Disposal products resulting from mining operations are called tailings. Typically in copper, gold and zinc mines, the extracted ore is crushed to the size of fine sand to clay, in order to recover the minerals. In copper mines, about one percent of the mass of the milled ore retrieved corresponds to the valuable minerals. Therefore, in general mining operations have to manage large quantities of tailings which are around 99 times the weight of the copper, gold or zinc production. In addition, due to the large amounts of water involved in the mining processes related to the extraction of the minerals, the resulting tailings are fully saturated.

The engineering practice have registered catastrophic failures of tailings dams triggered by earthquakes, causing severe losses to the private property, destruction of agricultural lands and in many cases loss of human lives. Most of the seismic failures of tailings dams are attributed to the development of excess pore water pressure, causing liquefaction. After the failure, the existence of almost horizontal terraces has been observed, which has been attributed to the low post liquefaction strength developed by weak layers of the stratified structure of the tailings disposed at the basin.

In spite of these failures in countries with a substantial mining industry, such as Australia, Canada, Chile, Chine, Peru, Poland, South Africa, and USA, among others, the design and construction of enormous tailing disposals is a crucial requirement that has been a great challenge for geotechnical engineering. The mining industry generates everyday millions of cubic meters of waste disposal material, which must be kept safe and at minimum cost. This trend indicates that conventional tailings dams with large dimensions in terms of height and extension are reasonable solutions for the management of mining waste products, being the assessment of their stability one of the main concerns. Additionally, in regions with a high seismic activity, the dynamic stability and liquefaction resistance requirements are the main issues to address. Furthermore, because all tailings disposals will exist well after the mining operation is ended, the seismic stability must be guaranteed for a large period of time after the closure of the mine.

Accordingly, the Organizing Committee of this International Conference on Earthquake Geotechnical Engineering is pleased to extend the invitation to participate in the special workshop “seismic design and stability analysis of tailings disposals”.

Recent Advances on Liquefaction Analysis and Remedial Methods

Soil liquefaction is a phenomenon in which the strength and stiffness of a saturated cohesionless soil are reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible of large damage in historical earthquakes around the world, like the 1964 Anchorage earthquake (USA), the 1985 Loma Prieta earthquake (USA), the 1994 Northridge earthquake (USA), the 1995 Kobe earthquake (Japan), the 1999 Kocaeli earthquake (Turkey), and the 1999 Chi-Chi earthquake (Taiwan). For instance, the 1964 Niigata earthquake (Japan), caused more than US$ 1 billion in damage and most of this damage was related to soil liquefaction. On the other hand, after the 1971 San Fernando earthquake (USA), 80,000 people living downstream of the dam had to be evacuated.

The failures commonly associated with soil liquefaction are:

• • Sand boils, causing subsidence and relative minor damage.

• • Flow failures of slopes involving movements of a large mass of soil.

• • Lateral spreading, caused by the lateral displacement of gently sloping ground.

• • Ground oscillation where liquefaction of a soil deposit beneath a site leads to back and forth movements of intact blocks of surface soil.

• • Loss of bearing capacity causing foundation failure.

• • Buoyancy, which in extreme cases can take buried structures, like tanks, to the surface

• • Ground settlement, often associated with some other failure mechanism.

• • Failure of retaining walls due to increase lateral loads from liquefaction backfill soil or loss of support from liquefied foundation soils.

Remedial procedures, costing hundreds of millions of dollars annually, are usually undertaken to address concerns over the liquefaction susceptibility of soils in seismically active areas. Historically, numerous foundations, dams and other systems were constructed with little to none effects due to earthquake excitations and must now be reevaluated in order to check for earthquake potential damage. Bridges have shown to be among the most vulnerable structures to earthquake damage. In the United States for example, about 70% of the approximately 600,000 highway bridges were constructed prior to 1971, with little or no earthquake design. In fact, the vulnerability of highway bridges to liquefaction phenomena has been clearly demonstrated by the extensive damage observed in past earthquakes.

Even though considerable knowledge have been gained from past experiences, considerable uncertainties associated with liquefaction remain, such as scale effects, pore water migration, strain localization, confinement stress, soil-structure interaction, etc. Liquefaction occurs worldwide and is of paramount importance to keep developing the state of the art for the safety of people and infrastructure.

The Organizing committee of this International Conference on Earthquake Geotechnical Engineering is pleased to extend the invitation to participate in the special workshop “Recent advances on liquefaction, analysis and remedial methods” to be held during the conference. We invite and encourage the experts in this area and all the people interested in this important topic to submit abstracts. This workshop will be an opportunity for presentations, discussions and revision of the state of the art of soil liquefaction.

Performance Based Design in Earthquake Geotechnical Engineering: Concepts, Advantages and Limitations

Performance-Based Design is increasingly being used in earthquake geotechnical engineering and in the design of buildings and civil structures around the world, since it provides a comprehensive methodology for assessing the performance of structural and geotechnical systems subjected to seismic loading. The seismic performance of these systems is estimated for a sliding scale of seismic hazard levels from frequent to rare earthquake events, and the consequences of that performance are expressed in terms of quantities that a client understands, such as the number of deaths and injuries, repair cost, and downtime.

Performance-Based Design, however, has not been sufficiently established in geotechnical engineering practice, and there is a need to reconsider how new buildings and new civil engineering structures are being designed, as severe seismic ground motions are pushing conventional limit design methodologies beyond the point where they can be applied with confidence.

Just recently, many researchers and practitioners from all over the world participated in the International Conference on Performance-Based Design in Earthquake Geotechnical Engineering held in Tsukuba, Japan, and one of the objectives of this workshop is to build on the outcomes of that conference, Defining appropriate performance criteria, shifting from limit to performance-based design, and the explicit incorporation of uncertainties in order to make it useful for practitioners still remain as some of the major challenges we face in geotechnical earthquake engineering.

The aim of this workshop is to present and discuss the state of the art of PBD in earthquake geotechnical engineering, its key concepts, advantages, and limitations. On behalf of the organizing committee we cordially invite all geotechnical academics and practitioners to participate in this workshop, submitting papers in Performance-Based Design and related topics.

Post conference technical visit

The city of Valdivia is located in the south of Chile, 840 km from Santiago of Chile. It has become recently the capital of the new region de los Ríos. The name of Valdivia comes from the Spanish conqueror Pedro de Valdivia, who founded the city in 1552. Since its foundation to present, Valdivia has been an important strategical center of the south of Chile, having . Valdivia’s population is about 400.000 people. The weather is humid and chilly due to its annual average rain of 2.000 mm and an average temperature of 11º C, which occur mostly during autumn and winter. However, the weather during summer and particularly during January is mild and even warm with temperatures up to 25ºC.

Valdivia is famous for the nice promenades along the rivers Calle-Calle and Valdivia. These rivers along with the rivers Cau-Cau, Cruces, Angachilla, Tornagaleones and Naguilán form an incredible network of navigable rivers, where it is possible to make journeys in comfortable boats while observing the beautiful scene, eating or even dancing aboard.