Andrew Ridley - Academia.edu (original) (raw)

Papers by Andrew Ridley

Research paper thumbnail of Analysis of a rainfall-triggered landslide at rest and be thankful in Scotland

E3S Web of Conferences

Weather and climate are key influences upon the triggering of landslides in Scotland. One of the ... more Weather and climate are key influences upon the triggering of landslides in Scotland. One of the primary factors influencing the landslide and debris flows occurrence is rainwater infiltration into an initially unsaturated slope. This leads to an increase in both degree of saturation and pore-water pressure and, consequently, to a decrease in the shear strength of the soil, which eventually triggers a landslide event. The A83 trunk road at the Rest and Be Thankful in Scotland is an area prone to risk from landslide and, because of climate change, this risk is going to become higher. An increased frequency of heavier rainfall has been observed in recent years and forecasts for the next decades are not more reassuring. In 2014, the biggest landslide event has occurred at the Rest and Be Thankful Pass. More than 2000 tonnes of landslip debris have been removed in efforts to reopen the route A83. Although the route is now open again, still many are the aspects related to the triggering of such event that have not been clarified yet. The aim of this paper is to address the problem of developing a simple numerical model to analyse rainfalltriggered shallow landslides.

Research paper thumbnail of Volumetric behaviour of compacted London Clay during wetting and loading

Unsaturated Soils. Advances in Geo-Engineering, 2008

Research paper thumbnail of Osmotic system in long term testing of unsaturated soils

Research paper thumbnail of Soil suction — what it is and how to successfully measure it

Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, 2015

Soil suction (or negative porewater pressure) is important to the development of strength and cha... more Soil suction (or negative porewater pressure) is important to the development of strength and changes of volume in soils that lie above the natural water table. The presence of soil suction is particularly important in the study of slopes where, should the porewater pressure increase, stability brought about by suction-induced increases of strength can be compromised. Over the last 20 years, methods for measuring soil suctions in laboratories and on sites have been developed. These have made it possible to make reliable measurements and have been be used to further our understanding of the role that suctions play in slope stability. This paper presents the background to the presence of soil suctions in ground, advances made in instrumentation for measuring soil suctions and field measurements made by the author. 2 What is soil suction and where can I get some? Historically, soil mechanics theory has concerned itself mainly with the behaviour of what are termed saturated soils. This is not surprising, given that geotechnical engineering developed in temperate regions of the world where water tables are generally close to the surface and the foundations of most major https://papers.acg.uwa.edu.au/p/1508_0.2_Ridley/ Soil suctionwhat it is and how to successfully measure it AM

Research paper thumbnail of Update on European and international geotechnical monitoring standards

Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, 2015

On the occasions of the previous International Field Measurements in Geomechanics (FMGM) symposia... more On the occasions of the previous International Field Measurements in Geomechanics (FMGM) symposia in Boston 2007 and Berlin 2011, contributions were made on the issue of developing a set of international geotechnical monitoring standards. Efforts, initially undertaken under the auspices of DIN, the German Standardisation Organization (Bock & Thaher 2007), and subsequently of CEN, the European Standardisation Organization (Steiner 2011) were referred to. This paper presents an update on the process, covering the developments, which have taken place since 2011, the current state, and future perspectives. It is foreseen that the set of the international geotechnical monitoring standards will consist of ten parts. Currently, the committee work is carried out by the authors of this paper, under the auspices of CEN, in cooperation with the International Standardization Organization (ISO). In 2013 it was decided to label the new standards as EN ISO 18674 under the heading of 'Geotechnical investigation and testing-Geotechnical monitoring by field instrumentation'. Since 2011, the first part, namely 'General rules', has been finalised and is expected to be published in 2015. Drafts for the following two parts are nearing completion:

Research paper thumbnail of Preliminary analysis on the impacts of the rhizosphere on occurrence of rainfall-induced shallow landslides

