Abstract: To investigate the seismic performance of a wind turbine that is influenced by both the ice load and the seismic load, the research proposes a numerical approach for simulating the seismic behavior...

Abstract: Laboratory Directed Research and Development program of Los Alamos National Laboratory [20170103DR]; LANL Applied Machine Learning Summer Research Fellowship; National Science FoundationNational Science Foundation (NSF) [1855651]

Abstract: In the recent times, many studies have been devoted toward rectangular excavations but only a few studies have considered the “corner effect” in the optimized design of soil nail wall-retaining pile-anchor cable supporting systems, especially in large-scale deep foundation pit environments excavated by the central-island technique. Corner effect not only increases the construction costs but also may pose a risk to the safety and stability of such pits. In this paper, changes in the lateral displacement of retaining pile, soil at 1 m away from the foundation pit, crown beam, and the settlement of ground surface and surrounding buildings were extensively investigated based on the field measurements and numerical simulations of a large-scale deep foundation pit in Gaoxin zone, Xi’an, China. In addition, the supporting structure was optimized by considering the lateral influence zone of the corner effect. The optimization scheme proposed in this study not only satisfies the safety requirements of foundation pit supports, but also reduces the construction costs.

Abstract: Centrifuge modeling was used to study the performance of loose sand treated with microbial-induced calcium carbonate precipitation (MICP) to improve liquefaction resistance to triggering an...

Abstract: Geocells are three-dimensional cellular expandable mats used to improve the load-carrying capacity of weak subgrades. The expanded geocell pockets take the shape of a honeycomb connected to their n...

Abstract: The monopile is the most common form of foundation employed in offshore wind turbines. These foundations are subjected to millions of repeated load cycles, owing to wind and wave action. I...

Abstract: Water is one of the major risk sources in the excavation of deep-large foundation pits in a water-rich area. The presence of intrusive broken diorite porphyrite in the stratum aggravates the risk level of deep foundation pits. Based on a geological survey report and design documents of parameter information, MIDAS/GTS software was used to perform the numerical simulation of an engineering example of a deep foundation pit project of ultradeep and water-rich intrusion into the broken rock station of subway line 4 in a city. The simulation results show the characteristics of seepage path evolution, seepage aggregation areas and points, and the effect of seepage on the deformation of a deep foundation pit during the whole construction of this deep foundation pit. The results show that with the precipitation-excavation of the deep foundation pit, the pore water pressure at the bottom of the foundation pit follows a distribution of three “concave” shapes. High-permeability pressure zones are found around the foundation pit, intruding broken diorite porphyrite zones, and middle coarse sand zones. With further excavation of the foundation pit, the seepage pressure in the middle part of the foundation pit gradually decreases, and the two “concave” distributions in the middle gradually merge together. After excavation to the bottom of the pit, the pore water pressure at the bottom is distributed in two asymmetrical “concave” shapes, and the maximum peak of pore water pressure is found at the intrusion of fractured porphyrites prone to water inrush. The four corners of the foundation pit are prone to form seepage accumulation zones; therefore, suffosion and piping zones are formed. The surface settlement caused by excavation is found to be the largest along the longitudinal axis of the deep foundation pit, whereas the largest deformation is found near the foundation pit side in the horizontal axis direction of the foundation pit. With the excavation of the deep foundation pit, the diaphragm wall converges to the foundation pit with the maximum deformation reaching about 25 mm. After the first precipitation-excavation of the deep foundation pit to the silty clay and the bottom of the pit with the largest uplift, with further precipitation-excavation of the deep foundation pit, the uplift at the bottom of the deep foundation pit changes only slightly.

Abstract: The rigid pile composite foundation is widely used in highway projects in soft soil area as it can effectively increase the bearing capacity and stability of the foundation. While the research on the behavior and failure mode of rigid pile composite foundation under embankment is not enough, instability failure of rigid pile composite foundation often occurs in practical projects. This paper presents a centrifuge model test to investigate the load transfer mechanism, settlement characteristic and failure mode of rigid pile composite foundation under embankment. The test results show that: the soil displacement of different region in rigid pile composite foundation was different, obvious vertical displacement occurred in the soil under the center of embankment and the horizontal displacement was very small in this region; both vertical and horizontal displacement occurred in the soil under the shoulder of embankment; and obvious horizontal displacement occurred in the soil under the slope toe of embankment; moreover, ground heave also occurred near the slope toe of embankment. The soil displacement in rigid pile composite foundation had a large influence on the stress characteristic and failure mode of rigid piles, the compressive failure and bending failure would probably occur for the piles under the center and shoulder of the embankment, respectively, and the tension-bending failure would probably occur for the piles under the slope toe of embankment. The different failure modes of piles at different regions should be considered in the design of rigid pile composite foundation under embankment. The test results can be used to improve the design method for rigid pile composite foundation under embankment in practical projects.

