Geotechnical design practices and soil-structure interaction effects of an integral bridge system : a review

Integral bridges are a class of bridges with integral or semi-integral abutments, designed without expansion joints in the bridge deck of the superstructure. The significance of an integral bridge design is that it avoids durability and recurring maintenance issues with bridge joints, and maybe bearings, which are prevalent in traditional bridges. Integral bridges are less costly to construct. They require less maintenance and therefore cause less traffic disruptions that incur socio-economic costs. As a consequence, integral bridges are becoming the first choice of bridge design for short-to-medium length bridges in many countries, including the UK, USA, Europe, Australia, New Zealand and many other Asian countries. However, integral bridge designs are not without challenges: issues that concern concrete creep, shrinkage, temperature effects, bridge skew, structural constraints, as well as soil–structure interactions are amplified in integral bridges. The increased cyclic soil–structure interactions between the bridge structure and soil will lead to adverse soil ratcheting and settlement bump at the bridge approach. If movements from bridge superstructures were also transferred to pile-supported substructures, there is a risk that the pile–soil interactions may lead to pile fatigue failure. These issues complicate the geotechnical aspects of integral bridges. The aim of this paper is to present a comprehensive review of current geotechnical design practices and the amelioration of soil–structure interactions of integral bridges

Application of engineered compressible inclusions to mitigating soil-structure interaction issues in integral bridge abutments

The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck. The forward and backward movements of the abutment in response to the expansion/contraction of the bridge deck lead to the formation of settlement trough and surface heaving, frequently creating a bump at the bridge approach and increasing the lateral earth pressure behind the abutment. Measures to reduce the bump at the bridge approach, including several treatment methods, such as compaction of selected backfill materials, grout injection, installation of approach slab, and using a layer of compressible inclusion material behind the abutment were proposed. However, these guidelines still lack sufficient design details and there are limited experimental findings to validate design assumptions. In this paper, the use of engineered compressible materials to alleviate the lateral earth pressure ratcheting and settlement at the bridge approach is investigated. The comparative study is presented for the soil-inclusion, material-structure and soil-structure interactions for an integral bridge under three different backfill conditions, i.e. (a) sand, (b) sand and EPS geofoam, and (c) sand and Infinergy. The study was conducted in a special large-scale test chamber with a semi-scale abutment to gain better insights into the soil-structure interaction (SSI). The kinematics and rearrangement of the soil during the cyclic loading have been investigated to identify the mitigating effects of compressible inclusions. The comparative study indicates that both compressible inclusions perform comparatively well, however, Infinergy is a better alternative than the medium-density EPS geofoam, as it works more effectively to reduce the backfill settlement and heaving as well as soil ratcheting effects under cyclic translational movement

The Unconventional Strength Towards STEM Cohort

Science, Technology, Engineering and Mathematics (STEM) play a critically important role in Australia’s ability to innovate, expand and remain a competitive force globally. Indeed, ensuring that the workforce has the relevant skills in sufficient quantities through a reliable educational pipeline is quite challenging and requires an understanding of how these skills are and will be used within the Australian economy. Moreover, successfully delivering these skills for a knowledge economy will depend not only on producing the correct number of graduates but also on the education system supplying graduates from under-utilised groups (i.e. women & indigenous people) and diverse backgrounds. Currently, millions of children and young people are not developing the required skills to participate effectively in STEM environments. Young indigenous and female groups, in particular, are deprived of the opportunities to build their skills, including STEM literacy that is valued towards career progression in traditionally male-dominated fields (i.e. engineering and construction). As this white paper outlines, the challenges are drawn from recent literature, and a comprehensive review of existing initiatives is presented based on the observations of key partners, including Western Sydney University, the Australian government, research sector, industry, policymakers and communities. However, to build the STEM capacity of graduates with the right knowledge, competencies and qualities, two-way collaboration between the communities, educational institutions (from an early age), Australian workplaces and the government is essential, as no single sector can entirely solve the current STEM skills shortage. Western Sydney University is well-positioned within the high-density indigenous areas to respond to these issues, particularly by monitoring, engaging and promoting all graduates with STEM qualifications to meet the demand from the economy. In fact, by supporting equity and diversity throughout the STEM cohorts, educational institutions not only drive innovation but also establish a thriving STEM-skilled workforce that is fit for the future

A case study of a dcm column-supported embankment over soft clay

This paper investigates a case study of a highway embankment in Thailand constructed over Deep Cement Mixed (DCM) column improved ground. The case study was simulated using a 2D plane-strain model adopting the equivalent area approach for columns. Field measurements for deformations and excess pore pressures are compared with the finite element results to verify the numerical model, and to understand the load transfer mechanism. The most likely failure mode of the embankment was investigated by computing the Factors of Safety (FOS) against the bearing failure and bending failure of individual DCM columns, and the overall stability of the embankment. Results show that the most likely failure mode for this embankment is the bending failure of attached columns underneath side slopes. In the case study, attached columns are used to control the lateral deformations. In the paper, three other approaches used in practice for lateral deformation control are investigated: (i) Load transfer platform (LTP) with a geosynthetic layer above DCM columns with single columns near the side slopes (ii) T-shaped single columns near the side slopes and (iii) that in this particular case, due to the presence of a relatively deep fill layer above the soft clay deposit, lateral deformation control measures applied closer to the column heads such as LTP or T-shaped columns are not effective. However, the use of double columns with increased bending stiffness throughout the soft clay layer or increasing the length of columns underneath the embankment is the most effective solution in reducing lateral deformations

