Pile Slope Research Articles

Potential of organic wastes typical of the Brazilian Amazon for fertilizer use in agriculture

Characterization of different organic wastes is essential to reveal alternative nutrient sources useful for agriculture. The objective of this work was to characterize a variety of organic wastes generated in the Brazilian Amazon in order to identify nutrient sources for potential use as organic fertilizers. Samples of nine different organic wastes from agricultural, livestock and forestry activities were collected in the state of Pará, Amazon region, Brazil. These samples were characterized using reference methods for analyses of organic fertilizers. Palm oil mill boiler ash was highly concentrated in P, K, Ca, and Mg and also highly alkaline, being considered a promising material for use as fertilizer and lime in acid soils. Palm oil mill decanter cake was the best N source; it also contained relevant amounts of K, S, and Zn. Cattle manure was more concentrated in N and oil palm empty fruit bunch in K. Residual eucalyptus charcoal was high in Ca but also in Na and Al. Oil palm fruit fiber, oil palm fruit shell, wood sawdust of the pile top, and wood sawdust of the pile slope were consistently poor in nutrients. All wastes presented low concentrations of As, Ba, Cd, Cr, Hg, Pb, and Se. This study identified organic wastes differing in prevalent nutrients for potential use as organic fertilizers. Such a difference could be explored in further studies by combining two or more wastes with complementary prevalent nutrients in order to better meet the nutritional requirements of different crops in the Brazilian Amazon.

WAVE TRANSMISSION COEFFICIENT OF INCLINED PILE BREAKWATER BASED ON A PHYSICAL MODEL

WAVE TRANSMISSION COEFFICIENT OF INCLINED PILE BREAKWATER BASED ON A PHYSICAL MODEL

Numerical analysis of horizontal bearing capacity of pile in clay slope

In this study, a series of numerical calculations were performed to investigate the lateral behavior of piles in slopes and in horizontal ground. First, a numerical model is created and then verified by comparing the numerical results with the results of model tests. The numerical results agree well with the results of model tests. Second, numerical calculations of different slopes were conducted to explore the effect of slope angle on the horizontal displacement of pile and bending moment. Then, the effect of slope angle on the foundation stiffness proportional coefficient m is investigated. The stress distribution of soil around the pile and the deformation of pile at different slope angles are also compared. Finally, the p–y curves of the different slope angles are compared. An improved p–y method is proposed to consider the effect of slope angle based on the numerical results. The results show that the bearing capacity of piles decreases with an increase in slope angle. The horizontal displacement of pile nonlinearly decreases along the pile body with the depth of pile. The bending moment of piles increases along the pile body with an increase in pile depth, and until 0.5 times of the pile length, the bending moment reaches the maximum value. As the slope angle increases, the maximum of bending moment tends to decrease. The distance from the slope toe to the pile section has a little influence on the pile bending moment and horizontal displacement. With an increase in slope angle, the horizontal foundation coefficient m gradually decreases.

Characterization of particle size segregation and heterogeneity along the slopes of a waste rock pile using image analysis

Large amounts of waste rock are produced during mining operations and often disposed of in large piles. Particle size segregation usually occurs during waste rock disposal, which can lead to high variations of particle size distribution (PSD) along the pile slope, increasing the risk for hydrogeotechnical instabilities. Determining segregation in situ is, therefore, critical to implement control measures and optimize deposition plans. However, characterizing PSD at field scale remains challenging because of the large dimensions of the pile, the instability of the blocks and the steep slopes. In this study, images, covering a 1400 m wide and 10 m high section of a waste rock pile, were taken and analyzed using image analysis to characterize segregation along the slope of the pile. PSD curves in different sections along the slope were determined and the segregation degree and characteristic diameters (e.g., D10, D50, D80,D95) were quantitatively compared. Results allowed to quantify segregation along the vertical direction of the pile, showing that segregation degree increased from − 0.77 ± 0.39 in the top (finer zone) to + 0.4 ± 0.14 in the bottom (coarser zone). Significant lateral heterogeneity was also observed with maximum diameters varying between 80 and 180 cm in the bottom section. Such segregation and lateral heterogeneity could induce significant variations of waste rock properties, with, for example, hydraulic conductivities varying by more than 2 orders of magnitude within the pile.

