Pile group response to liquefaction-induced lateral spreading: E-Defense large shake table test

This paper presents the results of a large-scale shake table test at E-Defense facility on a pile group located adjacent to a gravity-type quay wall and were subjected to liquefaction-induced large ground displacements. Extensive liquefaction-induced large ground lateral spreading displaced the quay wall about 2.2 m and damaged the pile foundation. The pile foundation consisted of a six-pile group which supported a footing and a superstructure model. Large lateral soil displacements were measured by several sensors such as inclinometers and the results favorably agreed with the directly observed deformations. Soil lateral displacement decreased as the distance from the quay wall increased landward. The piles were densely instrumented and the measured bending strain records were able to explain the damage to the piles. Lateral pressures of the liquefied soil exerted on the piles were measured using earth pressure (EP) sensors. The application of two design guidelines (JRA [1] and JSWA [2]) for estimation of liquefaction-induced lateral pressure on piles is discussed and their advantages and shortcomings are addressed. Furthermore, two simplified methods (Shamoto et al. [3] and Valsamis et al. [4]) are employed to predict the extent of liquefaction-induced large ground displacements and they are compared to the measured deformations. Finally, their accuracy for predicting the liquefaction-induced lateral displacements is evaluated and practical recommendations are made.     

Shaking table tests on the lateral response of a pile buried in liquefied sand

This paper presents an experimental study on the lateral resistance of a pile subjected to liquefaction-induced lateral flow. To observe the soil surrounding the pile during liquefaction, it was modeled as a buried cylinder that corresponded to a sectional model of the prototype pile at a certain depth in the subsoil. In order to create a realistic stress condition in the model ground, the model was prepared in a sealed container and the overburden pressure was applied to the ground surface by a rubber pressure bag. The model pile was actuated back and forth through rods attached on each side by an electro-hydraulic actuator.This paper focuses on observing the deformation of the liquefied soil surrounding the pile when a large relative displacement between the pile and the soil is induced. The loading rate effect on the lateral resistance of the pile in the liquefied sand and the influence of the relative density are also investigated.Test results show that a larger resistance is mobilized as the loading rate becomes higher. When the loading rate is higher, the cylinder displacement required for the lateral resistance becomes smaller. It has been also observed that as the relative density of the soil increases, dilatancy of the soil in front of the pile also increases.     

Response of a pile group behind quay wall to liquefaction-induced lateral spreading:a shake-table investigation

The response of pile foundations near a quay wall under liquefaction-induced lateral spreading remains a complex problem. This study presents the results of a shake-table test on a 2×2 pile group behind a sheet-pile quay wall that was subjected to lateral spreading. The quay wall was employed to trigger liquefaction-induced large lateral ground deformation. The discussions focus on the behavior of the pile and the soil and on the bending moment distributions within the group pile and the restoring force characteristics at the superstructure. Overall, the piles exhibited apparent pinning effects that reduced soil deformation. In addition, the rear-row piles near the quay wall experienced larger bending moments than did the front-row piles, indicating significant pile group effects. The tests showed that lateral spreading could be a primary cause of larger monotonic deformations and bending moments. It can also be concluded that the monotonic bending moments were significantly decreased due to the presence of slow soil flow. The stiffness at the superstructure was reduced because of accumulated excess pore pressure before liquefaction, and it was recovered during lateral spreading. The present study further enhances current understanding of the behavior of low-cap pile foundations under lateral spreading.     

Prediction of pile response to lateral spreading by 3-D soil–water coupled dynamic analysis: Shaking in the direction perpendicular to ground flow

The 1995 Kobe earthquake seriously damaged numerous buildings with pile foundations adjacent to quay walls. The seismic behavior of a pile group is affected by movement of quay walls, pile foundations, and liquefied backfill soil. For such cases, a three-dimensional (3-D) soil–water coupled dynamic analysis is a promising tool to predict overall behavior. We report predictions of large shake table test results to validate 3-D soil–water coupled dynamic analyses, and we discuss liquefaction-induced earth pressure on a pile group during the shaking in the direction perpendicular to ground flow. Numerical analyses predicted the peak displacement of footing and peak bending moment of the group pile. The earth pressure on the pile in the crustal layer is most important for the evaluation of the peak bending moment along the piles. In addition, the larger curvatures in the bending moment distribution along the piles at the water side in the liquefied ground were measured and predicted.     

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 1. Hydraulic theory of reactive transport

This is the first of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory (also known as Dupuit or Boussinesq theory). Here, we examine the effect of lateral flow on the downward fluxes of water and solutes through perched groundwater at steady state. We derive analytical expressions describing the decline in the downward flux rate with depth. Using these, we obtain analytical expressions for water age in a number of cases. The results show that when the permeability field is homogeneous, the spatial structure of water age depends qualitatively on a single dimensionless number, Hi. This number captures the relative contributions to the lateral hydraulic potential gradient of the relief of the lower‐most impermeable boundary (which may be below the weathering front within permeable or incipiently weathered bedrock) and the water table. A “scaled lateral symmetry” exists when Hi is low: age varies primarily in the vertical dimension, and variations in the horizontal dimension x almost disappear when the vertical dimension z is expressed as a fraction z/H(x) of the laterally flowing system thickness H(x). Taking advantage of this symmetry, we show how the lateral dimension of the advection–diffusion‐reaction equation can be collapsed, yielding a 1‐D vertical equation in which the advective flux downward declines with depth. The equation holds even when the permeability field is not homogeneous, as long as the variations in permeability have the same scaled lateral symmetry structure. This new 1‐D approximation is used in the accompanying paper to extend chemical weathering models derived for 1‐D columns to hillslope domains.     

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles,drainage hydraulics,and solute export pathways

The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile.     

Hydraulic model tests for propagation of flow and sediment in floods due to breaking of a natural landslide dam during a mountainous torrent

During mountain torrents, large-magnitude floods may result from heavy rainfall and cause the breakage of landslide dams naturally formed by heavy rainfall, earthquakes, and so on. The characteristics of longitudinal spreading of clear water discharge and changes in flow depth must be clarified because the changes in peak depth have not yet been examined in steep-slope torrents and because there are few data on spreading of flash floods and related sedimentation in mountainous torrents. In the present study, experimental data were collected through hydraulic model tests over a rigid bed, and the spreading of water, fine sediment, bed load, and large boulders due to flooding are discussed assuming that flash flooding/debris flows occur in the upstream reach. The effects of changes in flow width, such as expansions and contractions in the flow width, as well as changes in meandering channels, sediment transportation, and spreading flow depth resulting from bores are examined using flume data for a steep-slope torrent. The data obtained in the present study reveal that fine sediment components are transported to the downstream reach if large-magnitude floods occur and that the spreading rate and peak lags of the fine sediment and water level indicate the occurrence of a flood in the upstream reach.