Back-analyses using the finite-element method were undertaken to evaluate the performance of three bi-directional pile load-tested (BPLT) drilled shafts socketed into weak rock (sandstone) for a cable-stayed bridge structure. The hardening soil (HS) model was employed to define the stress–strain relationships of the soil, rock strata and the bored pile–soil or bored pile–rock interface, using the shear modulus of the interface element Ginter, strength reduction factor Rinter and power coefficient m. Certain parameters relating to the weak rock could not be determined from the available rock quality designation and the uniaxial compressive strength. A back-analysis procedure was therefore proposed to calibrate the parameters for the corresponding rock strata by comparing the results of the finite-element analysis with those of the BPLTs. In this study, it was demonstrated that the parameters of the HS model and zero-thickness interface element could effectively capture the behaviour of soil–bored pile interaction in weak rock. The proposed parameters will subsequently be applied to the analysis of the full-scale foundation beneath the pylon of the bridge.
A methodology is presented for evaluating past and future settlements of an area where fill was placed over soft clay some time before the site development – a situation frequently encountered in engineering practice. The proposed approach integrates field and laboratory tests to assess the consolidation stage and estimate settlement development over time. The case study addresses a fill constructed to raise the grade of an area of the campus of the Federal University of Rio de Janeiro, Brazil, which was subsequently developed as a Technological Park. The company leasing the land for a 50-year period required an assessment of the magnitude and rate of settlements expected during the lease term. The testing programme was designed to be cost- and time-effective while still providing results with reasonable accuracy. The consolidation stage was evaluated using in situ pore-pressure measurements obtained with a small-diameter piezometric probe, while the clay consolidation properties were determined from laboratory tests. Established consolidation theories were used to estimate settlement development over time, considering both primary and secondary consolidation.
In this study, the vertical vibration of a single pile under construction disturbance in a transversely isotropic soil is examined. The formulation of the soil’s governing equation is based on the constitutive relations of a transversely isotropic medium, with construction-induced radial heterogeneity modelled by segmenting the soil into concentric zones. Subsequently, the shear stress exerted on the pile by the surrounding soil during vibration is calculated by recursively solving the governing equations for these zones. Furthermore, the vertical vibration equation for the viscoelastic pile is derived from the one-dimensional bar model and is solved to obtain an analytical solution for the frequency-domain response at the pile head. This result is then transformed into the time domain using inverse Fourier transformation, leading to a semi-analytical time-domain solution. The model is validated against well-known solutions to check the accuracy. Simultaneously, the investigation unveils novel aspects regarding the impact of soil transverse isotropy on pile vertical vibration characteristics under various pile parameters and construction disturbance scenarios.
Climate warming and wetting are accelerating permafrost degradation on the Qinghai-Tibet plateau, leading to widespread settlement and cracking of highway infrastructure. Significant deformation has been observed during service, even in embankments incorporating block-stone cooling layers. This study focuses on a section of the Gongyu expressway situated in a permafrost region, integrating field investigations, geological drilling and ground-penetrating radar (GPR) surveys. The results indicate that the main internal distress of the block-stone embankment includes gravel cushion detachment, infilling-induced densification of the block-stone layer, settlement deformation and loosening of rock blocks. A GPR-based porosity inversion method was further proposed to identify structural anomalies in the apparent porosity of the block-stone layer. The continuous accumulation of internal structural deterioration weakens the effective pore structure and pore connectivity of the block-stone layer, thereby reducing its cooling capacity and diminishing its cooling effect on the underlying permafrost. In addition, water accumulation along both sides of the road acts as a persistent heat source, intensifying thermal field asymmetry and accelerating the development of embankment settlement. These findings provide technical support for the rapid diagnosis of distress in block-stone embankments in permafrost regions of the Qinghai-Tibet plateau.
With rapid urbanisation in China, tunnelling near historical buildings on soft soil has grown common, yet its dynamic impact on vulnerable structures remains insufficiently investigated. In this study, a field investigation was performed into the influence of a large-diameter tunnel excavation on a 300 year old pagoda only 8.3 m away. Ground settlement, excess pore water pressure () and deep horizontal displacement were monitored during tunnelling and for 200 days afterward. Field data show that the surrounding soft soil was dynamically disturbed, primarily due to excavation activities. Specifically, slurry pressure and synchronous grouting altered the stress state within the foundation, mobilising the deformation potential of the soft soil. The synchronous grouting, a volume twice that of the over-excavated soil, raised by up to 80 kPa, causing 9 mm horizontal displacement near the tunnel bottom and 10 mm ground heave. Meanwhile, the pagoda experienced uniform uplift without significant tilting. Within 30 days after the passage of the tunnel-boring machine, however, dissipation and soil consolidation induced rapid settlement. Non-uniform distribution led to differential settlement, making the pagoda incline toward the tunnel up to 0.18 degrees. The results highlight the non-negligible delayed effects of tunnelling on historic structures, and that soft soil foundation disturbance should be minimised for protection.
