Editorial

This issue features eight articles. The first three papers by deLeeuw et al. (2021), Wang et al. (2021) and Mortara (2021)deal with interfaces. The first article (de Leeuw et al., 2021)investigates the interface shear strength of polypropylene pipe-line coatings and sandy soils by means of direct shear interfacetests. Experimental evidence is provided to guide engineers toselect the interface friction coefficient between polypropylenepipeline coatings and marine sands characterised by differentparticle size distributions. Indeed, just a reliable pipe–soil inter-face strength characterisation allows robust predictions of pipe-line response under different loading conditions, like the onesencountered in the subsea environment. The second article(Wang et al., 2021) presents a push-out method to investigatethe mechanical response of mortar–rock interfaces for anchorsystems at different loading rates. In particular, higher loadingrates were associated to a stick–slip behaviour of the interface,characterised by discontinuous and oscillating sliding. Theauthors also provided a micromechanical interpretation of thestick–slip phenomenon, which allowed the definition of a rheo-logical visco-elastoplastic model for the interface. The thirdpaper (Mortara, 2021) presents a simple but effective model topredict sand–structure interface response, highlighting the roleof the stress–dilatancy relation. Model predictions have beencompared with literature results, and a clear calibrationprocedure is presented.The next three articles by Zhu et al. (2021), Ye et al. (2021)and Xiao (2021) deals with piles. Zhu et al. (2021) describe aseries of centrifuge tests performed to investigate the cycliclateral response of a tetrapod pile jacket foundation in a kaolinclay, measuring not only the overall load–displacementresponse, but also the internal forces within the piles. Thepaper by Ye et al. (2021) reports on the response of a freshcast-in-place concrete pile induced by the penetration of anadjacent pile casing in a clay soil. Large-deformation finite-element analyses have been performed to reproduce thepenetration process: numerical results have been used topropose a practical analytical expression to predict themaximum lateral displacement of the fresh concrete pile due toadjacent casing penetration. The numerical model has beenvalidated by means of both centrifuge test and field monitor-ing data. The paper by Xiao (2021) examines the role of theaxial force in a slope-stabilising pile in the context of thekinematic theorem of limit analysis. If compared with otherapproaches that neglect the role of the axial force in the pile(e.g. Ausilio et al., 2001), the method presented in the paperpredicts different locations of the slip surface and allows aconservative calculation in terms of required pile length.The next article (Chodorowski et al., 2021) presents a veryinteresting case history set in London, UK, describing theinteraction between the Crossrail tunnel and a building situ-ated directly over it. The paper discusses the ‘geotechnicalpath’ followed by the authors to overcome the original plan ofdemolition of the building and extraction of the existing foun-dation piles, achieving a solution that keeps the building andreduces construction costs. The final article in this issue is adiscussion article (Zhang et al., 2021) of a research paper byZhang et al. (2020) about the challenges of earth pressurebalance tunnelling in weathered granite with boulders.