Vertical Piles Research Articles

Behavior of batter pile group models embedded in sandy soil under monotonic loading

This paper introduces an attempt to examine the effect of vertical monotonic load on the batter pile group models on its ultimate vertical load capacity. A fourteen steel solid pile models are used in this research. Three lengths of piles are selected (300, 400, and 500 mm) for embedment ratios (depth to width) 15 and 25, respectively. Batter piles are embedded in three different relative densities of sand bed (loose, medium and dense). The constant rate penetration test (CRPT) method was selected using a manufactured driving hammer to install the pile models in a steel box with dimensions (1000, 750 and 700) mm. The vertical cyclic load is conducted by a special hydraulic apparatus. The results indicate that the batter-vertical load capacity (BVLC) ratio increased by the increase in the embedded pile length. The batter pile group has a higher capacity at 20 degrees batter angle as compared with the vertical groups. Vertical pile groups exhibited more efficiency, which increases when pile length increases while decreases when the relative density is increased. The batter-vertical load capacity ratio increases when the embedded pile length increases and decreases with the increase in the relative density.

Seismic reliability of axially loaded vertical piles

The reliability of single vertical pile foundations subjected to seismic loads is assessed and compared with the minimum acceptable reliability level for static load conditions mandated by the Canadian codes. The analysis is executed for a site with a mean shear-wave velocity of the top 30 m of the ground equal to 250 m/s subjected to the ground motion hazard of five Canadian cities. Using both a full probabilistic analysis and simplified probabilistic model, the results seem to indicate that the current design practice is unable to achieve the reliability target of the codes. The shortfall is particularly significant when the limiting pile settlement is relatively small. The calculated reliability level of small limiting settlements is impacted by the geotechnical variability, whereas the seismic hazard variability affects large pile limiting settlements. Finally, the simplified probabilistic model produces the same results as the full probabilistic model for large pile settlement and is a convenient tool to execute code calibration.

Centrifuge modeling of the pile foundation reinforcement on slopes subjected to uneven settlement

Uneven settlement often induces the slope instability problem and the consequent inclination in upper structure. The response of the slopes with shallow foundation, vertical pile foundation, and inclined pile foundation subjected to uneven settlement are investigated using centrifuge model tests. The uneven settlement induces a significant progressive failure in the slopes with shallow and vertical pile foundation. By contrast, the slope with inclined foundation maintains good stability. Full displacement field of the slope-foundation system is obtained by employing an image-based measurement method. The inclined pile foundation exhibits much smaller top center displacement and inclination angle than the shallow foundation and vertical pile foundation. The slope failure mechanism is revealed through an integrated analysis of deformation localization and local failure. On that basis, the reinforcement mechanism of the inclined pile foundation is illustrated by the weakening of the deformation localization in the slope and hence preventing the local failure. The corresponding reinforcement effect on the slope is further presented in terms of the reduction of deformation and the restriction to uneven settlement influenced area. Therefore, the inclined pile foundation with an angle of 60° is confirmed to be effective in resisting the uneven settlement and reducing the slope deformation within acceptable foundation inclination.

Performances and Working Mechanisms of Inclined Retaining Structures for Deep Excavations

Because of the limits of struts, braceless retaining structures (BRS) have become a preferred option in deep excavation engineering. A type of BRS, that is, inclined retaining system, has been successfully applied in several projects. However, its performance and working mechanism have not been systematically studied. A case study and finite element results in this study show that inclined piles (IP) are more effective than vertical piles (VP), while composite inclined retaining structures (CIRSs) are more effective than IP in terms of deflection and bending moment reduction. The deformation‐control mechanism of IP mainly comes from the decrease in the active earth pressure. For CIRSs, the working mechanism is governed by several combined effects, that is, the rigid frame effect, inclined strut effect, earth berm effect, and gravity wall effect. For instance, in composite vertical and inward‐inclined piles (VIIP), inclined piles function as struts for the vertical piles in this rigid frame system and frictional force between the soil and the inclined piles significantly influences its retaining performance; the soil between the vertical and inclined piles plays a role similar to an earth berm; additionally, the entire retaining system is similar to a gravity retaining wall, which has relatively high overturning stability.

