Pile Arrangement Research Articles

Performance of isolation piles in protecting subway tunnels adjacent to foundation pits: Experimental and numerical investigations

Laboratory model tests and numerical simulations were conducted to investigate the control effect of different arrangements of isolation piles on the additional deformation and stress of tunnels adjacent to pit excavation. Four different arrangements of isolation piles were discussed in this work: arched, curved, double-row, and single-row. The results indicated that considering the burial depth, the four arrangements of isolation piles had significant control effects on the horizontal and vertical deformation, as well as the bending moment of the tunnel. Among them, arch-shaped isolation piles have better isolation effects than other types discussed in this work. Subsequently, taking the arch-shaped isolation piles as an example, the effects of the burial depth, pile position, height-span ratio, and the optimal buried depth of the arch-shaped isolation piles on the tunnel were investigated. The arch-shaped isolation piles have a critical height-span ratio of 0.123, and the closer to the tunnel, the better the protective effect on the tunnel. The optimized embedding depth of isolation piles depends on the depth of the tunnel and the relative position to the foundation pit. The results of this study have great guiding significance for the design of isolation piles to protect adjacent tunnels near excavations.

Analysis of hydrodynamic behavior in response to diverse pile arrangements adjacent to an impermeable dike

ABSTRACT Intense energy flow near the dike head significantly influences the development of the dike field zone (DFZ), momentum exchange zone (MEZ), and mainstream zone (MSZ), leading to potential partial or full failure of the dike in the MEZ. To address this, laboratory experiments were conducted to observe flow changes and rate of energy reduction around a single impermeable dike, with alterations made to the pile group length (HL: half-length = 11.5 cm and FL: full length = 23 cm), location (U: upstream, D: downstream), and shape (C: Circular, DV: Delta Van, ST: Streamlined tapered, APF: Angled Plate footing). Modifications in the MEZ flow structure were studied to mitigate concerns about intense energy vortices and dike head flows. These piles helped to assess factors like flow deflection, backwater rise, energy reduction rate, velocity fluctuations, and discharge distribution percentages across the zones. The data revealed that when the pile group length was increased from HL to FL, there was an inverse effect on depth-averaged velocity, MEZ discharge distribution percentage, and flow deflection toward the DFZ. Conversely, there was a direct influence on the rise in backwaters, rate of energy reduction, and discharge distribution percentages in the DFZ. The U-FL-APF pile dike showcased optimal results, displaying a reduction in maximum energy by 52% and streamwise velocity by 96%, while also increasing the backwater rise and discharge distribution by 22% and of only 5% in the MEZ, respectively, compared to a single impermeable dike. During flood events, these suggested measures can mitigate the intensified swirls formed in the DFZ, protect the dike head from direct momentum exchanges in the MEZ, and enhance flow deflection into the MSZ.

Response of group piles subjected to coupled vertical-eccentric lateral-seismic loads

In seismic prone regions, analyzing loaded pile groups can be challenging because of limitations in conventional design methods and the inability of small-scale laboratory tests to accurately replicate the real behavior. Studying how pile group response is affected by the combined impact of vertical, concentric, and seismic loads is challenging. One of the limitations pertains to the intricacy of scaling up experiments, particularly in creating large-scale laboratory models. Thus, a numerical analysis may be appropriate for capturing the response. This study aimed to understand the pile group response in dense sand subjected to vertical, eccentric lateral, and seismic loadings via a large-scale 3D nonlinear finite element model. The validation results indicate that the numerical approach accurately predicts the behavior of pile groups in dense sand. Then, two different layouts of pile groups are analyzed under various loading scenarios on the basis of the recorded data from the El Centro earthquake. The results revealed that the number and arrangement of piles significantly affect the induced settlement. Compared with the 5-pile groups, the 3-pile groups presented higher maximum bending moments under vertical loading. However, the response of the 5-pile groups varied, as they experienced higher bending moment values without vertical loading. The peak lateral soil pressures were higher in the 3-pile groups. Some significant variations appeared in the induced torque resistances when the 5-pile groups were compared with the 3-pile groups. This study demonstrated the reliability of the used numerical approach for analyzing the response of pile groups in dense sand, as an alternative to laboratory test models.

