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Sands consisting of pumice particles are found in the northern part of the North Island of New Zealand. These pumice sands are highly crushable, compressible, and lightweight due to the vesicular nature of the particles, making engineering assessment of their properties problematic. When performing geotechnical assessments of these deposits, questions have been asked whether existing empirical correlations derived primarily from normal (hard-grained) soils apply to the crushable natural pumiceous (NP) soils. Such lack of guidance for the geotechnical characterization and liquefaction assessment of NP soils has long been highlighted by the local geotechnical community. In this research, laboratory experiments, such as cyclic triaxial and bender element tests, were performed on reconstituted and high-quality undisturbed NP samples. These were supplemented by field-based shear wave velocity (Vs) profiling conducted at the same sites where the undisturbed samples were collected. For comparison purposes, similar laboratory tests were also performed on the hard-grained Toyoura sand. The laboratory results showed that NP sands have considerably different behavior when compared to Toyoura sand. For instance, NP sands have lower small strain shear modulus (Gmax) and Vs and higher liquefaction resistance under the same level of packing. Next, results from the laboratory studies and field characterization were synthesized considering the effect of various parameters, such as the degree of packing, overburden pressure, and pumice contents, on the liquefaction assessment of NP sands. Based on the results, attempts were made to develop a Vs-based chart to estimate the liquefaction resistance of such problematic soils for use by the geotechnical profession. Finally, the applicability of the proposed Vs-based chart was examined using available case studies from the 1987 Edgecumbe earthquake and then compared with an existing empirical Vs-based method developed for normal sands. The results showed that the proposed approach better reflected the reported liquefaction manifestation at the sites. [ABSTRACT FROM AUTHOR]

This paper focuses on the small-strain shear modulus (Gmax) of natural pumiceous (NP) sands, a type of crushable volcanic soil commonly found in the North Island of New Zealand. These sands are also compressible and lightweight, resulting in difficulty to accurately evaluate their geotechnical properties. To better understand the Gmax dependency of these NP sands on effective confining pressure (σc′) and void ratio (e), bender element tests are performed on three types of locally sourced NP sands and, for comparison purposes, similar tests are conducted on hard-grained Toyoura sand. The results illustrate that the Gmax of NP sands are considerably lower than that of Toyoura sand over a wide range of e and σc′. Furthermore, materials with higher pumice content show higher dependency on σc′ and lower dependency on e compared with those with lower pumice content as well as Toyoura sand. Particle characteristics (e.g., particle shape, particle-size distribution, particle crushing, pumice content, compressibility, and fines content) are taken into consideration to explain the different response of the tested materials. [ABSTRACT FROM AUTHOR]

Abstract Pumice particles are volcanic soils which are highly crushable, compressible and lightweight, due to their vesicular nature. After a series of volcanic eruptions in the North Island of New Zealand and due to flooding and erosion, some pumice particles have become mixed with hard-grained materials and have been distributed over some parts of the Waikato Basin; these mixtures are referred to herein as natural pumiceous (NP) sands. The post-liquefaction behavior of NP sands is important not only for the purpose of investigating ground deformation induced by liquefaction but also for assessing the impact of these deformations on buried structures. For this purpose, reconstituted NP sands were obtained from three sites along the Waikato River in order to perform multi-stage triaxial testing. Three parameters – initial Young's modulus (E 1), Young's modulus at recovery (E 2) and recovery strain (Ɛ r) – were used to express the stress–strain behavior of NP sands that had undergone liquefaction. For comparison purpose, similar tests were performed on hard-grained Toyoura sand. The liquefied NP sands recovered their strength at a considerably lower strain level than Toyoura sand due to the formation of stable soil skeleton during cyclic loading and the high angularity of the pumice particles. In addition, the E 1 values of liquefied NP sands were higher than those of Toyoura sand while the values of E 2 were lower; such differences in the stress-strain behavior of liquefied NP sands can be attributed to the unique characteristics of pumice components, i.e. their irregular particle shape and crushability features. Highlights • Natural pumiceous (NP) sands had irregular surface texture. • NP sands experienced particle crushing during multistage triaxial testing. • Post-liquefaction behavior of NP sand was different from that of Toyoura sand. • Liquefied NP sands recovered their strength at a considerably smaller strain level compared with Toyoura sand. • The E 1 values of NP sands were higher than Toyoura sand while, the values of E 2 were lower. [ABSTRACT FROM AUTHOR]