Landslides, 2019

Rainfall-induced diffuse shallow landslides are one of the most critical natural hazards as they ... more Rainfall-induced diffuse shallow landslides are one of the most critical natural hazards as they often evolve into highly destructive flow slides and debris flows. Vegetation is recognised to play a key role in landslide occurrence and is frequently invoked as a potential remedial measure for slope stabilisation at the catchment scale. The beneficial action of vegetation is generally associated with mechanical (root anchoring) and hydrological (suction generated by root water uptake) effects. There is indeed a third effect that has thus far been little explored. The rhizosphere, the portion of soil directly affected by plant roots, is characterised by hydraulic conductivity higher than the underlying soil horizons. This significantly affects hillslope hydrology by promoting lateral diversion of rainwater. This paper presents a case study in Scotland where the rhizosphere is demonstrated to play a major role in controlling shallow landslides. Field investigation and laboratory testing were carried out to characterise the hydraulic conductivity of the rhizosphere and deeper horizons. In turn, this formed the basis for the development of a physically based model for the slope. The model was first validated against its capability to simulate failure of two historical landslides and then exploited to demonstrate the beneficial effect of the rhizosphere. The lesson learned from this study is that shallow landslide hazard can be mitigated by enhancing the capacity of the rhizosphere to act as a natural lateral drainage. This implies that plants with root-system architecture that enhances lateral subsurface flow should be privileged when designing vegetation-based remedial measures.

Research paper thumbnail of Collapse Behavior of Compacted Silty Clay in Suction-Monitored Oedometer Apparatus

Journal of Geotechnical and Geoenvironmental Engineering, 2007

This paper presents a methodology to investigate the collapse behavior of unsaturated soils using... more This paper presents a methodology to investigate the collapse behavior of unsaturated soils using suction-monitored oedometer tests. By incorporating independent suction measurement, the oedometer apparatus is capable of following the same stress paths as ...

Research paper thumbnail of Discussion A new instrument for the measurement of soil moisture suction

Géotechnique, 1994

The tensiometer probe developed by the Authors is an important contribution to the measurement of... more The tensiometer probe developed by the Authors is an important contribution to the measurement of suction in porous materials, and opens up many possibilities of furthering the understanding of many aspects of the mechanical behaviour of saturated and unsaturated soils. In this discussion we present the techniques required to avoid cavitation in the probe, and experimental results which show that the Authors' tensiometer may be influenced by osmotic phenomena. Probably the most impressive aspect of the Authors' tensiometer probe is that it is able to measure high suctions in water (+ 1 atm) without cavitation occurring in the system. To avoid cavitation in the measurement system, and thus improve the measurement of negative water pressure, the main requirements are as follows.

Research paper thumbnail of Evolution of microstructure in compacted London Clay during wetting and loading

Géotechnique, 2010

The influence of fabric on mechanical behaviour is explicitly considered in some of the current c... more The influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils. These are based on assumptions regarding the interaction between different levels of structure, which still require experimental validation. A study has been carried out to investigate the evolution of fabric in a compacted natural clay during wetting and loading, and the results are presented in this paper. Samples of London Clay were statically compacted to the same initial conditions, dry of optimum moisture content in a Proctor plot, and subsequently taken along complex stress paths involving wetting, loading, or a combination of both. Mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) microstructure investigations were carried out to observe and quantify the change in fabric associated with each path. The soil fabric was observed to change from an aggregate to a matrix type structure along all wetting p...

Research paper thumbnail of The Suitability of the Osmotic Technique for the Long-term Testing of Partly Saturated Soils

Geotechnical Testing Journal, 2007

The understanding of partly saturated soil behavior can be enhanced with the help of additional s... more The understanding of partly saturated soil behavior can be enhanced with the help of additional specialist testing in the laboratory. From the various techniques available to do so at present, the osmotic technique is probably the simplest one. However, there are concerns with the response of this system over time, and in particular its ability to sustain suctions for long periods of time. In this study, the response of a synthetic semi-permeable membrane in conjunction with a solution of high molecular weight has been investigated. The behavior of the osmotic system has been studied both in isolation and in full scale tests, by incorporating it into a purposely built oedometer. Not only was it possible to establish a calibration curve of osmotic potential versus concentration of solution but, additionally, it was possible to perform tests which extended for up to five months. The results suggest that with the correct choice of semi-permeable membrane and solution, it should be possible to use the osmotic technique in a satisfactory manner to perform any desired test on partly saturated soils, regardless of its duration.