Integrated Assessment of Bearing Capacity and GHG Emissions for Foundation Treatment Piles Considering Stratum Variability

Foundation treatment piles are crucial for enhancing the bearing capacity and stability of weak foundations and are widely utilized in construction projects. However, owing to the complexity of geological conditions, traditional construction methods fail to meet the demand for low-carbon development. To address these challenges, this study introduced a comprehensive decision-making approach that considers the impact of stratum variability on greenhouse gas (GHG) emissions and pile bearing capacity from the design phase. During the design process, the GHG emissions and bearing capacities of deep cement mixing (DCM) and high-pressure jet grouting (HPJG) piles were quantitatively assessed by analyzing the environmental and performance impacts of foundation treatment piles related to materials, transportation, and equipment usage. The results suggest that the bearing capacity of piles in shallow strata is highly susceptible to stratum variability. Using piles with a diameter of 800 mm and a length of 20 m as an example, compared with DCM piles, HPJG piles demonstrated a superior bearing capacity; however, their total GHG emissions were 6.58% higher, primarily because of the extensive use of machinery during HPJG pile construction. The GHG emissions of foundation treatment piles in shallow strata were influenced more by geological variability than those in deep strata. Sensitivity analysis revealed that the pile diameter is a critical determinant of GHG emissions and bearing capacity. Based on the bearing capacity–GHG emission optimization framework, a foundation treatment strategy that integrates overlapping and spaced pile arrangements was introduced. This innovative construction method reduced the total GHG emissions by 22.7% compared with conventional methods. These research findings contribute to low-carbon design in the construction industry.

Propagation attenuation of elastic waves in multi-row infinitely periodic pile barriers: A closed-form analytical solution

Periodically arranged media exhibit attenuation zones for elastic waves, and the related periodic structures play a crucial role in the design of seismic isolation and vibration mitigation. From the perspective of wave theory, this paper presents a closed-form analytical solution for the propagation attenuation of elastic waves through infinitely periodic, multi-row pile barriers. The innovative approach begins by deriving the extended Graf’s addition theorem to transform wave potentials across arbitrary coordinate systems, overcoming the constraints of traditional formulas that limit pile centers to linear configurations. Subsequently, it completes the wave function expansion by utilizing the phase differences in the frequency domain of wave fields around different periodic elements, thus skillfully integrating the effects of incident and scattered wave fields. For the first time, this study delivers exact expressions for the scattering of various types of plane waves (SH, SV, and P) by multi-row pile barriers with an infinite periodic array, addressing the complexities of large pile numbers in previous theoretical studies. The proposed solution increases computational efficiency by tens of times and markedly reduces the majority of resource usage, improving the analysis of complex vibration isolation systems involving numerous piles. Building on the accuracy verification and convergence analysis, several numerical examples are conducted to explore the effects of pile row, pile spacing, and pile arrangement on the propagation attenuation. The findings elucidate the mechanisms driving vibration reduction design using periodic wave barrier, furthering its application in engineering structures.

Experimental study on wave-induced loads and nonlinear effects for pier-pile group foundations of sea-crossing bridges: Wave slamming and suction effect

