Learning of Soil Behavior from Measured Response of a Full Scale Test Wall in Sandy Soil

In urban deep excavations, instruments are placed to monitor deformations and to control construction and reduce the risk of excessive and potentially damaging deformations. The second author has introduced a new inverse analysis approach that utilizes measured excavation performance to extract the underlying soil behavior. The extracted soil behavior can be used in predicting the behavior of similar excavations. This paper provides a first implementation of this inverse analysis approach to a well instrumented full scale test wall in a sand deposit. A wall consisting of soldier beams with wood lagging was instrumented to study anchored (one and two level tie backs) wall behavior in sandy soil deposits at Texas A&M. Strain gauges, load cells, inclinometers, and settlement points were placed in two sections of the excavation to monitor the excavation behavior. The measured excavation response for the section with two-level tie-backs is used to extract the constitutive model through the inverse analyses approach. The extracted constitutive model is used in predicting the underlying soil behavior for the section with one tie-back level. The predicted behavior of the excavation and its agreement with measurements at the site are discussed in detail

Non-Linear Site Response Analysis for Deep Deposits in the New Madrid Seismic Zone

The New Madrid Seismic Zone, the most seismically active zone in the Eastern US, is overlain by deep unconsolidated deposits of the Mississippi Embayment. The deposits range in thickness from about 20 m in the St. Louis area to about 1 km in the Memphis Area and consist of silts, clays and sands. The influence of these deposits on the propagation of seismic waves to the ground surface remains a major source of uncertainty. A new non-linear one-dimensional site response analysis model is introduced for the vertical propagation of horizontal shear waves in deep soil deposits. The model accounts for the effect of large confining pressures on the strain dependent modulus degradation and damping of the soil. The capability of the new model is illustrated using soil columns at three typical locations within the Mississippi Embayment including a 1000 m column representative of conditions in Memphis. The analyses show that high frequency components usually filtered using conventional wave propagation methods, are preserved. The analyses show that spectral amplification factors for the deep deposits in the period range of 0.6-5sec range between 2 and 6, and at longer long periods (up to 10 set) can be as high as 8

Site-Specific Response Analysis in the New Madrid Seismic Zone

A coal-fired power plant, Plum Point Energy Station, is being built in the city of Osceola, Arkansas, which is located in the New Madrid Seismic Zone (NMSZ). The project site is characterized as Site Class F, according to ASCE-7-05, because the soils at the site are prone to liquefaction. The depth of soil to rock is approximately 1 kilometer (km). A site-specific response study was required by the building code to determine the uniform hazard spectrum at the ground surface. The site-specific study included a probabilistic seismic hazard assessment to determine the Maximum Considered Earthquake (MCE) spectrum at an equivalent rock outcrop and a one-dimensional site response analysis to determine the ground surface response, given the rock outcrop motions. Spectral matching was used to generate the MCE ground motions at the rock outcrop. The equivalent linear site response code, SHAKE, and two nonlinear site response codes, SUMDES and DEEPSOIL, were used to generate the ground surface acceleration histories. The mechanical properties of the soils in the column were varied to assess the impact of changes in soil properties on free-field response. The function of the equivalent linear and nonlinear site response codes was identified. The amplification of the rock motion to the free field is discussed herein in terms of the site class factors presented in ASCE-7-05

Structural and geotechnical observations after the April 25, 2015 M7.8 Gorkha, Nepal earthquake and its aftershocks

The April 25, 2015 Gorkha (Nepal) Earthquake (M7.8) and its related aftershocks had a devastating impact on Nepal. The earthquake sequence resulted in nearly 9,000 deaths, tens of thousands of injuries, and left hundreds of thousands of inhabitants homeless. With economic losses estimated at several billion US dollars, the financial impact to Nepal is severe and the rebuilding phase will likely span many years. To investigate the effects of this event, the University of Illinois at Urbana-Champaign Department of Civil and Environmental Engineering (CEE) sponsored a team to visit Nepal, funded by a CEE Rapid Response Grant. From May 22-28, 2015, Youssef Hashash visited Nepal, in collaboration with a Geotechnical Extreme Events Reconnaissance (GEER) Association team, and collected data primarily related to geotechnical response. From June 7-13, 2015, Larry Fahnestock visited Nepal and collected data related to structural response of buildings, with focus on reinforced concrete frame structures. This report briefly summarizes geotechnical aspects of the events, which are documented more extensively in a GEER Association report, and thoroughly summarizes structural observations.CEE Rapid Response Grant, Department of Civil and Environmental Engineering at the University of Illinois at Urbana-ChampaignOpe

