scholarly journals Mechanisms of rainfall-induced landsliding in Wellington fill slopes

2021 ◽  
Author(s):  
◽  
Bradley Mark Cosgrove
Keyword(s):  
Particle Size ◽  
Shear Zone ◽  
Pore Water ◽  
Failure Mechanisms ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Mitigation Measures ◽  
Pore Water Pressures ◽  
Failure Conditions ◽  
Excess Pore

<p>Recent landslides from Wellington fill slopes have occurred as potentially hazardous, mobile debris flow-slides with long runouts during heavy rainstorms. Globally, catastrophic landslides from fill slopes are well documented, and in many instances their rapid failure and long runout suggests that their shear zones may be subject to liquefaction. Various generations of fill slopes throughout Wellington, and urban New Zealand, have been constructed using different practices and at variable scales. Despite this, very few laboratory based studies to determine how different fill slopes may perform during rainstorms have been attempted, as conventional laboratory tests do not adequately simulate the failure conditions in the slope.  This study uses a novel, dynamic back-pressured shear box to conduct rapid shear and specialist pore pressure inflation tests in order to replicate rainfall induced failure conditions in fill slopes with different consolidation histories and particle size characteristics. During each test, excess pore-water pressures and deformation were monitored until failure in order to determine the failure mechanisms operating.  This study demonstrates that the failure mechanisms in fill slopes are strongly influenced by the consolidation history and particle size characteristics of the shear zone materials. In over-consolidated and fine grained (< 0.4 mm) fills where cohesion is present, brittle failure was observed. In these materials, failures occur more rapidly but require much higher pore-water pressures to initiate. Conversely, normally-consolidated fill slopes constructed from coarser material (0.4 - 2 mm) fail through ductile deformation processes, which typically initiate at much lower pore-water pressures but result in a less rapid slope failure. Although liquefaction was not observed, excess pore-water pressures can be generated during rapid shearing, indicating that liquefaction could occur after a landslide has initiated in conditions where excess pore-water pressures are unable to dissipate away from the shear zone. These results provide new insights into the types of failure that may be anticipated from different fill slopes, the hazards they may pose and potential mitigation measures that could be implemented.</p>

scholarly journals Mechanisms of rainfall-induced landsliding in Wellington fill slopes

2021 ◽  
Author(s):  
◽  
Bradley Mark Cosgrove
Keyword(s):  
Particle Size ◽  
Shear Zone ◽  
Pore Water ◽  
Failure Mechanisms ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Mitigation Measures ◽  
Pore Water Pressures ◽  
Failure Conditions ◽  
Excess Pore

<p>Recent landslides from Wellington fill slopes have occurred as potentially hazardous, mobile debris flow-slides with long runouts during heavy rainstorms. Globally, catastrophic landslides from fill slopes are well documented, and in many instances their rapid failure and long runout suggests that their shear zones may be subject to liquefaction. Various generations of fill slopes throughout Wellington, and urban New Zealand, have been constructed using different practices and at variable scales. Despite this, very few laboratory based studies to determine how different fill slopes may perform during rainstorms have been attempted, as conventional laboratory tests do not adequately simulate the failure conditions in the slope.  This study uses a novel, dynamic back-pressured shear box to conduct rapid shear and specialist pore pressure inflation tests in order to replicate rainfall induced failure conditions in fill slopes with different consolidation histories and particle size characteristics. During each test, excess pore-water pressures and deformation were monitored until failure in order to determine the failure mechanisms operating.  This study demonstrates that the failure mechanisms in fill slopes are strongly influenced by the consolidation history and particle size characteristics of the shear zone materials. In over-consolidated and fine grained (< 0.4 mm) fills where cohesion is present, brittle failure was observed. In these materials, failures occur more rapidly but require much higher pore-water pressures to initiate. Conversely, normally-consolidated fill slopes constructed from coarser material (0.4 - 2 mm) fail through ductile deformation processes, which typically initiate at much lower pore-water pressures but result in a less rapid slope failure. Although liquefaction was not observed, excess pore-water pressures can be generated during rapid shearing, indicating that liquefaction could occur after a landslide has initiated in conditions where excess pore-water pressures are unable to dissipate away from the shear zone. These results provide new insights into the types of failure that may be anticipated from different fill slopes, the hazards they may pose and potential mitigation measures that could be implemented.</p>

A new approach to the stability analysis of thawing slopes

1980 ◽  
Vol 17 (4) ◽  
pp. 607-612 ◽  
Author(s):  
Luis E. Vallejo
Keyword(s):  
Stability Analysis ◽  
Water Content ◽  
Pore Water ◽  
Active Layer ◽  
Necessary Conditions ◽  
Mass Movements ◽  
New Approach ◽  
Pore Water Pressures ◽  
The Stability ◽  
Excess Pore

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.

