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

Recent Advances in Non-Linear Site Response Analysis

Studies of earthquakes over the last 50 years and the examination of dynamic soil behavior reveal that soil behavior is highly nonlinear and hysteretic even at small strains. Non-linear behavior of soils during a seismic event has a predominant role in current site response analysis. The pioneering work of H. B. Seed and I. M. Idriss during the late 1960’s introduced modern site response analysis techniques. Since then significant efforts have been made to more accurately represent the non-linear behavior of soils during earthquake loading. This paper reviews recent advances in the field of non-linear site response analysis with a focus on 1-D site response analysis commonly used in engineering practice. The paper describes developments of material models for both total and effective stress considerations as well as the challenges of capturing the measured small and large strain damping within these models. Finally, inverse analysis approaches are reviewed in which measurements from vertical arrays are employed to improve material models. This includes parametric and non-parametric system identification approaches as well as the use of Self Learning Simulations to extract the underlying dynamic soil behavior unconstrained by prior assumptions of soil behavior

Networked Geotechnical Near Real-Time Monitoring for Large Urban Excavation Using Multiple Wireless Sensors

A massive urban excavation is required to construct the below-grade rail platforms for the Transbay Transit Center. A performance-based approach was used to design the minimum stiffness of the shoring system to limit excavation-induced ground movements to appropriate magnitudes and minimize impact to adjacent infrastructure. During construction, a fully-automated near real-time digital geotechnical monitoring system that integrates wireless sensor data streams into an integrated database and decision support system called the Global Analyzer is used to track the performance of this excavation. Instrumentation used for monitoring includes inclinometers, deep settlement markers, extensometers, piezometers, and an automated total station network. Some of the advantages of the Global Analyzer system include (a) integration of all project monitoring data and construction history information in a centralized database, (b) the ability to compare measured and estimated or target performance, (c) the use of early indicators to understand problems areas prior to excavation reaching critical stages, (d) the distribution of geotechnical monitoring data to adjacent building owners and other stakeholders through a web-based portal, and (e) the generation of computer generated email alerts when threshold values are exceeded by a given instrument. The Global Analyzer is a key tool in supporting an efficient decision process informed by more complete and timely performance data. It represents a component of the decision support process needed in the observational approach and deformation control. This application is relatively new to such a large scale project in the US and provides an example of a large complex data collection and distribution system. The monitoring process used for this project takes advantage of the latest communications technologies in the monitoring of the construction of the Transbay Transit Center excavation in its complex urban environment

Using Tactile Pressure Sensors to Measure Lateral Spreading Induced Earth Pressures Against a Large, Rigid Foundation

Two centrifuge tests were performed at the NEES facility at Rensselaer Polytechnic Institute (RPI) to observe lateral earth pressures mobilized against a rigid foundation element during liquefaction-induced lateral spreading, as part of a larger NEESR study aimed at developing novel approaches to mitigate the effects of seismically-induced ground failures on large, rigid foundation elements. Models were constructed in a laminar box to allow unimpeded downslope soil displacement, and the sand in the model was liquefied during the centrifuge test. Lateral pressures prior to, during, and after shaking and liquefaction were directly measured using a novel device: tactile pressure sensors. Prior to testing the production models, several 1g and centrifuge experiments were conducted to determine whether the tactile pressure sensors would accurately measure pressures. Using the tactile pressure sensor and configuration described in this paper, geostatic pressures measured prior to the shaking agreed well with the anticipated theoretical at-rest earth pressures. In this paper, we describe these initial tests, the challenges that were encountered, methods employed to overcome these challenges, and the production centrifuge tests

Bridge Lessons Learned from the Wenchuan China, Earthquake

A strong earthquake of M7.9 occurred in Wenchuan County in Sichuan Province, China, on May 12, 2008. This paper presents the field observations on various types of bridge damages, including unseating of girders, longitudinal and transverse offset of decks, pounding at expansion joints, shear key failure, bearing displacement, column shear, and flexible cracks. Plausible causes of damages and collapses are discussed and the lessons learned from this event are briefly summarized. Some of the postearthquake temporary constructions are also reported

Effects of Ground Failure on Bridges, Roads, and Railroads

The long duration and strong velocity content of the motions produced by the 27 February 2010 Maule earthquake resulted in widespread liquefaction and lateral spreading in several urban and other regions of Chile. In particular, critical lifeline structures such as bridges, roadway embankments, and railroads were damaged by ground shaking and ground failure. This paper describes the effects that ground failure had on a number of bridges, roadway embankments, and railroads during this major earthquake

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.This is the publisher’s final pdf. The published article is copyrighted by Seismological Society of America and can be found at: http://www.seismosoc.org/publications/srl

Liquefaction probability mapping in greater Boston

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1988.Includes bibliographical references.by Youssef M.A. Hashash.M.S

Analysis of deep excavations in clay

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1992.Includes bibliographical references.by Youssef M.A. Hashash.Ph.D