Study On The Classification Method Of Tunnel Surrounding Rock Levels In Northern Shaanxi

Presently, the current classification methods, ruled in the surveying and designing specifications of our country, of highway tunnel surrounding rock are qualitative and semi-quantitative. Restricted in the technical means used in investigation stage, the accuracy compared to the actual tunnel excavation situation, is erroneous apparently in local parts. The imperfection of the current specifications will trigger two consequences:conflicts between designing and specifications; large amount of engineering changes.Waste of construction and insecurity of operation will be caused by the inaccuracy of the surrounding rock classifications. In detail, if the adoptive level of surrounding rock is stronger than the actual level, insecurity will be caused when supporting intensity values are weaker than actual need; conversely,waste will be caused. Therefore, it is significant to classify the surrounding rock levels scientifically, reasonably and practically for the tunnel designing and construction.Based on the nine engineering examples of rock tunnels of the highway from Yanan to YanChuan, five aspects below were studied by the means of taking photos,measurement, sampling, experimental research and numerical analysis.(1) Firstly, two different kinds of point load testing methods were designed based on a large number of tests of point loading strength of rock mass and its uni-axial compressive strength in a saturated state. Then the influence of different testing methods on the relationship between the rock point loading strength and its uni-axial compressive strength in a saturated state was exploded in order to determine the suitable testing method.(2) The formula suitable in Northern Shannxi was put forward through the statistical analysis of the correlation between point loading strength of rock mass andits compressive strength in a dry state, providing a reference for the construction of highway tunnel engineering in Northern Shannxi.(3) It summarized the results of rock mechanics research in recent years and analyzed the rock mass parameters of surrounding rock of highway from Yanan to YanChuan. And then a suitable formula on surrounding rock classification of sedimentary rocks in Northern Shannxi was raised through correcting BQ, surrounding rock basic quality system, so as to guide the investigating and designing work of the road tunnels in Northern Shannxi. Meantime, the access methods or means of each classification indexes in the construction phase were introduced.(4) Ground Penetrating Radar were used on Advanced Geological Prediction 。Surrounding rock structure development situation,integrity of the rock mass,containing water situation,the fault activities and fracture zones and other bad geological phenomenons and theirs scales, size, may causing deformation and failure of the surrounding rock.(5) Based on the highway tunnels under construction in Northern Shannxi and through specifications for design of road tunnels and the correction formula for Northern Shannxi region, respectively, detailed classifications of surrounding rock were carried out and the originally designing levels and practical levels of tunnel surrounding rock were analyzed in the method of Midas-GTS numerical simulation.