Variability in Earthen Levee Seismic Response Due to Time-History Selection

In seismic slope stability analyses the single most important input parameter is the ground motion. Time-history selection is a challenging engineering problem since the variability in ground motion characterization is in part due to the complexity of the mechanisms that result in a seismic event taking place and the path and soil conditions from the origin of the seismic event to the location of interest. In this study, the effect of key ground motion parameters to the dynamic response of earthen levees is investigated. Specifically, the effect on the induced cyclic shear stress ratio (CSR) and/or seismically induced Newmark-type, permanent displacements (U) for prescribed sliding surfaces is discussed. Results were obtained by performing 2-D equivalent linear finite element dynamic analyses for a total of 1,000 ground motions. The mean period, Tm, of the ground motion, and the peak ground velocity, PGV, are among the parameters identified by this study as being good indices for seismic levee response. Identifying the parameters that correlate best with the variability in response will allow the formulation of time-history selection criteria for the seismic response of earthen levees

The May 25th 2011 railroad embankment failure in Ann Arbor, Michigan, as a means for teaching geotechnical engineering

A 30-m long railroad embankment failure that occurred on May 25 2011 in the city of Ann Arbor, Michigan, is presented. Emphasis is given on the field observations of the failure, the characterization of the site conditions and the seepage and slope stability analyses, all of which represent important components of the training and practice of a geotechnical engineer. The failure occurred following a record wet season that resulted in ponding water against the embankment and high enough water pressures and exit gradients that resulted in instability of the railroad embankment. Detailed background material and the methodology for using the case history in geotechnical engineering education are presented

Ground vibration measurements near impact pile driving

Pile driving is a complex dynamic process where little insight has been garnered in terms of the energy transfer from the driver to the soil and surrounding structures. Ground motion measurements during driving of full scale steel H-piles with diesel hammers are presented. The key feature of this work is the in-depth sensor installation starting very close to the pile (0.2 m), at other radial distances from the pile, and at various depths in the ground. Differences in wave sources from the tip and the shaft of the pile as well as wave attenuation coefficients are revealed from the sensor measurements. Attenuation relationships fitted through the data could be used to predict ground motion that could cause shakedown settlement. A conventional line array of surface mounted geophones was also used and results are presented

Factor of Safety Reduction Factors for Accounting for Progressive Failure for Earthen Levees with Underlying Thin Layers of Sensitive Soils

The effects of progressive failure on flood embankments with underlying thin layers of soft, sensitive soils are investigated. Finite element analysis allows for investigation of strain-softening effects and progressive failure in soft and sensitive soils. However, limit equilibrium methods for slope stability analysis, widely used in industry, cannot capture these effects and may result in unconservative factors of safety. A parametric analysis was conducted to investigate the effect of thin layers of soft sensitive soils on the stability of flood embankments. A flood embankment was modeled using both the limit equilibrium method and the finite element method. The foundation profile was altered to determine the extent to which varying soft and sensitive soils affected the stability of the embankment, with respect to progressive failure. The results from the two methods were compared to determine reduction factors that can be applied towards factors of safety computed using limit equilibrium methods, in order to capture progressive failure

Measurement of ground motion near piles during driving

Two types of vibration damage caused by driving piles have been reported in the literature: direct structural damage and damage due to settlement. Direct damage results from vibratory excitation of structures at amplitude exceeding the structural tolerance. Damage from settlement is a consequence from vibratory densification of loose soils resulting in total or differential settlement of structures. Problems of settlement due to pile driving have been experienced recently by the Michigan Department of Transportation (MDOT) during operations associated with replacement of deteriorating bridges. The work described here represents an attempt to understand the mechanisms of energy transfer from steel H-piles driven with diesel hammers to the surrounding soil and the energy attenuation through the soil by measuring ground motion in the near vicinity of the pile. The main feature of this study consisted of installing motion transducers very close, within 0.5 foot, to piles and measuring the resulting ground motion during pile driving. Selection, fabrication, and installation of the transducers and preliminary measured pile driving vibrations are presented

Asset Management for Retaining Walls

The work described here represents an attempt to develop a comprehensive risk management framework for the asset management of retaining wall structures. The work presented includes the development of a sensing strategy that can be used by structural inspectors to assess the coupled performance of the wall structure and the geotechnical system it supports. A reliability framework was developed using first-order reliability methods (FORM) to assess the reliability factor (β) for wall components and incorporates the consequences of failure with the estimated structural reliability factors to provide a basis for risk assessment of retaining walls. A new inspection manual was developed to reflect the instrumentation strategies and risk analyses developed

Measuring User Satisfaction for the Natural Hazards Engineering Research Infrastructure Consortium

The User Forum is a Natural Hazards Engineering Research Infrastructure (NHERI)-wide group focused on providing the NHERI Council with independent advice on community user satisfaction, priorities, and needs relating to the use and capabilities of NHERI. The User Forum has representation across NHERI activities, including representatives working directly with the Network Coordination Office (NCO), Education and Community Outreach (ECO), Facilities Scheduling, and Technology Transfer efforts. The User forum also provides feedback on the NHERI Science Plan. As the community voice within the governance of NHERI, the User Forum is composed of members nominated and elected by the NHERI community for a specified term of 1–2 years. User Forum membership spans academia and industry, the full breadth of civil engineering and social science disciplines, and widespread hazard expertise including earthquakes, windstorms, and water events. One of the primary responsibilities of the User Forum is to conduct an annual community user satisfaction survey for NHERI users, and publish a subsequent Annual Community Report. Measuring user satisfaction and providing this feedback to the NHERI Council is critical to supporting the long-term sustainability of NHERI and its mission as a multidisciplinary and multi-hazard network. In this paper, the role and key activities of the User Forum are described, including User Forum member election procedures, User Forum member representation and roles across NHERI activities, and the processes for measuring and reporting user satisfaction. This paper shares the user satisfaction survey distributed to NHERI users, and discusses the challenges to measuring community user satisfaction based on the definition of user. Finally, this paper discusses the evolving approaches of measuring user satisfaction using other methods, including engaging with the twelve NHERI research infrastructures

H-pile driving induced vibrations: reduced-scale laboratory testing and numerical analysis

Ground vibrations due to impact pile driving operations can become a major concern when affecting nearby structures and underground utilities. In an effort to better understand the transmission and dissipation of energy into the ground during impact pile installation, reduced-scale pile driving tests were conducted in an indoor cylindrical (6.5 m diameter and 1.8 m deep) sand pit at the University of Michigan. Sensors were placed at various depths from the ground surface and distances from the driven pile to record ground motions. In addition, the model pile was equipped with the pile driving analyzer (PDA) system to accurately assess the energy transfer from hammer to pile. The pile installation process was then simulated using 3D finite element (FE) dynamic analyses. The combination of ground vibration monitoring data and records of the impact force from the PDA testing collected from the small-scale pile driving tests in a controlled laboratory environment, offer a great opportunity to validate the numerical code. The recorded ground motion measurements from the impact driving of the model pile are compared with the calculated velocity-time histories from the FE numerical simulation of the pile driving test. Both measured and calculated ground motions verify the hypothesis of the wave propagation field generated by impact driven piles, as presented by Woods (1997)