Strong nonlinear effects, such as wave slamming, suction effects, and wave overtopping, may be induced during wave-bridge interaction. However, an accurate understanding of these nonlinear effects is still insufficient. This study comprehensively investigates the wave slamming and suction effects on pier-pile group foundations of sea-crossing bridges in a 1:50 scale laboratory experiment. Random and regular waves with different strengths are generated based on wave conditions at the bridge site. Five water depths with a 2 cm spacing are designed to simulate varying pile cap clearances. Various pile arrangements are also set up to explore the influence of piles. Results show that wave slamming is low-aeration and is triggered mainly on the cap bottom wall, whereas the wave action on the vertical wall of the pile cap is quasi-static. The suction effect is generally recorded in the quasi-static phase of pressures and depends on the water exit process and the wave crest height. Moreover, the pressure oscillation after the impact phase results from the flow separation and rotation at structure corners. The wave slamming enhances with the increasing wave frequency when the impact area is constant, otherwise, it depends on the impact area. On the cap bottom wall, the wave slamming on inter-pile areas is enhanced, but the suction effect is less affected by pile arrangements. The increase in pile cap clearances reduces vertical forces but has less effect on horizontal forces. Additionally, a sustained increase in the wave crest height may reduce the slamming force. An empirical method for predicting wave forces is finally proposed based on the water entry theory and experimental findings. This work enhances the physical understanding of nonlinear effects during wave-bridge interaction and aims to support the design of substructures for sea-crossing bridges.

Landslide–Tunnel Interactions and Control Countermeasures under an Orthogonal System

When a tunnel crosses a landslide orthogonally, this interaction can easily lead to instability in both the landslide and tunnel structures. Based on the relative positional relationship between a landslide and a tunnel, we studied the stress mode and deformation characteristics of the tunnel in three positional relationships: within the landslide mass, the sliding surface, and the sliding bed. The tunnel is a typical type located on a sliding surface at an engineering site, so we established a numerical model showing the intersection of the tunnel and the sliding surface. The plastic zone distribution, stress characteristics, and displacement distribution characteristics of the surrounding rock before and after tunnel excavation were studied. Based on the simulation results, we analyzed the control effect of anti-slide piles in controlling the tunnel’s deformation in the surrounding rock from four perspectives: the arrangement of anti-slide piles, the spacing between piles and tunnels, the diameter of anti-slide piles, and the depth of piles embedded in the bedrock. By analyzing the deformation law of the landslide mass and the force characteristics of the tunnel structure under the orthogonal conditions of a tunnel landslide, we provide theoretical guidance for the adoption of anti-slide piles to control instability in tunnel structures.

Deformation mechanism and treatment effect of deeply excavated expansive soil slopes with high groundwater level: Case study of MR-SNWTP, China

Taking a 4 km long deeply excavated expansive soil canal segment of the South–North Water Transfer Project Middle Route (MR-SNWTP) in China as an example, a comprehensive investigation of the deformation mechanism and effect of treatment work on the slope with high groundwater level was carried out. First, the project background and initial behaviour were introduced. Second, a series of site investigation, including visual inspection, exploration pit, and geological penetrating radar, was employed to identify the deformation characteristics, appearance damage, and groundwater distribution. Third, the environmental factors were analyzed, and the spatio-temporal deformation characteristics were identified. Then the zoned numerical model was built to analyze the slope stability. Finally, the deformation mechanism and effect of treatment work were discussed. The results show that although the slope surface was replaced with a cement-treated weak expansive soil layer, the water vapor exchange between the undisturbed expansive soils and atmosphere is not completely isolated. The perched groundwater is also still replenished by precipitation infiltration. Groundwater, perched groundwater, long-large fissure and dense fissure zone induce the lateral creep deformation of the slope, and result in significant trend changes. The stability of the deformed body is in a critical state. The critical sliding surface is a broken line consisting of a gentle dip angle at the leading edge and a steep dip angle at the trailing edge. The depth of the potential sliding surface varies due to the geological condition and arrangement of anti-slide piles. Drainage wells can discharge deeper groundwater, thus can lower groundwater level and discharge perched groundwater. Supporting and unloading measures should also be taken to improve the slope stability.

