Study On The Assessment Method Of Geostress In The Southeastern Margin Of The Tibet Plateau

The value of Geo-stress is an important parameter for the design of long and deep buried tunnel engineering.And field drilling is a reliable method of obtaining initial Geo-stress.But in the feasibility study stage of railway route selection,while the line scheme is not yet determined,it is infeasible for large-scale drilling to identify geostress values,but it hopes to draw lessons from existing data or empirical formulas to grasp the situation of in-situ stress.Based on a large number of historical seismic records,crustal thickness detection points and in-situ stress data,the distribution maps of focal depth,seismic density and crustal thickness are draw out in this area.Based on the existing research and hypothesis,the focal depth and relative focal depth should have a negative correlation with the in-situ stress,while the seismic density should have a positive correlation with the in-situ stress.Accordingly,three methods are proposed to correct the maximum horizontal stress with the statistical formula of depth distribution,that is,the correction of depth of source,the correction formula of seismic density,and the correction formula of relative focal depth.On the southeastern margin of the Tibetan Plateau as an example,in the area of each measuring point depth is H and the relative focal depth of X(or earthquake focal depth density D or D)as independent variables,after inspected by the data measured in Lhasa to Linzhi railway tunnels,compared with the current method which uses the depth as the only independent variable,the assessment accuracy is obviously improvedThree ways to modify the traditional statistical regression formula,the focal depth correction and relative correction for focal depth is more than 400 m of the value assessment should be relative to the source power,and modified as the main method for detecting the thickness of crust;less,the crustal thickness is not easy to obtain and the depth is more than 400 m,can be modified to the focal depth as auxiliary evaluation method;and for the depth of less than 400 m stress value assessment,can be modified to compute seismic density.When the overall plan of the line is determined,when the local scheme is selected,it is hoped to have a more accurate grasp of the local stress value.Alpine valley region,the specific effects of topography on ground stress can not be ignored,studies have shown that canyon area stress has three obvious zoning,according to the original ground denudation thickness of delta H,terrain information can roughly estimate the stress with depth,and according to the tunnel buried depth of H and stress the value can be modified based on the stress assessment of seismic information,which is more close to the true value.