With the objective of better and more environmentally friendly recycling methods, many researchers are now examining the use of scrap tires as a new geomaterial. Based on past research, it was clear that tire chips reduce the rise of excess pore-water pressure when subjected to earthquake shaking. Based on such characteristics, online pseudodynamic response tests were conducted in this study on model grounds consisting of either tire chip-mixed sand or alternating layers of sand and tire chips with the aim of clarifying the seismic response characteristics of tire chips and tire chip-sand mixtures. Online testing is a method of feeding soil response characteristics directly from soil samples into a one-dimensional modeling algorithm. The test results showed that when tire chips with low stiffness were either mixed with sand or placed as layers, more significant damping and seismic isolation effects were observed. The presence of tire chips also reduced the accumulation of excess pore-water pressure in the layer, preventing the occurrence of liquefaction. In addition, when tire chips are installed as layers beneath the sand, liquefaction is not generated in the upper sandy layer because the amplitudes of the seismic waves are attenuated. Finally, the effectiveness of tire chips mixed with sand increased as the mix ratio was increased. When they were installed as pure layers, tire chips were more effective when placed at a deeper location or when the layer was thicker. [ABSTRACT FROM AUTHOR]

In order to simulate the effect of drainage on soils adjacent to gravel drains that are installed as countermeasure against liquefaction, several series of cyclic triaxial tests were performed on saturated sands under partially drained conditions. The condition of partial drainage under cyclic loading was simulated in the laboratory using triaxial testing equipment installed with a drainage control valve to precisely regulate the volume of water being drained from test specimens. Effects of both drainage conditions and loading frequencies on cyclic response were incorporated through the coefficient of drainage effect, α*. Experimental results showed that for sand exhibiting strain softening, the partially drained response was controlled by the critical effective stress ratio while for sand showing strain hardening behavior, the controlling factor was the phase transformation stress ratio. Moreover, test results indicated that the minimum liquefaction resistance under partially drained conditions can be used as a parameter to describe the liquefaction resistance of sands improved by the gravel drain method. From these results, a simplified procedure for designing gravel drains based on the factor of safety (FL) concept was proposed. [ABSTRACT FROM AUTHOR]

Previous post-earthquake damage investigations have indicated that inclined piles have either performed satisfactorily or poorly during seismic events; hence their effectiveness is still questionable. This paper aims to clarify the performance of inclined piles installed in the liquefiable ground during earthquakes. To this end, a three-dimensional finite element model has been developed using the OpenSees program. The effects of soil-pile interaction have been evaluated by applying interface elements between the soil and the pile. Subsequently, the behavior of sand is described with the help of a multi-yield-surface plasticity constitutive relation. By changing the pile configurations and the amplitude of loading patterns, a series of parametric analyses are conducted, and the system responses (i.e., soil, cap, and pile responses) are compared. The results clearly illustrate that the presence of inclined piles has a beneficial effect on the dynamic response of the soil-pile-cap system in non-liquefied soils and of the cap response in liquefied soils. However, highly detrimental effects of inclined piles on the soil and pile responses have been observed as the soil liquefies. Based on the results, the conditions wherein inclined piles may perform satisfactorily or poorly are highlighted. • A 3D finite element model has been developed via OpenSees. • Pile configurations and soil liquefaction have significant effects on the soil, cap, and pile responses. • The presence of inclined piles generally has a beneficial effect on the soil-pile-cap system in non-liquefied soils. • As the soil liquefies, the effect turns detrimental to the system, except the cap response with small pile inclinations. • Adjusting the pile configuration can magnify the advantages and reduce or even eliminate the disadvantages of inclined piles. [ABSTRACT FROM AUTHOR]

Understanding the behaviour of soils under cyclic/dynamic loading has been one of the challenging topics in geotechnical engineering. The response of liquefiable soils has been well studied however, the post liquefaction behaviour of sands needs better understanding. In this paper, the post liquefaction behaviour of sands is investigated through several series of multi-stage soil element tests using a cyclic triaxial apparatus. Four types of sand were used where the sands were first liquefied and then monotonically sheared to obtain stress-strain curves. Results of the tests indicate that the stress-strain behaviour of sand in post liquefaction phase can be modelled as a bi-linear curve using three parameters: the initial shear modulus ( G 1 ), critical state shear modulus ( G 2 ), and post-dilation shear strain ( γ p o s t − d i l a t i o n ) which is the shear strain at the onset of dilation. It was found that the three parameters are dependent on the initial relative density of sands. Furthermore, it was observed that with the increase in the relative density both G 1 and G 2 increase and γ p o s t − d i l a t i o n decreases. The practical application of the results is to generate p-y curves for liquefied soil. [ABSTRACT FROM AUTHOR]