A new theoretical procedure for the determination of seismic active earth pressure is developed by adopting a modified logarithmic spiral trace following a limit equilibrium-based pseudo-static approach. Explicit expressions are derived and expressed in the normalised form for the assessment of variation of parameters under the influence of wall soil backfill parameters. A detailed analysis emphasising the non-linear distribution of active earth pressure is discussed under the impact of critical and conventional directions of seismic load, prioritising discussions on the critical angle of the failure surface. A generalised moment-based equation is adopted to determine the point of application considering surcharge and cohesion under seismic effect. Seismic coefficients for active earth pressure corresponding to unit weight, surcharge and cohesion components are determined and design charts for the variation of backfill inclination and wall batter angles on the active earth pressure are demonstrated. The results obtained from the present study are found to be in good agreement with the literature studies.
The research focuses on ancient landslides in south-west China's mountainous areas, which are often overlooked due to their blending with the natural terrain. A case study from a bridge slope in Yunnan Province is used to investigate the reactivation of these landslides. This study explores the reactivation mechanisms of ancient landslides triggered by construction excavation disturbances combined with rainfall infiltration, a topic rarely examined in mountainous plateau regions. Through extensive monitoring of both surface and deep displacements during highway construction, the study reveals the dynamics of landslide resurgence. It identifies engineering excavations and pre-existing ancient sliding zones as the primary triggers for slope instability, with rainfall infiltration exacerbating the issue and causing a complex, layered sliding pattern. Numerical simulations are employed to recreate the landslide's resurgence, forecast its future behaviour and guide reinforcement strategies. This research underscores the significance of correctly identifying ancient landslides and implementing appropriate mitigation measures in construction projects, offering valuable insights for hazard management in similar geological settings.
In practical engineering, transient impact loads such as pile driving are common. In this study the dissipation mechanisms of excess pore water pressure (EPWP) in saturated sand under impact loading were investigated through integrated experimental and theoretical approaches. Controlled impact tests were conducted on one-dimensional soil columns with varying particle sizes (coarse, medium and fine) and impact amplitudes. The results revealed a two-stage dissipation process: stage I, characterised by gradual dissipation due to particle rearrangement, and stage II, marked by relatively rapid dissipation driven by drainage. The duration of stage I is strongly dependent on permeability, following fine sand > medium sand > coarse sand. A higher load amplitude notably prolonged stage I, especially in the low-permeability fine sand. A distinct ‘solidification front’ between the two stages was found to migrate linearly from the bottom to the top of the soil layer, differentiating impact loading from the non-linear migration observed under cyclic loading. Theoretically, a modified non-linear compression relationship incorporating an atmospheric pressure term (e-σ′/paα) outperformed the traditional semi-logarithmic model in simulating EPWP dissipation in sand. Experimental validation confirmed good agreement with the theoretical predictions. The findings of this work provide a predictive framework for post-liquefaction EPWP evolution, with practical implications for foundation stability assessment and liquefaction mitigation under transient impact loads.
Compacted loess samples with different dry density (ρd) and water content (w) were subjected to freeze–thaw cycles, and subsequent laboratory tests were conducted to reveal their mechanical strength degradation and internal structural evolution. Results indicate that freeze–thaw action significantly reduces the unconfined compressive strength (UCS) of compacted loess, with the UCS reduction ratio (DUCS) strongly correlated with both w and ρd. At low water content, compacted loess presents a cellular structure, where aggregates act as the primary soil skeleton and are highly sensitive to freeze–thaw damage. During the freeze–thaw process, the water within aggregates freezes into ice, destroying this metastable structure and leading to a high DUCS. As water content increases, a more uniform and stable soil skeleton forms, showing lower freeze–thaw sensitivity and thus a lower DUCS. At a given water content, the water-filled pore volume remains nearly unchanged, while the total pore volume decreases with increasing dry density. This increases the ice volume ratio in the total pores during freezing, causing more severe structural damage and a higher DUCS. For loess subgrade in seasonal frozen regions, within allowable ρd and w ranges, relatively lower dry density and higher water content are recommended to alleviate freeze–thaw-induced subgrade deterioration.