Research paper thumbnail of A new instrument for the measurement of soil moisture suction

Research paper thumbnail of Use of the tensile strength of water for the direct measurement of high soil suction

Canadian Geotechnical Journal, 1997

Research paper thumbnail of Assessing the deformation of geomaterials through field measurements

Geomechanics for Energy and the Environment

Research paper thumbnail of Mechanical behaviour of unsaturated expansive clay under K0 conditions

Engineering Geology, 2015

Research paper thumbnail of Stability monitoring of a rail slope using acoustic emission

Proceedings of the ICE - Geotechnical Engineering, 2015

Research paper thumbnail of Fabric Changes in Compacted London Clay Due to Variations in Applied Stress and Suction

Springer Proceedings in Physics, 2007

Summary. In this study, the evolution of fabric in compacted London Clay has been studied in deta... more Summary. In this study, the evolution of fabric in compacted London Clay has been studied in detail. Samples were statically compacted to the same initial condi-tions and taken along a number of stress paths – involving both wetting and loading – to different final conditions. Wetting ...

Research paper thumbnail of The mechanical behaviour of a reconstituted unsaturated silty clay

Research paper thumbnail of Evaluation of an Active System to Measure Lateral Stresses in Unsaturated Soils

Geotechnical Testing Journal, 2014

Research paper thumbnail of Random Uncertainty in the Measurement of Matric Potential Using the Miniature Tensiometer

Geotechnical Testing Journal, 2012

Research paper thumbnail of Field Measurement of Suction, Water Content, and Water Permeability

Geotechnical and Geological Engineering, 2008

Abstract This paper presents a review of techniques for field measurement of suction, water conte... more Abstract This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity (permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance are given. ...

Research paper thumbnail of Analysis of a rainfall-triggered landslide at rest and be thankful in Scotland

E3S Web of Conferences

Weather and climate are key influences upon the triggering of landslides in Scotland. One of the ... more Weather and climate are key influences upon the triggering of landslides in Scotland. One of the primary factors influencing the landslide and debris flows occurrence is rainwater infiltration into an initially unsaturated slope. This leads to an increase in both degree of saturation and pore-water pressure and, consequently, to a decrease in the shear strength of the soil, which eventually triggers a landslide event. The A83 trunk road at the Rest and Be Thankful in Scotland is an area prone to risk from landslide and, because of climate change, this risk is going to become higher. An increased frequency of heavier rainfall has been observed in recent years and forecasts for the next decades are not more reassuring. In 2014, the biggest landslide event has occurred at the Rest and Be Thankful Pass. More than 2000 tonnes of landslip debris have been removed in efforts to reopen the route A83. Although the route is now open again, still many are the aspects related to the triggering of such event that have not been clarified yet. The aim of this paper is to address the problem of developing a simple numerical model to analyse rainfalltriggered shallow landslides.

Research paper thumbnail of Volumetric behaviour of compacted London Clay during wetting and loading

Unsaturated Soils. Advances in Geo-Engineering, 2008

Research paper thumbnail of Osmotic system in long term testing of unsaturated soils

Research paper thumbnail of Soil suction — what it is and how to successfully measure it

Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, 2015

Soil suction (or negative porewater pressure) is important to the development of strength and cha... more Soil suction (or negative porewater pressure) is important to the development of strength and changes of volume in soils that lie above the natural water table. The presence of soil suction is particularly important in the study of slopes where, should the porewater pressure increase, stability brought about by suction-induced increases of strength can be compromised. Over the last 20 years, methods for measuring soil suctions in laboratories and on sites have been developed. These have made it possible to make reliable measurements and have been be used to further our understanding of the role that suctions play in slope stability. This paper presents the background to the presence of soil suctions in ground, advances made in instrumentation for measuring soil suctions and field measurements made by the author. 2 What is soil suction and where can I get some? Historically, soil mechanics theory has concerned itself mainly with the behaviour of what are termed saturated soils. This is not surprising, given that geotechnical engineering developed in temperate regions of the world where water tables are generally close to the surface and the foundations of most major https://papers.acg.uwa.edu.au/p/1508_0.2_Ridley/ Soil suctionwhat it is and how to successfully measure it AM

Research paper thumbnail of Update on European and international geotechnical monitoring standards

Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, 2015

On the occasions of the previous International Field Measurements in Geomechanics (FMGM) symposia... more On the occasions of the previous International Field Measurements in Geomechanics (FMGM) symposia in Boston 2007 and Berlin 2011, contributions were made on the issue of developing a set of international geotechnical monitoring standards. Efforts, initially undertaken under the auspices of DIN, the German Standardisation Organization (Bock & Thaher 2007), and subsequently of CEN, the European Standardisation Organization (Steiner 2011) were referred to. This paper presents an update on the process, covering the developments, which have taken place since 2011, the current state, and future perspectives. It is foreseen that the set of the international geotechnical monitoring standards will consist of ten parts. Currently, the committee work is carried out by the authors of this paper, under the auspices of CEN, in cooperation with the International Standardization Organization (ISO). In 2013 it was decided to label the new standards as EN ISO 18674 under the heading of 'Geotechnical investigation and testing-Geotechnical monitoring by field instrumentation'. Since 2011, the first part, namely 'General rules', has been finalised and is expected to be published in 2015. Drafts for the following two parts are nearing completion:

Research paper thumbnail of Preliminary analysis on the impacts of the rhizosphere on occurrence of rainfall-induced shallow landslides

Landslides, 2019

Rainfall-induced diffuse shallow landslides are one of the most critical natural hazards as they ... more Rainfall-induced diffuse shallow landslides are one of the most critical natural hazards as they often evolve into highly destructive flow slides and debris flows. Vegetation is recognised to play a key role in landslide occurrence and is frequently invoked as a potential remedial measure for slope stabilisation at the catchment scale. The beneficial action of vegetation is generally associated with mechanical (root anchoring) and hydrological (suction generated by root water uptake) effects. There is indeed a third effect that has thus far been little explored. The rhizosphere, the portion of soil directly affected by plant roots, is characterised by hydraulic conductivity higher than the underlying soil horizons. This significantly affects hillslope hydrology by promoting lateral diversion of rainwater. This paper presents a case study in Scotland where the rhizosphere is demonstrated to play a major role in controlling shallow landslides. Field investigation and laboratory testing were carried out to characterise the hydraulic conductivity of the rhizosphere and deeper horizons. In turn, this formed the basis for the development of a physically based model for the slope. The model was first validated against its capability to simulate failure of two historical landslides and then exploited to demonstrate the beneficial effect of the rhizosphere. The lesson learned from this study is that shallow landslide hazard can be mitigated by enhancing the capacity of the rhizosphere to act as a natural lateral drainage. This implies that plants with root-system architecture that enhances lateral subsurface flow should be privileged when designing vegetation-based remedial measures.

Research paper thumbnail of Collapse Behavior of Compacted Silty Clay in Suction-Monitored Oedometer Apparatus

Journal of Geotechnical and Geoenvironmental Engineering, 2007

This paper presents a methodology to investigate the collapse behavior of unsaturated soils using... more This paper presents a methodology to investigate the collapse behavior of unsaturated soils using suction-monitored oedometer tests. By incorporating independent suction measurement, the oedometer apparatus is capable of following the same stress paths as ...

