Effect Of Joint Spacing Research Articles

The effects of joint spacing on transmission characteristics of stress waves through layered composite rock masses

AbstractThe effects of joint spacing on the transmission characteristics of stress waves through layered composite rock masses were investigated. First, a model of layered composite rock masses containing multiple parallel joints with different media in front of and behind the joints was introduced to study multiple reflections between joints. Second, wave transmission through layered composite rock masses was investigated and compared with wave transmission through traditional layered homogeneous rock masses. Finally, the effects of joint spacing and wave impedance ratio on particle velocity transmission coefficient were discussed. The results indicate that for wave propagation through rock masses with the same joint spacing, the onset time and amplitude of the transmitted wave in layered composite rock masses are smaller than those in layered homogeneous rock masses. For wave transmission through rock masses with the same nondimensional joint spacing, the onset time of the transmitted wave in the layered composite rock masses is similar to that in the layered homogeneous rock masses, while the amplitude of the transmitted wave in the layered composite rock masses is smaller than that in the layered homogeneous rock masses. In addition, the particle velocity transmission coefficient first increases and then decreases to be constant as the joint spacing increases, while it continues to increase as the wave impedance ratio increases for wave transmission through both layered composite rock masses and layered homogeneous rock masses.

Analysis on Effects of Joint Spacing on the Performance of Jointed Plain Concrete Pavements Based on Long-Term Pavement Performance Database.

With the day-night temperature and moisture levels changing every day, expansion and shrinkage of concrete slabs is always occurring; therefore, joints provide extra room for concrete slab deformation. The joint spacing in jointed plain concrete pavement (JPCP) is continuously affecting long-term pavement behaviors. In this study, data from the Long-Term Pavement Performance (LTPP) program were analyzed, and the behaviors of JPCP with different joint spacings were compared to discover the joint spacing effects. Since LTPP has an enormous database, three representative sections located in different states were selected for analysis, where the variable factors such as temperature, moisture, and average annual daily truck traffic (AADTT) were almost the same between the three sections. Three different joint spacings, including 15 ft (4.5 m), 20 ft (6 m), and 25 ft (7.5 m), were compared based on the collected LTPP data. The involved long-term pavement performances, such as average transverse cracking (count), average JPCP faulting, international roughness index (IRI), and falling weight deflectometer (FWD) deflections were compared between JPCP with different joint spacings. Based on the comparative analysis, the JPCP constructed with a 15 ft joint spacing demonstrated the best long-term performance. It showed no transverse cracking, the lowest average JPCP faulting, the best IRI value, and the smallest FWD deflection during the entire in-service period. With proper joint spacing, the cost of road maintenance throughout the life cycle could be significantly reduced due to there being less distress. Therefore, it is recommended to optimize the joint spacing to about 15 ft in JPCP in future applications.

Uniaxial compressive study on mechanical properties of rock mass considering joint spacing and connectivity rate

To explore the effect of joint spacing and joint connectivity rate on the uniaxial compressive strength (UCS) and elastic modulus of jointed rock mass, compression tests on preset intermittent fractured specimens were performed. Test results show that the anisotropy of UCS of jointed rock mass tends to increase with joint connectivity rate. The decreasing rates of UCS and elastic modulus of jointed rock mass, when the loading direction is perpendicular to the joint plane, are higher than those when the loading direction is parallel to the joint plane with respect to joint connectivity rate and jointing index (the ratio of the length of jointed rock mass specimen to the joint spacing). The fourth-degree polynomial function proposed in this study is appropriate to analyze the nonlinear variation law of equivalent peak UCS of jointed rock mass with joint connectivity rate. The power function proposed in this study is suitable to describe the nonlinear variation law of equivalent peak UCS and equivalent elastic modulus of jointed rock mass with jointing index. However, the number of times and the number of parameters of multiple polynomial function and the number of power function need to be determined according to site-specific test results of practical project.

Numerical Analysis of the Mechanical Behaviors of Various Jointed Rocks under Uniaxial Tension Loading

In a complex stress field of underground mining or geotechnical practice, tension damage/failure in rock masses is easily triggered and dominant. Unlike metals, rocks are generally bi-modularity materials with different mechanical properties (Young’s modulus, etc.) in compression and tension. It is well established that the Young’s modulus of a rock mass is directly related to the presence of the fracture or joint, and the Young’s modulus estimation for jointed rocks and rock masses is essential for stability analysis. In this paper, the tensile properties in joint rocks were investigated by using numerical simulations based on the discrete element method. Four influencing parameters relating to the tensile properties (joint dip angle, joint spacing, joint intersection angle, and joint density) were studied. The numerical results show that there is an approximately linear relationship between the joint dip angle (α) and the joint intersection angle (β) with the tensile strength (σt), however, the changes in α and β have less influence on the Young’s modulus in tension (Et). With respect to joint spacing, the simulations show that the effects of joint spacing on σt and Et are negligible. In relation to the joint density, the numerical results reveal that the joint intensity of rock mass has great effect on Et but insignificant effect on σt.

