Tam Larkin

Hard-Site κ0 (Kappa) calculations for Christchurch, New Zealand, and comparison with local ground-motion prediction, models

The 2010–2012 Canterbury earthquake sequence generated a large number of near‐source earthquake recordings, with the vast majority of large events occurring within 30 km of Christchurch, New Zealand’s second largest city. We utilize the dataset to estimate the site attenuation parameter, κ0, at seven rock and stiff‐soil stations in New Zealand’s GeoNet seismic network. As part of this study, an orientation‐independent definition of κ is proposed to minimize the influence of observed high‐frequency 2D site effects. Minimum magnitude limits for the traditional high‐frequency fitting method are proposed, based on the effect of the source corner frequency. A dependence of κ0 on ground‐shaking level is also observed, in which events with large peak ground accelerations (PGAs) have lower κ0 values than events with small PGAs. This observation is not fully understood, but if such a trend holds in future investigations, it may influence how κ0 is used in hazard assessments for critical facilities. κ0 values calculated from Fourier amplitude spectra of acceleration (κ0,AS) are compared with the native κ0 of local, empirical, ground‐motion prediction equations (GMPEs), calculated using the inverse random vibration theory method (κ0,IRVT). κ0,IRVT is found to be independent of magnitude and distance and agrees with the average κ0,AS for the region. κ0,IRVT does not scale strongly with VS30, indicating that current GMPEs may be capturing the average kappa effect through the VS30 scaling. The results from this study are of particular interest for site‐specific ground‐motion prediction studies as well as for GMPE adjustments between different regions or rock types.

Impact of Vertical Ground Excitation on a Bridge with Footing Uplift

Ground motions recorded in the epicentral region of an earthquake often have a strong vertical component with dominant high frequencies. Damage to bridges in near-source regions due to strong vertical ground motion has been reported. The beneficial effects of footing uplift on structural performance in form of reduction of seismic response of structural members have been confirmed in previous research. The uplift of bridge piers has been utilised in a very limited number of bridge structures, e.g., the South Rangitikei railway bridge in New Zealand. However, the near-fault seismic behaviour of bridges with footing uplift has been even less addressed. In this study shake table investigations were carried out on the response of a single-span bridge model with footing uplift subjected to simultaneous vertical and horizontal excitations. Near-fault ground motions recorded in the Canterbury earthquake sequences of 2010 and 2011 were used. The experimental results show that inclusion of vertical ground motions produce stronger axial force in the pier and larger bending moment in the deck. Concurrent horizontal and vertical excitations may also cause more frequent footing uplift than the solely horizontal excitations.

Permanent Strain Behavior of Marginal Granular Material

To better understand the marginality of marginal granular materials (i.e., an aggregate that does not fully meet a premium quality specification), this study investigated the permanent strain behavior of two granular materials with different geological and mineralogical characteristics under repeated loading and different moisture conditions. The secant permanent strain rate and shakedown approach were used to analyze the permanent strain behavior of the materials. A one-dimensional swelling test was used to explain the mechanism of the permanent strain behavior of the soaked materials under repeated loading. The results show that compared with a New Zealand premium quality aggregate, the marginal aggregate exhibits a more significant increase in the cumulative permanent strain and the secant permanent strain rate after the 4-day soaking process. The results of the shakedown approach illustrate that the marginal aggregate performs reasonably well to resist permanent deformation in a dry condition, but the performance will considerably deteriorate when in contact with water under high stress. This change is a result of the presence of swelling clay minerals (e.g., smectite) in the marginal aggregates. The result of the one-dimensional swelling test indicates the high swelling potential of marginal aggregate, which provides an explanation for its poorer resistance to permanent strain. The marginal aggregate gains undesirable internal lubrication when surrounded by (moist) swelling clay mineral particles; thus, its shear strength reduces and permanent strain rate increases under repeated loading.

Amendment of biosolids with waste materials and lime: Effect on geoenvironmental properties and leachate production

Residuals from wastewater treatment operations (biosolids) were mixed with lime, fly ash, lime kiln dust, or two smelter slags to assess their efficacy as potential stabilisation agents by assessing their effects on the shear strength, compressibility, and solids content of mixtures. In addition, the minerals formed and leachate produced during stabilisation were determined. Tests were performed to explore the change of the geoenvironmental properties of the amended biosolids, while under pressure, at different scales using laboratory, pilot and field scale tests. The settlement characteristics of the amended biosolids under a range of applied pressures were determined using a consolidometer. All amended biosolids mixtures showed higher strength than the unamended biosolids, with mixtures containing a combination of 20% fly ash and 20% lime giving the highest (up to eightfold) increase in strength, and that with lime kiln dust and the smelter slags showing the lowest (up to twofold). The biosolids mixtures with only lime gave the second highest increase in strength (up to fourfold), but produced the largest amount of leachate, with higher level of dissolved calcium. The increase in strength correlated with availability of calcium oxide in the mixtures which lead to calcium carbonate formation, accompanied with higher leachate production and settlement during consolidation. Copper, nickel and zinc concentrations increased with alkaline additives and corresponded to higher pH and DOC levels. Nonetheless, concentrations were within the New Zealand regulatory limits for Class A landfills.

