Research

Geotechnical Earthquake Engineering and Related Problems

Liquefaction and large deformation characteristics of sands in sloping ground

Recent major seismic events in New Zealand, Japan and Italy have shown that a significant portion of earthquake-induced damage to the natural and built environments was related to ground failure associated with soil liquefaction, a phenomenon that mostly occurs in saturated loose sandy soils during earthquakes. The catastrophic effects of liquefaction are most evident in sloping ground, where the liquefaction-induced total loss of soil shear strength and stiffness results in very large horizontal ground deformation.

While the consequences of liquefaction have been well documented, there is still a lack of knowledge as to the mechanics of earthquake-induced large deformation of liquefied sands in sloping ground due to the insufficient understanding of the combined effects of key factors such as:

  • sloping ground conditions

  • earthquake characteristics

  • confining stress level

  • soil density

  • fines content

  • soil structure and fabric

which limit the ability to foresee susceptible soils in advance.

To address these issues, we combine state-of-the-art laboratory testing (Fig. 1), advanced constitutive models for liquefiable soils (see below) and post-earthquake field observations (see below). Our goal is to make it possible to predict earthquake-induced large deformation of liquefied sands in sloping ground with significantly better accuracy than current empirical approaches, and thus improve the assessment and mitigation of liquefaction hazards.

Fig. 1 - (a) Stress condition in sloping ground during earthquakes (Chiaro et al., 2017); (b) Large-strain torsional shear apparatus (collaboration with the University of Tokyo); (c) Large deformation of a Toyoura sand specimen subjected to torsional simple shear tests with initial static shear; and (d) Proposed method for the evaluation of earthquake-induced flow liquefaction and shear failure for sands in sloping ground

Refer to the following publications for more details:

  • Chiaro G., Koseki J. & Sato T. (2012). Effects of initial static shear on liquefaction and large deformation properties of loose saturated Toyoura sand in undrained cyclic torsional shear tests. Soils and Foundations, 52(3): 498-510.

  • Chiaro G., Kiyota T. & Koseki J. (2013). Strain localization characteristics of loose saturated Toyoura sand in undrained cyclic torsional shear tests with initial static shear. Soils and Foundations, 53(1): 23-34.

  • Chiaro G., Koseki J. & Kiyota T. (2015). New insights into the failure mechanisms of liquefiable sandy sloped ground during earthquakes. In: Proc.of the 6th International Conference on Earthquake Geotechnical Engineering, Nov. 1-4, Christchurch, New Zealand, CD-ROM, pp.8.

Liquefaction potential of problematic soils

Gravelly soils (i.e. gravelly sands, sandy gravels, and uniform gravels) are generally recognized to have no or very low liquefaction potential. However, field observations from historic earthquakes (e.g. 1983 Borah Peak, Idaho Earthquake - Youd et al., 1985; 1993 Hokkaido Earthquake - Kokusho et al., 1995; 1995 Kobe Earthquake - Soga, 1998) and recent earthquakes (e.g., 2016 Kaikoura Earthquake - Cubrinovski et al., 2017) have demonstrated that liquefaction of gravelly soils can produce significant damage to civil infrastructure.

There are significant deposits of crushable soils worldwide that require sound liquefaction assessment tools and methods (Bray et al., 2016), including calcareous sands, volcanic pumice, waste materials to mention a few. Field observations of recent earthquakes (e.g., 2016 Kumamoto Earthquake - Chiaro et al., 2017) have shown that liquefaction of crushable volcanic soils can induce flow failure of sloping ground and cause significant damage to residential structures and civil infrastructure. However, the engineering properties and the undrained cyclic response of these crushable soils are less understood than the traditionally studied soils composed of hard, quartz, rounded/subrounded particles.

Our research focuses on understanding the liquefaction mechanism and developing proper analysing techniques for problematic soils (e.g. gravelly soils, crushable volcanic soils) that are necessary to characterise the hazards presented by these materials, so that engineers may effectively and economically minimize damage and loss caused by liquefaction of such problematic soils.