Limit Analysis for 3D Stability of Unsaturated Inhomogeneous Slopes Reinforced with Piles

Achieving slope stabilization by placing anti-slide piles has become an effective slope-reinforcement technique in geotechnical engineering. Based on the limit analysis method, this study investigated the 3D stability of unsaturated inhomogeneous piled slopes, incorporating three failure patterns: toe-failure, face-failure, and base-failure. The suction and effective unit weight profile under different effective saturation were considered and the soil cohesion was assumed as varied linearly with depth. A theoretical analysis of the lateral force acting on a row of rigid anti-slide piles with the same spacing in a row through plastically deforming soils is described while considering the soil suction and inhomogeneity. In addition, a new formula was developed to calculate the lateral forces provided by a row of piles. The genetic algorithm (GA) was used to obtain the minimum value of the factor of safety FS and the corresponding critical slip surface. The results of the study were compared with those of the existing literature to verify the feasibility of the proposed approach. In addition, the influences of key parameters on FS of 3D piled slopes were investigated by parametric analysis. The numerical results indicate that piled slope stability will be underestimated when the 3D effects and suction are not considered, and soil inhomogeneity has a negative impact on piled slope stability. It was also found that the probability for the occurrence of face-failure increases with increasing inhomogeneity and decreasing suction-induced effect, and the occurrence of face-failure significantly reduces the pile reinforcement effect. In addition, when the anti-piles are located at the slope toe, the base-failure mechanism yields the critical values of FS in most cases. This study can provide several reasonable suggestions for engineering applications and a theoretical basis for further studies on the stability of slopes reinforced with piles.

Evaluation of Liquefaction-induced Lateral Force on Pile in Slope by Centrifuge Tests

Pile foundations in liquefied ground may be subjected to a substantial force induced by lateral soil movement, which is crucial in the seismic design of pile-supported structures. Thus, this study aims to investigate the liquefaction-induced lateral force to piles by conducting centrifuge tests. Pile–deck systems installed in liquefiable finite slope with an angle of 27° were constructed and tested with different base motions. Results show that the liquefied slope pushes the piles toward the downslope, causing a large bending moment. The linear and uniform distributions of lateral soil pressure, which have been previously suggested for pile analysis in liquefied ground, were examined and compared with the measured maximum bending moment. The linear soil pressure profile reasonably predicted the bending moment compared to the results of the uniform profile. The empirical gradient factor of the linear profile was calibrated for the single piles and then implemented in the pile group analysis. The calibrated factor improved conventional methods for predicting the bending moment profile of group piles.

Experimental Analysis of Vertical Deformation and Bearing Characteristics of Bridge Piles in High and Steep Slopes

More and more rigid frame bridges with high piers and large spans are built in the high and steep slope areas of deep valleys in southwest China. The slow deformation of the slope in the geological sense often causes the problems of piles, which in turn causes damage of the upper bridges. The vertical bearing characteristics of bridge piles in slope still need to be conducted because of the peculiarity of slope topography. The vertical deformation and bearing characteristics of piles in the slope area were experimentally studied by considering different influencing factors and the fitting formula for the ultimate bearing capacity of the piles under vertical load is obtained. The results show that the vertical deformation and ultimate bearing capacity (defined by vertical limit settlement deformation of 0.013 times the pile diameter) of the pile are closely related to its position in the slope. The pile in the middle of the slope has the lowest vertical ultimate bearing capacity. Moreover, the side frictional resistance transfer depth of the pile in continuous slope is greater than that of the pile in unilateral slope. Additionally, the slope angle has a significant influence on the vertical bearing performance of piles. The delayed settlement of the pile top decreases approximately 40% at most and the vertical ultimate bearing capacity of the pile increases 48.6% at most as the slope angle decreases by 15°. Meanwhile, the side friction resistance of the pile increases with the decrease of slope angle. The bending moment applied to the pile top reduces the vertical ultimate bearing capacity of the pile and increases the axial force of the pile body. The results can provide data support for pile design and instability judgment with similar geological conditions.

Application of a damage constitutive model to pile–slope stability analysis

Piles were regarded as elastic materials in the traditional numerical simulation. The elastic pile would not reflect the damage of the pile in engineering, which would misjudge the reinforcement effect of piles on slopes. The specific objective of this study was to propose a damage constitutive model to replace the traditional elastic constitutive model in the numerical analysis of pile–slope stability. In this study, the pile was simulated by a damage constitutive model, which can reflect the plastic deformation of the pile. The factors of pile position and reinforcement ratio on a slope’s factor of safety (FOS) are investigated by the finite difference method using FLAC3D. The lateral displacement, bending moment, shear force, and soil pressure of balance-reinforced piles are used to study the difference between damage and elastic constitutive models. The results showed that the FOS considering the damage constitutive model could be smaller, approximately 15% less than that considering an elastic constitutive model under specific conditions. Furthermore, the difference between the two evaluation results of the internal force of the same pile can reach about 30%. It was observed that the elastic constitutive model would overestimate the reinforcement effect of the pile on the slope, which will cause potential safety hazards in engineering. This study provides a realistic damage constitutive model for the design and evaluation of slope-stabilizing piles.