Effects of joint spacing and dynamic friction angle on the travel distance of rock debris

Effects of joint spacing and dynamic friction angle on the travel distance of rock debris

Effect of joint spacing and pavement thickness on concrete overlay performance

Concrete overlays provide cost-effective maintenance and rehabilitation strategies for pavement systems. A database has been developed in Iowa that records the historical performance of overlays based on records of International Roughness Index (IRI) and Pavement Condition Index (PCI) over a 20-year period. Based on these data concrete overlay service life has been modeled for various joint spacings. The data demonstrate that durability and service life can be improved. A review of PCI data indicates that improving construction quality to eliminate premature failure has the potential to add at least 10 years to the service life of PCC overlays. Even though concrete overlay technology is not a new concept, most of its design procedures still follow empirical methods, therefore this study applied AASHTOWare Pavement ME Design (Version 2.3.1) software to identify the effects of design para ms on concrete overlay service life. The theoretical insights provided by Pavement ME Design were compared with historical performance data and used to provide recommendations with respect to optimized joint spacing in overlay pavement structures. Comparison of the historical performance-related data with Pavement ME Design software results indicates that the Pavement ME Design software is conservative in predicting concrete overlay service life.

Mechanical and failure characteristics of rock-like material with multiple crossed joint sets under uniaxial compression

The strength and deformation of rock masses transected by persistent joints are controlled by the fracture network. In this work, bonded particle model modeled by particle flow code in three dimensions was used to study the effect of geometry parameters on the strength and behavior of jointed rock masses under uniaxial compression. The effect of the number of crossed joint sets, joint orientation, and joint spacing on the uniaxial compressive strength was investigated, and this article presents the results of the numerical simulations. Rigorous validation process had done before the numerical experiments. Four types of blocks (Series A, B, C, and D) with different numbers of joint sets were considered in this article. Then, a sensitivity study is undertaken to investigate the effects of joint set numbers and joint geometry configuration on the failure mode, unconfined compressive strength, and Young’s modulus of jointed rock mass. The interaction among the crossed joint sets was found to have marked effects on the mechanical properties and failure modes. A study about the effects of joint spacing on the failure modes, unconfined compressive strength, and Young’s modulus was also conducted. Joint spacing was found to have no significant effect on the failure modes of jointed rock masses in a certain range. It is also shown that the range and variance of unconfined compressive strength are affected principally by joint set numbers and decreased slightly with the decrease in joint spacing. The effect of crossed joint sets on the stress field was carried out. Stress concentration was found to be the reason for relatively lower strength of blocks with crossed joint sets compared to the block with the same weakest single joint set. The result in this article is of great help to reveal the mechanism of damage and fracture of jointed rocks under uniaxial compression.

Practical Use of the Ubiquitous-Joint Constitutive Model for the Simulation of Anisotropic Rock Masses

Anisotropic rock masses, the behavior of which is dominated by closely spaced planes of weakness, present particular difficulties in rock engineering analyses. The orientation of discontinuities relative to an excavation face has a significant influence on the behavioral response. At the present time, discontinuum modeling techniques provide the most rigorous analyses of the deformation and failure processes of anisotropic rock masses. However, due to their computational efficiency continuum analyses are routinely used to represent laminated materials through the implementation of a Ubiquitous-Joint model. The problem with Ubiquitous-Joint models is that they do not consider the effects of joint spacing, length and stiffness. As such, without an understanding of the limitations of the modeling approach and detailed calibration of the material response, simulation results can be misleading. This paper provides a framework to select and validate ubiquitous-joint constitutive properties.

RETRACTED: Effect of joint spacing and joint dip on the stress distribution around tunnels using different numerical methods

Different conditions may affect the stability of tunnels by the geometry (spacing and orientation) of joints in the surrounded rock mass. In this study, by comparing the results obtained by the three novel numerical methods i.e. finite element method (Phase2), discrete element method (UDEC) and indirect boundary element method (TFSDDM), the effects of joint spacing and joint dips on the stress distribution around rock tunnels are numerically studied. These comparisons indicate the validity of the stress analyses around circular rock tunnels. These analyses also reveal that for a semi-continuous environment, boundary element method gives more accurate results compared to the results of finite element and distinct element methods. In the indirect boundary element method, the displacements due to joints of different spacing and dips are estimated by using displacement discontinuity (DD) formulations and the total stress distribution around the tunnel are obtained by using fictitious stress (FS) formulations.