2 - (a) Liquefaction of micaceous silty soil in Trishuli (Nepal) observed following the 2015 Mw7.8 Gorkha Earthquake (Chiaro et al., 2015); (b) Liquefaction-induced flow failure of a gentle slope of volcanic soils observed after the 2016 Mw7.0 Kumamoto Earthquake (Chiaro et al., 2017); c) Liquefaction of gravelly soils at the Wellington CentrePort, NZ induced by the 2016 Mw7.8 Kaikoura Earthquake (Cubrinovski et al., 2017, 2018); d) DPT investigation of gravelly soil liquefaction case histories in Blenheim, New Zealand

Refer to the following publications for more details:

  • Chiaro G., Kiyota T., Pokhrel R.M., Goda K., Katagiri T. & Sharma K. (2015). Reconnaissance report on geotechnical and structural damage caused by the 2015 Gorkha Earthquake, Nepal. Soils and Foundations, 55(5): 1030-1043.

  • Chiaro G., Alexander G., Brabhaharan P., Massey C., Koseki J., Yamada S. & Aoyagi Y. (2017). Reconnaissance report on geotechnical and geological aspects of the 2016 Kumamoto Earthquake, Japan. Bulletin of the New Zealand Society for Earthquake Engineering, 50(3): 365-393.

  • Cubrinovski M, Bray J.D., de la Torre C., Olsen M.J., Bradley B.A., Chiaro G., Stocks E. & Wotherspoon L. (2017). Liquefaction effects and associated damages observed at the Wellington CentrePort from the 2016 Kaikoura Earthquake. Bulletin of the New Zealand Society for Earthquake Engineering, 50(2): 152-173.

  • Cubrinovski M., Bray J.D., de la Torre C., Olsen M.J., Bradley B.A., Chiaro G., Stocks E., Wotherspoon L. & Krall T. (2018). Liquefaction-induced damage and CPT characterization of the reclamations at CentrePort, Wellington. Bulletin of the Seismological Society of America, 108(3B): 1695-1708s.

Geo-disaster investigation and mitigation

Reconnaissance missions and post-disaster field investigations

There is much to learn from recent earthquakes and geo-disasters occurring worldwide. Thus, to gain valuable lessons from these extreme events, we often participate and lead post-disaster field damage investigations. The survey trips are planned in such a way that relatively large geographical areas that are affected by the earthquakes (or other geo-disaster) are covered to grasp spatial features of the damage in the earthquake-hit regions. A unique aspect of our investigations is that the data are often collected at the early stage of disaster response and recovery (within a few weeks after the main-shock), and thus first-hand earthquake damage observations can be obtained before major repair work. The collected damage data, in the form of geo-tagged photos and some measurements (e.g., size of a landslide), are useful for other earthquake damage reconnaissance teams who visit the damaged areas several weeks after the main-shock, and serve as a starting point of longitudinal research of a recovery process from the earthquakes.

Earthquake and geo-disaster missions carried out to date:

  • 2014 Sinkhole damage in Pokhara Valley, Nepal (Fig. 3)

  • 2015 Gorkha Nepal Earthquake, Nepal (Fig. 2a and Fig. 4)

  • 2016 Christchurch Earthquake, New Zealand

  • 2016 Kumamoto Earthquake, Japan (NHK World Newsline) (Fig. 2b and Fig. 5)

  • 2016 Kaikoura Earthquake, New Zealand (Fig. 2c)

Fig. 3 - Sinkhole damage reconnaissance in Armala, Pokhara Valley, Nepal: (a) Detailed map of the sinkhole damaged area (Pokhrel et al., 2015); (b) and (c) Typical sinkhole as seen in November 2014 and in May 2015, respectively; and (d) Soil profile and DCPT test results
Fig. 4 - 2015 Gorkha Nepal Earthquake reconnaissance: (a) Earthquake damage survey locations; (b) Aftershock distribution of the 2015 earthquake sequence;(c) Large-volume landslide near the epicenter; (d) Liquefaction-induced later spreading in Trishuli; (e) Damage in Melamchi; and (f) Collapse of the Basantapur Tower in the Kathmandu Durbar Square
Fig. 5 - The Takanodai landslide triggered by the 2016 Kumamoto Earthquake: (a) Google Earth image showing the location of the landslide; (b) View of the Takanodai landslide - looking uphill; (c) Traces of pumice soil on the slip surface; and (d) Back-analysis of slope stability under seismic conditions