Nonlinear Predictive Framework of the Undrained Clay Slope Effect on the Initial Stiffness of p-y Curves of Laterally Loaded Piles by FEM

The hyperbolic p-y curve method is commonly used to design laterally loaded piles, in which the initial stiffness is one of the two key parameters that need to be determined. In this paper, the effect of an undrained clay slope on the initial stiffness of p-y curves of laterally loaded piles was explored, and nonlinear models of the reduction factor (μ) were proposed. A series of finite-element analyses was performed for different pile–slope geometric relationships according to whether the slope geometry had influence on pile–soil interaction, in which the geometrical parameters were varied. Based on simulation results, a semi-empirical method was mainly used to derive nonlinear formulations for the undrained clay slope effect on the initial stiffness of hyperbolic p-y curves. The wedge failure theory was also used to analyze the effect of the dimensionless slope height on the initial stiffness. Comparing with other researchers’ reduction factor models, the results of the present model are in the reasonable range and can predict more cases. Test cases were used to validate the proposed model, and the results show that theoretical results are in better agreement with test results using the present model.

Numerical analysis of pile—slope stability and the soil arching around two adjacent piles

Numerical analysis of pile—slope stability and the soil arching around two adjacent piles

Study on pile cap effects of pile group foundations under linear wave action by a hybrid BEM and EEM method

For pile group foundations (PGFs) subjected to ocean wave action, diffraction waves from the large-scale pile cap can remarkably change wave loads on slender piles below the pile cap (i.e., pile cap effects). However, relevant influencing factors and the variation pattern of wave loads on piles are still unclear. To this end, this study develops a three-dimensional hybrid method for calculating wave loads on slender piles in PGFs under linear wave action. The presented method is implemented by combining the boundary element method (BEM) and the eigenfunction expansion method (EEM) and can consider the effect of diffracted waves from the pile cap. The proposed method is then applied to a truncated cylinder and a PGF with a square pile cap, and the calculated results are respectively compared with the analytical and numerical results. Excellent agreements verify the validity of the presented method. The effects of various factors, including cap shapes, cap dimensions, cap drafts, wave propagation directions, wave numbers, pile slopes, and pile tilt directions, on wave loads of piles are investigated using the presented method. The results show that wave numbers and cap horizontal dimensions have a very strong effect on wave forces on slender piles in PGFs, and wave forces on piles decrease substantially as they increase. However, the influence of cap drafts is weaker. The wave propagation direction determines the distribution pattern of wave load magnitudes at different pile locations, and this distribution pattern varies with different cap shapes. For tilted piles, the wave propagation direction and the pile tilt direction jointly affect (enhance or weaken) wave loads on piles, and the pile slope can amplify this effect. Wave loads on the external piles of the pile group are generally stronger and these external piles need to be reasonably strengthened. This research can assist with the design and optimization of PGFs for offshore bridges.

Stability Evaluation of Medium Soft Soil Pile Slope Based on Limit Equilibrium Method and Finite Element Method

The stability of an open-pit slope is an extremely important factor related to the safe production of an open-pit mine. It is the first safety technical problem encountered and should be solved in the process of mine design and production. By the means of an engineering geology and hydrogeological investigation of the waste dump area of the Nayuan open-pit coal mine and numerical simulation research, this paper analyzes and studies the slope stability of the stope and waste dump of the Nayuan open-pit coal mine in detail and puts forward measures such as slope prevention and automatic monitoring to achieve the goal of protecting the slope of the stope and waste dump and the surrounding environment. The main research results are as follows: (1) The geotechnical physical and mechanical indexes of stope and waste dump are collected and analyzed, and the geotechnical mechanical indexes in this report were determined, which basically meet the requirements of slope stability analysis. (2) The limit equilibrium method and finite element method were used to analyze and evaluate the current slope stability of the Nayuan open-pit coal mine. It was concluded that the foundation of the waste dump is basically stable, and the potential landslide modes of the slope are arc-shaped sliding surface and arc-shaped straight-line sliding surface. The numerical simulation and checking results showed that the current stope and waste dump slope are stable. (3) According to the analysis and evaluation results of slope stability, feasible slope prevention measures are put forward. The research results are of great significance to the safety of important facilities in open-pit mines and provide a basis for the design and safety implementation of open-pit slope engineering.

