Tony Gee and Partners

The indirect tension test is an important laboratory test for rock characterization. The presence of rock fabric, such as schistosity, complicates the assessment of test results. One hundred and forty-five indirect tension tests were conducted on mica schist specimens to investigate the effect of schistosity orientation on failure mode and tensile strength. Tensile strength results did not provide a clear relationship between schistosity orientation and tensile strength, so the failure patterns were investigated. A new naming scheme for failure modes was developed, incorporating fracture patterns observed in the specimen faces and edges. The Single Mode failure group specimens had only one failure pattern that appeared on both specimen faces, either axial failure (seventy-three specimens), schistosity failure (six specimens), or out-of-plane failure (seven specimens). The Mixed Mode failure group had thirty-two specimens that exhibited one failure pattern on one face and another on the other. The Hybrid Mode failure group had twenty-seven specimens with multiple failure patterns on both specimen faces. It was noted that Mixed Mode and Hybrid Mode specimens with components of axial failure had higher indirect tensile strengths than specimens without elements of axial failures. Statistical analyses of the tensile strength data using Levene’s Test for equal variances and two-sample t-tests showed no statistical difference between the Mixed Mode and Hybrid Mode failure groups. However, there was a statistical difference between the tensile strengths of the Single Mode axial failure specimens and the combined Mixed Mode and Hybrid Mode failure groups. These results clearly emphasize that indirect tensile strength should be assessed using schistosity orientation and failure mode.

There is no reason why concrete elements should be prismatic. Concrete is mouldable and can be cast in efficient forms which follow the stresses varying along the length of a concrete element. One option to achieve this is to use fabric as flexible formwork. Fabric deforms under the hydrostatic pressure exerted by wet concrete during construction, creating the shape of hardened concrete. The final shape needs to be known in advance to be able to perform the analysis and design of structural elements. This paper presents a form-finding approach capable of predicting the shape in cross-section of flexibly formed concrete elements. The approach is shown to predict geometry appropriately, based on the results of an experimental investigation, particularly when applied to complex shapes. The influence of construction tolerances, practical aspects and limitations of the approach are also discussed.

The railway from Folkestone to Dover opened in 1845, emerging from the Shakespeare Cliff tunnel to cross Shakespeare Beach on a 400m timber trestle viaduct to access the original station at Dover Harbour. Circa 1920 a coastal defence wall was constructed and the timber trestles backfilled with chalk rubble. The wall extends some 700m retaining up to 10m in height. Rail tracks were transferred to ballast. In the 1980s, construction of Samphire Hoe to contain fill from the Channel Tunnel affected migration of beach recharge material from the west, extending exposure of a wave cut platform in the chalk beneath Shakespeare Cliff; and causing progressive lowering the beach. The process continued until a series of storms in late 2015 undermined the wall leading to rapid loss of fill and severe damage to the coastal protection, triggering the closure of the railway on Christmas Eve 2015. The paper describes the events leading to the damage, the emergency stabilisation works undertaken, the assessment of the nature and causes of the problem, and the necessary design and construction of a new 250m rail support structure and 700m of coastal protection comprising 100,000t of rock armour to protect and supplement the existing sea defence wall. The perspectives of asset manager, designer and contractor are provided, which will inform practitioners and serve as a record of a significant coastal defence project with rapid response permitting reopening of the railway within 207 days from closure.

Abstract The introduction of Eurocodes to engineering practice represents an importantchange in the approach to geotechnical engineering, as for the first time there is a unified set of codes dealing with the main structural materials including the ground. All of the Eurocodes adopt a limit state design philosophy which is different from the lumped factor of safety approach adopted by traditional geotechnical design practice. This paper examines the implications of the introduction of the Eurocodes, in particular EN1997, when assessing the stability of earthworks. It outlines the various committees responsible for the development of the codes and discusses the application of EN1997 to the assessment of the stability of slopes highlighting the difficulties in applying the various design approaches. Examples from practice are used to highlight where the code is different from traditional practice. A survey of practice in other European countries is outlined which indicates the differing approaches to ensuring adequate reliability being taken across Europe highlighting options that could be considered by the geotechnical community. The paper concludes that the introduction of the Eurocodes does not require a significant change to the way stability analysis is carried out.

Eurocodes were used for the design of a new metro, for which the contractor's design was undertaken largely between 1996 and 1999, when the Eurocodes were in their infancy. This paper discusses the experience, the difficulties encountered and the benefits gained by the project, with particular reference to the geotechnical design of the underground stations. Eurocodes 1, 2 and 7 were used for the design of the retaining walls for the deep stations. Two design parameters created challenges for the structural design of the reinforced concrete embedded retaining walls: a restriction on the maximum allowable crack width, and a large cover to the reinforcement, required by the construction method. Benefits were gained by using the observational method.