Rolando P. Orense

Bio: Rolando P. Orense is an academic researcher from University of Auckland. The author has contributed to research in topics: Liquefaction & Soil liquefaction. The author has an hindex of 22, co-authored 164 publications receiving 1630 citations. Previous affiliations of Rolando P. Orense include Yamaguchi University & Waseda University.

Geotechnical reconnaissance of the 2010 Darfield (Canterbury) earthquake

Abstract: On 4 September 2010, a magnitude Mw 7.1 earthquake struck the Canterbury region on the South Island of New Zealand. The epicentre of the earthquake was located in the Darfield area about 40 km west of the city of Christchurch. Extensive damage was inflicted to lifelines and residential houses due to widespread liquefaction and lateral spreading in areas close to major streams, rivers and wetlands throughout Christchurch and Kaiapoi. Unreinforced masonry buildings also suffered extensive damage throughout the region. Despite the severe damage to infrastructure and residential houses, fortunately, no deaths occurred and only two injuries were reported in this earthquake. From an engineering viewpoint, one may argue that the most significant aspects of the 2010 Darfield Earthquake were geotechnical in nature, with liquefaction and lateral spreading being the principal culprits for the inflicted damage. Following the earthquake, an intensive geotechnical reconnaissance was conducted to capture evidence and perishable data from this event. The surveys were performed on foot, by car and from a helicopter over a period of six days. A broad-brush field reconnaissance was conducted in the first two days, followed by pin-point investigations at specific locations including detailed site inspections and field testing using: Dynamic Cone Penetration Test (DCPT), Swedish Weight Sounding (SWS), and Spectral Analysis of Surface Waves (SASW). This paper summarizes the observations and preliminary findings from this early reconnaissance work.

Instrumented Model Slope Failure due to Water Seepage

Abstract: Many slope failures have been observed to occur during or immediately after rainfall. Although conditions leading to these failures have been described as caused by a rapid rise in pore-water pressure as a result of rainwa- ter infiltration, the important factors that influence the initiation of slope failures have not been adequately clari- fied. To investigate these factors, a series of laboratory experiments was conducted on model sandy slopes to determine the initiation process of rainfall-induced slope failure. In the tests, failures were induced in small-scale model slopes either by water percolation from the side upslope or by artificial rain falling on top of the slope. Besides monitoring pore-water pressure, changes in soil moisture contents and ground deformation were mea- sured. Test results showed that slope failure was always induced when the soil moisture content within a certain region near the toe of the slope reached nearly full saturation, even though other parts of the sliding mass were still in a partially saturated state. In addition, minute deformations along the slope were shown to precede failure. The findings presented here show that by monitoring the soil moisture content of slopes and performing displace- ment measurements, it is possible to predict the occurrence of rainfall-induced slope failure.

Lateral spreading and its impacts in urban areas in the 2010–2011 Christchurch earthquakes

Abstract: In the 4 September 2010 (M W=7.1) and 22 February 2011 (M W=6.2) earthquakes, widespread liquefaction and lateral spreading occurred throughout Christchurch and the town of Kaiapoi. The severe soil liquefaction and lateral spreading in particular caused extensive and heavy damage to residential buildings, Christchurch business district (CBD) buildings, bridges and water supply and wastewater systems of Christchurch. After the earthquake, comprehensive field investigations and inspections were conducted to document the liquefaction-induced land damage and lateral spreading displacements and their impact on buildings and infrastructure. The results of ground surveying measurements of lateral spreads at approximately 120 locations along the Avon River, Kaiapoi River and streams in the affected area reveal permanent lateral ground displacements at the banks of up to 2–3 m that progressed inland as far as 200–250 m from the waterway, causing significant damage to structures located within the spreadin...

Shaking table tests on subgrade reaction of pipe embedded in sandy liquefied subsoil

Abstract: An interest in the behavior of liquefied sand during seismic flow failure led the authors to conduct shaking table tests in which an embedded pipe was pulled laterally and the required drag force was monitored. Test results showed that the amplitude of shaking acceleration affected the behavior of sand in both dry and water-saturated conditions. In dry sand, the induced inertia force decreased the shear strength and consequently the magnitude of the drag force. When the sand was saturated, a special consideration was made of the similitude of dilatancy between 1-G model tests and the in-situ situation. This goal was attained by employing very loose sand in model tests. The rate-dependency in which the drag force increased with the rate of pipe movement was focused on, leading to an apparently viscous behavior of sand. This is consistent with what several former studies reported.

