Measuring the behaviour of dual row retaining walls in dry sands using centrifuge tests

Soil Dynamics and Earthquake Engineering

2019

Multi-hazard threats from tsunami events preceded by large earthquakes have been put into sharp focus in recent times. Dual row retaining walls are soil-structure systems that can have large lateral capacity with a small horizontal extent, making them ideal for the next generation of coastal protection. However, the dynamics of their behaviour is a complex interaction problem. Centrifuge tests, with multiple earthquakes within a single flight as well as multiple flights with varied embedment ratio were conducted to elucidate the mechanics of these systems when founded in dry sand. The structural response shows permanent, plastic deformations during the early cycles dependent mainly on the PGA superposed with more elastic vibrations during prolonged shaking. The development of the soil stresses and stiffnesses mobilised is used to explain the overall system response. Finally, the recorded structural and soil behaviour during swing up and down are combined to show that the soil stress and strain state is effectively reset between flights. Overall, useful methods for judging the progressive response of a complex soil-structure system are presented which can help justify future comparisons between experimental datasets and understand the implications of practical dynamic design.

Section: Measuring the System Responsementioning

confidence: 92%

Section: Cyclic Shear Responsementioning

confidence: 99%

Centrifuge testing of dual row retaining walls in dry sand: The influence of earthquake sequence and multiple flights

Soil Dynamics and Earthquake Engineering

2019

“…The static equilibrium of DF666, following both swing up and a small sine shake has been discussed in Madabhushi and Haigh (2019) and Madabhushi and Haigh (2018c). In short, both of the flexible walls exhibit double curvature where the outward bending of the top section of the wall is restrained by the tie rod and external soil.…”

Section: Experimentally Observed Dynamic Responsementioning

confidence: 99%

On the dynamic response of flexible dual-row retaining walls in dry sand

2022

Géotechnique

Dual row retaining walls can be utilised to form embankment structures for protection against tsunamis or as port structures. The dynamic response of these walls involves a complex interaction between the soil and structural elements which is not well understood. In this paper, for the first time a combination of centrifuge and finite element modelling is used to better understand the mechanical response of the combined wall-soil system. The measured variation of the horizontal stresses leads to bending moment distributions featuring large, singly outward bending or double curvature with significant inward bending of the wall near the ground level. The numerical analyses are used to understand the stress state and highlight the dynamic variations of the vertical effective stress that drive this previously unexplained behaviour. The shear stresses that can develop at the wall-soil interface govern the mechanism by which the vertical effective stresses can vary. Further consideration of the dynamic soil stress state suggests a purer interpretation of the limiting loads in soil-structure interaction problems relative to the traditionally defined dynamic earth pressure coefficients. Combining the altered vertical soil stresses with earth pressure coefficients depending only on the soil friction angle adequately bounds the horizontal stresses that develop in the soil.

Using tactile pressure sensors to measure dynamic earth pressures around dual-row walls

International Journal of Physical Modelling in Geotechnics

2019

Following the destructive 2011 Tohoku earthquake and tsunami, dual-row retaining walls are being employed in Japan to protect coastal areas from these natural hazards. Dynamic centrifuge tests are conducted to investigate the system behaviour, in particular the earth pressures generated. Highfrequency tactile pressure sensors can measure the dynamic earth pressures. By directly measuring the stresses generated during earthquake events invaluable insight can be gained into the dynamic behaviour. However, the processing and interpretation of the raw output can be challenging. This paper describes a processing scheme that can be used to reduce the apparent scatter in the data. This is applied to the earth pressure data collected using the system developed by Tekscan. The calibration and sensitivity correction process is detailed, with attention to the limitations of the assumptions made in the proposed method. The variation of the processed earth pressures with time is considered to better understand the wall behaviour. The distribution along the wall is considered at several instants to gain further insight. To help verify the earth pressure measurements, equilibrium-based methods are used to investigate the consistency between the recorded earth pressures and the outputs from other instruments that directly measure the wall response.