Particle sensors can be used to obtain particle movement characteristics of a ballast bed, providing a particle-scale measure for assessing the state of the ballast bed. The sensor size, shape and wire fetter may have impacts on the applicable scenarios, measured results and subsequent analysis process. This paper conducts laboratory tests and discrete-element method () simulation to preliminarily discuss the influence of the particle sensor's configuration when obtaining details of ballast particles' motion. According to laboratory test results, particle motions from cubic sensors with two edge lengths show different magnitudes, where the influence of ballast packing is not effectively excluded. Hence, simulation is employed to systematically investigate the influences of sensor size and shape (regular polyhedrons) on particle motion. The results indicate that for cubic particle sensors, the acceleration shows a decreasing trend with increasing sensor size. Moreover, the z-angular acceleration decreases first and then stabilises, with 40 mm as the boundary point. The change of sensor shape leads to significant fluctuations in the angular acceleration. The impact of wire fetter on particle motion characteristics is obtained from laboratory tests. It is seen that particle motion characteristics from wireless particle sensors show similar variation tendencies and magnitudes, while the magnitudes of particle acceleration in three directions from wired particle sensors are quite different.
Temporary control of groundwater is required for excavations, tunnels or shafts that extend below groundwater level. It is typically needed early in the construction programme and any shortcomings in the groundwater control strategy will likely lead to delay, cost overrun and occasionally catastrophic failure. In appropriate hydrogeological settings, pumped groundwater-control strategies offer a relatively quick, low-cost and low carbon dioxide footprint solution. The variety of techniques and construction methodology and the very wide range of hydrogeological settings mean that the design of pumped groundwater-control (dewatering) systems is not readily codified. Also, pumped groundwater-control systems and other groundwater control strategies are increasingly subject to environmental regulation and legislative oversight. This had led to reliance on experienced specialist contractors, designers and operatives to deliver groundwater control services. However, there remains a need for general construction practitioners to have access to up-to-date information on the range of strategies available together with their attributes, limits of application and associated risks. This paper uses recent experience to review and update existing guidance on the application of pumped groundwater-control systems in a variety of hydrogeological settings.
Impact rock-breaking technology is widely used in drilling due to its high-energy transient nature and strong formation adaptability. Its core mechanism lies in rock damage caused by stress waves from the impact tool, making the study of this process essential. This research establishes a three-dimensional finite-element model of the impact system, incorporating stress wave propagation, rock constitutive relations and strain rate effects to simulate rock breaking. Results show that increasing stress wave amplitude (150-270 MPa) and duration (0.08-0.4 ms) improves rock fragmentation, with maximum energy transfer efficiency exceeding 60%. Below 210 MPa, elastic deformation dominates and specific energy increases; above 210 MPa, stress wave superposition and strain rate effects promote brittle failure, reducing specific energy. Longer durations lower the specific energy, stabilising near 16 MPa after 0.2 ms - below the 20 MPa from amplitude effects. Square waves break rock more effectively than triangular or sinusoidal ones but have lower energy efficiency (52.2% as opposed to 56.6%) due to elastic rebound from instantaneous loading. Square and triangular waves create larger fracture volumes but require higher energy, resulting in greater specific energy. These findings offer guidance for optimising impactor parameters and improving rock-breaking efficiency in deep, hard formations.
The main aim of this research is to investigate and analyse the non-linear behaviour of a single pile and pile groups with rigid pile caps subjected to torsional loading in clay soil. Plaxis 3D software is utilised, considering pile groups (1 & times; 2, 2 & times; 2, 3 & times; 2 and 3 & times; 3), different L/d ratios (L/d = 20, 30 and 50), spacing (S/d = 3, 4 and 6), depth of embedment (f/t = 1, 0.5 and 0), diameter (d = 0.76 m, 1.5 m and 2 m) and clay soil consistency (soft and stiff). The applied torque is found to be mainly resisted by the lateral and torsional resistances of each pile in a pile group, and quantitative evaluation of their contributions is conducted. From the numerical results, it is found that the failure torque of a single pile increases with pile length (57-257%), pile diameter (198-388%) and the depth of embedment of piles (6-206%). The torsional resistance of the groups increases with the pile length (7-22.5%), pile spacing (68-228%), pile diameter (176-281%), the depth of the embedment of piles (10-43%) and soil consistency (soft to stiff), but the torsional contribution decreases as the group size and spacing increases.
