An analytical solution for longitudinal impedance of a large-diameter floating pile in soil with radial heterogeneity and viscous-type damping

An analytical model is presented for solving the longitudinal complex impedance of a large-diameter floating pile in viscoelastic surrounding soil with radial heterogeneity and viscous-type damping, taking the effect of three-dimensional wave propagation of soil and lateral inertia of the pile shaft into account. The corresponding analytical solution for longitudinal impedance is also derived and validated via comparisons with existing solutions. The influences of the pile length, Poisson’s ratio of the pile shaft and the viscous damping coefficient, as well as the degree and radius of disturbed surrounding soil, on the longitudinal impedance of the pile shaft are examined by performing parametric analyses. It is demonstrated that the proposed analytical model and solution are suitable for the longitudinal vibration problem of a large-diameter pile and radially inhomogeneous surrounding soil, especially when the pile slenderness is low. In addition, the present solution can be easily degenerated to describe the longitudinal vibration problem relating to a large-diameter floating pile in radially homogenous soil or a pile with fixed-end support

New analytical solutions for longitudinal vibration of a floating pile in layered soils with radial heterogeneity

Based on the theory of wave propagation in three-dimensional (3D) continuum, a new analytical approach for the longitudinal vibration characteristics of a floating pile in layered soils with radial heterogeneity is developed by employing a viscous-type damping model. Firstly, an analytical solution for the longitudinal complex impedance at the pile head is deduced by employing the Laplace transform and complex stiffness technique with the compatibility conditions of the pile and radially inhomogeneous surrounding soil. Secondly, a semi-analytical solution in the time domain is further acquired by using the inverse Fourier transform method. Furthermore, the corresponding analytical solutions are validated through contrasts with previous solutions. Finally, parametric analyses are underway to investigate the effect of radial heterogeneity of surrounding soils on longitudinal vibration characteristics of floating piles. It is indicated that the proposed approach and corresponding solutions can provide a more wide-ranging application than the simple harmonic vibration for longitudinal vibration analysis of a floating pile in soils

Probabilistic method for the size design of energy piles considering the uncertainty in soil parameters

Energy piles have attracted increasing attention as profitable solutions for the utilization of shallow geothermal energy. Although various complex geotechnical design models of energy piles have been proposed, a simplified sizing method that considers the uncertainty propagation in the soil is required. In this study, a Monte Carlo Simulation-based method was proposed for the size design of energy piles considering the uncertainty of parameters in the soil, such as thermal conductivity and friction angle. The small-sample analysis method of Markov chain Monte Carlo simulation combined with the Bayesian theoretical framework was developed to generate equivalent samples. Subsequently, the thermal response function and thermomechanical load transfer methods were employed to address the failure probability of the energy pile in the serviceability limit state and ultimate limit state. In addition, a case study was presented to illustrate the implementation of the proposed probabilistic sizing method. The analysis results of the case study confirm the necessity of modeling the soil uncertainty in the energy pile size design

Measurement of Additional Strains in Shaft Lining Using Differential Resistance Sensing Technology

As is well known, shaft lining fracture is the main disaster resulting in a large amount of fatalities and property loss. Thus, the additional strain is a key parameter to evaluate the safety condition of existing shaft linings. In this study, a new type of safety monitoring system based on differential resistance sensing technology is developed to measure the additional strain in shaft linings. In this paper, the theatrical study, the working principle, and the function of the newly developed monitoring system are fully presented. To investigate the reliability and effectiveness of the monitoring system, the differential resistance sensors are used to measure the horizontal and vertical strains at different elevations in a shaft lining during reinforcing the fracture inside the shaft lining. It can be found that from the test results the monitoring system based on differential resistance sensing technology can measure the deformation of the existing wall lining during stratum grouting. Therefore, it can be concluded that the newly developed monitoring system is significant for fracture warning and reinforcement engineering

Multipoint measurement of early age shrinkage in low w/c ratio mortars by using fiber Bragg gratings

In this study, a systematic sensing method has been proposed and developed to measure the early age shrinkage in low w/c ratio mortars. Fiber Bragg grating (FBG) strain and temperature sensors have been installed using a specialized installation method and utilized for measuring the internal strains and temperatures in a cylindrical mortar specimen. To achieve multipoint measurement of strains and temperature, two groups of FBG sensors with different initial wavelengths connected with two optical lines were taken as strain and temperature sensor series respectively. To keep the FBG vertical, copper tubes, as the channels for distributing the optical lines with FBGs, were employed during casting. Finally, the copper tube protecting the FBG strain sensors was removed slowly from the specimen while the FBG temperature sensors were kept in the other copper tube through the whole testing process. In this way, shrinkage strains and temperatures were collected at the beginning of the setting. It is found that there is no significant difference between the temperature values measured at different elevations in the specimen. (C) 2014 Published by Elsevier B.V

