Build-up Of Excess Pore Water Pressure Research Articles

Seismic performance of sheet pile walls in liquefiable soil using centrifuge tests and an assessment of nonlinear effective stress analysis using PM4Sand

Past earthquakes have revealed that damage to sheet-pile walls under saturated conditions is closely linked to excess pore water pressure buildup in the surrounding soil. Nonlinear effective stress analysis (ESA) is commonly employed to assess the seismic performance of sheet-pile walls in liquefiable soils, incorporating constitutive models for liquefaction simulation. However, ESA results are sensitive to uncertainties in input parameters, model calibration, and modeling techniques. Dynamic centrifuge tests conducted in the Liquefaction Experiments and Analysis Project (LEAP) offer valuable insights into important response mechanisms and validate ESA. Seven centrifuge tests on a cantilevered sheet-pile wall model showed that liquefaction did not occur in the backfill near the wall due to net seaward wall displacement but did occur farther away. In addition, the mechanism of wall displacement was mainly due to the shear deformation of the softened backfill, with the displacement magnitude depending on the relative density of soil, peak ground acceleration of base motion, and wall displacement during gravity loading. Nonlinear ESA was performed for three centrifuge tests using FLAC2D and the PM4Sand constitutive model for soil. Gravity analysis captured static wall displacement and initial stress distribution in the soil. Two calibrations of the PM4Sand model were pursued at the element level: C1 calibration for liquefaction strength and C2 calibration for liquefaction strength and the post-liquefaction shear strain accumulation rate. System-level simulations showed similar liquefaction behavior as observed in the tests for both calibrations. However, the C2 calibration provided closer predictions of wall displacements, while the C1 calibration (default for PM4Sand) resulted in larger and more conservative displacements. Overall, the PM4Sand model performed well with minimal calibration, making it suitable for nonlinear ESA of sheet-pile walls.

Numerical analysis of the tunnel uplift behavior subjected to seismic loading

Seismic loading has always been a major concern for any engineering structures, and thereby, underground facilities (e.g., tunnels) are not exceptional. It is due to the seismically induced uplift and instability of tunnels caused by the large deformation of liquefiable soils. Therefore, the tunnel uplift behaviors subjected to seismic loading are always taken into account in any designing stages of tunnels. This study's main goal was to evaluate how a tunnel buried in liquefiable and non-liquefiable soils would behave when subjected to seismic stress. Seismic and liquefaction potential assessments of the soils surrounding the tunnel were carried out using the finite-element method. In this study, PM4sand, an advanced constitutive model was adopted in all finite-element models. In addition, the uplift displacement and excess pore pressure of liquefiable soils were studied, under a typical earthquake. Investigations were also conducted into how the thickness of the non-liquefiable soil affected seismic loading, tunnel uplift displacement, and the buildup of excess pore water pressure. As a result, during the earthquake, liquefaction was triggered in most parts of the sand layer but not in the clay layer. In addition, the tunnel uplift displacement was triggered due to the relative motion and interaction at both sides of the tunnel. In addition, this study found that the thickness of the non-liquefiable soil layer (sand layer) had a significant impact on the build-up of excess pore water pressure and, consequently, the tunnel uplift displacement. The uplift displacement and excess pore water pressure build-up were higher the thinner the non-liquefiable layer was.

Poro-elastic and poro-elasto-plastic modeling of sandy seabed under wave action

The seabed could be liquefied due to the wave-induced accumulation of residual excess pore water pressure (EPWP), resulting in the instability of offshore and marine structures. Thus, it is of importance to consider both the buildup of EPWP and the associated deformation behavior of the seabed. In this study, a dynamic poro-elasto-plastic seabed model, integrated with a state-dependent plasticity model, is developed in COMSOL Multiphysics. The numerical model of seabed is validated against the analytical solutions and model tests. The elliptical trajectories of soil particle at different depths of the poro-elastic seabed under the progressive wave are illustrated. The ratio of the amplitude of vertical displacement to that of horizontal displacement generally decreases as the depth increases for the poro-elastic seabed. In the poro-elasto-plastic seabed, however, the soil particles tend to move following the direction of the wave propagation. Moreover, the soil particles at the shallow part of the seabed go downwards before the initial liquefaction, while the soil particles at the lower position initially go upwards and then turn to go downwards when the initial liquefaction occurs. Particularly, the surface seabed with lower relative density is more prone to lose the stability, resulting in a dramatic upward vertical displacement.

Experimental Study on the Influence of Pipeline Vibration on Silty Seabed Liquefaction

Free-spanning submarine pipelines are usually affected by vortex-induced vibration (VIV). Such vibration could influence the liquefaction of the supporting soil at both ends of the free spans and could have catastrophic consequences, including the failure of the local seabed and the displacing, sinking, or floating of pipelines. The influence of pipeline vibration on soil liquefaction has not been studied sufficiently. Therefore, we explored the influence of vortex-induced pipeline vibration on the excess pore pressure of silty soil around a pipeline using flume experiments. Our results showed that pipeline vibration could induce the buildup of excess pore-water pressure, even without wave loading. A fully liquefied zone was found close to the pipeline, where excess pore pressure reached the soil liquefaction criterion, which was surrounded by a partially liquefied zone. The extent of liquefaction depended on the vibration conditions and the weight and burial depth of the pipeline. The pipeline vibration amplitude increased after soil liquefaction. Unlike wave-induced liquefaction, pipeline-induced vibration liquefaction occurred at a critical value smaller than the initial mean normal effective stress. Considering the possibility of pipeline-vibration-induced seabed liquefaction, conventional approaches could underestimate the potential risks to pipeline stability and result in unsafe maintenance practices.

