Analysis On Relaxation Zone And Some Stabilizing Structures In High Rock Slope Projects

The study background is high rock slope projects in the motorway project from Beijing to Zhuhai in the north of Guangdong province. On the basis of the concept and analysis method of slope geological structure, four typical slope geological structures are selected by some investigations on more than one hundred high rock slopes in the motorway project. These structures are thick sandstone stratum, stratum including weak coal, stratum made of red or brown plastic clay and soft rock mass and stratum made of remnants rock mass. The practical slope geological structures are compact basis of geological mechanical model for the analysis of relaxation zone in high rock slope projects. According to the analysis of stress field and displacement field as the result of cutting slope, effected zone by cutting in the slope is analyzed and the definition of relaxation zone related to one safety factor is given. In the effected zone of the slope, relaxation zone will be varied if corresponding safety factor is varied. In other words, the process of analyzing relaxation zone related to one safety factor can also be regarded as the process of searching potential slide surface related to the same safety factor. Elastic wedge model is used for analysis of relaxation zone of cutting homogeneous slope. On the basis of elastic plane-strain theory, the relaxation zone can be calculated according to Mohr-Coulomb or Drucker-Prager law and single tension intensity principle which are both related to one safety factor after three-dimensional stress field of the cutting slope is got. The calculation procedure is provided. It is interpreted in detail by an example. Numerical analysis method of relaxation zone is provided and its procedure by analyzing stress field or displacement field is given in detail by some practical high rock slope projects. Analysis results of relaxation zone of four typical worksites corresponding to foregoing four slope geological structures are presented. Moreover, calculation methods of slope pressure on two kinds of stabilizing structure are discussed on the basis of analyzing relaxation zone and slope geological structure. The two stabilizing structures are prestressed anchor-cable beam-on-foundation and anti-slide pile. As for anti-slide pile, the pressure on its section above slope potential slide surface can be calculated by parabola distribution mode. The distance from figure center of the parabola to the potential slide surface is less than half of the section length. Mechanical conditions of this method include not only forceequilibrium but also moment equilibrium. As for the beam-on-foundation, its pressure can be calculated by homogeneous hypothesis or Winkler foundation hypothesis or infinite half elastic foundation hypothesis on the pulling anchor-cable step and by Coulomb active earth pressure theory approximatively on the long term working step. By geological mechanical model test, the relaxation zone and pressure on the two stabilizing structures in high rock slope projects are studied. After the comparison between the test results and the corresponding theoretical analysis results, the theoretical analysis-methods are proved because its results are in line with the test ones. In addition, calculation methods of internal force of prestressed anchor-cable beam-on-foundation (including single and frame beam) are provided. It is mainly shown that internal force of the beam-on-foundation should be respectively calculated on the pulling anchor-cable step and long term working step. The worst combination of internal force on the two different steps should be as the basis of design for the beam-on-foundation. Being calculated, the frame beam-on-foundation may be disconnected to two single beams. On the pulling anchor-cable step, the internal force of single beam-on-foundation can be calculated by Winkler hypothesis in the case of weak rock mass and infinite half elastic foundation hypothesis in the case of stratums that are of some elastic characteristics. The internal force of frame beam-on-foundat...