Vibratory Compaction of Base Course Aggregates

The focus of this paper is on laboratory compaction of unbound granular base course material for road pavement construction. The primary variables evaluated in this research were particle size distribution and dry density. This research addresses the applicability of current laboratory compaction techniques and outlines the changes needed to minimize the gap between laboratory and field compaction. The target density achieved in laboratory studies with the New Zealand standard test methodology, which is then used to target field compaction levels, is often too high to realistically achieve in the field. It was found that there is a ratio of maximum aggregate average least dimension (ALD) to specimen diameter and specimen height that must be adhered to when using laboratory testing as a means to evaluate, design, or construct pavement base course layers. In addition, the power input of laboratory vibratory hammers used for compaction must be controlled to minimize aggregate degradation, especially for test molds that do not satisfy the minimum diameter to ALD ratio. The ultimate goal of laboratory compaction should be to accurately simulate field compaction and provide realistic targets that can be achieved in the field. If unrealistic field compaction density targets are specified, then overcompaction can occur and cause aggregate breakdown. The research concluded that changes are required for test standards to better reflect field conditions, such as less lateral constraint, and better reflect achievable target field densities.

An investigation into premium and marginal pavement aggregates from New Zealand

Aggregates used in pavement construction in New Zealand are classified as either premium or marginal depending on their quality. Using marginal materials in a pavement may cause significant problems, such as fatigue cracking, rutting and swelling. One likely reason for these problems can be the mineralogical composition of the aggregates, particularly if they contain swelling minerals. The present paper investigates how swelling minerals can affect the properties of New Zealand aggregates. Standard engineering tests were conducted on five New Zealand materials, two of which are regarded as meeting the local NZTA (New Zealand Transport Agency) M4 premium specification and three regarded as marginal. The geological properties and mineralogical compositions of all aggregates were also determined by petrographic examination and X-ray powder diffraction analysis (XRD), and the swelling potential identified using a one-dimensional swelling test. It was found that clay minerals generally exist in all five aggregates and swelling minerals in the three marginal aggregates and a premium aggregate; the last mentioned also proved to have a high swelling potential. It is concluded that the test methods specified by the NZ standard and currently used to distinguish between and categorize premium and marginal aggregates appear insufficient when they are water saturated. Additional test methods (XRD and a swelling test) are suggested to complement the standard test methods.

NUMERICAL ANALYSES OF THE INFLUENCE OF STRUCTURAL SLENDERNESS ON THE SEISMIC RESPONSE OF SINGLE AND CLUSTERED STRUCTURES

The seismic design of structures generally considers a fixed base assumption, thus neglecting interaction with the supporting soil. The main structural property considered is usually the fundamental period. However, when the influence of soil-foundation-structure interaction (SFSI) is taken into account, other parameters such as structural slenderness, may play an important role in the response. Current design codes, (e.g. FEMA-440 and FEMA450), assume that SFSI always has beneficial effects in the form of a reduction in the fundamental period spectral acceleration or base shear. This assumption has been studied and discussed by several authors. Additionally, in major urban areas structures are generally closely adjacent, and this situation is more complex than that of a structure whose response may be considered independent of all others. This study sets-out to improve the understanding of the behaviour of a clustered structure-soil-structure system. A 2D numerical model is used to simulate the behaviour of single and multiple structures on sand considering a range of slenderness ratios. Linear single degree-of-freedom (SDOF) structures and nonlinear soil are considered. The role of key parameters, e.g. effective building period and slenderness ratio of the structure-foundation system, will be elucidated.

EFFECT OF HIGHER MODES ON STRUCTURAL RESPONSE WITH NONLINEAR SOIL-FOUNDATION-STRUCTURE INTERACTION

Abstract. To calculate the response of a multi-storey structure (MDOF model) with structure-foundation-soil interaction (SFSI), for simplicity the structure is often assumed as a SDOF model corresponding to the fundamental mode. However, depending on the distribution of mass and stiffness of the structure, the contribution of the fundamental mode may vary. The contribution of the higher modes to the response of the structure could become more significant. This study reveals the effect of higher modes on the response of structure including SFSI. The response of a multi-storey structure and the response associate with the fundamental mode of the structure are compared. To calculate the response of structures with SFSI, a macro element model is used to simulate the plastic soil deformation. The consequence of using a SDOF model for the structural response including nonlinear SFSI is discussed.