Earthquake Geotechnical Engineering Design

A reliable shear wave velocity model is a prerequisite for the assessment of seismic site response at regional and local scale. 2D or 3D velocity models can be obtained by interpolation of tests at different locations. Surface wave tests are often used in this context because of their cost effectiveness and efficiency. As any characterization method based on the solution of an inverse problem, surface wave analysis suffers from solution non-uniqueness. Laterally constrained inversion provides a robust framework for the interpretation of surface wave data in the perspective of building pseudo-2D/3D shear wave velocity models. In the chapter three case histories in different geological settings and with different characteristics of the experimental dataset are reported and discussed.

A global dataset of more than 3,000 ground motion records from 536 sites from Greece, Italy, Turkey, USA and Japan is used to propose elastic acceleration response spectra and soil amplification factors for a new site classification system, which uses parameters such as the thickness of soil deposits, the average shear wave velocity to the seismic bedrock and the fundamental period of the site. The dataset is also used to derive soil amplification factors for the soil classes of Eurocode 8 (EC8). Uncertainties in the estimation of soil amplification factors are captured using a logic-tree approach, which allows the use of alternative models and methods in an effective way. The results indicate that estimated soil factors for EC8 class C are significantly higher than the ones proposed in the provisions. The performance of the proposed classification system is compared to that of EC8 classification system in terms of an inter-category error, which represents the average dispersion of data within all categories of a given classification scheme and the results indicate some improvement. Error terms for the new classification system are lower than the error terms for EC8 classification system at all periods.

During the 2011 Tohoku Pacific Ocean earthquake (M9.0), liquefaction occurred extensively in reclaimed land in Kanto area more than 200km far from the earthquake fault. The liquefied sand generally contained a lot of non-plastic fines with fines content more than 50% in some places. Almost all sand deposits along the Tokyo bay area reclaimed in 1960s or later liquefied, while in a good contrast, those older than that did not.

In order to study the aging effect on liquefaction strength of sands containing fines, a series of basic laboratory tests combining innovative miniature cone penetration and subsequent cyclic undrained loading were carried out in a modified triaxial apparatus on sand specimens containing fines. A unique curve relating cone resistance q _t and liquefaction strength R _L was obtained for reconstituted specimens, despite the differences in relative density D _r and fines content F _c , quite contradictory to the current liquefaction potential evaluation practice. Then a small amount of cement was added to fines in the sand specimens to simulate a geological aging effect in a short time. It was found that the liquefaction strength R _L increases with increasing F _c more than the penetration resistance q _t , resulting in higher liquefaction strength under the same cone resistance. Thus it has been clarified that not the fines content itself but the aging effect by cementation, which becomes more pronounced in sands with higher F _c , can facilitate reasonable basis why liquefaction strength is modified with increasing fines content in the evaluation practice.

In addition to the accelerated tests on the reconstituted specimens with cement, intact samples recovered from in situ Pleistocene and Holocene deposits with known ages have been tested and confirmed the similar trend to the above-mentioned results.

Severe damage to houses, roads and buried pipelines caused by liquefaction of the ground was the characteristic feature of destruction at the time of the 2011 Great East Japan in 2011. Widespread areas along the Tokyo Bay and in the downstream reaches of the Tone River suffered the liquefaction-associated damage, despite of the distance as long as 450–500km from the epicenter of the quake. Typical examples of the damage are presented herein with reference to conditions of soil profiles. As a measure to gauge its destructiveness, the ground settlements resulting from liquefaction were calculated based on volume decrease characteristics of sandy soils and their outcome was compared with the settlements actually observed on the ground surface.

There were several accounts by eye-witnesses and video-pictures which are tacitly indicative of advent of surface waves or sloshing-like movements of the ground surface. Although conceptionally, some interpretation is given to these new features of motions which have not been hitherto addressed.

