LEAP Projects: Concept and Challenges

The Liquefaction Experiment and Analysis Project (LEAP), an international research collaboration among researchers from the US, UK, Japan, China and Taiwan, is a validation campaign to assess the capabilities of existing numerical/constitutive models for liquefaction analysis by using laboratory experiments and centrifuge tests. The nature, goals, and scope of the project are presented in this paper. The goals of the planning phase of the project that is currently ongoing in the US are briefly discussed. The main components of the validation campaign and their corresponding challenges are outlined. ties in the US (UCD, RPI, University of Colorado at Boulder, and Princeton University) and Cambridge University in the UK. A large number of “Class A” (i.e., true prediction of an event made prior to the event) numerical simulations of these centrifuge tests were submitted and compared at a symposium. The two key lessons learned from this exercise were that: (1) none of the numerical techniques available at that time were reliable for producing high quality predictions of liquefaction problems, and (2) there was significant variability in many of the centrifuge test results. Over the past few decades, the geotechnical engineering community has seen remarkable advances in experimental and computational simulation capabilities. Experimental research using increasingly reliable element scale laboratory tests, in-situ tests, and centrifuge experiments have provided the community with significantly improved understanding of the response of geosystems to earthquake loading. In the same vein as the VELACS project, a recent exercise was conducted in Italy, on predicting the tunnel-soil interaction using numerical procedures that are matched to centrifuge test data. This project titled Round Robin Tunnel Tests (RRTT) has involved seven different numerical modeling teams that were involved in predicting the centrifuge test results in terms of tunnel lining forces and bending moments amongst other parameters, Bilotta et al (2014). The tremendous advances in computational power and computational methods have provided an unprecedented opportunity for the analysis of very large geo-structural systems using sophisticated constitutive and numerical modeling techniques. Compared to 25 years ago, there are far better computational and numerical modeling techniques available for the analysis of soil liquefaction and its consequences. In the realm of constitutive modeling, there are several well-established constitutive models for saturated granular soils (Elgamal, et al., 2003; Ling and Yang, 2006; Manzari and Dafalias, 1997; Cubrinovski and Ishihara, 1998; Dafalias and Manzari, 2004; Taiebat, 2009). Moreover, several commercial finite element/finite difference codes (e.g., FLAC) provide nonlinear fully-coupled effective stress capabilities for analysis of geostructures involving liquefiable soils. New advances in meshfree (Manzari and Regueiro, 2005), finite element analysis (Regueiro and Borja, 2001; Manzari, 2004; Manzari and Yonten, 2010, 2011-a, 2011-b) and discrete element techniques (Zeghal and El Shamy, 2004) have provided the community with powerful tools to model liquefaction as well as postfailure response of geostructures. All these advanced computational tools still need to be assessed and validated against high-fidelity experiments. Without validation, the profession will remain rightfully skeptical and reluctant to adopt such tools. Given the significant advances in numerical modeling over the past twenty five years, it is time for a reassessment of the reliability of modern numerical modeling techniques in analysis of geotechnical engineering problems involving liquefaction. 1.2 Development of LEAP The Liquefaction Experiments and Analysis Project (LEAP) is an international effort to produce a set of high quality centrifuge test data that can be used for validation of existing numerical simulation procedures for liquefaction analysis in a class-A prediction exercise. Evaluation of a wide range of analysis procedures requires a wide range of experiments and analysts. International collaboration widens the scope, gravitas, and impact of the findings. LEAP is an ongoing collaboration that encompasses the writers and their research groups and a team of researchers from the UK led by Cambridge University, the geotechnical earthquake engineering research group at Kyoto University, the geotechnical engineering group at National Taiwan University, and researchers from Zhejiang University in China. The birth of the LEAP collaboration may have been in November 2011 when the writers submitted a NEESR proposal that included significant international collaboration. The writers had shared their proposal with a team of Japanese and a team of UK researchers, and in return they committed to submit parallel proposals to their respective national fund-