Effect of height on delayed collapse of cuttings in stiff clay

Ellis, E; O’Brien, Anne

doi:10.1680/geng.2007.160.2.73

Cited by 17 publications

(15 citation statements)

References 8 publications

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“…The analyses are performed for a generic slope geometry with dimensions known to be unstable in London Clay without any stabilisation measures (Potts et al, 1997;Ellis & O'Brien, 2007). The slope is 10 m high with a 1 in 3 vertical to horizontal slope angle.…”

Section: Description Of the Numerical Model Analysis Arrangement And mentioning

confidence: 99%

Stabilisation of excavated slopes in strain-softening materials with piles

2017

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The use of a row of discrete vertical piles is an established method, successfully used to remediate failure of existing slopes and to stabilise potentially unstable slopes created by widening transport corridors. This paper challenges the assumptions made in current design procedures for these piles, which treat the pile only as an additional force or moment and simplify soil-pile interaction. Two-dimensional planestrain finite-element analyses were performed to simulate the excavation of a slope in a stiff clay and the interaction of vertical piles within the slope. A non-local strain-softening model was employed for the stiff clay to reduce the mesh dependency of the solution. An extensive parametric study was performed to systematically examine the impact of pile position, dimensions (length and diameter) and time of pile construction on the stability of a cutting in London Clay, which was chosen as a representative strainsoftening material. A variety of different failure mechanisms were identified, depending on pile location, dimensions and time of construction. The variability of the pile and slope interaction that was modelled suggests that an oversimplification during design could miss the critical failure mechanism or provide a conservative stabilisation solution. Given the prevalence of stiff clay slopes in the UK, increased capacity requirements of transport infrastructure and the age of slopes in this material, an informed and more realistic design of stabilisation piles will become increasingly necessary.

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Section: Description Of the Numerical Model Analysis Arrangement And mentioning

confidence: 99%

Stabilisation of excavated slopes in strain-softening materials with piles

2017

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“…It has been demonstrated in various technical publications (Ellis & O'Brien 2007) and in the modelling conducted for Phase 1 of this study that strains initiate at the toe and subsequently progress into the slope along a near horizontal surface. Strain levels increase with time until there is a zone at the base of the cutting where the soil has reached residual strength.…”

mentioning

confidence: 66%

“…Stability is very sensitive to groundwater pressures. This is clearly shown by the numerical modelling studies carried out by Ellis & O'Brien (2007). For example, for a 1:3 (V:H) slope in weathered London Clay the stable height increases from about 6.5 m to 8.5 m if the water table level drops from 1.0 m to 2.0 m below ground level.…”

Section: Analytical Basismentioning

confidence: 88%

“…The strains within the slope cause the shear strength to reduce such that the average mobilized shear strength along a potential slip surface is part way between peak and residual. Figure 1 illustrates the development of this mechanism, simulated by the FLAC numerical modelling of progressive failure (Ellis & O'Brien 2007). Thus the two, time dependent, features of delayed, deep-seated failure are a long-term increase in pore pressures coupled with a reduction in available strength.…”

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confidence: 99%

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The identification and management of cuttings at risk from deep-seated, delayed failure on the Highways Agency network

Parry

2012

EGSP

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The UK trunk road network includes a considerable number of cuttings constructed through high plasticity, overconsolidated clays. These materials are prone to the process of delayed, deep-seated failure whereby instability can occur some considerable time after construction. The timescale between excavation and failure can be anywhere between 20 and 120 years. Many of the recorded deep-seated failures in the literature are from railway cuttings in the UK which are generally much older than cuttings on major highways. The bulk of trunk road construction in the UK occurred during the 1960s and 1970s and many cuttings are at, or approaching, an age when delayed, deep-seated failures might be expected to occur.The Highways Agency (HA) has been aware of this issue and has sought to understand the causes and associated risks of these types of failure. The first phase of a study (concluded in 2007) provided a framework for assessing the likelihood of failure. The selection criteria were based on a combination of cutting height and slope angle. Mott MacDonald was commissioned to undertake the second phase of the study to focus on the application of the Phase 1 recommendations to the HA asset base. This paper describes the work undertaken during this study and conclusions reached.The UK trunk road network includes a considerable number of cuttings constructed through high plasticity, overconsolidated clays. Theses materials are prone to the process of delayed, deep-seated failure whereby instability can occur some considerable time after construction. The timescale between excavation and failure can be anywhere between 20 and 120 years.The term deep-seated failure is defined as those failures extending to more than 2 m depth below the slope surface and these may extend beyond the toe or crest of the slope (Perry et al. 2003). Shallow failures are less than 2 m deep and occur entirely within the cutting side slope. The results of a review of the occurrence and distribution of shallow failures on the Highways Agency (HA) network is contained within the Transport Research Laboratory report RR199 (Perry 1989). At the time of preparing RR199, shallow failures were by far the most common.This study concentrates on first time slides only, that is, it is assumed that there were no pre-existing shear surfaces present prior to construction. Cutting slopes that contain preexisting shear surfaces will behave in a different manner and have been excluded from this study. Many of the recorded deep-seated failures in the literature are from railway cuttings which are generally much older than cuttings on major highways. The bulk of trunk road construction in the UK occurred during the 1960s and 1970s and many cuttings are at, or approaching, an age when delayed, deep-seated failures might be expected to occur.

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“…As such the higher stiffness values should lead to more rapid mobilisation of strength and so cause a reduced rate of progressive failure. The above mechanism was originally described in work undertaken by Ellis and O'Brien (2007), see Figure 14. Figure 14.…”

Section: Lessons Learned So Farmentioning

confidence: 92%

Research-informed design, management and maintenance of infrastructure slopes: development of a multi-scalar approach

Glendinning¹,

Helm²,

Rouainia³

et al. 2015

IOP Conf. Ser.: Earth Environ. Sci.

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Abstract. The UK's transport infrastructure is one of the most heavily used in the world. The performance of these networks is critically dependent on the performance of cutting and embankment slopes which make up £20B of the £60B asset value of major highway infrastructure alone. The rail network in particular is also one of the oldest in the world: many of these slopes are suffering high incidents of instability (increasing with time). This paper describes the development of a fundamental understanding of earthwork material and system behaviour, through the systematic integration of research across a range of spatial and temporal scales. Spatially these range from microscopic studies of soil fabric, through elemental materials behaviour to whole slope modelling and monitoring and scaling up to transport networks. Temporally, historical and current weather event sequences are being used to understand and model soil deterioration processes, and climate change scenarios to examine their potential effects on slope performance in futures up to and including the 2080s. The outputs of this research are being mapped onto the different spatial and temporal scales of infrastructure slope asset management to inform the design of new slopes through to changing the way in which investment is made into aging assets. The aim ultimately is to help create a more reliable, cost effective, safer and more resilient transport system.

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Effect of height on delayed collapse of cuttings in stiff clay

Cited by 17 publications

References 8 publications

Stabilisation of excavated slopes in strain-softening materials with piles

Stabilisation of excavated slopes in strain-softening materials with piles

The identification and management of cuttings at risk from deep-seated, delayed failure on the Highways Agency network

Research-informed design, management and maintenance of infrastructure slopes: development of a multi-scalar approach

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