Reinforcement Effect of Inclined Prestressed Concrete Pipe Piles on an Inclined Soft Foundation

The embankment slope is vulnerable to slip and collapse, when prestressed concrete pipe (PCP) piles are used to reinforce the inclined soft foundation to bear the load of the embankment. Accordingly, this study puts forward new programs for strengthening embankment foundation with inclined, rather than vertical, PCP piles. Based on an actual engineering accident with embankment slope collapse, this study establishes a finite element model, accompanied by analysis of engineering characteristics and reinforcement effects of the foundation. The main conclusions are drawn as follows: (1) when a pile‐supported foundation is used to strengthen the inclined soft foundation, PCP piles in the lower part of the embankment are subjected to bending moments, with their maximum value appearing in the upper part of the PCP pile at the embankment slope foot. During the embankment filling, the maximum pile bending moment may reach the ultimate bending load, resulting in bending failure accompanied with large lateral displacement and even slope collapse. The maximum horizontal displacement of the foundation is located at the foot of the embankment slope. (2) Reinforcement using inclined PCP piles contributes to smaller maximum pile body bending moments than that using vertical PCP piles and loading berms, and such contribution is enhanced when the inclination angle of PCP piles in the lower part of the slope gets larger. Therefore, inclined PCP piles with high angles are optimum in improving the overall stability of the foundation. (3) Compared with vertical PCP piles, inclined PCP piles contribute to smaller horizontal displacement and vertical settlement in foundation reinforcement, which means better reinforcement effects. Moreover, as the inclination angle of PCP piles increases, the maximum displacement decreases rapidly, associated with greatly enhanced lateral stability.

Ultimate Load Tests on Bearing Behavior of Large‐Diameter Bored Piles in Weathered Rock Foundation

Based on the vertical compressive static load test and pile mechanics test of three large diameter bored piles (one of the test piles was treated with postgrouting) in granite gneisses foundation, the bearing capacity, deformation characteristics, and influencing factors of the single pile under the limit state are analyzed and compared with the recommended values of survey report and the recommended values of current codes. By comparing the measured and theoretical values of pile axial force, the bearing capacity of cast‐in‐place pile under normal and limit conditions is analyzed. The experimental results show that the Q-s curve of large‐diameter rock‐socketed mud wall retaining bored pile with a length‐diameter ratio of 25–33 and rock‐socketed depth of 5–8 d shows a rapid growth. After grouting treatment, the ultimate compressive bearing capacity of single pile is improved, the maximum settlement is reduced by 6.6%, the rebound rate is reduced by 11.1%, and the settlement effect of controlling pile top is not significant. The bearing capacity and deformation characteristics of the three test piles are less affected by length‐diameter ratio and rock‐socketed depth. For postgrouting piles, the ratio of frictional resistance of rock‐socketed segment and the ratio of pile lateral resistance are less affected by length‐diameter ratio and rock‐socketed depth, while, for postgrouting piles, the ratio of pile lateral resistance is more affected by rock‐socketed depth. The pile end resistance ratio of the three test piles is significantly affected by the rock‐socketed depth, whether or not the pile side postgrouting treatment is carried out.

Strength characteristics of fiber-reinforced light shotcrete

The article presents the regularities of the flexural and compressive strength variation, as well as the energy intensity of destruction of light heat-shielding vermiculite concrete, depending on the content of polypropylene or basalt fiber. The paper stresses that the greatest increase in flexural strength of 40% is observed at the polypropylene or basalt fiber that the greatest increase in flexural strength of 40% is observed at the polypropylene or basalt fiber of 2 and 2-4% respectively. As the basalt fiber content increases from 1 to 4%, the compressive strength increases from 42 to 83%. The resistance of vermiculite concrete to dynamic bending loads when the polypropylene fiber ranges from 0.5 to 2% by a factor of 2.5 4.2. With basalt fiber content of 1 to 4% the energy intensity of destruction increases 1.5 2.5 times.Specific energy intensity of destruction of samples reinforced with basalt fiber increases by 2.3 ÷ 2.7 times during volumetric destruction of the specimens under study on a vertical pile driver. The regularities obtained in the course of the studies indicate that fiber reinforcement of light heat-shielding vermiculite concrete increase its strength characteristics and thereby expand the scope of its application.

