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Due to the unclear mechanisms behind tunneling-induced deformation of pile-raft foundations, there are strict global restrictions on tunneling beneath embankments of high-speed railways. This study conducted a series of two-dimensional tunneling model tests to investigate the tunneling-induced deformation characteristics and mechanisms of pile-raft foundations. Soil displacement field and pile settlement were measured using particle image velocimetry and displacement transducers. The changes in soil displacement and the flexure of the pile-raft foundation in response to varying tunnel-pile distances, ground surface loads, and tunnel volume loss were analyzed. The results indicate that the tunneling-disturbed zone can be categorized into a loosened zone and an arch zone as identified by the propagation and separation of shear bands, with significant soil settlement occurring in the loosened zone. The maximum settlement of piles in a pile-raft foundation is greater than that in greenfield due to the larger loosened zone. However, the settlement width at the ground surface in pile-raft foundations is reduced due to the blocking effect of the piles. According to the relative position between the piles and the formed arch structure, three patterns of tunneling-ground-pile systems can be identified. As the tunnel-pile distance increases, the maximum settlement of the piles decreases. Increasing surface loads hardly affects the maximum settlement value of the pile, while the tunneling-induced arch zone expands significantly. This study provides a fundamental understanding of pile settlement behavior for tunneling beneath the pile-raft foundations of high-speed railways.

Combined Pile-Raft Foundations (CPRF) are widely employed to mitigate vertical settlement in building and engineering structures. For structures resting on cohesive and organic soils, understanding the time required for complete stabilization of settlement is crucial. The total settlement involves instantaneous settlement (elastic ground deformation), consolidation settlement (water squeezing from pore space), and secondary settlement (structural changes in the ground skeleton, known as secondary consolidation or soil creep). Urban expansion, notably in cities like Warsaw, compels developers to construct in previously overlooked areas, potentially containing organic carbonate sediments like gyttja and chalk. Buildings on such organic soils often settle due to gyttja consolidation during construction and operation. Analyzing long-term settlement, especially of CPRF on reconsolidated organic soils, becomes paramount. Model tests on a laboratory scale offer a cost-effective alternative to large-scale tests, providing quantitative insights into CPRF settlement reduction through piles. This study presents results from model tests conducted on natural organic soils, enabling the prediction of CPRF settlement solely based on gyttja’s geotechnical parameters.

The piled raft foundation (PRF) combines the bearing capacities of piles, rafts, and soil into a composite structure. This study evaluated the performance of different piled raft configurations, including unpiled raft (UPR), disconnected piled raft (DPR), vertical piled raft (VPR), and battered piled raft (BPR), on granular soils. The experiments were conducted across varying soil densities, from loose to dense. The results reveal that the BPR configuration exhibited the highest load-bearing capacity among all systems. BPR outperformed VPR by 11.5% in dense soil and 23.3% in loose soil. Furthermore, the bearing capacities of UPR, DPR, VPR, and BPR increased by 328.6%, 722.3%, 502.7%, and 442.6%, respectively, in dense soil compared to loose soil. Connected piled rafts (CPR) further enhanced load distribution and stability, achieving a 6.1% higher load-bearing capacity in dense soils and 15.9% in loose soils compared to DPR. The analysis of axial load and skin friction distribution along pile length indicated that BPR systems provided the best resistance against both vertical and lateral loads, leading to reduced settlement and improved load transfer efficiency. Overall, the BPR system demonstrated optimal performance across varied soil conditions, while CPR configurations improved settlement control and load distribution.

The construction industry is a significant contributor to global carbon emissions, particularly raft foundations which are a major source of stored carbon. This research investigates methods to optimize raft foundation design to reduce carbon footprint. This study quantifies the impact of design and material selection on carbon emissions by exploring the changes in raft foundation design and concrete quality. The results indicated that higher concrete grades and increased foundation thickness led to a significant increase in embodied carbon. This is due to the increased use of cement and reinforcing steel, which have high carbon factors. Parametric design techniques, including the optimization of reinforcement spacing and material usage, can reduce carbon emissions. These findings highlight the importance of efficient design for achieving sustainable construction practices while maintaining structural integrity.

Piled raft foundations are a popular solution for supporting heavy structures on weak soils, but their design and analysis can be complex due to interaction among the raft, piles and subsoil underneath. The present study utilises finite element method to analyse the parametric dependence of ratio of average settlement (λ avg ), ratio of differential settlement (λ diff ), ratio of shear force (SFR), ratio of bending moment (BMR) and ratio of load-sharing (χ pr ), for square raft with underneath connecting circular cross section piles for uniformly distributed surcharge all over the top surface of raft. The parameters varied are spacing to diameter ratio (S/D) of 2-20, diameter of piles (D) of 0.4 m-1.6 m, length to diameter ratio (L/D) of 8, 12 and 16, pile group to width of raft ratio (W g /W r ) of 0.15-0.9 and raft-soil stiffness (K rs ) of 0.069, 0.558 and 1.88 corresponding to raft thickness (t r ) of 0.5 m, 1.0 m and 1.5 m respectively. The results of the present study depicts that the minimum values of λ avg and λ avg are observed at S/D ratio of 5 (approx.), lower K rs and larger W g /W r . To enhance χ pr , smaller pile spacing (S) and larger pile length (L) are needed. Minimum SFR and BMR are achieved at lower and larger L/D ratios, respectively. The findings can be used to guide the design and analysis of pile raft foundations for a variety of applications, including high-rise buildings, bridges, and industrial structures.