Nonlinear numerical simulation of dynamic response of pile site and pile foundation under earthquake

AbstractTo study the influence of the nonlinear connection of pile and soil on the dynamic response characteristics of the pile foundation, this article proposes to study the dynamic response of the bridge pile foundation to the slope by combining the centrifugal shaking table test and OPENSEES open source finite element program. This article introduces the pressure-dependent multiyield surface model based on confining pressure. Through the inverse calculation of the similarity ratio of the centrifuge model test, the OPENSEES two-dimensional nonlinear finite element model of the pile group in the slope section can be established. The centrifuge shaking table test is to input the preset seismic wave horizontally at the bottom of the model box. The form of seismic wave is El Centro wave verification of two-dimensional finite element model of the pile group in slope section under earthquake. The reliability of the model is verified by comparing the test and calculated values of dynamic response (residual horizontal displacement and final bending moment) of the pile body under five different peak acceleration seismic wave loading conditions. In the dynamic response experiment of slope pile foundation, in the embedded part below the bedrock surface, the residual horizontal displacement of each pile body is zero. Constrained by the cap beam and tie beam, the displacement of the free section of the pile group at these two positions is basically the same. Through comprehensive analysis, the displacement of P1 and P2 piles is basically the same. The calculated value of the final bending moment of P1 and P2 piles shows the same change trend as the test value, and the test value is slightly larger than the calculated value. The relative errors of the maximum final bending moment of P1 pile under each loading condition are 7.4, 7.8, 12.6, 3.9, and 9.6%, respectively, and the relative errors of P2 pile are 4.6, 3.6, 12.5, 13.6, and 11.5%, respectively. The analysis relative error is caused by the elastic element used in the calculation of the pile body, which is different from the mechanical behavior of the simulated pile body material in the test. Dynamic response of slope site according to the existing centrifuge test results can be seen that the deformation at the slope shoulder of slope site is the most obvious under the earthquake. The inclined interface of soft and hard rock and soil layer will aggravate the dynamic response of the overburden layer on the slope, weakening its ability of seismic energy consumption.

An Optimization and Adjustment Method of Pile Orientation for a Pile‐Supported Wharf Based on a Genetic Algorithm

The pile‐supported wharf is widely used in port wharf design due to its excellent adaptability. However, it may intersect in space because a large number of batter piles are used. In the design process of the pile‐supported wharfs, pile orientation adjustment is an essential process to avoid pile intersection. The arrangement of pile orientation in a structural section often takes several days manually. Sometimes, designers cannot avoid pile intersections after many attempts. At present, the software can only check pile intersections, but it cannot optimize pile orientations. Considering the priority order of adjusting the pile slope, the rotation angle, and avoiding a pile intersection, the objective function for optimization is designed, and the pile orientation is optimized and adjusted by a genetic algorithm. Then the performance of the algorithm is analyzed. Finally, the algorithm is applied to two practical cases of pile‐supported wharfs. One case involves the designers who failed to arrange the pile orientation. Moreover, satisfactory results of pile orientations are obtained in a few minutes. Therefore, the proposed method greatly improves labor efficiency.

Seismic stability analysis of two-stage slopes reinforced with one row of piles

Seismic stability of a two-stage soil slope reinforced by one row of piles is analyzed using the upper bound theorem combined with pseudo-static method considering the pile axial force. For a specified safety factor of the piled slope, explicit expression of the required pile shear resistance is derived, in which the effect of axial force of the piles on the potential slide mass omitted in most of previous studies is reasonably introduced. Analysis results of examples show that the pile shear resistance and potential slip surface by the proposed method are in good agreement with those by numerical simulation. The pile reinforcement effect on the slope is operational under smaller seismic conditions, whereas it is limited and not significant with the increase of the seismic excitations. The pile shear resistance and range of the critical slide mass increase with the horizontal seismic acceleration coefficient. Compared with the existing results omitting the pile axial force, more conservative upper bound solutions of the pile shear resistance are obtained by the proposed method, especially under higher design safety factor and seismic loads. Widening the bench and constructing the pile row near the slope crest are conducive to practicably optimize the reinforcement effect on the two-stage slope under seismic excitations.

