Adjacent Piles Research Articles

REINFORCEMENT OF SUBGRADE DOUBLE-CONE PILES

Statement of the problem. The problem of designing the reinforcement method of weak seasonally freezing soils in subgrade base by using double-cone hollow piles and geotechnical materials for roads in the northern regions of the Russian Federation is investigated. Results. As a result of the study, the construction of the subgrade in the form of pile strip foundation of double-cone piles reinforced by geotechnical materials on weak heaving soils taking into account traffic loads and weight of subgrade is considered. A method has been developed of calculating the road base in the form of pile strip foundation of double-cone piles reinforced by geotechnical materials on weak heaving soils taking into account traffic loads and weight of subgrade is considered. The developed method of calculation is based on the formation of soil compaction zones in the near-pile space as a result of pile driving into the ground, which leads to an increase in the structural strength of the weak soil, and also takes the arch effect that occurs in the soil between adjacent pile heads. Conclusions. The obtained research results allow us to conclude that the developed subgrade design and its calculation method are of great interest both to scientists and design engineers, and can be used in construction practice.

Spudcan-pile interaction in thick soft clay and soft clay overlying sand: A simplified numerical solution

A drilling jack-up is often deployed to perform drilling activities or well intervention at an existing fixed jacket platform. Depending on the clearance distance between the aft spudcan and the nearest pile, the installation of the spudcan may have an adverse effect on the platform pile which in turn could compromise the integrity of the jacket structure. This paper presents a simplified method for assessing the effect of spudcan installation on the pile foundation of a jacket platform in thick soft clay and soft clay overlying sand layers. Adopting a two-stage uncoupled approach, in which predetermined free-field lateral soil displacements are applied to a beam-column model with soil modelled using p-y curves, the soil displacements around a penetrating spudcan is estimated by an analytical solution derived from spherical cavity expansion theory. With appropriate consideration for the volume of soil displaced by the penetrating spudcan for the cases of thick soft clay and consideration for soil squeezing for soft clay overlying sand, the computed free-field lateral soil displacements are in fair agreement with the measured profiles in centrifuge tests and can be used in a beam-column model to estimate the induced bending moment in the pile in practice.The pile response to the free-field lateral soil displacements is assessed using a beam-column model incorporating p–y curves, considering the effect of soil remoulding caused by the installation of the spudcan where appropriate. A numerical model which considers the evolving lateral soil displacements due to the progressive advancement of the penetrating spudcan is also studied. The computed pile bending moment profiles are consistent with the measured profiles in the centrifuge tests and those computed by 3D large deformation finite element (LDFE) model. The proposed practical method is simple but yet effective to assess the influence of the installation of a spudcan foundation on an adjacent pile of a jacket platform in thick soft clay and soft clay overlying sand.

Driven Pile Effects on Nearby Cylindrical and Semi-Tapered Pile in Sandy Clay

A pile foundation is commonly adopted for transferring superstructure loads into the ground in weaker soil. They diminish the settlement of the infrastructure and augment the soil-bearing capacity. This paper emphases the pile-driving effect on an existing adjacent cylindrical and semi-tapered pile. Driving a three-dimensional pile into the ground is fruitfully accomplished by combining the arbitrary Lagrangian–Eulerian (ALE) adaptive mesh and element deletion methods without adopting any assumptions that would simplify the simulation. Axial forces, bending moment, and lateral displacement were studied in the neighboring already-installed pile. An investigation was made into some factors affecting the forces and bending moment, such as pile spacing and the shape of the already-installed pile (cylindrical, tapered, or semi-tapered). An important response was observed in the impact of the driven pile on the nearby existing one, the bending moment and axial forces were not negligible, and when the pile was loaded, it was recommended to consider the coupling effect. Moreover, the adjacent semi-tapered pile was subjected to less axial and lateral movement than the cylindrical one with the same length and volume for taper angles smaller than 1.0°, and vice versa for taper angles greater than 1.4°.