A fully coupled flow deformation model for seismic site response analyses of liquefiable marine sediments

This paper presents a fully coupled flow deformation model to characterize the nonlinear seismic site response of liquefiable marine sediments, considering the ocean wave environment. Emphasis is placed on extending a simplified soil hysteresis model for the effective stress analysis of nonlinear site seismic response. The proposed model addresses the limitations of existing one-dimensional (1D) hyperbolic soil models to simultaneously capture the 3D hysteretic stress–strain behavior and the accumulated volumetric deformation of soil skeleton. The volume strain formulation of soil skeleton is included in the Biot's volumetric compatibility equation as the source term for excess pore water pressure buildup. The proposed method is implemented into an explicit time matching finite difference analysis platform, and validated against the recordings of the KSRH10 site for North–South (NS) direction of KiK-net borehole arrays in Japan. Finally, the influences of ocean wave loading upon the seismic wave propagation behavior in liquefiable marine sediments are examined with reference to the Bohai Strait site condition, China. The obtained results indicate that the ocean wave environment has significant effect on the nonlinear seismic site response of liquefiable seabed at shallow depth.

The 2015 Shenzhen catastrophic landslide in a construction waste dump: analyses of undrained strength and slope stability

The 2015 catastrophic landslide in a 110-m-high waste dump in Shenzhen is recognized as one of the largest landfill failure worldwide. An earlier comprehensive field investigation revealed that the dominant component of the fill was completely decomposed granite (CDG), and the dumping operation was accompanied by a rise of the groundwater level. In this paper, the complex stress paths for the initially unsaturated fill materials being subjected to both rapid filling and wetting were investigated. A simplified method was proposed for estimating the gain of undrained shear strength under the complex stress paths. Soil samples were taken from the site to a laboratory to measure the undrained shear strength and validate the estimation method. Total stress-based stability analyses were carried out to calculate the factor of safety of the dump at failure. The triggering mechanism of the landslide is clarified as follows: The gain of shear strength with the surcharge loading for the wet layer in the lower part of the waste dump was limited by a build-up of excess pore-water pressure. The gain of shear strength for the relatively dry fill material was attenuated with the rise of groundwater level. When the shear strength was not enough to resist the increasing slip force with the surcharge loading, a deep-seated translational failure took place in the lower wet layer of the waste dump. The proposed method for analyses of undrained strength and slope stability are proven to be applicable to the waste-dumping operation with rapid filling and rising groundwater level.

A two-surface thermomechanical plasticity model considering thermal cyclic behavior

In thermal-related engineering such as thermal energy structures and nuclear waste disposal, it is essential to well understand volume change and excess pore water pressure buildup of soils under thermal cycles. However, most existing thermo-mechanical models can merely simulate one heating–cooling cycle and fail in capturing accumulation phenomenon due to multiple thermal cycles. In this study, a two-surface elasto-plastic model considering thermal cyclic behavior is proposed. This model is based on the bounding surface plasticity and progressive plasticity by introducing two yield surfaces and two loading yield limits. A dependency law is proposed by linking two loading yield limits with a thermal accumulation parameter nc, allowing the thermal cyclic behavior to be taken into account. Parameter nc controls the evolution rate of the inner loading yield limit approaching the loading yield limit following a thermal loading path. By extending the thermo-hydro-mechanical equations into the elastic–plastic state, the excess pore water pressure buildup of soil due to thermal cycles is also accounted. Then, thermal cycle tests on four fine-grained soils (natural Boom clay, Geneva clay, Bonny silt, and reconstituted Pontida clay) under different OCRs and stresses are simulated and compared. The results show that the proposed model can well describe both strain accumulation phenomenon and excess pore water pressure buildup of fine-grained soils under the effect of thermal cycles.

Volcaniclastic debris avalanche on Motomachi area of Izu-Oshima, Japan, triggered by severe storm: Phenomenon and mechanisms

