Mitigation measures for pile groups behind quay walls subjected to lateral flow of liquefied soil: Shake table model tests

This paper presents experimental results of a series of 1g shake table tests on mitigation measures for a model consisting of a 3×3 pile group and a sheet-pile quay wall in which the pile group was subjected to liquefaction-induced lateral spreading. First, general observations associated with the mechanism of lateral spreading and pile response are presented based on tests without remedial measures, followed by in depth discussions. Second, three remedial techniques were deployed to provide an adequate seismic performance of the pile group and the quay wall: (i) mitigating sheet pile of floating type, (ii) mitigating sheet pile of fixed end type, and (iii) anchoring the quay wall to a new pile row. The main objective of these mitigation methods was to restrict ground distortion behind the quay wall, enhancing seismic response of pile group and quay wall. This mitigation philosophy was decided based on the outcome of the first part, which consisted of a series of tests without mitigation measures. In addition, it should be noted that the proposed countermeasures were selected to be applicable for existing vulnerable pile groups, which are at risk of liquefaction and lateral spreading. Results of different mitigation tests are comparatively examined using a parameter called reduction factor, and the effectiveness of each countermeasure is discussed in detail. The results demonstrate that by applying the proposed mitigation measures the seismic performance of both pile group and quay wall can be improved, as a result of reduction in soil displacement and velocity of soil flow.     

1-G model tests and hollow cylindrical torsional shear experiments on seismic residual displacements of fill dams from the viewpoint of seismic performance-based design

This paper concerns technological efforts for the general acceptance of performance-based seismic design principle of geotechnical structures. Among many problems to be solved, a particular emphasis was placed on the prediction of residual displacement that remains after a strong earthquake. Because of the complicated behavior of soils undergoing cyclic loading, the prediction is often either complicated/costly or not very accurate. The aim of this study is to examine the capability of existing prediction measures and propose some future scopes. To achieve these goals, shaking table model tests and laboratory shear tests were conducted by taking fill dams as an example target structure. It is concluded that performance-based design is possible if the necessary time and cost are spent and if the required accuracy of prediction is reasonable.     

An approach to digitize analog form of accelerograms recorded at Tarbela—Pakistan

Pakistan has a long history of seismological activity. The devastation caused by Kashmir earthquake has been administered all over the world. In Pakistan first seismological network, consisting of analog accelerograms and seismographs, was setup in early 1969 at Tarbela, where the largest water reservoir of the country is located. An approach to convert analog ground motion records into digital form is explained using a simple technique. The digitized data was compared with the original analog record and found in good agreement. The data has been used to plot response spectra. The digitized data will be available for seismic response analysis of structures and seismic risk analysis of the region.     

Geotechnical Characteristics of Volcanic Soils Taken from Recent Eruptions

Recent volcanic eruptions at Mt. Unzen (Japan) in 1990 and Mt. Pinatubo (Philippines) in 1991 produced voluminous amounts of ash and sediments which inundated widespread areas. In later rehabilitation and reconstruction, it is practical and economical to use these freshly deposited sediments as materials for foundations and embankments. However, the geotechnical properties of young volcanic products have not been fully investigated. Accordingly, we investigated the geotechnical characteristics of volcanic soils associated with three recent eruptions, namely, the Unzen and Izu-Oshima eruptions of 1990 and 1986, respectively, in Japan and the Pinatubo eruption of 1991 in the Philippines. We specifically investigated index properties, permeability and compaction characteristics, and strength and deformation behavior in drained conditions. Additionally, we examined the dynamic properties and liquefaction characteristics of samples taken from Mt. Pinatubo. The results showed that the geotechnical characteristics of the deposits generally varied with the sampling sites. Depending on the location, either upstream or downstream from a volcano, the preferential sizing due to alluvial deposition affects engineering properties of the deposits. For example, volcanic sediments upstream from Mt. Pinatubo have high compressibility and low cyclic strength, whereas those taken downstream show dilative tendencies and high liquefaction strength.     

Estimation of ground response and local site effects for Vishakhapatnam,India

Natural Hazards - Ground motion intensity due to an earthquake changes as it disseminates through the soil media from bedrock to the surface. As the ground motion intensity and damage levels mainly...     