Influence of Cairo Metro Tunnel Excavation on Pile Deep Foundation of the Adjacent Underground Structures: Numerical Study

Day by day the call to solve traffic congestion problems is increasing. Subway tunnels and high-speed railway are commonly used for transportation. Therefore, tunnel construction induces soil movement, which in turn affects the stability and integrity of adjacent existing buildings. A series of numerical simulations have been established to investigate the effects of tunnel construction of the Greater Cairo Metro–Line 3-Phase-1 on adjacent pile cap foundations of Garage El-Attaba building. Many parameters have been investigated such as tunnel diameter and the distance between pile and tunnel at different tunnel axis and deep and shallow tunnel. After thorough analysis of the results’ simulation, it was found that the tunneling induces additional axial forces and bending moment as well as increasing axial settlement and lateral deflection. Moreover, the results obtained from the parametric study for the shallow and deep tunnel show that the tunnel depth has a much significant effect on piles responses. Finally, the tunnel diameter has an impact on pile responses as well as the pile cap foundation influenced by the tunnel when the tunnel is in very close vicinity of the pile, and its effect is modest to negligible if located far away from the buildings.

Internal Force on and Deformation of Steel Assembled Supporting Structure of Foundation Pit under Thermal Stress

The steel assembled support structure of a foundation pit can be assembled easily with high strength and recycling value. Steel’s performance is significantly affected by the surrounding temperature due to its temperature sensitivity. Here, a full-scale experiment was conducted to study the influence of temperature on the internal force and deformation of supporting structures, and a three-dimensional finite element model was established for comparative analysis. The test results showed that under the temperature effect, the deformation of the central retaining pile was composed of rigid rotation and flexural deformation, while the adjacent pile of central retaining pile only experienced flexural deformation. The stress on the retaining pile crown changed little, while more stress accumulated at the bottom. Compared with the crown beam and waist beam 2, the stress on waist beam 1 was significantly affected by the temperature and increased by about 0.70 MPa/°C. Meanwhile, the stress of the rigid panel was greatly affected by the temperature, increasing 78% and 82% when the temperature increased by 15 °C on rigid panel 1 and rigid panel 2, respectively. The comparative simulation results indicated that the bending moment and shear strength of pile 1 were markedly affected by the temperature, but pile 2 and pile 3 were basically stable. Lastly, as the temperature varied, waist beam 2 had the largest change in the deflection, followed by waist beam 1; the crown beam experienced the smallest change in the deflection.

Static and dynamic lateral non-linear pile–soil–pile interaction

Three-dimensional finite-element analyses are performed to compute the interaction factors between two neighbouring piles, under both static and dynamic horizontal displacements. The fixed-head elastic piles are flexible, embedded in a homogeneous saturated clay stratum, and loaded under undrained conditions. Soil inelasticity and soil–pile interface separation are modelled in a rational way. With the aim of improving fundamental understanding of pile–soil–pile non-linear interaction mechanisms, it is found that the effect of a loaded (‘source’) pile on an adjacent (‘receiver’) pile diminishes rapidly with increasing amplitude of imposed displacement, at a rate which depends on the angle of departure from the direction of loading between source and receiver piles. Gap formation at the back of a displaced pile affects the response of the group. Using the interaction factors developed, the behaviour of 2 × 2 and 3 × 3 pile groups is analysed and compared with the three-dimensional analysis of the whole group. Under static conditions the differences between front (‘leading’) and back (‘trailing’) piles are illustrated. Under cyclic dynamic conditions, the separation gap forms on each side of a pile alternately, leading to the peaks in stiffness diminishing, and leading to larger (than the elastic) group efficiencies. Superposition using proper non-linear interaction factors offers reasonable approximation, but only for moderate amplitudes of load, smaller than about one-half of the ultimate lateral pile capacity.

Study the working of piles on the slope ground subjected to horizontal loading by numerical simulation method

Numerical modelling is an efficient method to investigate the effects of the distance from pile centreline to pile centreline on the working of laterally loaded piles considering the shear plastic deformations of the ground. The paper presents the research results the effects of piles spacing on the sloping ground including sand and clay layers subjected to horizontal loading according to the finite element method by ABAQUS software. Group of authors simulate the soil-pile interface, capable of incorporating the gapping and sliding in the soil-pile interfaces for both sand and clay layers. The research results are used to predict the lateral load-deformation of piles for different cases and comparison with published research results. On that basis predicting the suitable distance horizontal loading piles that a pile negligible influenced from adjacent pile on a slope. This is a matter of high scientific and practical significance in foundation engineering in general, as well as in calculating pile foundations on a slopes in particular.

