stress, the stress history, and consolidation parameters of the supporting soils. Considering the laboratory data, the anticipated anisotropic stress distribution and strength gain theory, a relationship was developed for undrained strength gain for the saturated fine-grained soils at the site. Finally, the duration to develop the required strength gain was calculated. Monitoring of construction was performed using pore pressure transducers and settlement plates. This paper will discuss the subgrade investigation, laboratory testing and design analyses necessary to provide the necessary subgrade improvement beneath the segmental retaining walls.
Subgrade Improvement for Segmental Retaining Walls
At a large development site in Malvern, Pennsylvania, twelve segmental retaining walls were required to achieve the proposed grades. The subgrade investigation in the karst geology underlying the site revealed a pinnacled bedrock surface underlying partially saturated overburden varying from low plasticity silts to silty sands. Blow counts within the overburden were generally less than 10, and many were observed to be weight-of-hammer. As part of the subsurface investigation a substantial laboratory testing was performed on recovered samples. Subsequent design analyses that subgrade improvement was required beneath six of the twelve retaining walls. Subgrade improvements selected included staged construction, subgrade surcharging, and surcharging with vertical strip drains. For staged construction analyses, the maximum height of retaining wall that could be constructed with the initial undrained cohesion value and comply with required total stress safety factors were determined. The undrained shear strength required to adequately support the total height of the retaining wall under total stress conditions was then calculated where needed. The amount of strength gain and duration needed to develop the strength gain is a function of the distribution of the applied stress, the stress history, and consolidation parameters of the supporting soils. Considering the laboratory data, the anticipated anisotropic stress distribution and strength gain theory, a relationship was developed for undrained strength gain for the saturated fine-grained soils at the site. Finally, the duration to develop the required strength gain was calculated. Monitoring of construction was performed using pore pressure transducers and settlement plates. This paper will discuss the subgrade investigation, laboratory testing and design analyses necessary to provide the necessary subgrade improvement beneath the segmental retaining walls.
Subgrade Improvement for Segmental Retaining Walls
McKelvey, James A. III (author) / Mislinski, Corey D. (author)
2013
8 Seiten, Bilder, Quellen
Conference paper
Storage medium
English
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