Numerical simulation of deep penetration of a Piezocone in a strain-softening clay

This paper presents a numerical model which has the ability to simulate Piezocone penetration starting from the ground surface in saturated soft clays. The constitutive behavior of the soil is modeled using the Modified Cam Clay model and the model has been verified using centrifuge model tests. The variation of cone resistance is examined with various parameters, which influence the penetration resistance of the cone, such as rigidity index of the soil, in situ stress anisotropy, roughness at the cone-soil interface and the overconsolidation ratio of the soil. A correlation has been developed incorporating the influence of above parameters on the Piezocone resistance and results are compared with previous correlations based on the finite element method. Finally, the strain-softening behavior of the soft clay on the penetration resistance is investigated. The brittleness or sensitivity of the soil increases with the increase in degree of strain-softening but the results do not show significant reductions in computed cone penetration resistance. The cyclic penetration tests simulated using the proposed model show that the Ball and T-bar penetration tests are better than Piezocone test in predicting the degree of soil sensitivity

Application of compund deep cement mixed walls for retaining structures in excavations

Deep cement mixed (DCM) columns are widely used as retaining structures to support deep excavations due to low cost and their ability in reducing seepage. However, the tensile strength of DCM walls is very low. Hence, large wall sections are necessary to avoid development of high tensile stresses when DCM walls are used to support deep excavations. In this paper application of compound DCM walls, which integrate DCM walls and bored piles, to support deep excavations are investigated aiming to develop resilient design methods for compound DCM walls. Three-dimensional finite element modelling is used in simulating the wall behaviour during deep excavations, considering the full geometry of the compound DCM wall. Numerical model is validated using a case study of a compound DCM wall constructed in Shanghai, China. Finally the use of arched DCM walls with different curvatures in between bored piles is investigated. Results of this study clearly demonstrates the advantages and limitations of increased curvature of compound DCM walls with respect to both ground deformations surrounding the excavation and tensile stresses developed in the compound DCM wall

An investigation into the contribution of student profile, student-lecturer interaction and student workload in teaching evaluations

This paper investigates the influence of student profile, student-lecturer interaction and increased student workload on teaching evaluations. Also the paper investigates whether there is any correlation between teaching evaluations and student grades

Strength variability of deep cement mixed columns on the overall performance of column-supported embankments

Deep Cement Mixed (DCM) column improved ground is known to have large strength variability across the material domain. However, the effect of strength variability on the performance of embankments supported by DCM columns is not well studied due to scarcity of numerical modelling facilities to incorporate spatial variability of material properties directly into a finite element analysis and lack of comprehensive field monitoring data. This paper investigates the effect of spatial variability on the performance of an embankment with attached DCM column walls beneath the side slopes. The analysis was carried out using numerical models developed using ABAQUS finite element program incorporating the spatial variability of DCM columns. The strength field in the material domain was randomly generated, from a lognormal distribution, using a computer program written in MATLAB. The sensitivity of embankment deformations to spatial correlation length, coefficient of variation (COV) and partial factor of safety (PFOS) was investigated by analysing a series of models. The reliability of the embankment in each analysis case was assessed using 1500 Monte Carlo realizations. Results demonstrate that the spatial correlation length of strength properties has a great influence on the reliability-based performance of the embankment. Larger spatial correlation lengths resulted higher upper bound in the lateral deformation data of the embankment. COV also affected the upper and lower bounds of the lateral deformation data. The PFOS significantly affected the skewness of the deformation distribution, however PFOS does not affect the upper and lower bounds of the distribution

Application of EPS geofoam in attenuating ground vibrations due to vibratory pile driving

Keynote Lecture 1: Modern day urban construction activities are largely carried out adjacent to existing buildings due to scarcity of land for construction. In order to utilise the available land in the most efficient way, often high-rise buildings are constructed necessitating pile foundations to transfer large design loads to strong and deep soil layers below the ground surface. Although a number of methods are available to install pile foundations, in urban areas several factors need to be taken into consideration when selecting the suitable method. Due to the proximity of new and existing structures, noise disturbance and damages to existing nearby structures resulting from pile installation should be kept to a minimum. In that respect, vibratory pile driving is the most suitable pile installation method for urban construction activities. However, ground vibrations induced by vibratory pile driving may cause damages to existing structures depending on the proximity and sensitivity of the structure. Hence, it is necessary to take proper mitigation measures against vibratory pile driving induced ground vibrations. A possible remedy is to use in-filled wave barriers with concrete, bentonite, water or expanded polystyrene (EPS) geofoam, which can diminish the construction induced vibrations. EPS geofoam offers a number of advantages over other fill materials because of its light weight, cost effectiveness, energy absorbing characteristics, efficiency in terms of construction time and ease of handling. There have been many research studies carried out to investigate the mechanical behaviour of EPS geofoam. However, the full potential of EPS geofoam is yet to be realised. Therefore this thesis aims to investigate the severity of ground vibrations induced by vibratory pile driving and effectiveness of EPS geofoam wave barriers in protecting nearby structures. These investigations are carried out using both two- and three-dimensional finite element models developed based on the Arbitrary-Lagrangian-Eulerian approach. They are discretised in both space and time to capture the wave propagation within ground