Effect of Joint Spacing on the Earth Pressure Against the Support System in a Jointed Rock Mass

This study examined the magnitude and distribution of earth pressure on the support system in a jointed rock mass due to the different joint spacing as well as varying the rock type and joint condition (joint shear strength and joint inclination angle). Based on a physical model test and its numerical simulation, a series of numerical parametric analyses were conducted using a discrete element method. The results showed that the magnitude and distribution of earth pressure were strongly affected by the different joint spacing as well as the rock type and joint condition. In addition, the study results were compared with Peck`s earth pressure for soil ground, which indicated that the earth pressure in a jointed rock mass could be considerably different from that in soil ground. The study suggests that the joint spacing as well as the rock type and joint condition are important factors affecting the earth pressure in a jointed rock mass and they should be considered when designing a support system in a jointed rock mass.

Experimental Study on the Effect of Joint Spacing on Fragmentation Modes and Penetration Rate under TBM Disc Cutters

Joint spacing is one of the significant factors affecting the rock fragmentation by TBM cutters. Based on laboratory test, the effect of joint spacing on the fragmentation modes and penetration under TBM disc cutters is studied. In the test, two kinds of concrete with different strengths are adopted to simulate rock sample. The joint spacing varies from 50mm, 80mm, 200mm and the intact samples are also tested for comparison. Firstly, four kinds of fragmentation modes for single-set jointed rock are found: (1) the crack initiates from the joint plane and propagates to free surface, to form fragmentation chipping. (2) The side crack and median crack initiate beneath the crushed zone and propagate to joint plane to produce chipping. (3) In the rock block indirectly indented by cutter, the crack initiates from the joint plane and propagates to adjacent joint plane to produce chipping. (4) Normal fragmentation mode. Basically, the first two kinds are generally for jointed rock, while the other two kinds are respectively for the jointed rock with small and large joint spacing. Secondly, from the viewpoint of the fragmentation modes, the effect of joint spacing on tunnel face stability is investigated and then compared with field data of Jinping II Hydropower Station. Finally, it is shown that highest penetration rate can be achieved with the joint spacing of 50-80mm, and moreover, joint spacing gives more notable effect on fragmentation of the rock with higher strength.

Thermal reflective cracking of asphalt concrete overlays

Reflective cracking of asphalt concrete (AC) overlays is one of the most extensive pavement distress and damage mechanisms in composite pavement structures. Numerous studies have been performed to evaluate the reflective cracking potential of AC overlays under different loading scenarios. Most of these studies have focused on reflective cracking due to tyre loading. A very limited amount of work has been performed to evaluate non-load-associated thermal reflective cracking of overlays. Thermal reflective cracking mechanisms have been studied and are described in this paper using recently developed hot-mix asphalt mixture tests and fracture models. A series of finite-element-based pavement simulations were performed in an effort to better understand thermal reflective cracking mechanisms as a function of several key material and pavement structure variables. The enhanced integrated climatic model was used to estimate pavement temperature gradients as a function of position and time. A fracture mechanics-based cohesive fracture model was used for the simulation of damage and cracking, which was tailored for use with quasi-brittle materials such as AC. The pavement simulation model utilises creep and fracture properties from American Association of State Highway and Transportation Officials and American Society for Testing and Materials-specified tests and analysis procedures. Three asphalt mixtures manufactured with Superpave low-temperature performance grades of -22, -28 and -34 were studied in pavement structures with three distinct overlay thicknesses. Simulations were conducted with three Portland cement concrete (PCC) slab conditions to study the effects of joint spacing and rubblisation on thermal reflective cracking. The simulation results provide a new insight towards the mechanisms underlying the development of thermal reflective cracking. The curling of PCC slabs due to temperature differential and joint opening caused by pavement cooling was found to be critical in the initiation of thermal reflective cracking. This effect is greatly minimised or eliminated in the case of pavement rubblisation.

Effect of Opening on Design of Subsurface Drains

Theoretical effects of joint spacing on flow into drain tile and effects of perforations are presented in a form useful for the design engineer. The influence of these openings on the rate of water table drawdown between parallel drains is presented. Experimental field data support the theoretical results.