Cross validation of analytical solutions against the computational model predictions of the response of end bearing energy pile

Predictions of responses of a single energy pile to a combined mechanical and thermal loading are presented. They were obtained from computational and analytical models. The former model provided predictions based on a coupled thermal hydro-mechanical finite element analysis while the predictions of the latter were obtained from the recently derived analytical solutions. The energy pile is surrounded by a single uniform soil layer underlain by a very stiff bedrock. Two scenarios of temperature history were considered. In the first scenario the pile remained in a net heated state while the second one induced a net cooled state. In both loading scenarios a compressive axial load was applied at the pile head prior to the thermal loading. The net heating induced an upward axial displacement, tensile strain and compressive stress while the net cooling induced a downward vertical pile displacement, compressive strain and tensile stress. In spite of different methods of obtaining the soil stiffness for computational and analytical models the predictions of the axial pile displacement, stress and strain show a very good agreement.

Investigation of the effects of heat loss through below-grade envelope of buildings in urban areas on thermo-mechanical behaviour of geothermal piles

Harvesting geothermal energy through the use of thermo-active pile systems is an eco-friendly technique to provide HVAC energy demand of buildings. Mechanical behaviour of thermo-active piles is impacted by thermal cycles. Moreover, in urban areas, the temperature of the ground is higher than non-constructed areas due to the heat loss through the below-grade enclosure of buildings. This heat dissipation increases the thermal capacity of the soil and affects the mechanical response of the geothermal pile foundation subjected to thermo-mechanical loading. To investigate the effect of buildings heat loss on thermo-active piles, a numerical thermo-mechanical (TM) analysis was carried out on a proposed energy foundation system for an institutional building, the Stanley Pauley Engineering Building (SPEB) in the campus of the University of Manitoba, Winnipeg, Canada. The mechanical response of the geothermal piles to the thermal cycles with and without considering heat leakage through the basement of the SPEB is compared. Results showed that the cooling loads induced a maximum vertical pile head displacement of -1.18 mm. After 5 years operation of the system, the maximum vertical pile head displacement decreased to -1.05 mm for the case in which heat loss through the basement in considered in the models. In addition, the maximum axial load effective along the pile axis was 6% higher for the case that considers heat loss through the basement compared to the case without considering heat leakage through the building’s below-grade envelope.

Local Scour for Vertical Piles in Steady Currents: Review of Mechanisms, Influencing Factors and Empirical Equations

Scour induced by currents is one of the main causes of the bridge failure in rivers. Fundamental knowledge and mechanisms on scour processes due to currents are often taken as a basis for scour studies, which are the focus of this review. Scour development induced by waves and in combined wave–current conditions are also briefly discussed. For the design of structure foundations, the maximum scour depths need to be estimated. The mechanisms of local scour and predictions of maximum local scour depths have been studied extensively for many years. Despite the complexity of the scour process, a lot of satisfying results and progresses have been achieved by many investigators. In order to get a comprehensive review of local scour for vertical piles, major progresses made by researchers are summarized in this review. In particular, maximum scour depth influencing factors including flow intensity, sediments, pile parameters and time are analyzed with experimental data. A few empirical equations referring to temporary scour depth and maximum scour depth were classified with their expressing forms. Finally, conclusions and future research directions are addressed.

Experimental and Numerical Analysis of the Hydrodynamics around a Vertical Cylinder in Waves

The present study provides an extensive analysis on the hydrodynamics induced by a vertical slender pile under wave action. The authors carried out the study both experimentally and numerically, thus enabling a deep understanding of the flow physics. The experiments took place at a wave flume of the Università Politecnica delle Marche. Two different experimental campaigns were performed: In the former one, a mobile bed model was realized with the aims to study both the scour process and the hydrodynamics around the cylinder; in the latter one, the seabed was rigid in order to make undisturbed optical measurements, providing a deeper analysis of the hydrodynamics. The numerical investigation was made by performing a direct numerical simulation. A second order numerical discretization, both in time and in space, was used to solve the Navier–Stokes equations while a volume of fluid (VOF) approach was adopted for tracking the free surface. The comparison between experimental and numerical results is provided in terms of velocity, pressure distributions around the cylinder, and total force on it. The analysis of the pressure gradient was used to evaluate the generation and evolution of vortices around the cylinder. Finally, the relation between scour and bed shear stresses due to the structure of the vortex pattern around the pile was assessed. It is worth noting that the physical understanding of this last analysis was enabled by the combined use of experimental data on scour and numerical data on the flow pattern.

