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Although the thermomechanical behaviors of energy piles have been investigated through a limited number of full-scale tests with constant loads, the effect of multiple load levels on the bearing capacity of energy piles has not been fully implemented into these in situ tests in the past. We report six full-scale in situ tests on bored energy piles under heating or cooling conditions and multiple mechanical load levels in Shanghai, China. Each pile was tested with 24 h of mechanical loading, 48 h of heating or cooling, and 10 h of thermomechanical loading. We monitored the inlet and outlet water temperature, pile and soil temperature, pore water pressure in the soil, axial force of the pile, and pile head displacement, and analyzed the thermomechanical responses of the energy pile and the surrounding soil, as well as the bearing capacity of the energy pile. Our experimental results show that the mechanical responses induced by the temperature change in the pile were affected by mechanical load level. Larger mechanical load reduced the influence of temperature on the settlement of the pile top and on the variation of the axial force in the pile, and at the same time weakened the negative skin friction effect caused by heating and enhanced the positive skin friction effect caused by cooling. Furthermore, pore water pressure caused by changes in soil temperature decreased slightly, and excess pore water pressure increased with increasing mechanical load level and dissipated rapidly in low-permeability coefficient soil. Finally, we comprehensively discussed the vertical bearing capacity of the energy pile based on the thermomechanical responses of the pile and the surrounding soil. [ABSTRACT FROM AUTHOR]

This paper reports a forensic investigation on the unexpected collapse of a 13-storey high-rise residential building in Shanghai soft clay. Prior to the building collapse, a shallow excavation was carried out on one side of the building while a slope was filled on the opposite side. Despite the observed breakage of all the piles in the field, a preliminary forensic numerical analysis adopting a typical undrained shear strength (cu) profile in Shanghai suggests that the piles are very unlikely to break. The surprising contrast has led to this detailed forensic study on the underlying mechanisms for the building collapse, through a site-specific characterisation of the cu profile, three-dimensional centrifuge modelling and numerical back-analysis. Although the typical cu profile in Shanghai increases almost linearly with depth, the clay in this site consists of two major layers with distinctive strength – that is, a relatively soft clay layer (average cu = 23 kPa, thickness = 13·5 m) underlain by a relatively stiff clay layer (average cu = 58 kPa, thickness = 18·2 m). By reproducing this cu profile in the centrifuge test and numerical analysis, the resulting direction of the building collapse and the depths of pile breakage were broadly consistent with those observed in the field. It was found that the surcharge of the fill slope caused the bearing capacity to be exceeded in the upper soft clay layer. This led to the development of a sliding wedge under the surcharge, which extended horizontally (at a depth of 11 m) across the pile foundations to reach the excavation side, and therefore the breakage of the piles. If a typical strength profile in Shanghai (with cu linearly increasing with depth) were adopted, the failure mechanism could be significantly altered from the aforementioned deep slip failure to a shallow passive failure, causing much smaller bending moment in each pile. [ABSTRACT FROM AUTHOR]

• A semi–analytical force–method solution for a straight–jointed tunnel is proposed. • Nonlinear joint stiffness is considered and expressed as a function of M, N and θ. • An incremental iterative algorithm is established for the strong nonlinear system. • The tunnel ultimate bearing capacity under different load distributions is analyzed. The ultimate bearing capacity of a segmental tunnel lining significantly influences its service performance, particularly when the surrounding soil pressure changes. In this study, a semi–analytical force–method solution for a straight–jointed segmental tunnel lining was derived. The nonlinear joint stiffness was considered and expressed as a function of the bending moment, axial force, and rotational angle of the joint. An incremental iterative algorithm and the corresponding convergence criterion of the proposed model were established for the strong nonlinear system. The proposed model was then verified using the full–scale test results for the loading behavior of the joint and the segmental lining. The structural response of the tunnel under different external load distributions was analyzed using the proposed model, and the main conclusions are as follows. As the lateral pressure coefficient increases, the ultimate bearing capacity of the tunnel lining increases and the length of the first yield platform of the convergence deformation decreases. When P 3 /P 1 increases from 0.71 to 0.83, the ultimate bearing capacity of the tunnel lining increases by 20%, but it has no significant effect on the ultimate convergence deformation. For the lining of the shield tunnel of the Shanghai Metro, the recommended convergent deformation limit is 110 mm. [ABSTRACT FROM AUTHOR]

Reclaiming waste driven piles to use as the foundations of new buildings is an innovative and effective approach to manage waste driven piles for cleaner construction. A reclamation pathway for waste driven piles is proposed based on a renewal project in Shanghai. A detailed evaluation of the durability and bearing capacity of the waste driven piles is performed. Post-construction settlement in a normal building and a building with a foundation constructed with a combination of new and waste piles is compared to evaluate the performance of the waste piles. Technical suggestions are summarized to improve the reclamation pathway based on the findings of the renewal project. The results show that both the durability and bearing capacity of the waste piles meet the requirements of engineering applications. Reuse of waste piles reduced average settlement but increased the uneven settlement of the new buildings. Economic analysis indicates that reuse of waste driven piles in foundations of new buildings can save approximately $573,672 in construction costs and 1017.6 m3 in concrete for a project the size of the renewal project. Both technical and economic assessments corroborate the reclamation pathway for waste driven pile is necessary and appropriate for Shanghai. The proposed reclamation pathway benefits the management of waste piles and facilitates the cleaner production of construction industry. • Reuse of waste piles was realized in practice and a reclamation pathway was proposed. • Durability and bearing capacity evaluation show waste piles can be reused. • Waste piles application reduced average settlement but increased uneven settlement. • Economic performance approved the reclamation pathway was a sustainable approach. [ABSTRACT FROM AUTHOR]