China Earthquake Reconnaissance Report: Performance of Transportation Structures during the May 12, 2008, M7.9 Wenchuan Earthquake

This report documents the lessons learned from damage caused in the May 12, 2008, M7.9 earthquake in Wenchuan County, China. The damage to the 14 observed bridges reminded the researchers of damage suffered during the 1971 San Fernando Earthquake in California. The bridges had few seismic details such as long seats, large shear keys, or tightly spaced transverse reinforcement. Most arch and girder bridges collapsed due to surface rupturing of the seismic faults in the Longmen-Shan thrust zone. A significant portion of roadways and bridges were pushed away or buried by landslides in the steep slopes of mountainous terrain. Damage to bridge superstructure included unseating of girders, longitudinal and transverse offset of decks, pounding at expansion joints, and shear key failure. The bearings of several girder bridges were either crushed or displaced significantly. The substructure and foundation of bridges were subjected to shear and flexural cracks, concrete spalling, stirrup rupture, excessive displacement, and loss of stability. More damage occurred in simply supported bridges than in continuous spans. Curved bridges either collapsed or suffered severe damage. Evidence of directivity effects on bridges near the earthquake epicenter was observed during the earthquake. The San Fernando earthquake significantly changed the seismic design and construction of bridges in the United States. The Wenchuan earthquake is expected to have the same significance for China\u27s bridge engineers

Geotechnical Field Reconnaissance: Gorkha (Nepal) Earthquake of April 25, 2015 and Related Shaking Sequence

The April 25, 2015 Gorkha (Nepal) Earthquake and its related aftershocks had a devastating impact on Nepal. The earthquake sequence resulted in nearly 9,000 deaths, tens of thousands of injuries, and has left hundreds of thousands of inhabitants homeless. With economic losses estimated at several billion US dollars, the financial impact to Nepal is severe and the rebuilding phase will likely span many years. The Geotechnical Extreme Events Reconnaissance (GEER) Association assembled a reconnaissance team under the leadership of D. Scott Kieffer, Binod Tiwari and Youssef M.A. Hashash to evaluate geotechnical impacts of the April 25, 2015 Gorkha Earthquake and its related aftershocks. The focus of the reconnaissance was on time-sensitive (perishable) data, and the GEER team included a large group of experts in the areas of Geology, Engineering Geology, Seismology, Tectonics, Geotechnical Engineering, Geotechnical Earthquake Engineering, and Civil and Environmental Engineering. The GEER team worked in close collaboration with local and international organizations to document earthquake damage and identify targets for detailed follow up investigations. The overall distribution of damage relative to the April 25, 2015 epicenter indicates significant ground motion directivity, with pronounced damage to the east and comparatively little damage to the west. In the Kathmandu Basin, characteristics of recorded strong ground motion data suggest that a combination of directivity and deep basin effects resulted in significant amplification at a period of approximately five seconds. Along the margins of Kathmandu Basin structural damage and ground failures are more pronounced than in the basin interior, indicating possible basin edge motion amplification. Although modern buildings constructed within the basin generally performed well, local occurrences of heavy damage and collapse of reinforced concrete structures were observed. Ground failures in the basin included cyclic failure of silty clay, lateral spreading and liquefaction. Significant landsliding was triggered over a broad area, with concentrated activity east of the April 25, 2015 epicenter and between Kathmandu and the Nepal-China border. The distribution of concentrated landsliding partially reflects directivity in the ground motion. Several landslides have dammed rivers and many of these features have already been breached. Hydropower is a primary source of electric power in Nepal, and several facilities were damaged due to earthquake-induced landsliding. Powerhouses and penstocks experienced significant damage, and an intake structure currently under construction experienced significant dynamic settlement during the earthquake. Damage to roadways, bridges and retaining structures was also primarily related to landsliding. The greater concentration of infrastructure damage along steep hillsides, ridges and mountain peaks offers a proxy for the occurrence of topographic amplification. The lack of available strong motion records has severely limited the GEER team’s ability to understand how strong motions were distributed and how they correlate to distributions of landsliding, ground failure and infrastructure damage. It is imperative that the engineering and scientific community continues to install strong motion stations so that such data is available for future earthquake events. Such information will benefit the people of Nepal through improved approaches to earthquake resilient design

Geotechnical Effects of the 2015 Magnitude 7.8 Gorkha, Nepal, Earthquake and Aftershocks

This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes