Inner damage identification and residual strength assessment of a 3D printed tunnel with marble-like cementitious materials using piezoelectric transducers

Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.

A Study of Molecular Resection Margins for Esophageal Squamous Cell Carcinoma Using Large Pathologic Sections

OBJECTIVE It has been shown that application of molecular biological techniques to surgical margins of some cancers could predict risk of local recurrence. However, the optimal length of surgical resection with tumor-free surgical margins for esophageal squamous cell carcinoma （ES- CC） is unknown. This study was conducted to evaluate the optimal length of surgical resection for ESCC with molecularly tumor-free surgical margins marked by p53 and Ki67.METHODS Surgical specimens from 70 patients with ESCC were collected for study. The lengths of the upper margin, tumor, and lower margin of every specimen were measured during the operation. Each specimen was divided into three large pathologic sections, stained with H＆E and immunohistochemically for p53 and Ki67, and examined microscopically. The lengths of the upper and lower resection ends were measured for p53 and Ki67 positive expression. The actual surgical lengths were calculated by the principle of rational shrinkage.RESULTS All surgical margins were histologically tumor-free, while the positive rates of p53 and Ki67 were 66% and 54%. The positive rates of p53 and Ki67 in the upper resecti0n end were 17% and 20%. The mean lengths of the upper resection end showing p53 and Ki67 positive expression were 1.08±1.12 cm and 1.64±1.01 cm, and the maximum lengths were 3.73 cm and 3.26 cm. The positive,rates of p53 and Ki67 in the lower resection end were 20% and 23%. The mean lengths of the lower resection end of p53 and Ki67 with positive expression were 1.11±1.15 cm and 1.34±0.94 cm, and the maximum lengths were 3.73 cm and 3.61 cm.CONCLUSION The optimal length of surgical resection with molecularly tumor-free surgical margins of ESCC is not more than 5 cm.

节理岩体的一维动态等效连续介质模型的研究

基于黏弹性理论,提出平行节理岩体的一维动态等效连续介质模型,该模型适用于纵波(P波)垂直通过一组等间距平行节理岩体的动力学问题。该模型包含黏弹性介质模型和虚拟波源概念。黏弹性介质模型主要描述应力波通过节理的衰减和时间的滞后;而虚拟波源的概念则描述应力波在平行节理之间的多次反射。根据已有解析解可以确定黏弹性介质模型中的未知参数。通过和位移不连续方法的比较,验证平行节理岩体的一维动态等效连续介质模型的正确性;该模型可有效地应用于研究通过一组平行节理岩体的P波传播问题。结果表明,该研究可以简化应力波传播问题的复杂性。

Stochastic seismic wave interaction with a rock joint having Coulomb-slip behavior

Seismic wave interaction with a slippery rock joint with an arbitrary impinging angle is analytically studied based on the conservation of momentum on the wave fronts. Based on the displacement discontinuity method, the wave propagation equations are derived for incident P- and S-waves. By comparison, the calculated transmission and reflection coefficients for normal incident waves are the same as the existing results, which proves the wave propagation equation obtained in the paper is correct. The wave propagation derived in the context can be applied to incident waves with different waveforms. Stochastic seismic waves are then used to analyze the seismic wave interaction with the slippery rock joint, where the stochastic seismic waves are generated from frequency spectra. The parametric studies are carried out to investigate the effect of type, intensity and impinging angle of the incident seismic waves on the wave propagation across the slippery rock joint.

On the four-dimensional lattice spring model for geomechanics

Recently, a four-dimensional lattice spring model(4D-LSM) was developed to overcome the Poisson’s ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some aspects of the 4D-LSM on solving problems in geomechanics are investigated, such as the ability to reproduce elastic properties of geomaterials, the capability of solving heterogeneous problems,the accuracy on modelling stress wave propagation, the ability to solve dynamic fracturing and the parallel computational efficiency. Our results indicate that the 4D-LSM is promising to deal with problems in geomechanics.

A critical review of preparation design and workability measurement of concrete material for largescale 3D printing

In recent few years, significant improvement has been made in developing largescale 3D printers to accommodate the need of industrial-scale 3D printing. It is of great feasibility to construct structural components and buildings by means of 3D concrete printing. The major issues of this innovative technique focus on the preparation and optimization of concrete materials which possess favourable printable properties as well as the measurement and evaluation methods of their workability. This paper firstly introduces three largescale 3D printing systems that have been successfully applied in construction industry. It then summarizes the commonly used raw materials in concrete manufacturing. Critical factors that should be particularly controlled in material preparation are specified. Easy-extrusive, easy-flowing, well-buildable, proper setting time and low shrinkage are significant for concrete mixture to meet the critical requirements of a freeform construction process. Thereafter, measuring methods that can be employed to assess the fresh and hardened properties of concrete at early stages are suggested. Finally, a few of evaluation methods are presented which may offer certain assistance for optimizing material preparation. The objective of this work is to review current design methodologies and experimental measurement and evaluation methods for 3D printable concrete materials and promote its responsible use with largescale 3D printing technology.

Simulation of viscoelastic behavior of defected rock by using numerical manifold method

Numerical simulations of longitudinal wave propagation in a rock bar with microcracks are conducted by using the numerical manifold method which has great advantages in the simulation of discontinuities.Firstly,validation of the numerical manifold method is carried out by simulations of a longitudinal stress wave propagating through intact and cracked rock bars.The behavior of the stress wave traveling in a one-dimensional rock bar with randomly distributed microcracks is subsequently studied.It is revealed that the highly defected rock bar has significant viscoelasticity to the stress wave propagation.Wave attenuation as well as time delay is affected by the length,quantity,specific stiffness of the distributed microcracks as well as the incident stress wave frequency.The storage and loss moduli of the defected rock are also affected by the microcrack properties;however,they are independent of incident stress wave frequency.

Simulation of blast induced crater in jointed rock mass by discontinuous deformation analysis method

Rock blasting is a dynamic process accom panied with the propagations of shock waves and the dispersion of the explosion gas.This paper adopts the discontinuous deformation analysis(DDA)method to simulate the rock blasting process.A dynamic parameter adjustment and the non-reflecting boundary condition are implemented in the DDA method.The sub-block DDA method to simulate fracture problems is used.The blasting process in jointed rock mass is simulated by application of the explosion gas pressure on the expanding borehole walls and induced connected fracture surfaces around the boreholes.The blast craters with different overburdens are derived.The whole process including the explosion gas dispersion,borehole expansion,rock mass failure and cast,and the formation of the final blasting piles in rock blasting are well reproduced numerically.Parametric study for different overburdens is carried out,and the results are analyzed and discussed.

Transient electromagnetic detection method in water-sealed underground storage caverns

Taking advantage of the water sensitivity of the transient electromagnetic method(TEM),this study assesses the effectiveness of the water curtain system for underground LPG storage caverns during the excavation period.It also detects fracture water flow during the excavation process in light of the practice of two pilot large underground LPG storage caverns in China.Comparative maps of apparent resistivity derived from TEM measurements before and after water-filling during the excavation process have been discussed to improve the quality of the water curtain system.This is the first case to apply TEM to detect the quality of the water curtain system during the construction of underground LPG storage cavern projects,and it is found to be practical,more visualized and worth popularizing.

Micro-destructive assessment of subgrade compaction quality using ultrasonic pulse velocity

The ultrasonic pulse velocity(UPV)correlates significantly with the density and pore size of subgrade filling materials.This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality.The study measures the changes in UPV across dry density and compaction characteristics.The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve,primarily influenced by internal water molecules.The maximum dry density exhibits a positive correlation with the rock content,while the optimal moisture content demonstrates an inverse relationship.As the rock content increases,the relative error of UPV measurement rises.The UPV follows a hump-shaped pattern with the initial moisture content.Three intelligent models are established to forecast dry density.The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.

A review on effects of different factors on gas explosions in underground structures

Underground structures are normally located in highly-confined and congested spaces,which may lead to severe gas explosion accidents,with significant human and economic losses.For accurately evaluating the consequences of these explosions,a variety of influencing factors need to be considered,including concentrations of gas mixtures,vent conditions,obstacles,and ignition features.Moreover,a good review on these influencing factors is important for a better understanding of explosion behavior,e.g.,the deflagration to detonation phenomenon.In this study,some critical influencing factors for gas explosions in underground or confined spaces are investigated,and the effects of the factors on such gas explosions are examined.The results are discussed,along with findings from literature.The present study provides a reference for future studies on safety management and consequence mitigation for underground gas explosions.