Beneficial role of batter pile in slope under infinite uniform surcharge loading

Batter pile is used to find a more effective way to stabilize the slope. Thus, these two questions “where is the optimal location of batter piles on earth slopes?” and “which inclination angle is most beneficial for pile in earth slopes?” arise. The numerical simulation was conducted to investigate the performance of slope reinforced by batter pile. The surcharge loading, inclination angle and pile location were varied while keeping geometry of the slope and the soil property constant. The surcharge loading was applied on the slope crest by steps. The inclination angle varied from 0° to 20°. The pile was placed at middle-down (MD), middle (MI), middle-upper (MU) and upper (UP) part of slope, respectively. A finite length of batter pile (10 m) was adopted, and the pile toe was free. Four series of numerical models were proceeded to search the optimum location and inclination angle for pile, one that provided maximum lateral resistance. By analyzing the slope deformation and pile bending moment, the effects of position and inclination angle of pile were determined. The following conclusions could be drawn: (1) The surcharge loading on the slope crest will influence the deformation of slope remarkably. Both the lateral displacement and settlement increases simultaneously with the raise of loading. (2) The lateral displacement and settlement of slope vary as the pile location moves from the crest to the toe. The slope of UP condition has the the minimum lateral displacement, following by MI, MD and MU condition. The ranking of settlement is same with the lateral displacement. That is to say, the UP condition is the best location for piled slope, followed by MI condition. (3) The batter pile is beneficial for slope engineering, which can not only reduce the deformation of slope, but also decrease the bending moment exerted on pile shaft. The inclination angle should be in a reasonable range, a relatively small inclination angle could not fully utilize the potential capacity of batter pile, while exaggerated inclination degree is not befitting for construction. The inclination angle of 15° is an optimal choice for batter pile in slope. (4) The inclination angle has mutual effect with the pile location, they should be considered synchronously. For comprehensive consideration, UP 10°, UP 15°, MI 15° and MI 20° are preferred options for the piled earth slope when subjected to surcharge loading.

Euler–Bernoulli Pile Element for Nonlinear Buckling Analysis of Single Piles in Slope

Abstract Piles are sometimes unavoidably embedded in slopes for supporting buildings on hills. In contrast to a pile on a horizontal ground, a pile in slope is acted on by additional sliding force ...

Stability analysis of slope reinforced by double-row stabilizing piles with different locations

Slope failure occurring could generate enormous loss to both human lives and properties, and stabilizing piles are broadly used for slope reinforcement as a significant anti-slip retaining structure. The performance of the stabilizing piles is strongly affected by different locations. Presently, most literature focuses on the location selection of single-row stabilizing piles. This paper introduces a classic slope and makes further stability analysis of the slope reinforced by single- and double-row stabilizing piles in different locations. According to the potential sliding surface, the distribution of the bending moment and the thrust, the results show that the failure modes of the slopes reinforced by single- and double-row stabilizing piles are different. As the single-row piles move towards the top of the slope, the failure mode of the piled slope takes on a “shallow-deep-shallow” trend. Moreover, as the pile location and spacing change, the failure modes stabilized by double-row piles can be divided into five categories which could be classified as shallow and deep sliding, and the thrust ratio increases with the increasing pile spacing. Regarding the safety factor, it can be concluded that the optimal location for single-row stabilizing piles within a slope is the lower-middle part of the slope, and the optimal locations for double-row stabilizing piles are proposed at the lower and lower-middle parts of the slope, respectively. The presented analysis could provide significant insight into the design of slopes stabilized by stabilizing piles.

Kinematic and Inertial Interaction of Single and Group Piles in Slope by Displacement Phase Relation

ABSTRACT This study evaluated the phase relationship among the input motion, ground response, and pile response, which is a key consideration in the analysis of the kinematic–inertial interaction for piles. Dynamic centrifuge tests were conducted on single and group piles embedded in slopes of dry sands. Test results showed that the single pile moved in the opposite phase with the ground movement, whereas the group piles moved nearly in phase. The phase relationship was significantly affected by rocking motion. Therefore, the kinematic force acted as a resistance to the single pile and an additional load to the pile group.

Effect of Edge Distance on Lateral Capacity of Piles in Cohesionless Soil Slopes

Recent advances in the understanding of deep foundation mechanisms suggest that the pile foundations can be used in both level grounds and the sloping grounds to appropriately support the heavy axial and lateral loads coming from the superstructures. The lateral load-carrying capacity of the pile in the sloping ground is different from the level ground due to the presence of slope and pile location (i.e., edge distance). In this study, extensive numerical analyses were performed to understand the behavior of a laterally loaded pile in cohesionless soil slopes by using the three-dimensional finite element method. Effect of various influencing parameters like slope inclination, relative density, angle of internal friction, modulus of elasticity of soil, unit weight of soil, L/D ratio of a pile, and pile diameter on the laterally loaded pile with a change in edge distance was studied. Results from the numerical analyses were compared with the previous experimental studies. An attempt has also been made to find out critical edge distance (i.e., where the effect of slope angle is negligible on lateral capacity) of the pile for different cohesionless soils with varying slope configurations. The critical edge distance is found to be varying between 5.0–7.5D, 7.5–10.0D, and 10.0–15.0D with slope inclinations of 20°, 30°, and 40°, respectively.