Efficacy of the Combined Use of Bed Sill and Sacrificial Piles to Control Local Scour around Circular Bridge Piers

In this study, the results are presented and discussed from laboratory test campaigns specifically designed to investigate the behavior of sacrificial piles as a countermeasure against local scouring at a circular bridge pier and clear-water conditions with flow intensity slightly below the threshold of sediment motion. Sacrificial piles are assessed on the upstream side of the pier in two transverse and triangular arrangements. Piles can reduce scouring by deflecting the flow and creating a low-velocity wake region behind them. The efficiency of the piles against local scouring depends on the diameter of the piles, the number of piles, and the angle of the wedge. The investigation was aimed at evaluating the effectiveness of the sacrificial piles as a function of different dimensionless groups. It was found that the triangular arrangement of sacrificial piles has better results than the transverse arrangement. The results showed that the triangular sacrificial piles reduced the maximum local scour depth at the pier to 37.2% in the best configuration. Combined countermeasures were tested, which were composed of sacrificial piles and a bed sill downstream of the pier; in the best configuration, the scour depth reduction in front of the pier reached 51.1%. The increased efficiency of the combination of bed sill and sacrificial piles (BSSP) is an advantage that can reduce the risk of pier failure when the duration of the flood is short. This last result shows that a combination of BSSP may be a very effective countermeasure against local scouring at bridge piers. Finally, the coherent turbulent flow structure around the best combination of BSSP was investigated, and its effect on the bed scouring pattern was studied. A 3D analysis of the bursting process was used. Turbulence characteristics, as well as the occurrence and transition probabilities of bursting events, were calculated. The obtained results confirmed the quite effective effect of the combination of these two countermeasures in reducing the scour depth.

Machine induced dynamic field responses of group pile with different pile arrangements

AbstractThe main objective of the current investigation is to study the dynamic behaviour of a 3-pile group with different loading direction under coupled (horizontal and rocking) excitations. To accomplish this objective, machine-induced field excitation tests are conducted on small-scale hollow steel piles. The 3-pile group is driven into the ground in a triangular arrangement with 3d spacing. Two different soil-pile setups, i.e., Pile Group-I and Pile Group-II, are created based on dynamic force directions. In the case of Pile Group-I, the forces are applied to the direction of the median of the triangle, and for Pile Group-II, the forces are applied to other directional loads. From the test results, it is found that the resonant peaks of horizontal and rocking amplitudes for Pile Group-I are lower than Pile Group-II. In the case of resonant frequencies, the values of Pile Group-I are observed to be the same or a little bit higher as compared to Pile Group-II. It is found that the dynamic soil-pile-soil interaction effect is more prominent for Pile Group-II than for Pile Group-I. For numerical investigation, the continuum approach method is utilised with the inclusion of a dynamic group interaction factor to predict the dynamic coupled responses in terms of frequency and amplitude for these two soil-pile setups. To understand the behaviour of pile groups, boundary zone parameters and variations of impedance parameters (stiffness and damping) with operating frequencies are also measured using this theoretical approach.

Local scour depth at piles group exposed to regular waves: On the assessment of expressions based on classification concepts and evolutionary algorithms

An accurate estimation of local scour depth around piles group is inevitably essential to provide stability of marine structures. Over the past decades, many investigations have been made to understand the scouring process at piles group exposed to waves for field and experimental scales. This study aims to predict the wave-induced local scour depth by various robust Data Driven Models (DDMs) and Machine Learning Models (MLMs) developed by classification and evolutionary concepts: Model Tree (MT), Evolutionary Polynomial Regression (EPR), Multivariate Adaptive Regression Spline (MARS), and Gene-Expression Programming (GEP). From relevant literature, 125 data series were employed to provide empirical relationships for scour depth predictions. The raw variables were related to bed sediment, pile configuration, pile geometry, approaching flow, and wave characteristics. Non-dimensional parameters have been obtained through the Buckingham theorem in order to control local scour depth. In this way, the ratio of spacing between piles to pile diameter (G/D), sediment number (Ns), pile arrangement number (ratio of the number of piles parallel to the flow; m; to the number of piles normal to the flow; n), Shields parameter (θ), and Keulegan-Carpenter (KC) were considered. From the training and testing stages of Artificial Intelligence Models (AIMs), it was found that regression equation given by MARS model provided better performance (e.g., Correlation Coefficient [R] = 0.9297, Root Mean Square Error [RMSE] = 0.3489, and Scatter Index [SI] = 0.2765) than other AI models’ efficiency. Additionally, the performance of AI models was assessed for various ranges of dimensionless parameters (i.e., G/D, Ns, and θ) versus KC variation. MARS model had the best performance for G/D = 0–1 and KC < 10 (R = 0.9917 and RMSE = 0.2198) and 0.4≤θ < 0.5 and 15 < KC < 25 whereas EPR model had promising efficiency in the its highest level for Ns = 1–3 and 10 < KC ≤ 15 (R = 0.9941 and RMSE = 0.0771) than other AI models. For the sensitivity analysis, the mutation rate and number of chromosomes are examined for the GEP model, the K-fold number and number of parameters for the MARS model, and the number of algebraic terms and number of chromosomes for the EPR model. Furthermore, ranking analysis of AI models indicated that MARS model had the best performance (Ranking Performance Index [RPI] = 0.7348) and followed by GEP (0.3412), M5MT (0.2999), and EPR (0.2848).