Pile under torque in nonlinear soils and soil-pile interfaces

This paper presents a new method for analyzing the nonlinear response of a single, vertical pile with the circular cross-section under torque in layered soils. The nonlinear stress-strain relationships of both soil-pile interface and soil are approximated by the hyperbolic model, whereas the pile material is elastic. The torsional spring stiffness of the soil-pile interface and the soil are determined by traditionally available methods. A four-node finite element model for the soil-pile interface is proposed to represent nonlinear behaviors of the soil-pile interface and the soil, separately. A new iterative scheme for nonlinear analysis of a single pile under torque is also developed that avoids having to solve a large number of simultaneous equations found in traditional solution schemes. The new solution method is based on the tangential stiffness of the soil-pile interface and soil springs, which are determined at each load step. From this solution scheme, an equivalent stiffness of the soil-pile-interface system of each pile element is calculated from the bottom element to the top element while torque and angle of twist are calculated from the top to the bottom elements. The solution gives the distribution of the angle of twist and torque along the pile, and the equivalent stiffness of the soil-pile system and torque-angle of twist curves at any depth. The solution method can be easily applied to the practice field in nonlinear analysis and in designing a single pile under torque in layered soils. The analysis results using the new solution scheme compared well with the results from other analytical methods studied by previous researchers. The proposed method is also used to predict the behavior of two full-scale piles under torques. The predictions are in good to excellent agreement with measurements.

Study on the stiffness degradation and damping of pile foundations under dynamic loadings

This paper presents a comprehensive study on the different behaviour of batter and vertical pile foundations in terms of stiffness degradation and damping properties under dynamic loadings. Firstly, dynamic centrifuge tests were carried out and the variations of translational/rotational stiffness and the associated damping properties were identified from a series of hysteretic loops. Results show that for the rocking behaviour, the presence of batter piles causes a small decrease of the rotational stiffness and a great increase of the rotational damping; for the horizontal translation behaviour, batter pile foundation has much higher horizontal stiffness and translational damping compared to the vertical foundation. Then, a set of stiffness degradation and damping curves for the translational and rotational behaviour of batter and vertical pile foundations are proposed. Finally, the proposed stiffness degradation and damping curves were validated numerically by using equivalent linear approach. The numerical validation shows a good agreement with the experimental results.

The Effect of Vertical Loads and the Pile Shape on Pile Group Response under Lateral Two-Way Cyclic Loading

This paper is presented the lateral dynamic response of pile groups embedded in dry sand under influence of vertical loads and the pile shape in-group, which are subjected to the lateral two-way cyclic loads. The laboratory typical tests with pile groups (2×1) have an aluminum-pipe (i.e. circular, square) pile, embedded length to diameter of pile ratio (L/D=40) and spacing to diameter ratio (S/D) of 3, 5, 7 and 9 are used with different cyclic-load ratio (CLR) 0.4, 0.6 and 0.8. The experimental results are revealed that both the vertical and lateral pile capacity and displacement is significantly affected by the cyclic-loading factors i.e. (number of cycles, cyclic load ratio, and shape of pile) .In this study, important design references are presented. Which are explained that the response of the pile groups under cyclic lateral loading are clear affected by the attendance of vertical load and pile shape. Where, it is reduction the lateral displacement of group piles head and increase lateral capacity about (50) % compared without vertical loads. On the other side, the pile shape is a well affected to the pile response where the level of decline in lateral displacement at the pile groups head in the square pile is more than circular pile about 20 % at the same load intensity.

Experimental observation on laterally loaded pile in unsaturated silty soil

An experimental study was carried out to investigate the effects of soil partial saturation on the behaviour of laterally loaded piles. The proposed study was conducted by means of centrifuge tests at 100g, where a single vertical pile was subjected to a combination of static horizontal load and bending moment. The study was conducted on a silty soil characterized with laboratory testing under saturated and unsaturated conditions. During flight, two different positions of water table were explored. The influence of density was investigated by compacting the sample with two different void ratios. Finally, the effects of a variation of saturation degree on the pile response under loading were studied by raising the water table to the ground surface. Data interpretation allows drawing different considerations on the effects of partial saturation on the behaviour of laterally loaded piles. As expected, compared to saturated soils, partial saturation always leads to a stiffer and resistant response of the system. However, the depth of the maximum bending moment is related to the position of the water table and the bounding effects induced by partial saturation appear to be more important for loose soils.

