Investigating Earth Reaction to Pull-Out Process of Frictional Rock Bolts Using Distinct Element Method

The reaction of earth to pull-out process of frictional rock bolts was here modeled by the distinct element method (DEM). Ten frictional bolts were prepared;the expanding shells of five bolts included convex edges and the others had the shells with concave bits. The strength of bolts was measured by applying a standard pull-out test;the results confirmed that the strength of shells with convex edges was remarkably more than the strength of other shells. Furthermore, a two-dimensional DEM model of the test was developed by a particle flow code;the obtained results showed that the reaction of rock particles to the contacts occurring between the convex edges and earth was considerably more than those of the concave bits. In the other words, the convex edges transferred the pull-out force into a large area of the surrounded rock, causing these bolts to have the highest resistance against earth movements.

Pull-out tests and slope stability analyses of nailing systems comprising single and multi rebars with grouted cement

The pull-out capacities for soil nailing systems comprising of one single 29 mm diameter(type A) and four 16 mm diameter(type B) rebars with grouted cement were examined.A field test and numerical analysis for the type A and type B systems were carried out to investigate the pull-out capacities and the slope stability reinforcement efficiency in soil and rock slopes.The results of the pull-out tests show the mobilized shear force and load transfer characteristics with respect to soil depth.The load-displacement relationship was examined for both type A and type B systems.Slope stability analyses were carried out to study the relationships between soil and nail reinforcement and bending stiffness as well as combined axial tension and shear forces.Factors of safety were calculated in relation to the number of nails and their outside diameters.Both soil and rock slopes were included in this evaluation.

Bond Property Test of Reinforced Concrete with All Soaking and Impressed Current Method Corrosion

In order to research the bond properties between corroded reinforcement bars and concrete,reinforcement bars with different diameters and different types and concrete with different strength levels were treated specially with all soaking and impressed current method,and the bond properties were measured with the pull-out test.The comparative analysis of the bond properties of corroded reinforcement bars was carried out.The results showed that the types of reinforcement bars and concrete had great influence on the bond strength.The corrosion and volume expansion of reinforcement bars made concrete in tensile condition,which tended to produce cracks in parallel reinforced direction.The typical bond failure of plain reinforcement bars was pull-out,while the typical bond failure of ribbed reinforcement bars was split.The bond strength between corroded reinforcement bars and concrete increased with the increase of concrete strength.The bond strength of plain and ribbed reinforcement bars showed a decreasing trend after the first increase with the increase of the extent of corrosion.Through the test,the coefficients of the bond strength of plain and ribbed reinforcement bars were given,respectively.

Explicit reinforcement models for fully-grouted rebar rock bolts

This paper investigates the explicit use of rock reinforcement in a discontinuous stress analysis model.A series of numerical experiments was undertaken to evaluate the performance of local and global reinforcement models implemented in universal distinct element code(UDEC).This was made possible by calibrating the reinforcement models to the laboratory behavior of a fully-grouted rebar bolt tested under pure pull and pure shear loading conditions.The model calibration focuses on matching different loading stages of the force-displacement curve including the initial elastic response,the hardening behavior and the bolt rupture.The paper concludes with a discussion on the suitability of the different reinforcement models in UDEC including their advantages and limitations.Finally,it addresses the choice of input parameters required for a realistic simulation of fully-grouted rebar bolts.

Development and application of an interface constitutive model for fully grouted rock-bolts and cable-bolts

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results.A database was created combining published experimental data with in-house tests.By means of a comprehensive framework,a Coulomb-type failure criterion accounting for friction mobilization was defined.During the elastic phase,in which the interface joint is not yet created,the proposed model provides zero radial displacement,and once the interface joint is created,interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints.The results predicted by the proposed model are in good agreement with experimental results.The model has been implemented in a finite element method(FEM)code and numerical simulations have been performed at the elementary and the structural scales.The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

DEM investigation of rock/bolt mechanical behaviour in pull-out tests

Rock bolt anchorage performance is crucial for tunnel support safety.We investigate the mechanical behaviour of reinforced rock and the bolts that reinforce it from the micro-scale to the macro-scale.Bolt pull-out tests were performed on soft rock using the distinct element method,in which a new contact model that considers bond size,is employed to constrain the main rock mechanical behaviour.The minimum sample width and height values for which the boundary effect can be neglected are first proposed through numerous tests on the influence of sample size on peak load and bond breakage.The influence of sample width is substantially greater than that of sample height.We then select an appropriate sample size to study the influence of bolt embedment length and confining pressure on the mechanical behaviours of the rock and bolt.The results show that increased rock bolt embedment length and confining pressure can increase the peak load;however,the bolt length effect is limited when exceeding the critical anchorage length.In cases without confining pressure,bond breakage occurs in the rock around the grout-rock interface and the breakage zone is rectangular,whereas in cases under confining pressure,the breakage zone presents an inverted cone shape.We use our results to discuss the influence of bond strength at the bolt-grout interface on the peak load and failure mode.The failure mode changes gradually from complex failure to single failure along the bolt-grout interface with decreasing interfacial bond strength.

不同尺寸橡胶/帘线H型拉拔试验界面参数的归一化处理评价方法

H型拉拔试验被广泛应用于橡胶/帘线复合材料界面粘结强度的估算.然而,目前的国际标准只要求在橡胶/帘线H型拉拔试验中记录拔出力的大小,并强调从不同尺寸的样品中获得的结果不具有可比性.在本文中,我们研究了不同尺寸橡胶/帘线试验样品的H拔出结果的可比性,并提出了一种归一化的评价方法来处理这些结果.分别对尺寸为5 mm、6.4 mm、10 mm的试验样品进行橡胶/帘线H拉拔试验(尺寸为7.5 mm、8.5 mm的试件结果作为支撑性试验).在试验结果的基础上,采用有限元法内聚单元模型对界面粘结强度进行了分析,所得出的内聚力参数比国际标准中所规定的拔出力更能准确地反映界面粘结性能.因此,采用内聚单元法能够更合理地比较不同橡胶/帘线试样的界面粘结强度.我们首先基于6.4 mm尺寸样品的试验结果建立有限元模型,并确定满足条件的内聚单元参数,然后将其应用于其他尺寸的样品模型.尽管试验样品的尺寸大小在变化,但在保持内聚单元参数不变的前提下,模拟结果与试验结果仍然保持良好的一致性,这表明内聚参数不受样本尺寸的影响.在此基础上,我们提出了一种归一化方法,使不同尺寸样品的橡胶/帘线H拉拔试验的结果具有了可比性.本文提出的归一化方法是对现有国际、国内标准实验方法的扩展.