Steel Corrosion in Magnesia-Phosphate Cement Concrete Beams

The acoustic emission (AE) technique was employed to investigate the corrosion-induced deterioration of steel-reinforced magnesia-phosphate cement (MPC) concrete beams under the coupling effect of loading and accelerated chloride diffusion. A cement-based piezoelectric sensor was used for AE detection owing to its high sensitivity and good compatibility with the concrete matrix. Power spectral density analysis and continuous wavelet transform were used to process the detected AE signals. It was found that the average frequency shift was closely related to the damage accumulation level in the reinforced MPC concrete beams. Based on the frequency characteristics of the detected AE signals during wet-dry cycles, the corrosion-induced degradation process of MPC beams was divided into three stages, from micro-cracking to localised macro-crack propagation. Wavelet analysis revealed the energy density distribution of the AE waveform, which was used to differentiate signal features between reinforcement corrosion and concrete cracking. In addition, comparisons in terms of the accumulated AE event number and half-cell potentials showed that MPC and OPC concrete had comparable corrosion inhibition capabilities

Measurement of Early-Age Strains in Mortar Specimens Subjected to Cyclic Temperature

As well known, the volume change induced by environment temperature variation can lead to cracking at the surface of cementitious materials with low water-cement ratio. Thus, it can be said that there is a pressing need to reveal the early-age performance of cementitous materials in a variable environment temperature. Conventional thermocouple and strain gauge have been widely used for measuring temperature and strain in cementitious materials, respectively. However, conventional sensors have several limitations for measuring strain and temperature in cementitous materials such as too many cables for multipoint measurement, short circuit, and electromagnetic interference. Compared to conventional electrical strain gauge, fiber Bragg grating (FBG) has several inherent advantages including multiplexable, resistance to electromagnetic interference, and stable signal in long distance transmission. In this study, two lines mutiplexed with FBG strain and temperature sensors were fabricated and employed to measure the quasi-distributed strain and temperatures in mortar specimens subjected to cyclic temperature

Effects of water content, magnesia-to-phosphate molar ratio and age on pore structure, strength and permeability of magnesium potassium phosphate cement paste

In this study, the pore structure of magnesium potassium phosphate cement paste is investigated using mercury intrusion porosimetry. Several mix proportions, obtained by changing the magnesia-to-phosphate molar ratio (M/P) and the water-to-cement mass ratio (W/C) of the material, are involved. It is found that lower W/C and longer material age make the porosity lower and the pore structure finer. When the W/C is kept constant, both porosity and critical pore diameter are not monotonic functions of M/P, but the M/P of 6 gives the lowest porosity and the smallest critical pore diameter. Also, the M/P of 6 shows the highest compressive strength and the lowest intrinsic permeability. Based on the experimental results, empirical models describing the relations between the properties and pore structure parameters (porosity phi and critical pore diameter d(c)) of MKPC paste are developed. The compressive strength is inversely proportional to phi, and the intrinsic permeability is directly proportional to d(c)(2) phi. (C) 2014 Elsevier Ltd. All rights reserved

A new approach for longitudinal vibration of a large-diameter floating pipe pile in visco-elastic soil considering the three-dimensional wave effects

A novel approach is presented to describe the dynamic interaction system of a large-diameter floating pipe pile and surrounding soils, taking the three-dimensional wave effects into account. The corresponding analytical solutions for longitudinal complex impedance are obtained and subsequently validated via comparisons with existing solutions. Comparative analyses are also performed to illustrate the difference between the present and previous solutions, concerning the wave propagation effect in the radial direction on the longitudinal dynamic vibration of pile shaft. Furthermore, the effects of Poisson’s ratio and visco-elastic support beneath the pile toe, on the longitudinal dynamic vibration of pile shaft, are investigated. It is indicated that the presented approach and corresponding solutions provide a more wide-ranging application for longitudinal vibration analysis of a large-diameter floating pipe pile, which can also be reduced to analyze the longitudinal vibration problems of large-diameter floating solid pile and fixed- end pipe pile