Research paper thumbnail of Discussion A new instrument for the measurement of soil moisture suction

Géotechnique, 1994

The tensiometer probe developed by the Authors is an important contribution to the measurement of... more The tensiometer probe developed by the Authors is an important contribution to the measurement of suction in porous materials, and opens up many possibilities of furthering the understanding of many aspects of the mechanical behaviour of saturated and unsaturated soils. In this discussion we present the techniques required to avoid cavitation in the probe, and experimental results which show that the Authors' tensiometer may be influenced by osmotic phenomena. Probably the most impressive aspect of the Authors' tensiometer probe is that it is able to measure high suctions in water (+ 1 atm) without cavitation occurring in the system. To avoid cavitation in the measurement system, and thus improve the measurement of negative water pressure, the main requirements are as follows.

Research paper thumbnail of Evolution of microstructure in compacted London Clay during wetting and loading

Géotechnique, 2010

The influence of fabric on mechanical behaviour is explicitly considered in some of the current c... more The influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils. These are based on assumptions regarding the interaction between different levels of structure, which still require experimental validation. A study has been carried out to investigate the evolution of fabric in a compacted natural clay during wetting and loading, and the results are presented in this paper. Samples of London Clay were statically compacted to the same initial conditions, dry of optimum moisture content in a Proctor plot, and subsequently taken along complex stress paths involving wetting, loading, or a combination of both. Mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) microstructure investigations were carried out to observe and quantify the change in fabric associated with each path. The soil fabric was observed to change from an aggregate to a matrix type structure along all wetting p...

Research paper thumbnail of The Suitability of the Osmotic Technique for the Long-term Testing of Partly Saturated Soils

Geotechnical Testing Journal, 2007

The understanding of partly saturated soil behavior can be enhanced with the help of additional s... more The understanding of partly saturated soil behavior can be enhanced with the help of additional specialist testing in the laboratory. From the various techniques available to do so at present, the osmotic technique is probably the simplest one. However, there are concerns with the response of this system over time, and in particular its ability to sustain suctions for long periods of time. In this study, the response of a synthetic semi-permeable membrane in conjunction with a solution of high molecular weight has been investigated. The behavior of the osmotic system has been studied both in isolation and in full scale tests, by incorporating it into a purposely built oedometer. Not only was it possible to establish a calibration curve of osmotic potential versus concentration of solution but, additionally, it was possible to perform tests which extended for up to five months. The results suggest that with the correct choice of semi-permeable membrane and solution, it should be possible to use the osmotic technique in a satisfactory manner to perform any desired test on partly saturated soils, regardless of its duration.

Research paper thumbnail of A new instrument for the measurement of soil moisture suction

Research paper thumbnail of Use of the tensile strength of water for the direct measurement of high soil suction

Canadian Geotechnical Journal, 1997

Research paper thumbnail of Assessing the deformation of geomaterials through field measurements

Geomechanics for Energy and the Environment

Research paper thumbnail of Mechanical behaviour of unsaturated expansive clay under K0 conditions

Engineering Geology, 2015

Research paper thumbnail of Stability monitoring of a rail slope using acoustic emission

Proceedings of the ICE - Geotechnical Engineering, 2015

Research paper thumbnail of Fabric Changes in Compacted London Clay Due to Variations in Applied Stress and Suction

Springer Proceedings in Physics, 2007

Summary. In this study, the evolution of fabric in compacted London Clay has been studied in deta... more Summary. In this study, the evolution of fabric in compacted London Clay has been studied in detail. Samples were statically compacted to the same initial condi-tions and taken along a number of stress paths – involving both wetting and loading – to different final conditions. Wetting ...

Research paper thumbnail of The mechanical behaviour of a reconstituted unsaturated silty clay

Research paper thumbnail of Evaluation of an Active System to Measure Lateral Stresses in Unsaturated Soils

Geotechnical Testing Journal, 2014

Research paper thumbnail of Random Uncertainty in the Measurement of Matric Potential Using the Miniature Tensiometer

Geotechnical Testing Journal, 2012

Research paper thumbnail of Field Measurement of Suction, Water Content, and Water Permeability

Geotechnical and Geological Engineering, 2008

Abstract This paper presents a review of techniques for field measurement of suction, water conte... more Abstract This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity (permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance are given. ...