Stability Analysis of Slopes Supported by Anti-slip Piles under Different Working Conditions

In the reinforcement of slope management measures, the arrangement of anti-slip piles is often used to keep the slope stable, and anti-slip piles, as a typical landslide prevention and control structure, occupy a more important position in landslide management. Relying on a landslide in Gansu Province, this paper carries out numerical simulation research on landslide reinforced by anti-slip piles to study the change rule of the stability coefficient of the landslide under natural, rainfall and earthquake conditions as well as the displacement law under earthquake conditions, and then evaluates the reinforcing effect of anti-slip piles in the management of landslides. The results of the study show that, before the landslide was reinforced by anti-slip piles, the landslide mass was in a stable state and a basically stable state under natural conditions and rainfall conditions, respectively, and the probability of failure was small. Under the earthquake condition, the landslide is in an unstable state and is prone to localized failure, and the displacement of the landslide mass in the X direction is larger; The stability coefficients of the landslide mass under each condition were greatly improved after the stabilization of the landslide by anti-slip piles and the X-direction was limited under the earthquake condition, and the landslide was in a stable state. The effect of anti-slip pile reinforcement is good, and it can provide reference for future anti-slip pile reinforcement slope projects.

ANALYSIS OF CONFIGURATION OF PILE GROUP ON SUPPORTING CAPACITY AND PILE EFFICIENCY IN TANJUNG BALAI FLAT CONSTRUCTION

In the TanjungBalai Flats creation project, the inspiration used is a mini pile basis with a set pile device. The organization pile device on the inspiration withinside the creation of this flat is deliberate to have a exclusive wide variety of piles, particularly piles, 3 piles, 4 piles. Therefore, on this look at diverse pile configurations might be completed with the aid of using modelling exclusive configurations with the equal wide variety of piles as the development of this flat. Furthermore, the sporting ability and performance values might be as compared that is the first-class value. Calculations on this look at had been the usage of the direct method (Direct One) and the pile performance component for the evaluation of the pile bearing ability. The calculation is accomplished primarily based totally at the soil statistics received withinside the shape of sondir statistics. The significance of the pile performance value (Eg) in a pile organization is encouraged with the aid of using the pile arrangement, the wide variety of rows, the wide variety of piles in a single row, and the pile distance inclusive of the three pile configuration of the project (V3) has an performance value (Eg) = 0,817 and (Qg) = 205.27 whilst the evaluation of the layout pile (V3-1) has an performance value (Eg) = 0.861 and (Qg) = 216.32. From the calculation effects it could be concluded that the affect of organization pile configuration at the pile bearing ability is encouraged with the aid of using the significance of the pile performance (Eg), the more the pile performance, the more the sporting ability.

