Static And Dynamic Model Tests And Seismic Design Methods Of Anchored-cable Frame-beam Structures

The anchored structure is a type of structures, which can interlock the structure and rock together tightly and rely on shear strength produced between the bolt and rock/soil around the bolt to take the pull forces transformed from structures. The function of the anchor bolt is buried in rock to maintain the stabilization of the structures or rock/soil by stabilizing the rock/soil, and so it is considered as an economic and efficient approach and widely used to stabilize slope engineering. From the investigations on road slope and anchored engineering damage triggered in "5.12" Wenchuan earthquake, it was found that the anchored frame-beam structures have better seismic performance, but few studies on their work mechanism in ground shaking have been performed, although a number of static experiments were performed, as a result, the type of anchored structures used to strong seismic areas have some limitations. In this thesis, firstly a number of investigations on subgrade and slope damage triggered in "5.12" Wenchuan earthquake were performed,then some centrifuge tests were carried out, after that some dynamic tests on anchored structures were performed, and finally a large scale shaking table test were carried out. The achievements from the thesis not only improve the static and seismic design methods of the anchored frame-beam structure, but also provide valuable reference for the seismic design of the high and steep slopes. The main achievements and conclusions are as follows:(1) The seismic damage investigation of the highway subgrade and slope in the Wenchuan earthquakeA detailed investigation was conducted on the national or provincial main highways and part of rural roads in the quake-affected areas of Sichuan Province, Gansu Province, and Shanxi Province. The investigated highways and roads are about 7081 km long. The relations between the damaged slope and the epicentral distance, rock material property,slope height, slope angle, angle between faults are obtained. It is found that the number of the unreinforced damaged slopes is proportion to the slope height, however, it does not have the same rule for the reinforced slopes. The reinforced structures for the slopes should be selected with consideration to the rock property, degree of rock weathering, and so on. The investigation enriches the database of the earthquake damage and guides the selection of the retaining structures for the slope located at high intensity seismic areas.(2) Deformation characteristics and Design approach of cable-anchored frame-beam structures under static loadBased on centrifuge tests and numerical analyses of FLAC3D, the distribution of soil pressure and bending moment for the cable-anchored frame-beam structures was obtained. It was found that the positive bending moment of the beam is larger near the anchor cable. The soil pressure is larger in the middle of the beam, while the both ends are smaller, as a result,subgrade reaction can be not considered as uniform distribution or linear distribution. Also it is found that the materials of rock and soil (ground) on the slope and anchored force in the cable have a significant impact on the stress distribution of the frame-beam structures. The initial parameter method of Winkle is suitable for the design calculation of the cable-anchored frame-beam structures, as it can well reflect the actual working mode of the cable-anchored frame-beam structures.(3) Bonding characteristics of the rock anchor system under dynamic loads10 tests of rock anchor system under dynamic loads in laboratory were designed and finished. The strain on the bonding surface of the bolt and the displacement at the anchor head were measured. It is found: 1) the bearing capacity of the rock anchor system decreases with the increase of the loading cycle number; 2) the failure procedure of the rock anchor system contains four stages: elastic, initial separation between the contact surfaces,development of the separation between the contact surfaces, and the separation of the contact surfaces. What's more, the displacement-controlled design method for the rock anchor system is proposed based on critical displacements in different phases during the failure process.(4) Seismic mechanism of slopes reinforced by prestressed cable-anchored frame beam structuresShaking table tests of slopes reinforced by cable-anchored frame-beam structures were conducted. From the tests, the distribution characteristics of acceleration and displacement in the slope, axial load of the anchored cables, and displacement of the frame-beam structures were obtained. From the study, it is found: 1) the displacement of the slope is not the same as the frame beam structures. It is because the slope is stabilized, although part of the slope was hollowed out, and it slides downhill during the earthquake, the slope is still stable; 2) the shared force design method in low intensity areas and partition design method for the upper to the lower parts of the slope in high intensity areas are recommended.(5) Seismic design method on pre-stressed cable-anchored frame-beam structuresThe numerical calculations by using FLAC3D verify the reliability of shaking table model test, and the safety factor calculation method is deduced, in which the horizontal and vertical earthquake acceleration components and the water pressure in the slope cracks can be considered. Moreover, according to the method of lumped mass, axial force calculation formula for anchor cable is given under horizontal seismic action.