Parametric study on the axial performance of a fully grouted cable bolt with a new pull-out test

Modified cable bolts are commonly used in underground mines due to their superior performance in preventing bed separation when compared with plain strands. To better test the axial performance of a wide range of cable bolts,a new laboratory short encapsulation pull test(LSEPT) facility was developed. The facility simulates the interaction between cable bolts and surrounding rock mass,using artificial rock cylinders with a diameter of 300 mm in which the cable bolt is grouted. Furthermore,the joint where the load is applied is left unconstrained to allow shear slippage at the cable/grout or grout/rock interface.Based on this apparatus,a series of pull tests were undertaken using the MW9 modified bulb cable bolt.Various parameters including embedment length,test material strength and borehole size were evaluated. It was found that within a limited range of 360 mm,there is a linear relationship between the maximum bearing capacity of the cable bolt and embedment length. Beyond 360 mm,the peak capacity continues to rise but with a much lower slope. When the MW9 cable bolt was grouted in a weak test material,failure always took place along the grout/rock interface. Interestingly,increasing the borehole diameter from 42 to 52 m in weak test material altered the failure mode from grout/rock interface to cable/grout interface and improved the performance in terms of both peak and residual capacity.

Fault-section Identification for Hybrid Distribution Lines Based on Principal Component Analysis

In this paper,we present a single-ended principal-component-analysis-(PCA-)based fault-section identification method for a hybrid distribution line(non-effective grounding system),which is an overhead line combined with an under-ground cable when a single-line-to-ground(SLG)fault occurs.Ground-mode currents are extracted from the single-ended measuring points when faults occur in underground cables or overhead lines,and then the method of fault-section identification based on PCA is utilized to deal with the ground-mode or aerial-mode currents to realize the fault-section identification of the hybrid system.First,a loading plot of PCA is used to compare the projection of ground-mode currents on the PC1 coordinate axis to 0.Then,Euclidean distance is used to realize the fault-section identification to improve the reliability of criterion and avoid threshold setting in the PCA method.The performance of the method is tested in 35 kV hybrid distribution lines for a distribution system based on PSCAD/EMTDC for different fault locations,different fault inception angles(FIAs),and fault resistances with satisfactory results.The impact of distributed generation(DG)and lengths of cable and overhead lines on the accuracy of the proposed method is also investigated.

A Theoretical Model for Characterizing the Internal Contact of the CICC Strands under Axial Strain

A theoretical model is proposed to calculate the internal contact distributions and contact forces of a 3×4×4×4 twisted NbSn cable under applied axial strain.The critical current density reduction of the whole cable can be calculated.The thin rod theory is employed to analyze the mechanical behavior of each strand.According to the regular helical structure,the contact distribution of each strand is obtained,and the contact force in the cable is analyzed.At last,a prediction about the critical current density of the twisted cable is made.The results show that decreasing the pitch length can reduce the contact forces between strands.