Performances of a large-scale deep excavation with multi-support types and zoned excavation technique in Shanghai soft soil Yingjie Jing, Lin Li, Jingpei Li, Haohua Chen Canadian Geotechnical Journal, 2025 This paper presents a comprehensive field investigation on a large-scale deep basement excavation in Shanghai soft soil propped by a multi-support system. Because of its large size, irregular shape, and different excavation depths, the excavation site was divided into Zone A and Zone B to optimize the construction process and improve the construction efficiency. The excavation was constructed using the “bottom-up” method following the principles of stratification and zone excavation. A notable innovation in this project is the implementation of three different support subsystems as a multi-support system to accommodate different deformation requirements in different areas. The excavation was densely instrumented to monitor the behaviors of retaining walls, columns, axial forces of struts, and surrounding ground throughout the whole construction process. The wall deformation and ground surface settlement of the three support subsystems are comprehensively compared to investigate the performances of the three support subsystems. The comparison of the corner-effect envelope summarized from nine reported cases indicates that the multi-support system can effectively alleviate the spatial corner effects of the excavation. The zoned construction technique in conjunction with the multi-support system presented in this case study provides an efficient and economic approach for large-scale deep excavation in soft soils.
Analytical and Numerical Investigations on the Failure Mode of 3D Concrete Printed Gravity Anchor Yu Lu, Haohua Chen, Ingrid Tomac, John S. McCartney Geotechnical Special Publication, 2025 Gravity anchors leverage sliding and passive bearing resistance to provide cost-effective anchorage for floating photovoltaic systems installed in lakes or shallow marine environments. In this study, analytical and finite element methods were employed to simulate the pullout loading capacity of circular-truncated conical gravity anchors in marine clay layers. Mooring loads were applied to the anchor padeye at various angles from horizontal, ranging from 0° to 70°. Results indicate that sliding primarily affects the anchor system at small mooring angles, while overturning becomes dominant at larger angles. Anchor efficiency demonstrates a non-linear relationship with increasing mooring angle with the optimal mooring angle of 45° for the circular anchor. This analysis provides insights into the failure behavior of gravity anchors, offering valuable information on the optimal mooring line configuration for anchoring floating photovoltaics.
Feasibility of coaxial deep borehole heat exchangers in southern California Haohua Chen, Ingrid Tomac Geothermal Energy, 2024 This paper investigates the feasibility of coaxial deep borehole heat exchanger (CDBHE) applications to the University of California San Diego (UCSD) campus. By collecting different geophysical source data for various formations and well logs around the UCSD campus, a multilayered thermophysical model for the ground on the site is established. Water circulation within a closed coaxial loop system considers the geothermal energy extraction under uncertainty consideration of the unknown deeper layers heat flow gradient as coupled with the variation of pipe insulation properties, flow rates, outer pipe diameter, grout, and depths between 1 and 4 km. A finite-element framework models the Navier–Stokes fluid flow and heat transfer in the CDBHE system, validated with a field test on CDBHE from the literature. Results show that a 4-km CDBHE could produce a thermal power of 600 kW under the optimum geological conditions at the UCSD site: the water flow rate of 2.78 L/s and a ground thermal gradient of 60 ℃/km. Thermal power shares from different layers indicate that deeper formation layers contribute more to the thermal power than the shallower layers because increasing the CDBHE length from 1 to 4 km can lead to a maximum of 900% increase in thermal power and a 50% expansion in thermal plume for a CDBHE with an insulated inner pipe between the upper and lower bound heat flow bounds. An inner pipe with an insulated depth of 2 km produces only 1–6% less power than a fully insulated inner pipe for the 4-km CDBHE, and thus, a partially insulated vacuum-insulated tube (VIT)-plastic inner pipe is suggested as the best practice. Furthermore, the CDBHE thermal power increases by 5% when the grout thermal conductivity increases from 1 to 3.65 W/(K∙m), close to the formation thermal conductivity, and then maintains almost the same, and the 4-km CDBHE with flow rates of 2.78–6.94 L/s at the UCSD site can directly supply a low-temperature heating radiator system for room heating. This study suggests practical ranges for geothermal energy extraction for southern California. A CDBHE with a well-insulated inner pipe of 0.05 W/(m∙K), the thermal power of lower and upper-bound heat flow cases can vary by 60% from the mean. Finally, water as the working fluid is more efficient than CO2, doubling CDBHE's thermal power. The effects of the investigated factors provide guidelines for future geothermal resource exploitation in southern California.