This paper develops a simplified calculation method for evaluating the horizontal dynamic impedance of a piled raft foundation on a layered soil medium. The proposed method combines a model of wave propagation that considers the reflection and refraction phenomena at the layer boundaries and a calculation method for estimating the dynamic impedance of a piled raft foundation on homogeneous soil. Numerical analyses of a piled raft foundation on layered soil subjected to harmonic horizontal loading are performed to investigate the effect of soil stratification on the frequency-dependent characteristics of dynamic impedance. The results show that the initial phase angle of propagating waves in layered soil related to the dynamic impedance of the piled raft foundation is slightly smaller than that for a spread foundation. Based on the analysis results, the calculation model is developed for the propagating waves that re-enter the foundation through reflection and refraction phenomena at the layer boundaries.

The paper proposes existing calculation methods and new designs of high-performance solid raft foundations with symmetric and non-symmetric cutouts (non-contact areas in the middle) in the bottoms for lightweight tower-type structures such as wind turbines, tower cranes, telecommunications aerials and others that are capable of taking significant eccentric loads with observance of the edge pressures on the soil base. An example of calculation for various alternate designs of tower crane foundations has been given, which shows the advantages of using foundations with a cutout in the bottom, ultimately leading to a significant saving in concrete consumption (over 50%) for the foundation depending on the design load on the soil base and its bearing capacity.

Connected and disconnected piled raft foundations have been evaluated under lateral cyclic loading in this study. Connected Piled Raft (CPR) and nonconnected piled (NPR) foundations were considered and evaluated in 1-g shaking table tests. FEM numerical modelling also was employed to evaluate the results. The responses were evaluated and compared using lateral movement of caps, moments and lateral loads along the piles and ground settlements. The results indicate that both nonconnected and connected piled raft foundations effectively reduce the ground settlements, however, connected piled rafts have much higher lateral stiffness and piles contribute to lateral load bearing mechanism more effectively; in connected piled raft, piles bear higher moments and lateral loads and reduce lateral movements more effectively. The cap weight and superstructure (central mass height) effect has been considered through supplementary numerical assessments for CPR case. Superstructure addition tends to increase the pile moment and raft inclination where the frequency effect is also critically important. Also heavier cap experiences higher rotations and associated with higher induced loads to piles.

Research on the development of prefabricated foundations has been quite extensive to date, while studies on prefabricated concrete raft foundations and their connection methods remain relatively scarce. This study proposes a novel type of prefabricated raft foundation and its corresponding grouted plug-in connection. The connection comprises two prefabricated units and achieves connection via steel inserts and grouting in pre-slots, possessing numerous advantages such as convenient construction, fast installation, and high construction quality. To verify the performance of the connection node and the bearing capacity of the foundation, based on the engineering practice of prefabricated raft foundations, this study fabricated a full-scale specimen composed of three prefabricated units of the raft foundation, conducted a stacking load test on it, and carried out finite element analysis afterwards. The main conclusion is that severe flexural failure occurred near the grouted plug-in connection of the prefabricated units when the specimen failed, implying that the node region has sufficient bearing capacity. The ultimate bending moments of the specimen obtained from the experiment and finite element analysis are 736.5 kN·m and 859.5·kN m, respectively, with a difference of 14%, indicating a good agreement between them. Ignoring the effect of the upper steel reinforcements, the calculated section bending capacity of the prefabricated unit is 892.8·kN m; the ultimate bending moment of the test specimen reached 0.83 of the section bending capacity of the prefabricated unit, indicating that the proposed raft foundation and its connection method have good bending bearing capacity.

Piled raft foundations are a reliable solution for improving load distribution and minimizing settlement, particularly in soils where shallow foundations are inadequate. This study focuses on the performance of floating piled raft systems in sandy soils, where controlling settlement is critical. A calibrated three-dimensional finite element (FE) model was developed and validated using experimental load–settlement data to investigate the effect of key parameters, including the number of the pile and the stiffness of the piled-raft foundations. The results show that an optimal configuration of 10 piles achieves a balanced load-sharing ratio of approximately 50% between the raft and piles, which effectively minimizes the settlement without any unnecessary structural redundancy. Beyond this point, additional piles reduce settlement by only 3–5%. The stress distribution analysis highlights the importance of raft–soil interactions, while parametric studies demonstrate how pile numbering and piled-raft stiffness affect the performance of the foundations. This research reinforces the value of numerical modeling as a predictive tool and offers practical design recommendations for cost-effective and sustainable foundation systems in sandy ground conditions.