Experimental Study On Compound Tunnel-Type Anchorage With Prestressed Cables

Based on theoretic analysis and testing data, this paper mainly discusses the force field and displacement field of different single and group cables in length when pulled. The ultimate anchor force, relationship between pulling stress and displacement of anchor end and distribution law of displacement field in surrounding rock are studied through pull-out test of single cable whose length is 8 meter, 10 meter and 12 meter separately, such content is also studied through pull-out test of group cables whose length is 8 meter, 10 meter separately Furthermore, anchor group effect is discussed by comparison between single cable and group ones under the same work conditions. Through male cone experiment, this paper also indicates the distribution proportion of load between male cone and prestressed cables, elementarily reveals the function mechanism of tunnel-type anchorage with prestressed cables.By researching and analyzing the test results, conclusion is as following.The maximum of axial force is at the top of fixed segment of anchor bar, graduallydecreases downwards along the bar, and is nearly zero at the bottom. For 8 meter long cable, the axial force attenuates in terms of law of negative exponential function when the anchor bar is long and of approximate straight linear when it is short. For 10 meter one, the axial force attenuates in terms of law of Boltzmann function. For 12 meter one, the axial force attenuates in terms of law of Gaussian function.The main carrying zone is within the confines of 3 meters away from the top of fixed segment of anchor bar.Relationship curve between pulling stress and displacement of anchor end assumes positive exponential curve for 8 and 10 meter long cable and assumes Gaussian curve for the 12 meter one. The ultimate anchor force of single cable is all larger than theoretical value, which is 1041.6KNThe tensile force of cable forms a surface compression zone in the surrounding rock mass around the cable. The compression effects of surrounding rock mass reinforces with the prestress increasing .Under the action of multi-prestressed cables, the deformation distribution of surrounding rock mass homogenizes.The ultimate anchor force Of 8 meter long group cables homogenizes as much 90.97% as theoretical ultimate anchor force and it is 89.25% for 10 meter ones.