Expansive soils exhibit poor engineering performance and substantial swelling potential. Therefore, stabilisation is crucial to mitigate geological hazards triggered by exposure to moisture or load changes. In this study, the effects of mixture ratio, curing time and curing temperature on the properties of cement-treated expansive soil were investigated. Specifically, soil specimens containing 0, 5, 10 and 15% cement were cured for 1, 7, 14 and 28 days at 20, 40 and 60°C, then evaluated for compaction and unconfined compressive strength. Furthermore, chemical and microstructural changes were analysed by way of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The findings indicate that increasing cement content non-linearly enhances soil properties. In addition, SEM and XRD analyses confirm that hydration and pozzolanic products effectively fill voids and strengthen particle bonds. The reaction is rapid for the first 7 days, then stabilises, with higher temperatures increasing the rate. Moreover, a refined model was developed to unify key curing parameters and address oversimplified linear cement-strength relationships prevalent in the existing literature. The model's results show strong agreement with the empirical findings (R2=0.97). Collectively, these findings offer a comprehensive insight into the cement stabilisation of expansive soil across diverse curing conditions and establish a robust framework for predicting strength development.
An asphalt concrete core wall is placed between transition layers of asphalt concrete core rockfill dam. The interface between the core wall and the transition layer is subjected to shear action due to lateral soil pressure, water load and varying material properties, which threaten the safety of the core wall. In this paper, the influence of the fine particle content in the transition layer on the shear behaviour of the interface is investigated. A series of shear tests is conducted on the interface between the asphalt concrete and the transition layer of coarse-grained soil under conditions of three fines contents, three shear rates and five normal stress levels. The shear behaviour and shear mechanism of the interface are analysed. The influence of fine particle content on the shear behaviour is discussed. A nuclear magnetic resonance imaging system is used to detect the pore distribution of an asphalt concrete sample after the shear action. Furthermore, a high-pressure permeability test is conducted to study the impact of shear action on asphalt concrete impermeability. The results indicate that shear stress and normal displacement of the interface increase with the fine particle content. The porosity and permeability of asphalt concrete after shear action increases with the decrease of fine particle content. Shear action would not significantly affect the anti-seepage performance of the asphalt concrete.
In the present paper, an analysis is performed on the movements undergone by some residential buildings in 1983, during their construction. A common feature of these buildings is an asymmetric superstructure that makes the vertical loads acting on the foundations highly eccentric. A sloping ground surface and a complex subsoil condition, characterised by the presence of strongly inclined layers of compressible soils, were other predisposing factors for the observed movements. The buildings underwent a significant rigid rotation (tilt) to the extent that their serviceability was compromised because of the resulting floor inclination. As a consequence, construction was suspended and a subsurface investigation consisting of boreholes, cone penetration tests and conventional laboratory tests was performed. In addition, the vertical displacement of some representative points of the building foundations was measured during a period of about 1 year. A finite-element analysis of the building displacements is carried out in the present study to highlight the different roles played by load eccentricity, soil layering and a sloping ground surface in causing the observed building movements. To restore the serviceability of the buildings, their foundations were underpinned with micropiles, some of which were pre-stressed. The effectiveness of this measure is also analysed.
An important factor to consider in geotechnical engineering is the site and the variability of its mechanical properties. In situ tests are interesting investigation techniques as they do not require soil sampling. Brazilian standards consider a minimum number of in situ tests for geotechnical projects; however, this number is not always sufficient to be representative of the study site. The geotechnical variability of a tropical soil site was evaluated based on the dynamic probing light (DPL), a simple and easy to use in situ test. The statistical analysis showed that the variability associated with the DPL data is epistemic; it could be reduced by increasing the number of tests. In this study it was found that the number of tests should be at least eight. As a way to understand the effect of site variability in geotechnical design, a probabilistic analysis using the first-order reliability method was used to evaluate the probability of the prediction of bearing capacity being against safety (P-p.a.s.) for a typical pounded pile. Bearing capacity and the P-p.a.s. showed the same trend as the resistance indexes, with the formation of a plateau after the eight tests.