The 2011 Tohoku-Pacific Ocean earthquake (Great East Japan earthquake) caused severe liquefaction not only in the Tohoku district of northeastern Japan, but also in the Kanto district. About 27,000 timber houses, a lot of buried sewage pipes and roads were damaged due to liquefaction. In Tokyo Bay area, the very long duration of the main shock and an aftershock 29min later probably caused serious settlement and inclination of houses. The maximum inclination in Urayasu City was about 60/1,000. In the heavily tilted houses, inhabitants feel giddy and nausea and difficult to live in their houses after the earthquake though no damage to walls and windows were observed. Then, on May 2011, Japanese Cabinet announced new evaluation standard for the damage of houses by the two factors, settlement and inclination. Tilted houses more than 1/20, 1/20 to 1/60, 1/60 to 1/100 are judged as completely destroyed, large-scale partially destroyed, and partially destroyed houses, respectively in the standard. Tilting of houses is derived from non-uniform settlement. Several factors affect to the non-uniform settlement. Among them effect of adjacent houses was dominant. If two houses are closely constructed these houses tilt inward, and if four houses are close these houses tilt toward the center. Many inhabitants along Tokyo Bay are facing to the serious problem how to restore the damaged houses. Complicated problem is the re-liquefaction during aftershocks or future earthquakes.

After the 2011 gigantic earthquake in Japan, the author has been investigating damage extents, damage mechanisms, restoration policies, and proposal of future technological development for river levees. Those activities are summarized here with emphasis on the difficult handling of liquefaction inside the levees and assessment of seismic performance. To mitigate the internal liquefaction, not only the field investigation technique but also numerical analysis for performance prediction has to be newly developed.

The seismic performance design of dams is based in good estimates of sliding displacements and crest settlements. Theoretical result has shown a good correlation between sliding displacement of slope and destructiveness potential factor P_D. Chilean practice of seismic dam design considers performance design with three limit estates: operational, maximum credible earthquake and second maximum credible earthquake. Crest dam vertical settlement recorded from seismic performance in real Chile earthquakes for P_D between 50 and 60 × 10⁻⁴ [gs³] confirm the good forecast of the theoretical values obtained in terms of P_D compare with PGA. In conclusion the use of P_D for performance design of dams is highly recommended.

In the last decades, the interest towards performance-based approaches in the field of seismic design and seismic adequacy assessment has rapidly grown, spreading an increasing awareness about the effects of the interaction between foundation and superstructure in particular under severe conditions. By the way, a lack of reliable methods for the seismic analysis of foundations is still apparent. To overcome this deficiency, the macro-element concept is in this paper suggested to be employed.

Although the macro-element approach is widely accepted to be very promising, it has not been supported so far by adequate experimental evidences, at least for seismic applications and few experimental results on the non-linear soil-foundation dynamic interaction are available in literature. Thus, in this paper, the macro-element theory in its different versions (elasto-perfectly plastic, elasto-strain-hardening plastic, bounding surface plastic and hypo-plastic) is first introduced and the mechanical response of shallow foundations under monotonic/cyclic loading, as it results from experimental tests, is outlined. All the critical issues concerning the employment of macro-element theory in Direct Displacement-Based approaches are then discussed and some application examples for solving practical problems are reported.

A numerical simulation of a large-scale highway interchange system under seismic loading conditions is conducted. A three-dimensional (3D) Finite Element (FE) model of an existing bridge system at the Interstate 10/215 interchange (Riverside County, CA) is developed. This interchange is comprised of three connectors at different bridge superstructure elevations. Herein, focus is placed on one of these three connectors (the North-West connector), using the OpenSees FE framework. A strategy to incorporate ground response and soil-structure interaction (SSI) is implemented based on the Domain Reduction Method (DRM) for three-dimensional earthquake simulation. Modeling of this bridge-foundation-ground system is based on blue-prints that were provided by Caltrans (California Department of Transportation). Vibration properties and seismic response behavior for the connector and the soil domain are examined. Different scenarios of bridge response are considered and compared, including fixed-base uniform excitation, and multiple-support excitation with and without the full ground/foundation soil domain.

