Papers by Michael J Brown
Physical Modelling in Geotechnics
International Journal of Physical Modelling in Geotechnics, 2019
Offshore pipeline ploughs have previously been modelled at 1g with small 1:50 scale models design... more Offshore pipeline ploughs have previously been modelled at 1g with small 1:50 scale models designed to derive the parameters required for prediction of ploughing in terms of tow force requirements and potential advance rates. This was scaled up to prototype with the validity of the scaling verified through ‘modelling of models’ and with comparison to typical prototype tow forces but without direct validation. To allow further validation, a long centrifuge box and actuation system was developed for use on a medium-sized beam centrifuge. Previous approaches to 1g ploughing were also improved through the use of micro-electro-mechanical systems accelerometers and new low-cost surface scanning techniques. A wide range of ploughing velocities were explored through increasing actuation speeds and the use of pore fluids of different viscosities. The study has shown that although there may be initial concerns over low effective stress scaling issues at 1g, in shallow problems with small-scal...
Tunnelling and Underground Space Technology, 2020
This paper examines the seismic response of a "horseshoe-shaped" tunnel, inspired by a recently c... more This paper examines the seismic response of a "horseshoe-shaped" tunnel, inspired by a recently constructed Metro tunnel in Santiago, Chile. A FE analysis has been conducted, investigating the effect of soil density, apparent cohesion, the interface between the tunnel and the surrounding soil, the intensity of the seismic excitation and the effect of volume loss due to tunnel construction on the seismic behaviour of tunnels. The presence of apparent cohesion leads to a reduction of tunnel distress and to smaller post-earthquake ground settlements over a reduced distance from the tunnel. The consideration of volume loss does not significantly affect the acceleration field around the tunnel, but does beneficially decrease the lining forces. Furthermore, although it leads to an increase of the pre-earthquake settlements, it is found to decrease the co-seismic settlements. Finally, it was found that the most conservative model regarding the design detailing of the tunnel lining would be considering a rough interface, zero cohesion, and negligible volume loss (i.e., an ideally-excavated tunnel).
International Journal of Physical Modelling in Geotechnics, 2015
When undertaking centrifuge studies on seismic soil–structure interaction, it is useful to be abl... more When undertaking centrifuge studies on seismic soil–structure interaction, it is useful to be able to define the pseudo-static ‘pushover’ response of the structure. Normally, this requires separate centrifuge experiments with horizontal actuators. This paper describes an alternative procedure, using Ricker ground motions to obtain the pushover response, thereby allowing both this and the response to seismic shaking to be determined using a centrifuge-mounted shaker. The paper presents an application of this technique to a 1:50 scale model bridge pier with two different shallow foundations, as part of a study on seismic protection using rocking isolation. The moment–rotation (‘backbone’) behaviour of the footings was accurately determined in the centrifuge to large rotations, as verified through independent three-dimensional dynamic non-linear finite-element modelling. Ricker wavelet ground motions are therefore shown to be a useful tool for the identification of pushover response wi...
Earthquake Engineering & Structural Dynamics, 2014
Experimental proof is provided of an unconventional seismic design concept, which is based on del... more Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil-footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking-isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self-centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism, exhibiting significant resistance to cumulative damage. Thanks to such mechanisms, the rocking pier survived, with no signs of structural distress, a deleterious sequence of seismic motions that caused collapse of the conventionally designed pier.
Soil Dynamics and Earthquake Engineering, 2019
Major seismic events have shown that tunnels in cohesionless soils may suffer extensive seismic d... more Major seismic events have shown that tunnels in cohesionless soils may suffer extensive seismic damage. Proper modelling can be of great importance for predicting and assessing their seismic performance. This paper investigates the effect of lining structural modelling on the seismic behaviour of horseshoe-shaped tunnels in sand, inspired from an actual Metro tunnel in Santiago, Chile. Three different approaches are comparatively assessed: elastic models consider sections that account for: (a) linear elastic lining assuming the geometric stiffness; (b) linear elastic lining matching the uncracked stiffness of reinforced concrete (RC); and (c) nonlinear RC section, accounting for stiffness degradation and ultimate capacity, based on moment-curvature relations. It is shown that lining structural modelling can have major implications on the predicted tunnel response, ranging from different values and distributions of the lining sectional forces, to differences in the predicted post-earthquake settlements, which can have implications on the seismic resilience of aboveground structures.