Heavy rainfall and strong wind associated with Typhoon Wipha hit Izu-Oshima Island, Japan, and triggered catastrophic landslides on the western slope of Oshima Volcano on 16 October 2013. These landslides were shallow but large in scale, and the displaced landslide materials were characterized by rapid and long runout movement. A massive landslide resulted in 36 people dead and 3 missing, with 46 buildings being completely destroyed in the downstream area of Motomachi district. To understand the initiation and movement of these shallow landslides, we surveyed the landslide area and found that in addition to heavy rainfall, strong wind may also have played a key role in increasing the instability of the slopes. We took samples from the source areas and examined their static and dynamic shear behaviors under naturally drained or undrained conditions. Test results showed that high pore-water pressure can be built up and maintained within the displaced landslide material and increase landslide mobility, even though the thickness of displaced landslide materials is 0.7–1.2 m. This may then give a rational explanation on the fluidization process of the displaced landslide materials. We also examined the windthrow features of trees subjected to different wind speed through monitoring the ground motion by seismometer and portable anemometer, and then performed cyclic shear tests on the materials laying above the sliding surface. The test results suggest that the windthrow may have promoted the buildup of excess pore-water pressure within the saturated soil layer and thus favoured the occurrence of slope failure. Therefore, it is suggested that in the prediction of shallow landslides on forested slopes subjected to heavy storm, both the effects of rainfall and strong wind should be taken into account.

Assessment of Lateral Displacements using Neuro-Fuzzy Group Method of Data Handling Systems

Lateral spreading is one of the most destructive effects of liquefaction. Liquefaction is known as one of the major causes of ground failure related to earthquake. This phenomenon is likely to occur when the rate of earthquake-induced excess pore water pressure buildup exceeds the rate of drainage. Estimation of the hazard of lateral spreading requires characterization of subsurface conditions. In this study, neuro-fuzzy group method of data handling (NF-GMDH) is utilized for assessment of lateral displacement in both ground slope and free face conditions. The NF-GMDH approach is improved using particle swarm optimization (PSO) algorithm. The comprehensive database used for the development of the model was obtained from different earthquakes. Contributions of the variables influencing the lateral displacement of soil are evaluated through a sensitivity analysis. Performance of the NF-GMDH-PSO models are compared with those yielded using empirical equations in terms of error indicators parameters and the advantages of the proposed models over the conventional method are discussed.

Simulation of excess pore water pressure during deep soil mixing columns installing

Most of current studies of deep soil mixing (DSM) methods are focused on the soil strength improvement and soil treatment effectiveness. But the DSM installation leads to excess pore water pressure and soil disturbance, which will bring great harm to adjacent structures, such as shell tunnels and historic buildings. The procedure of excess pore water pressure buildup while large number DSM columns are installed is complicated. In order to find methods to predict and simulate the excess pore water pressure during DSM column installation, the complicated dissipation and buildup of excess pore water pressure through in-situ test are studied in this paper. In-situ test was conducted in soft clay near the Huangpu River in Shanghai. The pore water pressure was investigated by an automatic monitoring system. Test results indicate that the excess pore water pressure induced by one DSM column installation is composed of the compaction pressure and the reversing pressure. The empirical equations of excess pore water pressure dissipation and buildup were built by mathematical fitting methods. A compound method is proposed to simulate the excess pore water pressure due to DSM installation. Using this method to predict the excess pore water pressure in the situ test, results show a well agreement between the prediction and the measurements.

Class A Prediction of the Behavior of Soft Estuarine Soil Foundation Stabilized by Short Vertical Drains beneath a Rail Track

In Australia, very few rail tracks have been constructed directly on deep estuarine deposits. In recent years, Kooragang Island has become a major export terminal and most coal trains need to cross the main lines at Sandgate to enter Kooragang Island. In this study, a rail track built on up to 30 m of thick soft estuarine soil was stabilized with relatively short vertical drains to consolidate the soil just beneath the track, and no additional preloading surcharge was provided, except the weight from the trains. The initial soil compression was caused by the passage of trains with a speed restricted at 40 km/h. From this study, it is shown that prefabricated vertical drains significantly decrease the buildup of excess pore-water pressure during cyclic loading, and also continue to dissipate excess pore-water pressure during the rest period. A preliminary finite-element analysis was employed to examine the performance of vertical drains, and a Class A prediction was obtained in terms of lateral and vertical displacements. The monitored settlement and lateral displacement results are presented and discussed. The study shows that relatively short vertical drains are sufficient for providing stability for rail tracks, without the need for driving deep vertical drains through the entire soft soil depth.

Experimental Study on the Shearing Behavior of Saturated Silty Soils Based on Ring-Shear Tests

The shearing behavior of saturated silty soils has been examined extensively by performing undrained and partially drained (the upper drainage valve of the shear box was open during shearing) ring-shear tests on mixtures of a sandy silt with different loess contents. By performing tests at different initial void ratios, the shear behavior of these silty soils at different initial void ratios is presented and discussed. Undrained-shear-test results showed that the liquefaction phenomena in ring-shear tests were limited within the shear zone; for a given void ratio or interfine void ratio, both the peak and steady-state shear strengths decreased with increase of loess content. The partially drained shear tests revealed that a great reduction in the shear strength could result after the shear failure, due to the buildup of excess pore-water pressure within the shear zone; the magnitude of reduction in shear strength after failure was affected by the initial void ratio, the shear speed after failure, as well as the loess content in the sample. For a given void ratio or interfine void ratio, with increase of loess content, the drained peak shear strength became smaller, while the brittleness index became greater. It was also found that due to localized shearing, the permeability of the soil within the shear box after drained shearing could be three orders of magnitude smaller than before shearing.