Slope stability analysis of coastal geotechnical structures under combined effects of earthquake and rainfall

The primary factors responsible for inducing landslide disasters are earthquakes and rainfall. Using the strength reduction method within the finite element analysis software Abaqus, a study was conducted to analyze the stability of coastal geotechnical slopes. This investigation considered the combined influence of rainfall and earthquakes, taking into account the geological conditions and characteristics specific to these coastal areas. The results indicate that, under the same seismic acceleration amplitude, the shear strength of the slope soil gradually decreases as the water content increases, resulting in a decrease in the stability coefficient. Similarly, with a constant water content in the slope, an increase in seismic acceleration amplitude leads to heightened soil shear stress, consequently decreasing the stability coefficient. Maintaining constant water content while increasing seismic acceleration results in elevated soil shear stress, reduced shear strength, and a subsequent decrease in the stability coefficient. The simultaneous occurrence of intense rainfall and a strong earthquake pushes the slope to its most precarious state, causing the most significant reduction in the stability coefficient. Incorporating anti-slip piles substantially enhances the slope’s stability coefficient, and an optimal arrangement of anti-slip piles for the most unfavorable conditions is proposed.

РІЗНИЦЯ В РОБОТІ БУРОВИХ І ЗАБИВНИХ ПАЛЬ У СКЛАДІ СТРІЧКОВОГО ПАЛЬОВОГО ФУНДАМЕНТУ

A comparative analysis of the results of the mathematical modeling of the strip pile foundation from driven and bored piles with one-row and two-row arrangement of piles with different longitudinal steps and different lengths in different types of soil was performed.&#x0D; It was established that the degree of implementation of the load-bearing capacity of piles and grids as part of a strip pile foundation depends not only on the relative length and pitch of the piles, but also on the method of their arrangement. Taking into account the actual operation of piles and grids as part of the pile foundation allows to increase the load-bearing capacity of the pile foundation as a whole and, accordingly, to save material and labor resources during construction work.&#x0D; Based on the results of the study, the difference in the operation of drilled and driven piles in the strip pile foundation was established. The load-bearing capacity of a low grid as part of a strip pile foundation on bored piles is 1.5-2 times greater than in pile foundations made of driven piles. The degree of implementation of the load-bearing capacity of the pile as part of the pile foundation is significantly greater for foundations made of drilled piles compared to foundations made of driven piles. For foundations made of driven piles, at step 3d - 6d, the piles in the strip do not fully realize their load-bearing capacity. Drill pile groups increase their load-bearing capacity by working in a group, even with a minimum pitch.&#x0D; Since pile foundations from drilled piles significantly increase their bearing capacity due to the joint work of their elements under load in comparison with pile foundations from driven piles, taking into account this joint work, pile foundations from drilled piles become competitive with similar foundations from driven piles.

Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme

To reduce traffic congestion and meet the demand for rail transportation, the diameters of shield tunnels are constantly expanded. The super-large diameter, deep depth and long distance of super-large-diameter shield tunnels, coupled with the limitation of existing structures on underground construction space, cause many problems in the construction of these tunnels, such as affecting existing structures. This study takes a shield project in Wuhan as the research object, uses the finite element method to simulate the influence of super-large-diameter shield tunnelling on the displacement of the existing Line 5 tunnel segments, and analyzes the influence of the isolation pile arrangement and length on the isolation effect. The analysis indicates that (1) the displacement of Line 5 decreases with an increasing horizontal center distance between the tunnels and increases with an increasing vertical center distance between the tunnels, with a maximum displacement of 17.9 mm; (2) the displacement direction and position of the maximum displacement of Line 5 vary with changes in the vertical center distance between the tunnels, but remain essentially constant with changes in the horizontal center distance; and (3) the isolation piles closer to the shield tunnel improve support, with its isolation effect on the Line 5 segment becoming limited.