scholarly journals Experiment Study of Lateral Unloading Stress Path and Excess Pore Water Pressure on Creep Behavior of Soft Soil

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Wei Huang ◽  
Kejun Wen ◽  
Dongsheng Li ◽  
Xiaojia Deng ◽  
Lin Li ◽  
...  
Keyword(s):  
Pore Water ◽  
Creep Behavior ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Stress Path ◽  
Deviatoric Stress ◽  
Excess Pore Water Pressure ◽  
Pore Water Pressures ◽  
Excess Pore

The unloading creep behavior of soft soil under lateral unloading stress path and excess pore water pressure is the core problem of time-dependent analysis of surrounding rock deformation under excavation of soft soil. The soft soil in Shenzhen, China, was selected in this study. The triaxial unloading creep tests of soft soil under different initial excess pore water pressures (0, 20, 40, and 60 kPa) were conducted with the K0 consolidation and lateral unloading stress paths. The results show that the unloading creep of soft soil was divided into three stages: attenuation creep, constant velocity creep, and accelerated creep. The duration of creep failure is approximately 5 to 30 mins. The unloading creep behavior of soft soil is significantly affected by the deviatoric stress and time. The nonlinearity of unloading creep of soft soil is gradually enhanced with the increase of the deviatoric stress and time. The initial excess pore water pressure has an obvious weakening effect on the unloading creep of soft soil. Under the same deviatoric stress, the unloading creep of soft soil is more significant with the increase of initial excess pore water pressure. Under undrained conditions, the excess pore water pressure generally decreases during the lateral unloading process and drops sharply at the moment of unloading creep damage. The pore water pressure coefficients during the unloading process were 0.73–1.16, 0.26–1.08, and 0.35–0.96, respectively, corresponding to the initial excess pore water pressures of 20, 40, and 60 kPa.

Ductile shear zones – future perspectives

2020 ◽  
Author(s):  
Christoph Schrank
Keyword(s):  
Shear Zone ◽  
Research Effort ◽  
Rheological Behaviour ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Field Observations ◽  
Ductile Shear Zones ◽  
In Situ Experiments ◽  
Ductile Shear ◽  
Physical Consequences

&lt;p&gt;About 50 years ago, John Ramsay and colleagues established the thorough foundation for the field-scale observational and mathematical description of the structures, deformation, and kinematics in ductile shear zones. Since then, these probably most important instabilities of the ductile lithosphere enjoyed an almost explosive growth in scientific attention. It is perhaps fair to say that this tremendous research effort featured four main themes:&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] The historic scientific nucleus &amp;#8211; quantification of shear-zone geometry, strain and associated kinematic history from field observations&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[2] Qualitative and quantitative analysis of microphysical deformation mechanisms in the field and the laboratory&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[3] Shear-zone rheology&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[4] The development of physically consistent mathematical models for shear zones, mainly using continuum mechanics.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;In concert, these four cornerstones of shear-zone research enabled tremendous progress in our understanding of why and how ductile shear zones form. So, what are some of the outstanding problems?&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;A truly comprehensive model for ductile shear zones must account for the vast range of length and time scales involved, each easily covering ten orders of magnitude, as well as the associated intimate coupling between thermal, hydraulic, mechanical, and chemical processes. The multi-scale and multi-physics nature of ductile shear zones generates scientific challenges for all four research themes named above. This presentation is dedicated to highlighting exciting challenges in themes 2, and 3 and 4.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;In the microanalytical arena [2], the nano-scale is an exciting new frontier, especially when it comes to the interplay between metamorphism and ductile deformation. The nano-frontier can be tackled with new synchrotron methods. I showcase some applications to fossil shear-zone samples and discuss opportunities for in-situ experiments. In the domain of rheology [3], I present some simple experiments with strain-softening materials and field observations that support the notion: transient rheological behaviour is very important for shear localisation. In the modelling domain [4], some recent examples for the intriguing physical consequences predicted by new multi-physics and cross-scale coupling terms in ductile localisation problems are illustrated.&lt;/p&gt;

Cyclic loading of an Ottawa area Champlain Sea clay

1977 ◽  
Vol 14 (1) ◽  
pp. 52-63 ◽  
Author(s):  
R. J. Mitchell ◽  
R. Douglas King
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Pore Water ◽  
Soil Structure ◽  
Shear Failure ◽  
Large Deformations ◽  
Cemented Soil ◽  
Pore Water Pressures ◽  
Excess Pore ◽  
Static Shear

Undrained cyclic loading of triaxial samples of a sensitive Champlain Sea clay at deviatoric stress levels in excess of 50% of the static shear strength is shown to produce large deformations and eventual shear failure. Continued deformation of the clay under repeated loadings is believed to result from a progressive destruction of the cemented soil structure. Effective stress failures result from an increase in the excess pore water pressures within the sample.

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