高墩大跨连续刚构梁桥0#块裂纹裂缝成因分析及消除措施

我国高速公路建设在进入“十四五”规划后,更加注重大型结构物在施工及运营过程中的安全,结合G85银昆高速公路友联红河特大桥19#主墩(主墩设计高度75 m)0#块施工为研究对象,通过0#施工中预埋混凝土温控元件与应力应变传感器,对比仿真模型分析计算结果,总结出西北地区高墩大跨连续刚构梁桥0#块裂纹裂缝产生的原因和机理,提出实时解决方案,为后期类似工程提供借鉴。

用分形方法研究水力压裂裂缝扩展机理

根据岩石断裂力学理论证明了水力压裂裂缝具有与缝内压力分布无关的自相似扩展特征,在此基础上,建立了裂纹扩展的分形弯折模型来描述裂纹的动态扩展,根据这个模型,推导了考虑裂纹分形扩展的裂缝宽度方程,从而可以在给定条件下计算出裂缝维数,缝内压力分布,裂缝延伸速度,裂缝尺寸等。

浅析混凝土常见裂缝成因及防治措施

混凝土是一种非匀质脆性材料。由于它本身变形、气温和施工工艺等因素,不可避免地存在裂纹或裂缝;为此,我们应认真分析常见裂缝的成因,并找出预防和处理有害裂缝的有效措施。

微波无损检测技术在工程中的应用研究

系统地介绍了微波无损检测的原理和微波无损检测技术在工程中的应用,指出了目前微波无损检测技术在应用中存在的问题,给出了今后研究工作的方向。

高效能红外线就地加热再生技术在石安改扩建工程中的应用

阐述高等级沥青混凝土路面早期损坏的原因及病害,利用高效能红外线就地加热技术,解决了沥青路面出现的裂纹、裂缝、坑槽、网裂的修补问题,提高了沥青路面的养护质量。

拖车的使用与保养

拖车的使用与保养１．出车前应认真检查轮胎气压、牵引装置和制动效果等。要求牵引销要锁定牢固，并另有保险铁链与拖拉机连接，以防销子丢失、折断和牵引三角架断裂等意外情况发生。如发现问题，应予排除，然后方可出车。２．装载的货物宽度不能超出拖车宽度，高度不能高...

Visual representation and characterization of three-dimensional hydrofracturing cracks within heterogeneous rock through 3D printing and transparent models

The heterogeneity of unconventional reservoir rock tremendously affects its hydrofracturing behavior. A visual representation and accurate characterization of the three-dimensional （3D） growth and distribution of hydrofracturing cracks within heterogeneous rocks is of particular use to the design and implementation of hydrofracturing stimulation of unconventional reservoirs. However, because of the difficulties involved in visually representing and quantitatively characterizing a 3D hydrofracturing crack-network, this issue remains a challenge. In this paper, a novel method is proposed for physically visualizing and quantitatively characterizing the 3D hydrofracturing crack-network distributed through a heterogeneous structure based on a natural glutenite sample. This method incorporates X-ray microfocus computed tomography （μCT）, 3D printing models and hydrofracturing triaxial tests to represent visually the heterogeneous structure, and the 3D crack growth and distribution within a transparent rock model during hydrofracturing. The coupled effects of material heterogeneity and confining geostress on the 3D crack initiation and propagation were analyzed. The results indicate that the breakdown pressure of a heterogeneous rock model is significantly affected by material heterogeneity and confining geostress. The measured breakdown pressures of heterogeneous models are apparently different from those predicted by traditional theories. This study helps to elucidate the quantitative visualization and characterization of the mechanism and influencing factors that determine the hydrofracturing crack initiation and propagation in heterogeneous reservoir rocks.

Fractal characteristics of cracks and fragments generated in unloading rockburst tests

True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.

Numerical simulation on effects of embedded crack on rock fragmentation by a tunnel boring machine cutter

Based on the simplification of cutting process,a series of numerical simulations were conducted using a 2-D discrete element method to explore the effects of embedded cracks with different dip angles on the rock fragmentation process,cutting characteristics and breaking efficiency.The results show that the simulated results are in a good agreement with previous theoretical study.The main crack propagates to the top tip of embedded crack,except when the dip angle is 90°.Side cracks which are more fully developed in the rocks containing embedded cracks tend to propagate towards the free surface.According to the history of vertical cutting force,it is shown that the peak force is decreased by embedded cracks.The study on cutting efficiency was conducted by combining the quantity of crack and cutting energy.And the results show that breaking efficiency can be treated as a decreasing or a increasing function when the dip angle is less or larger than 30°,respectively.Breaking efficiency is higher than that in intact rock when the dip angle is larger than 45°.

Study on mechanism of circumferential cracks in cold-region tunnels

There exists frost damage in cold-region tunnels. The circumferential cracks affect the function of tunnels. Using three-dimensional finite element method, the authors analyzed the mechanism of circumferential cracks in cold-region tunnels It is proved that the internal thermal stress in lining exceeds the tensile strength of concrete, which is the direct cause for circumferential cracks occurring. The laws of thermal stress in lining induced by parameters such as temperature drop, horizontal drag coefficient and length of lining are analyzed. The conclusions are valuable to the design and construction of cold-region tunnels considering the thermal stress.

Experimental study on tensile failure process of double-K fracture parameters in roller compacted concrete layer

Study on failure of soft stratum of roller compacted concrete (RCC) is an important aspect of stability of high RCC dam. Six kinds of specimens with different interfaces were investigated by wedge splitting method. Double-K fracture parameters (initial fracture parameter and unsteady fracture parameter) were calculated by the concrete double-K fracture theory. It is indicated that the approach of construction joint or old joint after RCC final set is the most efficient among the six cases, and its fracture parameter is the largest among them. Its propagation path is sinuous. Its failure surface is scraggly. Bedding plane crack fails at the underside of the concrete surface, bond course or the surface between them for each approach. So disturbance on the underside of the concrete surface should be avoided or decreased at best during RCC construction.