Horizontal vibration characteristics of offshore twin–pile foundations

Accurately estimating the horizontal dynamic parameters of offshore pile groups plays a critical role in offshore foundation engineering. Most of the current research ignored the hydrodynamic force applied to the piles, making it difficult to accurately simulate the operational conditions of offshore pile groups. This study considered the dynamic soil resistance and hydrodynamic pressure induced by pile horizontal vibration, providing a more accurate and comprehensive dynamic analysis of offshore twin–pile foundations. By incorporating the determined pile–soil and pile–water interaction forces and solving the horizontal vibration equations of piles, the dynamic impedance and displacement amplitude of the offshore twin–pile system were derived. After validating the rationality of the proposed solutions, the effects of hydrodynamic force, pile arrangement, and pile geometrical dimensions were extensively discussed. The main conclusions are as: (1) The influence of hydrodynamic force on the dynamic stiffness of the twin-pile system becomes gradually significant as the load frequency increases; (2) Neglecting the effects of hydrodynamic force leads to an overestimation of the natural frequency of twin–pile foundations; (3) Compared to a single pile, the natural frequency of twin–pile foundations is less sensitive to the changes in geometrical dimensions.

Performance evaluation of rail trackbed stiffness: pre and post stabilisation

Excessive deflection of a rail in response to axle loading can lead to discomfort for passengers and increased wear of both railway structures and trains. These oscillations are often caused by poor trackbed stiffness which may be due to either soft subgrade and/or contaminated ballast. A variety of trackbed stabilisation (TBS) techniques are available to remediate soft subgrades and increase the safety of tracks within the railway network. Traditional TBS methods require track removal, which is expensive, disruptive and often inefficient maintenance works. Micro-piling, using screw piles installed between sleepers, is an innovative low disruption TBS technique. This paper investigates the performance of a soft subgrade and contaminated ballast section of rail line in the UK, before and after screw pile TBS. Pre and post remediation, a computer vision-based system was used to measure rail vertical deflections during train passages and then analysed to quantify the trackbed stiffness. Additionally, 3D finite element models are created and validated by the site measurements. The finite element models are used to simulate a range of different scenarios exploring how changes to the TBS piling layout and/or further works, such as ballast improvement could add further improvements or design efficiencies. Site measurements show TBS reduced rail deflection by 20–30%, indicating that micro-piling is an effective technique for soft subgrades. The finite element analysis revealed the efficiency of micro-piling is highly dependent on the conditions of ballast, strength of the ground at the pile toe, and the pile arrangement. When the aforementioned are optimised the rail deflection could be reduced to approximately 50% of the pre TBS condition.

Numerical evaluations on the effects of different factors on thermo- mechanical behaviour of an energy pile group

Energy pile is a kind of economical and efficient underground energy structure. Obtaining the effects of different factors on the performance of energy pile help to improve the working efficiency of the energy pile. However, the thermo-mechanical behaviour of energy pile groups are more complex than that in single energy pile due to the mutual interference of energy pile groups. In this paper, the energy pile group with the layout of 3 × 3 was simulated by a 3-D numerical model. The influences of soil type, pile spacing, pile material performance and pile arrangement form on the thermo-mechanical behaviour of the energy pile group were investigated. The results show that increasing pile spacing can not only improve the thermal performance of energy pile group but also reduce the pile displacement, but it will lead to the increase of pile axial force because of the weakening of pile group effect. The thermal performance of energy pile group is the highest under the rock-soil condition, followed by sand and clay. However, the pile displacement is the largest when the soil type is sand, followed by clay, and the rock-soil is the smallest, and the influence of soil type on pile axial force is just opposite to pile displacement. At the same time, the increase of thermal conductivity of pile material benefits to heat transfer performance of energy pile group, but it also aggravates the heat accumulation and results in a larger top displacement and axial force of pile. As for concrete compression modulus, increasing the concrete compression modulus can increase the axial force of pile, but the change of concrete compression modulus has no effect on the pile displacement. In terms of layout of energy pile group, the per unit soil volume heat exchange rate of energy pile group in the cross arrangement form is larger than that in sequential arrangement form. However, the variation range of soil temperature in the cross arrangement form is larger than that in the sequential arrangement form, thus increasing pile displacement and reducing pile axial force.

A study on soil arching effect of anti-slide pile considering different pile arrangements

A study on soil arching effect of anti-slide pile considering different pile arrangements