Abstract: Foundation pit engineering has been developing rapidly with the challenges associated with modern urbanization. As a result, deep excavations can now be performed at the heart of coastal metropolises with dense existing structures and adverse soil and hydraulic conditions. On the other hand, foundation engineering is challenged with sustainability and economic viability such that cost-effectiveness is a key factor provided that the robustness and safety requirements are fully satisfied. This paper presents the design of the retaining system for a deep foundation excavation that is located in a second-tier inland city with less crowed existing structures and good soil and hydraulic conditions. This is representative of the current trend of the suburban development of major cities and the development of below first-tier cities, as a response to the saturating of the major cities. Different designs are reviewed for this case in order to strike the balance between structural capability and cost-effectiveness. The analysis indicates that a hybrid solution is particularly suitable for such type of construction. Specifically, results show that the maximum displacement, bending moment, and shear force in the pit can be reduced by over 50%, 40%, and 30%, respectively, by the combination of soil nailing wall and pile anchor compared with a single support solution. And for the combination of non-prestressed anchor bolts and prestressed anchor cables can effectively save the cost while improving the safety factor of foundation pit during excavation. The findings are instructive to similar projects with cost-effectiveness as a major factor.

Abstract: This study aimed to illustrate the seismic response and instability process of a double-row anti-slide pile-reinforced bridge foundation and gravel landslide. Selecting the gravel slope of Jiuzhai Valley along the under-construction Chengdu-Lanzhou high-speed railway as the site prototype, large-scale shaking table tests were first conducted at a similitude ratio of 1:70, with sine waves and El Centro waves as the seismic wave inputs. The amplitudes of the input seismic waves were increased, while the acceleration, dynamic earth pressure, and strain distribution were monitored in the gravel landslide. The dynamic response patterns of anti-slide pile-reinforced bridge foundations in gravel landslides were illustrated. The front-row and back-row anti-slide piles should be a reasonable distance from the bridge foundation. The response acceleration manifested an elevation amplification effect with an increasing elevation in the slope behind the anti-slide piles. Back-row anti-slide piles reinforcing the bridge foundation can reduce the effect of landslide thrust on the bridge foundation and maintain a uniform distribution of earth pressure behind the bridge foundation, mitigating seismic effects. The dynamic earth pressure peaked at the top of the bridge foundation and then decreased along the depth. The back-row anti-slide piles displayed greater resonance coupling and unloading effects before and after reaching the load-carrying limit, respectively. In seismic strengthening design involving bridge foundations and gravel landslides, when the earthquake-induced resonance coupling effect on inclined, loosely packed land masses is fully considered, pre-reinforcement measures (e.g., high-pressure grouting and anchor spraying) should be carried out on the gravel slopes.

Abstract: There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits.

Abstract: Monopiles are widely used as the foundation to support offshore wind turbines (OWTs). The response of monopile-supported OWTs is strongly affected by the natural frequency of the system rel...

Abstract: In this paper, the influence of the foundation configuration (raft or separate footings) on tunnel–soil–framed building interaction is investigated using geotechnical centrifuge testing Tunnelling

Abstract: The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations.

Abstract: Rigid piles are extensively used to support high-speed railway embankments resting on soft ground, and ground beams are structural elements at ground level to connect adjacent pile caps to improve the stability of pile-supported embankments. In this study, a validated three-dimensional numerical model of piled embankment was developed based on a well-documented centrifuge test, where the Mohr–Coulomb tension crack model was adopted for capturing the brittle failure behavior of concrete piles. The results showed that concrete piles are subject to a serious bending failure within the clay layer when the overlying embankment collapses. By introducing the ground beams in conjunction with rigid piles, the resultant displacement of the improved area was markedly decreased and the pile failure mode was changed. The combination of concrete piles and ground beams results in a synergistic effect. According to the mechanical response of individual piles, the foundation soil was divided into the extension-bending, bending, bending-compression, and compression zones to elucidate the reinforcement mechanism related to ground beams. A proper arrangement of ground beams was ultimately obtained based on the localized slip resistance performance of the improved ground. Overall, this research contributes to the knowledge of piled embankment performance evaluation and may further extend the practical application of ground beams.

Abstract: With the offshore wind industry rapidly expanding worldwide, geotechnical research is being devoted to foundation optimisation – most intensively for large-diameter monopiles. The analysis and desi...