Amir M. Kaynia

Static and dynamic simulation of a 700-m high rock slope in western Norway

Abstract Static and dynamic rock slope stability analyses were performed using a numerical discontinuum modelling technique for a 700-m high rock slope in western Norway. The rock slope has been investigated by the Geological Survey of Norway (NGU), which has been carrying out rock slide studies for the county More and Romsdal in western Norway. The purpose of numerical modelling was to estimate the volume of the rock mass that could potentially slide under static and dynamic forces. This estimation was required to assess the run-up heights (tsunami) in a fjord that could potentially be caused by the rockslide. Three cases have been simulated for predicting the behaviour of the rock slope. First, an initial static loading is applied in the numerical model to simulate the prevailing rock mass conditions at the site. Second, saturated and weathered joint conditions are modelled by reducing the residual friction angle along the discontinuities of the rock mass. In doing so, the model simulates the effect of degradation of discontinuities in the rock slope. Third, a dynamic loading, based on peak ground accelerations expected in the area, is applied to simulate dynamic earthquake conditions. These numerical studies have provided some useful insights into the deformation mechanisms in the rock slope. Both sliding and rotation of blocks start to occur once the residual friction angle along the discontinuities is reduced and when the region is shaken by a strong earthquake. The results indicate that, due to variations in the inclination of discontinuities, the entire slope does not become unstable and that down-slope sliding and rotation of blocks occur mainly on the top layers of the slope. Within the range of parameter values considered for this study, it is unlikely that the whole rock slope can be destabilised. The study provides an illustration of how the geo-mechanical properties of a rock mass can be integrated in a discontinuum rock slope model, which is used for predicting the behaviour of the slope under existing environmental and earthquake conditions. This model has helped not only to better understand the dynamics of the rockslide but also to estimate the potential rock volume that can become unstable when subjected to static and dynamic loads.

Dynamic response of pile groups with different configurations

A general methodology is outlined for a complete seismic soil-pile-foundationstructure interaction analysis. A Beam-on-Dynamic-Winkler-Foundation (BDWF) simplified model and a Greens-function-based rigorous method are utilized in determining the dynamic response of single piles and pile groups. The simplified model is validated through comparisons with the rigorous method. A comprehensive parameter study is then performed on the effect of pile group configuration on the dynamic impedances of pile foundations. Insight is gained into the nature of dynamic pile-soil-pile interaction. The results presented herein may be used in practice as a guide in obtaining the dynamic stiffness and damping of foundations with a large number of piles.

Site amplification in lava rock on soft sediments

Seismicity and volcanic activity in Iceland are related to the Mid-Atlantic plate boundary that crosses the island. Due to volcanic activity, different sea levels through the ages and glacial drift, the geology in Iceland is quite complex at many sites. In June 2000, two major earthquakes of magnitude 6.6 (Mw) and 6.5 (Mw) occurred in southern Iceland. Ground motion from these main shocks and a number of aftershocks were recorded at the Icelandic strong motion network operated by the University of Iceland. At one of the instrumented sites considerable amplification was recorded on lava-rock overlying alluvial deposits. This site fits poorly in the soil classification systems of most earthquake codes. In this paper the recorded data is analyzed with different methods and the results are compared with the results of a one-dimensional site response analysis. The different methods produce the same characteristic of soil amplification at the site. The findings of this study have important implications for design criteria for sites with similar geology. q 2002 Elsevier Science Ltd. All rights reserved.

Socioeconomic Clustering in Seismic Risk Assessment of Urban Housing Stock

A seismic risk assessment methodology based on socioeconomic clustering of urban habitat is presented in this paper. In this methodology, the city is divided into different housing clusters based on socioeconomic level of occupants, representing reasonably uniform seismic risk. It makes an efficient utilization of high resolution satellite data and stratified random sample survey to develop the building stock database. Ten different classes of socioeconomic clusters found in Indian cities are defined and 34 model building types (MBTs) prevalent on the Indian subcontinent have been identified and compared with the Medvedev-Sponheuer-Karnik (MSK) scale, European macroseismic scale (EMS), parameterless scale of seismic intensity (PSI), and HAZUS classifications. Lower and upper bound damage probability matrices (DPMs) are estimated, based on the MSK and EMS intensity scales and experience from past earthquakes in India. A case study of Dehradun, a city in the foothills of Himalayas, is presented. The risk estimates using the estimated DPMs have been compared with those obtained using the PSI scale. It has been observed that poorer people are subjected to higher seismic risk, both in terms of casualties and in terms of percent economic losses.