Lateral dynamic response of pile group embedded in unsaturated soil

A mathematical formulation is proposed for the analysis of a pile group embedded in unsaturated soil subjected to horizontal time-harmonic vibration. The unsaturated soil is governed by the motion theory of three-phase poroelastic medium, and the piles with fixed connection to cap are modeled as Timoshenko beam models. By introducing Helmholtz decomposition to the governing equations, the resistance and attenuation function of displacement of the surrounding soil are theoretically derived. Then, the impedances of pile group in frequency domain are evaluated by utilizing the superposition approach based on the dynamic interaction factors. The internal forces of piles induced by both kinematic effects arising from the adjacent pile motion and inertial effect from pile cap, as well as the degree of contribution of the two effects have been investigated. The accuracy of the proposed method was validated by its comparison with a benchmark solution for the corresponding single phase medium problem. A comprehensive parametric study is performed to depict the effects of saturation, permeability, and pile group arrangement, and indicating that the saturation and permeability exert considerable effects on the nearly saturated condition, by contrast, the unsaturated case is much less affected.

The Environmental Effects Induced by a Metro Shield Tunnel Side-Crossing on Adjacent Pile Foundations and Its Impact Partition

With the advantages of fast construction speed and small disturbance to stratum, shield tunneling is becoming the preferred construction scheme for metro construction. However, if the disturbance of stratum cannot be clearly understood, it will affect the safety of adjacent underground structures and aboveground buildings. Based on the construction of the interval tunnel between Shizishan station and Chuanshi station of Chengdu metro line 7 project, this paper proposed a simplified calculation method to analyze the impact of shield excavation on adjacent pile foundation. A two-stage method of modified Peck formula and Winkler elastic foundation model was used to investigate the additional displacement and internal force of pile. A three-dimensional numerical model validated with the field test data was performed to compare with the theoretical results. The impact factors and their impact degree were discussed. The results show that the additional displacement and internal force are at a reasonable and acceptable level. The permanent pile foundation should adopt the small diameter pile as far as possible. When the small diameter pile foundation cannot meet the stress requirements, the design scheme of the pile group should be adopted. The area around shield tunnel is divided into strong impact area of pile foundation (S ≤ 0.75 D), slight impact area (0.75 D ≤ S ≤ 1.5 D), and no impact area (S > 1.5 D). The pile researched in this paper (S = 0.83 D) is in the slight impact area.

Study of spun pile connection with steel jacket strengthening

The amount of spiral reinforcement in the spun pile manufactured in Indonesia is below the minimum requirement. Additional shear reinforcement is needed, particularly on a pile at the adjacent pile cap. To cope with the deficiency, steel jacket is initiated to strengthen the pile. A numerical study was performed to study the effect of steel jacket addition to spun pile behavior. Two different software, SAP and Abaqus were employed. Pushover analysis was performed with a monotonic loading approach. The parameters studied were the steel jacket’s thickness and the existence of adhesive between the steel and the concrete surface. Brittle behavior was detected with the presence of steel jacket which was indicated by the force displacement curve. The steel improves the strength of the spun pile connection but decreases the ductility. It seems that pile is in over reinforced condition. To get a thorough understanding, a 3D model with Abaqus software was performed. Steel jacket is applied on the spun pile without rebar inside concrete fill and thinner steel was selected to prevent over reinforce. Hence, different results were found where spun pile connections behave in a ductile manner. Steel jacket improves not only the strength of spun pile connection but also the ductility.

Nest Site Fidelity of Northern Map Turtles, Graptemys geographica

Northern map turtles (Graptemys geographica) are a species of conservation concern with a limited distribution in Pennsylvania. We examined nest site fidelity of G. geographica along the Juniata River at Mount Union, the largest reported nesting area in the commonwealth. Nesting habitat included a mitigation area bordering a highway, partitioned by a turtle exclusion fence, and an adjacent pile of coal tailings. A linear grid along the turtle fence allowed us to determine distances between nests of individual females. Our results indicate that female G. geographica at Mount Union exhibit nest site fidelity, as the frequency distribution of distances between nests of individual females was positively skewed, and distances between nests (both within and among seasons) were smaller than distances between randomly selected pairs of nests from different individuals. Females placed different clutches of eggs as close together as 0.30 m. Within-season (first and second clutch) internest distances were significantly smaller than internest distances among years, which increased over time. We also attached radio transmitters to a sample of adult females following nesting to determine the extent of riverine migrations, as long-distance nesting migrations are associated with fidelity to particular nesting sites. Following nesting, 2 females remained in the river near the Mount Union nesting habitat and 3 females moved downstream 4.3–5.6 km, yet all of the turtles returned to their previous nesting areas the following summer. Nest site fidelity can benefit map turtles if the habitat remains stable, results in high nest survivorship, and produces high-quality hatchlings, yet the behavior may be detrimental if it exposes turtles to significant risks such as road mortality or environmental contaminants. Our results indicate that maintaining long-term nesting habitat and ensuring suitable river quality at Mount Union may be essential for the conservation of G. geographica in central Pennsylvania.