Analytical and numerical investigation of gravity anchors for floating photovoltaic systems Yu Lu, Haohua Chen, Ingrid Tomac, John S. McCartney Ocean Engineering, 2024 Gravity anchors are a widely used anchoring solution for floating photovoltaic systems but can be costly and difficult to transport and install. To address this issue, 3D printed concrete gravity anchors can be fabricated offsite into a custom shape that optimizes the bearing resistance then filled with ballast onsite. This study evaluates the performance of gravity anchors with novel geometries enabled by 3D printing in representative sandy (drained) and clayey (undrained) soil layers for mooring angles ranging from 0 to 70°. The failure modes of gravity anchors were explored using numerical simulations with the goal of validating simpler analytical methods suitable for design. Results indicate that sliding primarily affects anchor efficiency (pullout capacity divided by buoyant weight) at small mooring angles, while overturning and plowing become dominant at larger mooring angles. Greater anchor efficiency is gained when using a skirt to enhance the passive bearing resistance, but difficulties may arise in the penetration of the skirt into sand. A C-shaped anchor with a padeye close to the center of gravity promoted plowing at high mooring angles. Analytical models are suitable fat lower mooring angles, but numerical simulations are recommended when evaluating anchor performance at mooring angles greater than 30°. • 3D concrete printing technology enables different anchor shapes to be created. • Analytical models for gravity anchor pullout only useful at low mooring angles. • Use of a skirt increases pullout capacity in clay but is difficult to install in sand. • Gravity anchors with a padeye location close to the center of gravity are ideal.
Semi-analytical solution for ultimate bearing capacity of smooth and rough circular foundations on rock considering three-dimensional strength Haohua Chen, Hehua Zhu, Lianyang Zhang International Journal for Numerical and Analytical Methods in Geomechanics, 2024 This paper proposes a semi‐analytical solution for the ultimate bearing capacity qu of both smooth and rough circular shallow foundations on rock mass. Specifically, a three‐dimensional (3D) Hoek–Brown (HB) is adopted, in conjunction with equilibrium equations under axisymmetric conditions, to derive the governing equations. The method of characteristics is utilized to solve the stress and failure characteristics mesh to determine the qu. The proposed solution is verified by using it to analyze test foundations. Comparison with an HB criterion‐based solution is performed to highlight the importance of 3D strength. Furthermore, parametric studies are performed to investigate the effects of rock mass properties (intact rock constant , geological strength index GSI, intact rock unconfined compressive strength σc) and foundation diameter (B) on the qu, failure surface size, and vertical stress distribution on the foundation base. The results indicate that ignoring the 3D strength and the rock mass weight would lead to underestimation of qu. Besides, the ultimate bearing capacity factor (ratio of qu to σc) increases with , GSI and B but decreases with . The failure surface size is significantly affected by , GSI, B, and rock mass unit weight. The stress distribution on the foundation base has higher variance (higher possibility of stress concentration) at smaller , GSI, and larger B, rock mass unit weight.
Three-Dimensional Analyses of Long-Term Settlement of Storage Tanks Supported by a Large Piled-Raft Foundation System Haohua Chen, Jianmin Hu, Lianyang Zhang Journal of Geotechnical and Geoenvironmental Engineering, 2024 Interactions between adjacent piled-raft foundations may induce additional settlement and cause the tilt of the structure. This case study investigates the long-term performance of a large piled-raft foundation system supporting high and heavy alumina solution storage tanks based on field measurements and three-dimensional (3D) numerical simulations. To properly consider the interactions among rafts, piles, and soils; the elastoplastic behavior of clayey and sandy soils; and the consolidation behavior of soil after construction, a 3D finite-difference code was utilized for the numerical modeling. Two undrained mechanical analyses were conducted to simulate the installation of foundations/tanks and the filling of alumina solution into the tanks, while two coupled hydromechanical analyses were performed to model the period between the two undrained stages and the stage after tank filling, respectively. The predictive capability of the numerical model was checked by comparing the simulation results first with single pile load test data and then with in situ settlement measurements at different locations of the piled-raft foundations. The long-term behavior of the piled-raft foundations was further investigated by analyzing various aspects including the axial force variation along the pile at different locations, the time-settlement relation at monitoring locations, the vertical effective stress increment and displacement of soil, and the differential settlement between monitoring locations. Based on the simulations, the tilt of the platform was mainly due to the superposition of additional stresses near the centerline of the two rows of piled-raft foundations. Finally, parametric studies were conducted to investigate the interactions among the piled-raft foundations at different pile length configurations. The results show that by properly increasing the length of the piles near the centerline of the two rows of piled-raft foundations, the differential settlement of the platforms can be mitigated.