Sound propagation over layered poro-elastic ground using a finite-difference model

This article presents an axisymmetric pressure-velocity finite-difference formulation (PV-FD) based on Biots poro-elastic theory for modeling sound propagation in a homogeneous atmosphere over layered poro-elastic ground. The formulation is coded in a computer program and a simulation of actual measurements from airblast tests is carried out. The article presents typical results of simulation comprising synthetic time histories of overpressure in the atmosphere and ground vibration as well as snapshots of the response of the atmosphere-ground system at selected times. Comparisons with the measurements during airblast tests performed in Haslemoen, Norway, as well as the simulations by a frequency-wave number FFP formulation are presented to confirm the soundness of the proposed model. In particular, the generation of Mach surfaces in the ground motion, which is the result of the sound speed being greater than the Rayleigh wave velocity in the ground, is demonstrated with the help of snapshot plots.

Finite element analysis of failed slope by shear strength reduction technique: a case study for Surabhi Resort Landslide, Mussoorie township, Garhwal Himalaya

ABSTRACT Finite element analysis of failed slope of the Surabhi Resort landslide located in the Mussoorie township, Garhwal Himalaya has been carried out using shear strength reduction technique. Two slope models viz. debris and rock mass were taken into consideration in this study and have been analysed for possible failure of slope in future. Critical strength reduction factor (SRF) for the failed slope is observed to be 0.28 and 0.83 for the debris and rock mass model, respectively. A low SRF value of the slope revealed significant progressive displacement in the zone of detachment. This has also been evidenced in the form of cracks in the building of Surabhi Resort and presence of subsidence zones in the Mussoorie International School. These results are consistent with the study carried out by other workers using different approach.

Fragility Functions of Highway and Railway Infrastructure

The experience of past earthquakes has revealed that highway and railway elements are quite vulnerable to earthquake shaking and induced phenomena such as soil liquefaction or landslide; damages to these elements can seriously affect the transportation of products and people in both short-term (emergency actions) and long-term period. The objective of this chapter is to propose appropriate fragility functions for roadway and railway components other than bridges that are presented separately in Chap. 9. To this end, the main typological features are summarized and a short review of earthquake damages together with damage states definitions are provided for these elements. Fragility curves from literature are collected and reviewed. In some cases these functions are modified and adapted, while in other cases new fragility curves are developed. A general procedure for the derivation of analytical fragility curves that was followed in SYNER-G is described. This approach takes into account the effect of structure geometry, ground motion characteristics, soil conditions and associated uncertainties. New fragility curves are presented for tunnels in soil, embankments, cuttings and bridge abutments based on numerical analyses due to ground shaking. Finally, the proposed fragility functions are summarized and a general scheme to identify the functionality of roadway and railway elements due to different damage levels is outlined.

GEODYNAMIC CHALLENGES IN HIGH SPEED RAILWAY PROJECTS

This paper discusses the geodynamic challenges in high speed and high axle load railway projects, especially for soft ground conditions. Three main issues need to be solved by the engineering community: critical speed and excessive dynamic response or the track structure and supporting ground, accelerated degradation of the track structure, and vibration in track-side dwellings and buildings that can inconvenience people and disturb sensitive equipment. The paper describes the nature of these three issuers and discusses the prediction tools and design strategies. The importance of knowledge on the ground characteristics, especially the dynamic properties, is emphasized. Countermeasures are discussed. Further needs are pointed out, including the most urgent needs for further research and development. The benefit of standardization solutions, international collaboration projects and the sharing of knowledge is highlighted.

Experimental Assessment of Seismic Pile-Soil Interaction

Physical modeling has long been established as a powerful tool for studying seismic pile-soil-superstructure interaction. This chapter presents a series of 1-g shaking table tests aiming at clarifying fundamental aspects of kinematic and inertial interaction effects on pile-supported systems. Pile models in layered sand deposits were built in the laboratory and subjected to a wide set of earthquake motions. The piles were densely instrumented with accelerometers and strain gauges; therefore, earthquake response, including bending strains along their length, could be measured directly. Certain broad conclusions on kinematic and inertial SSI effects on this type of systems are drawn.

Some important considerations in analysis of earthquake-induced landslides

BackgroundThe frequency of landslide disasters is increasing as a result of exploitation of natural resources, deforestation, and greater population vulnerability due to growing urbanization and uncontrolled land-use. Earthquakes are a major triggering factor of landslides, and earthquake-induced landslides pose a major threat to infrastructure and human life. This paper presents the effects of slope angle, soil sensitivity, ground motion orientation, and multidirectional shaking on the results of seismic slope stability analyses.ResultsThe results show that permanent shear stresses due to sloping ground, strain softening and sensitivity, ground motion orientation, and multidirectional shaking all have a large influence on the permanent displacements estimated from earthquake-induced landslide hazard analyses. Multidirectional shaking also predicts larger excess pore pressures in deep layers than unidirectional shaking.ConclusionsIt is important that site investigations provide adequate information to model the correct slope angle and soil sensitivity. The ground motion orientation should be considered and chosen based on the specific needs of a project. Analyses with only one ground motion component could give unconservative results.