Responses of the ground and adjacent pile to excavation of U-shaped tunnel

Although there are many studies on the impact of tunnel on the surrounding environment, most of them focused on the circular tunnels but very few on U-shaped tunnels. In order to obtain a better understanding of the impact of U-shaped tunnel excavation on the ground and adjacent pile foundations, a simplified analytical method is developed in this work. The U-shaped tunnel is projected into a unit circle using conformal mapping method. The displacement and stress of the soil around the tunnel are solved analyzed. The settlement of a single pile is obtained by the complex variable function and the load transfer method. The influence of grouting is considered in the calculation. The analytical solution is verified by the simulation results given by an equivalent numerical model and validated with the field-measured data in an engineering case in Beijing.

Method to Evaluate Effect of Spudcan Penetration on Adjacent Jacket Piles

When a jack-up drilling rig operates near an adjacent jacket platform, the effect of the large-diameter spudcan penetration on adjacent platform piles should be evaluated if the spudcan-pile clearance is less than one spudcan diameter. In this study, a method is developed to calculate the response of a pile subjected to spudcan penetration-induced load and pile head load transmitted from upper structure. The spudcan penetration-induced lateral pile deflection is first determined by large deformation finite element calculation. The spudcan penetration-induced load along pile shaft is then determined by transforming the pile lateral deflection into equivalent nodal loads in a nonlinear foundation beam finite element model. The pile response is finally calculated using an isolated pile finite element model subjected to penetration-induced loads and pile head loads transmitted from the upper structure or an overall finite element model which includes the upper structure and piles. Centrifuge model tests under 50g condition are conducted to verify the validity of the proposed method. To further investigate the applicability of the proposed method, the effects of pile head constraint, lateral pile head load magnitude and its direction, spudcan-pile clearance and undrained shear strength are studied. The effect of spudcan penetration on an adjacent pile is found to increase with rotation stiffness at the pile head. Spudcan penetration affects the adjacent piles most when the lateral pile head load is facing back to the spudcan. The effect of spudcan penetration decreases significantly when the spudcan-pile clearance is larger than the diameter of the spudcan and decreases with increasing undrained shear strength. Furthermore, the spudcan penetration has more influence on the pile deflection than the bending moment.

Optimisation on plane arrangement of stabilising piles subjected to spatial distributed lateral load in landslides with multilayer sliding masses

The paper develops an analytical method to design the plane arrangement of stabilising piles under spatial lateral load of 3D colluvial landslides with multilayer sliding masses. Firstly, an approach based on the geological map and binary Lagrange Interpolation method was presented to establish 3D landslide calculation models. The improved 3D limit equilibrium method was then proposed to calculate the stability coefficient and spatial distributed lateral load of landslide with multilayer sliding masses. And main sliding direction of 3D multilayer landslide can be determined by the developed principle of minimum potential energy. Moreover, through assuming the piles and soil as elastic transversely isotropic continuum medium, analytical approach was employed to accurately calculate the stress distribution of soil between adjacent piles; and the maximum pile spacing can be calculated. Finally, the reasonable arrangement of stabilising piles can be determined based on Monte-Carlo method and cost of all piles. The finite difference method was employed to validate the theoretical results through the case study of Bazimen landslide. And it is found that the proposed method for the design of piles' arrangement is economically beneficial compared with the traditional method on the premise of ensuring safety.

Group Pile Effect on Temperature Distributions inside Energy Storage Pile Foundations

Energy storage pile foundations are being developed for storing renewable energy by utilizing compressed air energy storage technology. Previous studies on isolated piles indicate that compressed air can result in pressure and temperature fluctuations in the pile, which can further affect safety of the pile foundation. Meanwhile, the temperature changes and distributions for the pile and surrounding soil also are influenced by adjacent piles in typical group pile constructions. Therefore, dynamic thermal transfer simulations were conducted in this paper to investigate the temperature changes and distributions in the concrete pile and surrounding soil for group pile construction. The main parameter in this study is the spacing of the piles. The analysis results show that the group pile effect significantly increases the temperature up to more than 100 °C depending on the location and changes its distribution in both concrete and soil due to the heat transferred from the adjacent piles. The final stabilized temperature can be as high as 120 °C in the concrete pile and 110 °C in the soil after numerous loading cycles, which is about 4 times higher than typical thermo-active energy pile applications. Thus, it is important to include the group pile effect for design and analysis of the energy storage pile foundation.