Refer to the following publications for more details:

  • Pokhrel R.M., Kiyota T., Kuwano R., Chiaro G., Katagiri T. & Arai I. (2015). Preliminary field assessment of sinkhole damage, Pokhara, Nepal. International Journal of Geoengineering Case Histories, 3(2): 113-125.

  • Goda K., Kiyota T., Pokhrel R.M., Chiaro G., Katagiri T., Sharma K. & Wilkinson S. (2015). The 2015 Gorkha Nepal Earthquake: insights from earthquake damage survey. Frontiers in Built Environment (Earthquake Engineering) 1(8): 1-15.

  • Chiaro G., Kiyota T., Pokhrel R.M., Goda K., Katagiri T. & Sharma K. (2015). Reconnaissance report on geotechnical and structural damage caused by the 2015 Gorkha Earthquake, Nepal. Soils and Foundations, 55(5): 1030-1043.

  • Chiaro G., Alexander G., Brabhaharan P., Massey C., Koseki J., Yamada S. & Aoyagi Y. (2017). Reconnaissance report on geotechnical and geological aspects of the 2016 Kumamoto Earthquake, Japan. Bulletin of the New Zealand Society for Earthquake Engineering, 50(3): 365-393.

  • Cubrinovski M, Bray J.D., de la Torre C., Olsen M.J., Bradley B.A., Chiaro G., Stocks E. & Wotherspoon L. (2017). Liquefaction effects and associated damages observed at the Wellington CentrePort from the 2016 Kaikoura Earthquake. Bulletin of the New Zealand Society for Earthquake Engineering, 50(2): 152-173.

  • Cubrinovski M., Bray J.D., de la Torre C., Olsen M.J., Bradley B.A., Chiaro G., Stocks E., Wotherspoon L. & Krall T. (2018). Liquefaction-induced damage and CPT characterization of the reclamations at CentrePort, Wellington. Bulletin of the Seismological Society of America. Kaikoura Earthquake Special Issue, in press.

  • Chiaro G., Umar M., Kiyota T. & Massey C. (2018). The Takanodai landslide, Kumamoto, Japan: insights from post-earthquake field observations, laboratory tests and numerical analyses. ASCE Geotechnical Special Publication, 293: 98-111 (Proc. of the 5th Geotechnical Earthquake Engineering and Soil Dynamics Conference, Austin, Texas, USA).

Geo-environmental engineering

Suitable reuse of end-of-life tyres (ELTs) in recycling geotechnical applications

Tyre recycling is the process of converting end-of-life or unwanted waste tyres into materials that can be utilized in new products or applications. End-of-life tyres (ELTs) typically become candidates for recycling when they become no longer functional due to wear or damage, and can no longer be re-treaded or re-grooved (Basel Convention Working Group, 1999). In many countries, ELTs are a controlled waste under environmental regulations, which place a duty of care on waste producers to ensure safe disposal through licensed carriers to licensed sites. In contrast, at present no national regulations are in place in New Zealand to efficiently manage waste tyre recycling, and with the ever-growing volume of ELTs, environmental and socio-economic concerns are urging the reuse of waste tyres through large-scale recycling engineering projects.

The current rate of ELTs production in New Zealand is over 5 million per year, including passenger vehicle tyres (approximately 4 million) and truck tyres (approximately 1 million), and is expected to grow over time with increased population and number of vehicles on roads. An estimated 30% of such waste tyres are exported or recycled; yet, the remaining 70% are destined for landfills, stockpiles, illegal disposal or otherwise unaccounted for (Ministry for the Environment, 2015; Cann, 2017), giving rise to piles of waste tyres that do not readily degrade or disintegrate.

