Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

On August 13, 2000, a massive landslide occurred in Northern New Jersey following an extreme rainfall event during which at least 381mm (15 in) of precipitation fell during a 4-day period. The composite earth slide-earth flow, with an estimated volume of 22,800 m3 (29,821 yd3) traveled up to 365 m (1200 ft) in a short period. While landslides do occasionally occur along the coastal bluffs of the Atlantic Coastal Plain, slides of this magnitude are uncommon in the glacial soils of the New Jersey Highlands section, where the slide occurred. A geotechnical investigation was undertaken to identify the causative factors of the slide. Soils within the rupture zone were found to be distinctly stratified in a direction parallel with the ground slope, which averaged 15% to 20%. The soil profile consisted of an Upper Till overlying a more compact Lower Till. A rupture surface developed at the stratigraphic contact between the two tills, with the Upper Till failing in translation. A significant factor in the location of the rupture surface was the density difference between the Upper and Lower Tills (averaging 16.11 kN/m3 (102.5 lb/ft3) and 20.44 kN/m3 (130 lb/ft3), respectively). Grain size analyses confirmed that the dominance of silt and sand in the Upper Till made it especially prone to sliding. Land use of the site was also a factor, since the rupture occurred on a hay field that was within a residential subdivision in the early stages of construction. The beneficial effects of root reinforcement were especially evident around the rupture scar, since headward and lateral migration of the slide were arrested by a bordering forest. Analyses suggest that the main trigger of the landslide was groundwater perching at the contact between the two tills leading to excess pore pressure which caused failure. Two other conditions contributing to elevated groundwater pressure were a small topographic swale and outcrops of low permeability granite bedrock directly above the rupture zone. The paper concludes with a brief discussion of the implications of the Sparta landslide on the burgeoning development of Northern New Jersey.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 13th, 12:00 AM Apr 17th, 12:00 AM

A Landslide in Glacial Soils of New Jersey

New York, New York

On August 13, 2000, a massive landslide occurred in Northern New Jersey following an extreme rainfall event during which at least 381mm (15 in) of precipitation fell during a 4-day period. The composite earth slide-earth flow, with an estimated volume of 22,800 m3 (29,821 yd3) traveled up to 365 m (1200 ft) in a short period. While landslides do occasionally occur along the coastal bluffs of the Atlantic Coastal Plain, slides of this magnitude are uncommon in the glacial soils of the New Jersey Highlands section, where the slide occurred. A geotechnical investigation was undertaken to identify the causative factors of the slide. Soils within the rupture zone were found to be distinctly stratified in a direction parallel with the ground slope, which averaged 15% to 20%. The soil profile consisted of an Upper Till overlying a more compact Lower Till. A rupture surface developed at the stratigraphic contact between the two tills, with the Upper Till failing in translation. A significant factor in the location of the rupture surface was the density difference between the Upper and Lower Tills (averaging 16.11 kN/m3 (102.5 lb/ft3) and 20.44 kN/m3 (130 lb/ft3), respectively). Grain size analyses confirmed that the dominance of silt and sand in the Upper Till made it especially prone to sliding. Land use of the site was also a factor, since the rupture occurred on a hay field that was within a residential subdivision in the early stages of construction. The beneficial effects of root reinforcement were especially evident around the rupture scar, since headward and lateral migration of the slide were arrested by a bordering forest. Analyses suggest that the main trigger of the landslide was groundwater perching at the contact between the two tills leading to excess pore pressure which caused failure. Two other conditions contributing to elevated groundwater pressure were a small topographic swale and outcrops of low permeability granite bedrock directly above the rupture zone. The paper concludes with a brief discussion of the implications of the Sparta landslide on the burgeoning development of Northern New Jersey.