Numerical simulation of soil-structure interaction experiments on shallow founded structures for different mass configurations

Soil-Structure Interaction (SSI) phenomena and foundation rocking can modify the structural response signifi- cantly with respect to the response predicted adopting the fixed-base assumption. The importance of SSI and rocking depends, among other factors, on the structural mass and the distribution of static stresses at the soil-foundation interface. Within this context, an experimental campaign was carried out aiming to investigate the SSI effects on the response of a 3m x 3m x 5m steel- framed structure. The prototype structure, called EUROPROTEAS, was founded on a shallow footing at the well-characterised Euroseistest site, while its mass was either 18Mgr or 9Mgr. The present study simulates free vibration experiments, placing particular emphasis on soil nonlinearity and soil-foundation interface. A novel approach to simulate gaps at the soil-foundation interface, foundation rocking and to manipulate interface stresses under static conditions is presented. The three aspects are shown to significantly affect the response, while they are found to be more important for the lighter structure

Optimisation of impact pile driving using optical fibre Bragg grating measurements

This paper reports the use of optical Fibre Bragg Grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length to diameter ratios of 6 to 20 were impact driven at an established chalk test site in Kent, UK. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high frequency (5kHz) fibre optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared time series of pile head PDA measurements and FBG strains measured below ground surface. Numerical solutions of the onedimensional wave equation were optimised by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high resolution strain measurements are made

Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method

Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

This paper describes and interprets tests on piles driven through glacial tills and chalk at a Baltic Sea windfarm, covering an advance trial campaign and later production piling. The trials involved six instrumented 1·37 m dia. steel open-ended tubes driven in water depths up to 42 m. Three piles were tested statically, with dynamic re-strike tests on paired piles, at 12–15 week ages. Instrumented dynamic driving and re-strike monitoring followed on up to 3·7 m dia. production piles. During driving, the shaft resistances developed at fixed depths below the seabed fell markedly during driving, with particularly sharp reductions occurring in the chalk. Shaft resistances increased markedly after driving and good agreement was seen between long-term capacities interpreted from parallel static and dynamic tests. Analyses employing the sites’ geotechnical profiles show long-term shaft resistances in the chalk that far exceed those indicated by current design recommendations, while newly proposed procedures offer good predictions. The shaft capacities mobilised in the low-plasticity tills also grew significantly over time, within the broad ranges reported for sandy soils. The value of offshore field testing in improving project outcomes and design rules is demonstrated; the approach described may be applied to other difficult seabed conditions

Keynote Lecture – The Interplay of Multiple Hazards and Urban Development: The context of Istanbul

Tomorrow’s Cities is the UK Research and Innovation (UKRI) Global Challenges Research Fund (GCRF) Urban Disaster Risk Hub – an interdisciplinary research hub with the aim to catalyse a transition from crisis management to multi-hazard risk-informed and inclusive planning in four cities in low-and-middle income countries. Istanbul in Turkey is one of the four cities investigated. It is one of the largest urban agglomerations in Europe where more than 15 million people reside in more than 1 million buildings. Considering that the population was 4.75 million in 1980, Istanbul’s urban sprawl was inevitable. Due to an imbalance between the population growth and housing supply, Istanbul’s urbanization was shaped by illegal construction processes producing the gecekondus in almost every part of the city (Gencer and Mentese, 2016). Unplanned urban expansion was so rapid that the urban master plan of 1980, which set the limits and strategies for urban development, became completely invalid by 1989 (Tapan, 1998). This situation led to the development of a new urban master plan in 1994 that included geoscientific analysis, and which highlighted the possibility of losses due to an earthquake on the segments of the North Anatolian Fault in the Marmara Sea. Uncontrolled and unplanned development continued in Istanbul until 1999 when two major earthquakes hit the region causing at least 18.000 deaths and $16 billion economic loss. These events changed the authorities’ perspective to earthquake risk and its mitigation. As a result, the 1998 earthquake resistant design code (published one year before the 1999 earthquakes) was widely embraced and implemented. Furthermore, several urban transformation projects have taken place in the last 20 years for reducing disaster risk. These have had varied success, with research to date showing that areas selected for urban transformation were often chosen on the basis of land value rather than hazard risk, and that a pro-poor approach is missing. Despite these efforts, Istanbul’s earthquake risk remains high. Furthermore, recent urban development plans are seeing the city expand into undeveloped lands to the west, increasing exposure to new hazards, namely flash flooding and landslides. The combined impact of these hazards is not evenly distributed, and the associated risks are heightened by poor infrastructural resilience and social vulnerabilities. Therefore, it is crucial to integrate different types of hazards and risks into the urban development context for future scenarios, so that a physically and socio-economically safer development that prioritizes the wellbeing of local communities can be facilitated. This presentation summarises the research conducted in Istanbul over the first 18 months of the Tomorrow’s Cities Project by a consortium of Turkish and UK researchers. This research spans the better characterisation of earthquake and landslide hazards, development of analysis methods for predicting the response of case study buildings to multiple hazards and a Bayesian network based approach for assessing road infrastructure resilience under multiple hazard scenarios. Furthermore, plans for building a Resilient Urban Development Decision Support Environment (RUD-DSE) for communicating the relevance of this research on future urban planning is described

Optimization of impact pile driving using optical fiber Bragg-grating measurements

This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length-to-diameter ratios of 6∶20 were impact driven at an established chalk test site in Kent, United Kingdom. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high-frequency (5 kHz) fiber optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared the time series of pile head PDA measurements and FBG strains measured below the ground surface. Numerical solutions of the one-dimensional wave equation were optimized by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high-resolution strain measuremen