A study on particle breakage behavior during pile penetration process using acoustic emission source location

Particle breakage is a common occurrence in granular systems when the external stress exceeds the individual particle strength.A large number of experimental evidences suggested that particle breakage may significantly influence the soil behavior.In the case of pile foundations,the subsoil below the pile tip experiences considerable high stress and consequently prone to break.Due to the lack of sufficient understanding on particle breakage mechanism,there is currently no consentaneous theoretical background for particle breakage analysis during the pile penetration process.This study aims to clarify the location of particle breakage and its evolving characteristics with the aid of acoustic emission(AE)source location method.The spatial distribution of AE hypocenters is interpreted to be associated with the mechanism of particle breakage.Results showed that the AE sources were not uniformly distributed,but concentrated within certain zones below the pile tip.This AE concentration zone was pushed downward with the advancing pile tip,and its distance from the real time pile tip position decreased after certain depth of pile penetration.The location of particle breakage interpreted from AE source location was verified with posttest excavations and the insights on the particle breakage evolution zone were further discussed.     

Geotechnical characteristics of volcanic soil from seismically induced Aratozawa landslide, Japan

This paper seeks to investigate the properties of volcanic soil from the Aratozawa landslide, the largest failure triggered by the 2008 Iwate-Miyagi Nairiku earthquake, Japan. The Aratozawa landslide, which extended about 1,200 m long and 800 m wide, consisted of a complex system of ridges and depressions, including a number of smaller failures that occurred within the slide body. Field investigation was carried out to study the geotechnical properties of pumice that was exposed at the scarp of two smaller slides. The pumice was found to be heavily weathered, having low dry density and high moisture content. Portable cone penetration tests were performed to evaluate the in situ properties of soil as well as to determine the thickness of the weathered zone. Laboratory examination included slake-durability tests, grain-size distribution analysis, and a series of cyclic loading triaxial compression tests conducted on undisturbed and reconstituted samples. Laboratory test data indicated that the soil had a high potential for generation of excess pore-water pressures, suggesting that liquefaction might have occurred in the weathered mass of pumice during the earthquake.     

Compressibility of natural soils subjected to long-term acidic contamination

This paper presents the results of a systematic analysis aimed at establishing whether acidic pore fluids can affect the properties of natural soils, in particular their compressibility. Marine deposits with different mineral compositions and undisturbed soil structure were collected for this research from three coastal areas in Japan. Pleistocene clays from the Osaka and Ariake Bays were obtained from boreholes at a depth of more than 10 m, whereas the Kawasaki mud, a relatively young deposit of Holocene, was dredged from the bed of the Tokyo Bay. Soil specimens were placed in special containers, which were designed to reproduce the process of long-term soil–water–chemical interaction, and leached with solutions of sulfuric acid for different periods of time, ranging from 1 to 9 months. At the end of each time interval, standard compression tests were performed to study the behavior of soil in an acidic environment. It was found that clay mineralogy and soil structure had a significant effect on the compressibility of clays at low pH. In the case of the Osaka and Ariake clays, the compressibility significantly increased with a decrease in pH values, a finding that was primarily attributed to changes in the soil’s structure. In contrast, the effect of acidic leaching on the properties of Kawasaki mud was observed to be the opposite. Laboratory data showed that in acidic medium the compressibility of soil decreased presumably due to the collapse of the diffuse double layer.     

Risk evaluation and warning threshold of unstable slope using tilting sensor array

Slope monitoring and early warning systems are a promising approach toward mitigating landslide-induced disasters. Many large-scale sediment disasters result in the destruction of infrastructure and loss of human life. The mitigation of vulnerability to slope and landslide hazards will benefit significantly from early warning alerts. The authors have been developing monitoring technology that uses a micro-electro-mechanical systems tilt sensor array that detects the precursory movement of vulnerable slopes and informs the issuance of emergency caution and warning alerts. In this regard, the determination of alarm thresholds is very important. Although previous studies have investigated the recording of threshold values by an extensometer which installation of an extensometer at appropriate sites is also difficult. The authors prefer tilt sensors and have proposed a novel threshold for the tilt angle, which was validated in this study. This threshold has an interesting similarity to previously reported viscous models. Additionally, multi-point monitoring has recently emerged and allows for many sensors to be deployed at vulnerable slopes without disregarding the slope’s precursory local behavior. With this new technology, the detailed spatial and temporal variation of the behavior of vulnerable slopes can be determined as the displacement proceeds toward failure.