Study on characteristics of pile–net composite foundation at 500 kV substation in China

The overall requirements of substation engineering are very high, and the differential settlement control of substation engineering is relatively strict. On the soft foundation of the tidal flats at the Zhenhai 500 kV substation in China, a field test was carried out to study the working characteristics of the pile–net composite foundation during the soil filling and consolidation stage. Variation laws of the settlement, earth pressure, pile–soil stress ratio, geogrid tension and axial force of pile were obtained and analysed. When the height of the filled soil increased to 2 m, a plane of the equal settlement was formed. Because of the soil arch effect, the earth pressure on the pile top was always higher than that between the adjacent piles. The pile–soil stress ratio rapidly increased from 1.2 at the stage of soil filling to 6.0 at the initial stage of consolidation. The ability of the geogrid to transfer the load was limited, and the soil arch effect was the main reason that the load was transferred to the pile top. Due to the lateral negative friction resistance of the pile in the shallow soil, the axial force of the pile first increased and then decreased along the depth.

Numerical stability analysis of piled embankments reinforced with ground beams

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.

Effect of slab stiffness on the geotechnical performance of energy piled-raft foundation under thermo-mechanical loads

Several studies have examined the geotechnical behaviour of energy piles; however, the behaviour of piled-raft foundations containing thermal piles is not fully understood. Because piled-raft foundations are optimally designed to bear mechanical loading from the top structure, the energy piles induce extra stress and bending moments on the raft foundation (slab) from the thermal loads, which may cause structural failure. The present study evaluated the thermo-mechanical behaviour of the energy piled-raft foundations using 3D FEM to simulate the geometrical and mechanical parameters of the pile group with an emphasis on slab stiffness. The interaction between the adjacent piles in a group as well as the bending moment induced through the slab have been evaluated. The results showed that, under thermo-mechanical loads, the stiffness of the slab prevented the free expansion and contraction of the energy pile. Increasing in slab thickness from 0.2 to 0.5 m reduced the energy-pile displacement about 50%. It also was observed that a heating load induced more stress than a cooling load along the longer piles. Cooling mechanical loads caused negative skin friction in the longer piles. It was shown that the equivalent pier method is generally applicable for a group of energy piles.

Monitoring of tunnel excavation based on the fiber Bragg grating sensing technology

The application of advanced sensing technology is of great significance for investigating the disturbance caused by tunnel excavation. In this paper, fiber Bragg grating (FBG) sensing technology is introduced into tunnel construction. To monitor the deformation in the surrounding soil, an FBG inclinometer based on the conjugate beam method is developed and then validated by laboratory calibration. Then the laboratory model test is carried out according to the actual tunnel excavation of adjacent piles. FBG-based inclinometers are used in the model test to measure the deformation of the surrounding soil, and FBG sensors are attached to the piles to monitor the pile disturbance induced by excavation. The results show that the horizontal displacement of the soil on both sides of the tunnel is distributed symmetrically up and down with the centerline of the cross-section of the tunnel. The stress redistribution of the soil above the tunnel causes a more significant surface settlement than the subsurface settlement. Moreover, the displacements of the existing piles decrease with depth and are more susceptible to the excavation sequence. Additionally, this study confirms that FBG sensing technology is suitable for monitoring tunnel excavation.

Centrifuge modelling of a combined pile-type anchor subjected to general inclined loading

One of the main challenges associated with anchoring offshore platforms is the logistic needed to install them in deep water. The growing need for high capacity anchors has prompted the development of new systems where the feasibility of transporting them out to sea is a crucial consideration. With respect to torpedo piles used by Petrobras in Brazil, new platforms installed in deep water required robust anchoring systems, and a cluster of small torpedoes was considered instead of one large torpedo. However, torpedo pile installation is hindered by deep water streams, which can deviate their trajectory during the fall. This is of great concern for the design of torpedo pile clusters because the distance between the piles cannot be controlled during installation. The present study aims to determine the variation in the load capacity of a cluster or array of single piles as a function of the distance between the piles and the load direction after installation on the seabed. To that end, a series of centrifuge tests were carried out on pile clusters installed in loose sand, varying the distance between the piles and the loading direction. The results show considerable interactions between the adjacent piles depending on the load direction and pile spacing. The optimal spacing for maximum cluster efficiency was determined, and comparisons were made with values from the literature for capped pile clusters.