Behavior of vertical and batter piles under lateral, uplift and combined loads in non-cohesive soil

Piles and pile groups are subjected to various kinds of loadings in onshore and offshore structures. To simulate field conditions, different kinds of loadings, i.e., lateral, uplift and combined loading, were applied on vertical and batter pile foundation. Mild steel piles having outer diameter 22 mm and inner diameter 20 mm were used. Various tests were performed on single piles having different length-to-diameter ratio, viz. 18, 28 and 38. Modeling of the pile was done using the physical scaling laws. Different angles, i.e., 15°, 25° and 35°, were considered for negative and positive batter piles. The mild steel tank was designed to avoid the effect of boundary conditions. It was observed from the experiments that a negative batter pile with 35° angle and L/D ratio 38 provides maximum load-carrying capacity in every loading condition. The load-carrying capacity of piles under combined loading condition, i.e., lateral as well as uplift load, is found to be more as compared to monotonic loads, i.e., lateral or uplift loads. Further, an ANN model was developed for predicting the behavior of pile under various loading conditions. It is observed that the deflection values obtained from the ANN model and the experiment are in close agreement.

Prediction of local scour around circular piles under waves using a novel artificial intelligence approach

The scour phenomena around vertical piles in oceans and under waves may influence the structure stability. Therefore, accurately predicting the scour depth is an important task in the design of piles. Empirical approaches often do not provide the required accuracy compared with data mining methods for modeling such complex processes. The main objective of this study is to develop three data-driven methods, locally weighted linear regression (LWLR), support vector machine (SVR), and multivariate linear regression (MLR) to predict the scour depth around vertical piles due to waves in a sand bed. It is the first effort to develop the LWLR to predict scour depth around vertical piles. The models simulate the scour depth mainly based on Shields parameter, pile Reynolds number, grain Reynolds number, Keulegan–Carpenter number, and sediment number. 111 laboratory datasets, derived from several experimental studies, were used for the modeling. The results indicated that the LWLR provided highly accurate predictions of the scour depths around piles (R = 0.939 and RMSE = 0.075). Overall, this study demonstrated that the LWLR can be used as a valuable tool to predict the wave-induced scour around piles.

Effect of Runup over a Vertical Pile Supported Caisson Breakwater and Quarter Circle Pile Supported Caisson Breakwater

Effect of Runup over a Vertical Pile Supported Caisson Breakwater and Quarter Circle Pile Supported Caisson Breakwater

Experimental Study on Wave Interaction with Multiple Row Pile Breakwater

Coastal works where the tranquillity requirements are low porous pile breakwaters are considered as a good cost-effective substitute for the conventional type of breakwaters. In this study, an experimental investigation has been carried out in a two-dimensional wave flume to study the wave interaction with vertical pile breakwater. At 50 cm still water depth (h), interactions between regular waves (wave period T = 1.5 sec, 1.6 sec, 1.8 sec and 2.0 sec) and the pile breakwater of two different porosity (n = 0.65 and 0.80) and three different structure heights (hb = 40 cm, 50 cm and 60 cm) have been studied experimentally. Experimental results reveal that, minimum transmission coefficient (Kt = 0.55) is obtained for breakwater with lowest porosity (n = 0.65) and with emerged condition (hb/h = 1.2) for short wave period (T = 1.5 sec). Minimum reflection coefficient is obtained for breakwater with highest porosity (n = 0.80) and with submerged condition (hb/h = 0.8). It is also noticed that porosity has an effect on wave energy loss coefficient.

Comparisons of Local Scouring for Submerged Square and Circular Cross-Section Piles in Steady Currents

The local scouring that occurs around submerged vertical piles in steady currents was studied experimentally in this paper. Three experiments were carried out for square cross-section (SC) piles and a circular cross-section (CC) pile with the same width. The key point scour depths, including the center of the upstream boundary point (KC) and the two upstream corners (KM), were observed over time. The two-dimensional profiles and the three-dimensional topography around each pile were measured using a Seatek. The different scouring characteristics of the SC and CC piles were investigated. The experiment results show that the scour depth at KC is much smaller than that of KM. The equilibrium scour depth of the CC pile is far less than that of the SC piles. The scour and deposition distributions were different between the CC and SC piles. The maximum scour depth was found at the lateral rear of the CC pile, and the maximum deposition was observed in sections of the SC piles. The evolutions of the scour depths at KM are predicted using a developed exponential equation.