Seismic Response Characteristics of Saturated Sand Deposits Mixed with Tire Chips

Abstract: 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.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

Abstract: The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Near-source Strong Ground Motions Observed in the 22 February 2011 Christchurch Earthquake

Abstract: On 22 February 2011 at 12:51 p.m. local time, a moment magnitude Mw 6.3 earthquake occurred beneath the city of Christchurch, New Zealand, causing an level of damage and human casualties unparalleled in the country's history. Compared to the preceding 4 September 2010 Mw 7.1 Darfield earthquake, which occurred approximately 30 km to the west of Christchurch, the close proximity of the 22 February event led to ground motions of significantly higher amplitude in the densely populated regions of Christchurch. As a result of these significantly larger ground motions, structures in general, and commercial structures in the central business district in particular, were subjected to severe seismic demands and, combined with the event timing, structural collapses accounted for the majority of the 181 casualties (New Zealand Police 2011). This manuscript provides a preliminary assessment of the near-source ground motions recorded in the Christchurch region. Particular attention is given to the observed spatial distribution of ground motions, which is interpreted based on source, path, and site effects. Comparison is also made of the observed ground motion response spectra with those of the 4 September 2010 Darfield earthquake and those used in seismic design in order to emphasize the amplitude of the ground shaking and also elucidate the importance of local geotechnical and deep geologic structure on surface ground motions. New Zealand resides on the boundary of the Pacific and Australian plates (Figure 1) and its active tectonics are dominated by: 1) oblique subduction of the Pacific plate beneath the Australian plate along the Hikurangi trough in the North Island; 2) oblique subduction of the Australian plate beneath the Pacific plate along the Puysegur trench in the southwest of the South Island; and 3) oblique, right-lateral slip along numerous crustal faults in the axial tectonic belt, of which the …

Dynamic soil–structure interaction of monopile supported wind turbines in cohesive soil

Abstract: Offshore wind turbines supported on monopile foundations are dynamically sensitive because the overall natural frequencies of these structures are close to the different forcing frequencies imposed upon them. The structures are designed for an intended life of 25 to 30 years, but little is known about their long term behaviour. To study their long term behaviour, a series of laboratory tests were conducted in which a scaled model wind turbine supported on a monopile in kaolin clay was subjected to between 32,000 and 172,000 cycles of horizontal loading and the changes in natural frequency and damping of the model were monitored. The experimental results are presented using a non-dimensional framework based on an interpretation of the governing mechanics. The change in natural frequency was found to be strongly dependent on the shear strain level in the soil next to the pile. Practical guidance for choosing the diameter of monopile is suggested based on element test results using the concept of volumetric threshold shear strain.

Damping formulation for nonlinear 1D site response analyses

Abstract: Measurements and observations of ground shaking during large earthquakes have demonstrated the predominant role of site effects in the response of infrastructure during a seismic event. Despite significant efforts to model the hysteretic response and nonlinearity of soils due to medium and large ground motions, the most widely accepted nonlinear site response methods are not able to represent simultaneously the changes of stiffness and energy dissipation (damping) observed in both laboratory tests and during earthquake events. This paper presents two new soil damping formulations implemented in nonlinear one-dimensional site response analysis for small and large strains. The first formulation introduces an approach to construct a frequency-independent viscous damping matrix which reduces the over-damping at high frequencies, and therefore, the filtering at those frequencies. The second formulation introduces a reduction factor that modifies the extended Masing loading/unloading strain–stress relationship to match measured modulus reduction and damping curves simultaneously over a wide range of shear strains. A set of examples are introduced to illustrate the effect of using the two proposed formulations, separately and simultaneously, in nonlinear site response analyses.

Earthquake losses due to ground failure

Abstract: Ground shaking is widely considered to be the primary cause of damage to structures, loss of life and injuries due to earthquakes. Nonetheless, there are numerous examples of earthquakes where the losses due to earthquake-induced ground failure have been significant. Whereas ground shaking causes structural and non-structural damage, with associated loss of function and income, ground failure is less likely to cause spectacular structural collapses, but is frequently the cause of major disruptions, particularly to lifelines, which can lead to prolonged loss of function and income, even for undamaged areas. Those involved in earthquake loss modelling are currently presented with three choices with respect to the incorporation of ground failure: they can choose to ignore it, assuming that any estimation of losses caused by shaking would effectively subsume the impact of these secondary hazards; they can include ground failure in a simple manner, using published approaches based upon qualitative data and a large degree of judgement; or, they can opt for a detailed site- or region-specific assessment of damage due to ground failure, with the associated time and expense. This paper presents a summary of the principal features of earthquake losses incurred in damaging earthquakes over the last 15 years. Survey data are impartially analysed, considering both ground failure and ground shaking as sources of damage, and their relative contribution to overall damage in each section of the regional infrastructure is presented. There are many other variables influencing these contributions, including the size of the earthquake, the economic status of the affected region, local geology and terrain and the building stock, which have been considered. The findings of the study are discussed from the point of view of loss modelling and which components of a model should merit the most time and resource allocation. The general assumption that ground shaking is the principal cause of damage and loss is strongly supported by the study. However, there are a number of scenarios identified where the failure to appropriately include the effects of ground failure would lead to unrealistic loss projections. Such scenarios include the assessment of building losses in small zones rather than on a regional basis, and the incorporation of lifeline damage or disruption and indirect losses into a model.