Tyres have a mixed composition of carbon black, elastomer compounds, steel wire, in addition to several other organic and inorganic components. From a civil engineering viewpoint, ELTs represent a great source of low-cost, environmentally friendly and sustainable construction material having excellent engineering properties.

Aimed at addressing the impelling problem of ELTs disposal and finding a sustainable way of recycling waste tyres in New Zealand, the Ministry for Business, Innovation and Employment (MBIE) funded a multi-disciplinary research project jointly put forward by researchers of the University of Canterbury and the Institute of Environmental Science and Research Limited (ESR). The main objective of this collaborative project is to recycle ELTs (in the form of granulated tyre rubber – GTR) mixed with gravelly soils and concrete to develop cost-effective seismic-isolation (with energy dissipation) foundation systems for low-rise residential buildings.

Visit the following site for more information: https://sites.google.com/view/ecorubberfoundation/project-overview

Fig. 6 - (a) Waste tyre disposal in NZ (Mitchel C and Wright, 2017); (b) Granulated tyre rubber (GTR) used in our laboratory tests; (c) soil-GTR mixtures used in our study; (d) compaction characteristics of Kaolin clay-GTR mixtures; (e) direct shear behaviour of sand-GTR mixtures (preliminary results); and (f) direct shear response of pea gravel-GTR mixtures (preliminary results).

Numerical modeling for geomaterials

Modelling the effects of sloping ground on the liquefaction and large deformation behaviour of sands

Sand behaves differently under different density states and confining pressures as well as loading conditions (e.g. triaxial compression and extension, plane strain, simple shear, torsional shear etc) as widely reported in the literature (e.g. Tatsuoka et al., 1982; Ishihara, 1993; Verdugo and Ishihara, 1996; Yoshimine and Ishihara, 1998; Nishimura and Towhata, 2004; Georgiannou et al., 2008). In view of its complex behavior, to predict in a very straightforward and reliable manner the response of sand undergoing monotonic shear loadings for a large range of initial void ratios and confining pressures without the need to make any change to the soil parameters remains a major challenge in geomechanics.

We developed a density- and stress-dependent elasto-plastic model for saturated sands undergoing monotonic and cyclic undrained torsional shear loading (Chiaro et al., 2013 & 2017). The model is developed under an extended general hyperbolic equation (GHE) approach, in which the void ratio and stress level dependence upon stress-strain response of sand is incorporated. Most importantly, a state-dependent stress-dilatancy relationship is introduced to account for the effect of density on the stress ratio. Such a stress-dilatancy relation is used for modeling the excess pore water pressure generation in undrained shear conditions as the mirror effect of volumetric change in drained shear conditions. By using the proposed model, numerical simulation of monotonic and cyclic undrained torsional shear tests have been carried out on Toyoura sand. The model predictions show that the undrained shear behavior, described in terms of stress-strain relationship and effective stress path for both loose and dense sands, can be modeled satisfactorily by using a single set of soil parameters.

Fig. 7 - Typical experimental observations and simulations of Toyoura sand behaviour in undrained cyclic torsional simple shear tests with initials static shear (Chiaro et al., 2017)

Refer to the following publications for more details:

  • Chiaro G., Koseki J. & De Silva L.I.N. (2013). A density- and stress-dependent elasto-plastic model for sands subjected to monotonic torsional shear loading. SEAGS Geotechnical Engineering Journal, 44(2): 18-26.

  • De Silva L.I.N., Koseki J., Chiaro G. & Sato T. (2015). A stress-strain description for saturated sand under undrained cyclic torsional shear loading. Soils and Foundations, 55(3): 559-574.

  • Chiaro G., De Silva L.I.N. & Koseki J. (2017). Modeling the effects of static shear on the undrained cyclic torsional simple shear behavior of liquefiable sand. SEAGS Geotechnical Engineering Journal, 48(4): 1-9.