Buckling Analysis of Piles in Multi-Layered Soils

Pile buckling is infrequent, but sometimes it can occur in slender piles (i.e., micropiles) driven into soils with soft layers and/or voids. Buckling analysis of piles becomes more complex if the pile is surrounded by multi-layered soil. In this case, the well-known Timoshenko’s solution for pile buckling is of no use because it refers to single-layered soils. A variational approach for buckling analysis of piles in multi-layered soils is herein proposed. The proposed method allows for the estimation of the critical buckling load of piles in any multi-layered soil and for any boundary condition, provided that the distribution of the soil coefficient of the subgrade reaction is available. An eigenvalue-eigenvector problem is defined, where each eigenvector is the set of coefficients of a Fourier series describing the second-order displaced shape of the pile, and the related buckling load is the eigenvalue, thus obtaining the effective buckling load as the minimum eigenvalue. Besides the pile deformed shape, the stiffness distribution in the multi-layered soil is also described through a Fourier series. The Rayleigh–Ritz direct method is used to identify the Fourier development coefficients describing the pile deformation. For validation, buckling analysis results were compared with those obtained from an experimental test and a finite element analysis available in the literature, which confirmed this method’s reliability.

A creep model of pile-frozen soil interface considering damage effect and ice effect

An important source of time-dependent pile deformation is creep behavior at pile-frozen soil interface in permafrost regions. A creep model for pile-frozen soil/ice interfaces was proposed based on a series of multistage creep tests. The test results show that the creep behavior of the pile-frozen soil/ice interfaces is easily observed at a steady rate larger than 0 even at a small load level, which increases as the increase of load level. The elastic shear modulus increases at a slowing down rate with the increase of load level. The interfaces are mainly strengthened during the creep process until the occurrence of the accelerating creep, which is more obvious for frozen soil. A large amount of ice in frozen soil can enhance the creep rate and reduce the carrying capacity of pile foundation. The viscosity [Formula: see text] reflecting steady creep rate, the instantaneous shear modulus [Formula: see text], and the critical stress [Formula: see text] required for describing damage behaviors distribute in the form of Bigaussian asymmetric peak function with ice content. The Burger model considering ice effect and damage effect is feasible to describe the entire creep behavior of the interfaces. Sensitivity analysis reveals that ice content in frozen soil has a marked influence on pile deformation, a cooling method can probably adjust the creep deformation of pile in frozen soil with high ice content.

Experimental Study on Deformation and Load Transfer Mechanisms of Symmetrical Batter Piles under Vertical Loading

Under the action of vertical loading, batter piles rarely appear individually, as they undergo horizontal and vertical displacements at the same time and produce a sizeable additional bending moment. However, previous studies have mainly focused on a single batter pile, which is inconsistent with engineering practices. Although single pile tests can easily reveal its working behavior, they also ignore two important factors, namely, the internal force redistribution caused by the deformation limitation of the mirror-like pile, and the interaction between the symmetrical piles and “clamped” soil (the soil between two symmetrical piles). Therefore, this paper took symmetrical batter piles as the test object to explore the influence of the two factors on the load transfer mechanism. Moreover, the deformation mode, distribution of inertial forces, and group effect of symmetrical batter piles were also discussed. The results showed that the “clamping effect” caused by the pile deformation had a significant impact on the load transfer. Under vertical loading, the flexible symmetrical floating batter piles were the only deformation mode. Under the constraint of the cap and mirror-like batter piles, the symmetrical conformation partially compensated for the disadvantage of the additional bending moment.

Model Uncertainty for Settlement Prediction on Axially Loaded Piles in Hydraulic Fill Built in Marine Environment

Model uncertainty is present in many engineering problems but particularly in those involving geotechnical behavior of pile foundation. A wide range of soil conditions together with simplified numerical models makes it a constant necessity to review the accuracy of the predictions. In this paper, the outputs of some seventy (70) pile axially-loaded tests have been reviewed with a classic numerical model to assess pile deformation. Probabilistic approach has been used to quantify uncertainties coming from soil tests, statistic uncertainty and also from the model itself. In this way, a critical review of the prediction method and a way to quantify its uncertainty is presented. The method is intended to be used in a wide range of engineering problems.

An Application of BOTDR to the Measurement of the Curing of a Bored Pile

In order to study the deformation of a bored pile during concrete curing, it is necessary to monitor the strain of the pile. In this paper, Brillouin optical time domain reflectometer (BOTDR) technology is used to monitor the pile strain during concrete curing, and reliable monitoring data are obtained. These data provide a basis for the study of pile deformation and pile–soil interaction during curing of bored cast-in-place piles. Compared with the traditional point strain sensor, the distributed fiber optic sensor is simple in layout and highly accurate; it can fully reflect the strain changes of the pile; the experiment also shows the advantages of distributed fiber optic sensing technology over the traditional point monitoring method.

Fiber Bragg Grating Sensors for Pile Jacking Monitoring in Clay Soil

The small deformation of the model pile in a pile jacking test makes its accurate measurement very difficult. Based on the installation method of clamping at both ends, a sensitized miniature fiber Bragg grating (FBG) strain sensor was developed to measure the pile strain of small-size model piles. This study investigated the working principle of the sensitized miniature FBG sensor and analyzed the strain transfer characteristics of the sensor by calibration test. The lateral resistance and the earth plug resistance of the model pile were measured accurately by the grooves embedded in the outer tube of the double-wall opening model pile and the sensors directly pasted on the surface of the inner tube. The results of this study show that the sensitized miniature FBG strain sensor has the advantages of high sensitivity, strong interference resistance, and high test accuracy. The FBG strain sensor was completely fixed on the pile by clamping supports at both ends, and the strain measured using the FBG strain sensor was found to be consistent with the pile deformation.

ELASTIC CHARACTERISTICS OF BRUSH PILE ON THE MUNICIPAL MACHINE WORKING EQUIPMENT

Introduction. The paper describes the actual problem of increasing the operating life of the brush working body (BWB) and improving the cleaning quality. Moreover, the authors discuss the factors affecting the quality of the road surface cleaning and the brush pile resource.Materials and methods. The research presents the results of the interaction process of the BWB pile with the cleaned surface of the roadway. In addition, the authors demonstrate the mathematical model of the interaction process with the basic surface. The simulation is carried out using the MATLAB software and Simulink extension. The authors also identify the factors that contribute the efficiency reduction of the municipal machine working process.Results. As a result of the simulation, the authors obtained the graphs of the pile deformation changing and the BWB pressing force changing. When processing the experimental data the researches also obtained the graphs of the brush pile plotted deformation from the BWB contact force and from 2, 3, 4 disks. For further mathematical modeling the authors determined the stiffness of the BWB pile under various loads. Therefore, the paper presents the approximation of the experimental dependence of the brush pile deformation on the pressing force and shows the regression equation.Conclusion. In conclusion, the authors determined the elastic characteristics of the BWB pile. By the comparing process of the experimental and theoretical data obtained from the mathematical model analysis, the authors found that the difference between them was less than 10%. The obtained results allowed confirming the mathematical model adequacy of the interaction process between the BWB pile and the cleaning surface.