Underground structures, tunnels, subways, metro stations and parking lots, are crucial components of the build environment and transportation networks. Considering their importance for life save and economy, appropriate seismic design is of prior significance. Their seismic performance during past earthquakes is generally better than aboveground structures. However several cases of severe damage to total collapse have been reported in the literature, with that of the Daikai metro station in Kobe during the Hyogoken-Nambu earthquake (1995) being one of the most characteristic. These recent damages revealed some important weaknesses in the current seismic design practices. The aim of this chapter is not to make another general presentation of the methods used for the seismic design of underground structures, but rather to discuss and highlight the most important needs for an improved seismic performance and design. In that respect it is important to consider that the specific geometric and conceptual features of underground structures make their seismic behavior and performance very distinct from the behavior of aboveground structures, as they are subjected to strong seismic ground deformations and distortions, rather than inertial loads. Several methods are available, from simplified analytical elastic solutions, to sophisticated and in principal more accurate, full dynamic numerical models. Most of them have noticeable weaknesses on the description of the physical phenomenon, the design assumptions and principles and the evaluation of the parameters they need. The chapter presents a short but comprehensive review of the available design methods, denoting the crucial issues and the problems that an engineer could face during the seismic analysis. The main issues discussed herein cover the following topics: (i) force based design against displacement based design, (ii) deformation modes of rectangular underground structures under seismic excitation, (iii) seismic earth pressures on underground structures, (iv) seismic shear stresses distribution on the perimeter of the structure, (v) appropriateness of the presently used impedance functions to model the inertial and the kinematic soil-structure interaction effects, (vi) design seismic input motion, accounting of the incoherence effects and the spatial variation of the motion and (vii) effect of the build environment (i.e. city-effects) on the seismic response of underground structures. The discussion is based on detailed numerical analysis of specific cases and recent experimental results in centrifuge tests. Other important issues like the design of submerged tunnels to liquefaction risk, or the complexity to evaluate the response of the joints of submerged tunnels are also shortly addressed. Finally we present the most recent developments on the evaluation of adequate fragility curves for shallow tunnels.

As a country affected by frequent earthquakes, Japan has accumulated experience on using reinforced soil wall technology as a seismic countermeasure. This paper briefly reviews the recent development of this technology in Japan. Approximately 1,600 case histories on the seismic performance of such walls during the 2011 Great East Japan Earthquake were collected and analyzed. Statistical data on the seismic damage revealed that all types of reinforced soil walls performed well during the 2011 earthquake. The case study where the damage was closely investigated was also particularly focused upon and discussed.

In current infrastructure projects, the most economical solution with the required performance is selected from several candidate solutions. In general, the term “most economical” implies that the initial cost is the lowest for that particular solution. Risk-induced seismic events are not usually considered in many projects. In this paper, a new design concept that considers the lifecycle cost including the geo-risk for a reinforced soil wall is proposed. A user-friendly cost estimation tool and a reliability analysis method along with its validation are also introduced. As a practical application of the geo-risk-based design, the selection of the best solution from the candidate solutions and the determination of the optimum reinforcing condition are discussed.

A performance-based methodology for seismic analysis and design of the geosynthetic elements of waste containment systems, including landfills and heap leach pads, has been developed. The methodology offers a rational alternative to the current state of practice for seismic design of geosynthetic containment system elements in which a decoupled Newmark-type displacement analysis is used to calculate a permanent seismic displacement. This calculated displacement is generally considered to be an index of the performance of the containment system in an earthquake. In the Newmark-type design methodology, no explicit evaluation is made of the stresses and strains in the geosynthetic elements of the containment system. In order to explicitly assess the ability of the geosynthetic elements of a containment system to maintain their integrity in a design earthquake, a finite difference model of waste-liner system interaction has been developed using the computer code FLAC^TM. A beam element with zero moment of inertia and with interface elements on both sides is employed in the model to represent a geosynthetic element in the liner system. This enables explicit calculation of the axial forces and strains within the liner system element. The beam element model was calibrated using available experimental data from shaking table tests of rigid and compliant blocks sliding on geomembranes. The model was then used to analyze the behavior of the Chiquita Canyon landfill in the Northridge earthquake. Results of the analysis provide insight into the reasons for the tears in the liner system at Chiquita Canyon observed after the Northridge event. This model provides a basis for direct performance based seismic design of geosynthetic elements not only in waste containment systems but in a variety of other civil structures that employ geosynthetic elements wherein earthquake ground motions cause relative displacement between the geosynthetic element and the surrounding soil.