Belled piles are expected to resist the uplift motion of buildings caused by rocking during earthquakes. In supertall buildings with pile foundations, uplift forces are assumed to increase owing to the increase in the spans and heights of such buildings. In order to understand the uplift resistance mechanism of a belled pile, the authors conducted two series of experiments in a centrifuge. One is the ground deformation visualization experiments, and the other is the measurement experiments. During the visualization experiments, ground behavior in the belled pile uplift was visualized using Digital Image Correlation (DIC). From the ground behavior visualized by DIC, it was revealed that the ground deformed area expands as the belled pile is uplifted, which is related to the uplift resistance, and that the uplift resistance is proportional to the belled angles. Because the friction between the observation window and the physical model (both ground and pile) is not negligible in visualization experiments, a full-cylinder soil box and a full-section model pile were employed in the following series of measurement experiments to quantitatively investigate the uplift resistance of the belled pile. Centrifugal experiments were performed using the same procedure and conditions as the visualization ones to obtain the load-displacement relationships of the belled piles with different belled angles and diameter ratios. The load-displacement relationships obtained from the measurement experiments were then analyzed and normalized in an integrated form. From the obtained experimental results, the maximum uplift resistance can be formulated by normalizing uplift stress acting on the bell vertically at the pile end, and the normalized uplift resistance is proportional to the belled angle and can be expressed by an exponential form of the diameter ratio. The formulation proposed above enables estimation of the uplift bearing capacity of a belled pile by considering both the belled angle and diameter ratio effects.

One of the authors has been developing a new composite foundation composed of piles and soil bags. The purpose of developing this foundation is to reduce bending moment of piles and response acceleration of structures by cutting off fixed connections between piles and footings. In particular, soil bags are laid between pile heads and footings to mitigate stress concentration to particular piles, etc. The effectiveness of this method for piers has been confirmed by an in-situ loading test and numerical simulations. When the proposed method is applied to frame structures, however, the seismic response such as uplifting behavior of footings is considered to be quite different from that of piers. In this study, therefore, shake table tests in 1/20-scale gravity field were conducted on frame structures supported respectively by a conventional cast-in-place piles foundation and the proposed foundation, and their seismic response characteristics were compared. The response acceleration and displacement of the structure, strains of the columns were measured to clearly identify the differences in seismic response characteristics between the frame structures supported by the conventional cast-in-place pile foundation and the proposed foundation. The test results showed that the response acceleration of the structure and the bending moment of the columns can be reduced dramatically in the proposed method compared to those in the conventional cast-in-place pile foundation, although the residual displacement increased in the proposed method due to the structure sliding during an earthquake.

The seismic upgrade of existing structures and the construction of earthquake-resistant foundations is a very current task in seismic regions worldwide. The use of composite tubular self-drilling micropiles allows simply and effective solutions also in very confined sites. Using this technology, the hollow bar simultaneously acts as drilling rod, injection tube and reinforcement for the micropile and can be used in any type of soil. This is a composite micropile: steel with a continuous thread and cement grout body just like reinforced concretes. Thanks to the very high skin friction between grout body and the ground this is a low settlement system which has an excellent behavior under seismic forces transferring a big percentage of the inertial forces to the ground. By using hollow steel loadbearing elements of several dimensions and designing the pile to transfer the forces to the ground, it is possible to install micropiles with many design loads, even for 2.000 kN and more. Former investigations and numerical simulations have shown the positive behavior of groups of inclined micropiles under seismic actions and possible liquefaction problems in comparison to big and massive piles. The paper presents the main features of this technology and illustrates a significant project carried out that highlighted the advantages of the system.

In order to clarify the soil-pipe-joint interactions of steel pipe sheet piles (SPSP) under large deformation conditions, the current study conducted reproduction analysis of air and soiled (with ground model) lateral loading tests. The proposed method uses a hybrid element that consists of beam and solid element to exhibit the stiffness of the joint part and pipe part. A spring element connects the beam element of the joint part to model the mechanical behaviors of joint part that including compression, tension, vertical and horizontal shearing. The properties of pipe & joint, joint mechanical behaviors, and soils are determined by mechanical calculation, element tests, and triaxial compressive tests, respectively. It was found that in air condition, the stiffness of lateral load of SPSPs depends on the mechanical state of pipe part. In soils, the stiffness of lateral load of SPSPs was also influenced by the vertical shear failure of joint. The SPSP models in both air and soils follows a behavior that resistance mode shifted from grouped state to

independent state due to the vertical shear failure of joint. Improving the strength and resistance ability of the joint part against vertical shearing displacement is a reasonable approach to enhance the lateral bearing capacity of SPSPs with large deformation.

The paper presents generalized failure envelopes for an indicative reinforced concrete (RC) pile group layout in the combined VHM loading space. The limit equilibrium method is employed, reproducing certain failure modes in function of the applied load path of interest. Emphasis is placed on the role of the axial load-dependent bending strength and stiffness of the RC piles, and the coupling between their lateral load- and moment-capacity. The importance of setting a conventional limit on the axial bearing capacity of the piles and its effect on the predicted failure modes is also critically evaluated. The advantages of the proposed methodology are illustrated through a worked example on pseudo-static seismic design of a bridge pile group. The code-compliant estimation of capacity (Lateral Load and Overturning Moment) is compared to the ultimate resistance, estimated using the proposed method. The study illustrates that conventional approaches, widely applied in practice, not only violate the physics of the problem but in some cases can also yield un-conservative estimates.

The seismic performance of piles in a river is susceptible to scouring. The removal of soil results in a decrease in lateral strength and an increase in lateral displacement of the piles. Therefore, scoured piles may undergo a pronounced P–Δ effect, which will cause a reduction in the pile’s strength. In this study, we numerically and theoretically investigate the P–Δ effect on the displacement ductility capacity of scoured fixed-head piles in cohesive soil. A long pile embedded in a Winkler-type soil with constant soil stiffness is simulated. The pile section has nonlinear flexural properties, which are assumed to be a bilinear moment–curvature relationship. The results show that the P–Δ effect has a different influence on the displacement ductility capacity depending on ultimate states. When the ultimate state is governed by the pile-head bending failure, considering the P–Δ effect increases the displacement ductility capacity; whereas when the ultimate state is governed by the occurrence of in-ground plastic hinging, the P–Δ effect can reduce the displacement ductility capacity.

Energy-efficient homes are constructed with a continuous and uniform thermal envelope and are commonly built on top of a thermal insulation (TI) layer that encloses the entire building. Lightweight aggregates such as foamed glass aggregate, expanded clay aggregate, and extruded polystyrene (XPS) insulation boards are commonly used as materials for the TI layer to prevent thermal bridging at the ground floor slab. However, the reinforced concrete slab foundation above the TI layer is susceptible to horizontal sliding during seismic loading. To improve the seismic behavior of buildings founded on TI layers, this study discussed the shear stiffness and damping characteristics of lightweight aggregates and three types of XPS boards through laboratory tests available in the literature. A 2-dimensional numerical analysis is performed, and the corresponding validation results of the simulations are presented. The effect of TI layers on the seismic performance of buildings constructed with TI layers made from these materials is assessed. A comparative analysis of various interface conditions of the TI materials under seismic loading is also conducted. Overall, this research aims to enhance the resilience and sustainability of energy-efficient homes by investigating the impact of TI layers on their seismic performance. The findings provide valuable insights for designing more robust structures that can withstand seismic events.