Cracking process of rock mass models under uniaxial compression

Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.

Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

Introduction of a JCl Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures, although there have been numerous efforts to eliminate cracks. Some cracks are very harmful and should be repaired as soon as possible. On the other hand, the other cracks are almost harmless. So, a good guideline about how to deal with cracks in concrete structures had been needed. JCI （Japan Concrete Institute） published the first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, the second version in 1987, the third version in 2003, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures-2009＂ was published. This Guideline is very practical, when cracks are observed in existed concrete structures, in any other countries as well as in Japan.

Fracture analysis of cracked metallic plate repaired with adhesive bonding composite patch

Fatigue crack growth test of cracked metallic plate repaired with adhesive bonding composite patch was conducted to study the fracture behavior of crack patching. The failure mode was that crack grows along with adhesive debonding. The crack length and debonding area were measured at different numbers of cycles. The nonlinear three- dimensional(3D)finite element(FE)model considering adhesive debonding and crack growth simultaneously was developed. The experimental and analytical results were in good agreement with each other.

Simulation of Corrosion Crack in Pretensioned Prestressed Concrete Members

Corrosion of PC tendon embedded in concrete deteriorates performance of PC （prestressed concrete） members. Corrosion crack observed in pretensioned PC members is different from that in reinforced concrete and post tensioned PC members. The purpose of this study is to clarify mechanisms of corrosion crack in pretensioned PC members. Contribution of compressive stress induced by prestressing force and arrangement of PC tendons on corrosion crack in pretensioned PC members is investigated through experiment and numerical analysis. Three dimensional finite element analyses were carried out to simulate corrosion crack in PC specimen. Based on the analytical and experimental results, the influencing factor of corrosion crack in pretensioned PC members is discussed. It was concluded that the contribution of compressive stress in concrete by prestressing force on corrosion crack is not significant and that the dominant reason for wider corrosion cracks in pretensioned PC members is the arrangement of PC tendons with small intervals.

Acoustic Emission Properties of Concrete Slab During Fatigue Testing with a Running-Wheel Load

AE （acoustic emission） signals from concrete slab during fatigue testing with a running-wheel load were evaluated. The signals were recorded by remote sensors connected to a computer network. The sensing equipment consisted of 60 kHz resonant-type AE sensors mounted on a reinforcing steel bar as a waveguide, together with a 16-channel sensor highway AE system. Because the detected AE signals included periodic mechanical noise from the motion of the wheel, these noises were eliminated by means of signal processing. The AE waveguide measurement over a length of 3 m detected fractures as vertical and horizontal cracks in the RC （reinforced concrete） slab. Those cracks were analyzed by correlating AE parameters with macroscopic distortions and the numbers of fatigue cycles. In the AE events and AE energy, two types of AE phenomena, active region and inactive region, were observed during fatigue testing. The vertical cracks were characterized by an AE amplitude of 58 dB, a peak frequency of 30 kHz, and a ratio of the rise time to the maximum amplitude value （RA） of 100. The horizontal cracks were characterized by an AE amplitude of 85 dB, a peak frequency of 60 kHz, and an RA value of 10.

Study on equivalent strength for crack directors of RCC arch dam based on size effect rule

The size effect rule of roller compacted concrete (RCC) fracture toughness was reached on the analysis of fracture toughness of RCC specimens, which have been done by project team. And then the rule was applied to the calculation formula of equivalent strength of crack director in the RCC arch dam, thus a simple and useful formula was reached. The study shows that the equivalent strength of crack directors increases with the increasing intensity of concrete, but the surplus rate of strength of crack directors section decreases with the increasing intensity of concrete and the distance between centers of adjacent crack directors, and that bilateral interval crack directors are more efficient in weakening the strength of section than unidirectional interval crack directors in the case of the same distance between adjacent crack director centers. A good design for crack directors of RCC arch dam is proposed via the rule.

Crack spacing threshold of double cracks propagation for large-module rack

Large-module rack of the Three Gorges shiplift is manufactured by casting and machining, which is unable to avoid slag inclusions and surface cracks. To ensure its safety in the future service, studying on crack propagation rule and the residual life estimation method of large-module rack is of great significance. The possible crack distribution forms of the rack in the Three Gorges shiplift were studied. By applying moving load on the model in FRANC3 D and ANSYS, quantitative analyses of interference effects on double cracks in both collinear and offset conditions were conducted. The variation rule of the stress intensity factor(SIF) influence factor, RK, of double collinear cracks changing with crack spacing ratio, RS, was researched. The horizontal and vertical crack spacing threshold of double cracks within the design life of the shiplift were obtained, which are 24 and 4 times as large as half of initial crack length, c0, respectively. The crack growth rates along the length and depth directions in the process of coalescence on double collinear cracks were also studied.

Abnormality diagnosis of cracks in the concrete based on double crack tip opening displacement criterion

The distinct characteristic of subcritical propagation requires at least two control parameters to completely express expansion of cracks in the concrete.The basic definition of crack tip opening displacement(CTOD)is corrected based on the monitored variable of crack mouth opening displacement(CMOD).The improved CTOD criterion,called the double CTODd criterion,for the abnormality diagnosis of cracks in the concrete is constructed based on the fictitious crack model and linear asymptotic superposition assumptions of the concrete.The double CTODd criterion is verified using two specimens of three-point bending notched beam.The verification results are reasonable and correct.The establishment of the double CTODd criterion lays a solid theoretical foundation for the abnormality diagnosis of cracks in concrete structures(such as concrete dams)based on CMOD.