Installation of offshore pipelines in the seabed can be efficiently achieved using pipeline ploug... more Installation of offshore pipelines in the seabed can be efficiently achieved using pipeline ploughs. Increased efficiency may be achievable through incorporating a smaller forecutter in advance of the main plough share. Currently guidance is limited and conflicting as to the advantages or disadvantages of incorporating a forecutter. To investigate the effect of forecutter inclusion model tests were undertaken at 1/50th scale under laboratory conditions in sand beds prepared at different relative densities in both dry and saturated conditions. Dry sand tests were used to determine the effect of the forecutter on the static or passive components of plough tow force. The currently adopted passive pressure coefficient (C s) did not appear to vary with relative density to the same degree as previously suggested and the forecutter increased the magnitude of the passive or static resistance to ploughing. Saturated tests were used to determine the effects of the forecutter on the rate dependant component of ploughing resistance and allow verification of a dimensionless form of rate effect representation. The forecutter acts to reduce the rate effect component of plough tow force in both fine sand (low permeability) and to a lesser extent in medium sand (higher permeability). In fine and silty sands, however, incorporating a forecutter would seem highly beneficial at all ploughing depths and soil densities but in medium sand (higher permeability) the benefits of incorporation are limited to an operating window at shallower trench depths and lower relative density.
International Journal of Physical Modelling in Geotechnics, 2015
Soil dynamics and earthquake engineering, 2019
Major seismic events have shown that tunnels in cohesionless soils may suffer extensive seismic d... more Major seismic events have shown that tunnels in cohesionless soils may suffer extensive seismic damage. Proper modelling can be of great importance for predicting and assessing their seismic performance. This paper investigates the effect of lining structural modelling on the seismic behaviour of horseshoe-shaped tunnels in sand, inspired from an actual Metro tunnel in Santiago, Chile. Three different approaches are comparatively assessed: elastic models consider sections that account for: (a) linear elastic lining assuming the geometric stiffness; (b) linear elastic lining matching the uncracked stiffness of reinforced concrete (RC); and (c) nonlinear RC section, accounting for stiffness degradation and ultimate capacity, based on moment-curvature relations. It is shown that lining structural modelling can have major implications on the predicted tunnel response, ranging from different values and distributions of the lining sectional forces, to differences in the predicted post-earthquake settlements, which can have implications on the seismic resilience of aboveground structures.
Tunnelling and Underground space technology, 2020
This paper examines the seismic response of a "horseshoe-shaped" tunnel, inspired by a recently c... more This paper examines the seismic response of a "horseshoe-shaped" tunnel, inspired by a recently constructed Metro tunnel in Santiago, Chile. A FE analysis has been conducted, investigating the effect of soil density, apparent cohesion, the interface between the tunnel and the surrounding soil, the intensity of the seismic excitation and the effect of volume loss due to tunnel construction on the seismic behaviour of tunnels. The presence of apparent cohesion leads to a reduction of tunnel distress and to smaller post-earthquake ground settlements over a reduced distance from the tunnel. The consideration of volume loss does not significantly affect the acceleration field around the tunnel, but does beneficially decrease the lining forces. Furthermore, although it leads to an increase of the pre-earthquake settlements, it is found to decrease the co-seismic settlements. Finally, it was found that the most conservative model regarding the design detailing of the tunnel lining would be considering a rough interface, zero cohesion, and negligible volume loss (i.e., an ideally-excavated tunnel).
ICE Proceedings Geotechnical Engineering Journal, 2019
Offshore pipeline ploughs have previously been modelled at 1g with small 1:50 scale models design... more Offshore pipeline ploughs have previously been modelled at 1g with small 1:50 scale models designed to derive the parameters required for prediction of ploughing in terms of tow force requirements and potential advance rates. This was scaled up to prototype with the validity of the scaling verified through ‘modelling of models’ and with comparison to typical prototype tow forces but without direct validation. To allow further validation, a long centrifuge box and actuation system was developed for use on a medium-sized beam centrifuge. Previous approaches to 1g ploughing were also improved through the use of micro-electro-mechanical systems accelerometers and new low-cost surface scanning techniques. A wide range of ploughing velocities were explored through increasing actuation speeds and the use of pore fluids of different viscosities. The study has shown that although there may be initial concerns over low effective stress scaling issues at 1g, in shallow problems with small-scale models, the large deformation nature of the ploughing problem can be replicated with appropriate scaling. This allows the use of 1g modelling for more efficient parametric studies for this application and has given further confidence to performance parameters for prototype modelling derived from 1g and centrifuge studies.
Earthquake Engineering & Structural Dynamics, 2014
Experimental proof is provided of an unconventional seismic design concept, which is based on del... more Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil-footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking-isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self-centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism, exhibiting significant resistance to cumulative damage. Thanks to such mechanisms, the rocking pier survived, with no signs of structural distress, a deleterious sequence of seismic motions that caused collapse of the conventionally designed pier. being therefore the same for both design alternatives. Yet, soil structure interaction is expected to drastically increase this value especially in the case of the rocking pier.
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Papers by Michael J Brown