Engineering Application Of Rapid Acquiring Rock Mass Fractures Information With Digital Close Range Photogrammetry

In the study of engineering geology, geotechnical engineering,rock mass mechanics, theproblems of rock mass stability will be constantly encountered.Through scientists' persistentendeavour and exploration, human beings gradually realize that the destruction of rockengineering is controlled by various discontinuities in rocks. Scientists in our country summed up"cybernetics of rock mass structure" through years of hard work., cybernetics of rock massstructure stressed the great importance of discontinuities in stability evaluation from theperspective of origin mechanism. The theory is widely recognized by domestic and foreignscholors. According Professor Gu Dezhen'analysis program of rock mass structure, Ⅳ,Ⅴ stagediscontinuities have the characteristic of large numbers of small-scale ,random distribution. In thepractical engineering, these small-scale discontinuities-joints and fractures directly affect thecharacteristic of deformation and stability. It is the information of rock fractures and itsprobability distribution that become the important reference to understand rock masscharacteristic. Therefore, all-round, rapid, accurate collecting the information of rock massfractures is the basis of engineering geological evaluation ,geological forecasting and geologicalcatastrophy prevention. It is of great importance to engineering construction and catastrophyprevention.Presently, information of discontinuities is mainly acquired by measuring in person on thespot. Not only is the method of high labour-intensity and low efficiency but also it is hard to meetthe requirement of rapid engineering construvtion. Any other ways as three-D laser scanningmeasuring and drilling methods exist high cost and have difficulty in acquiring large-scaleinformation and poor application effectiveness. The article is based on the tutor's "A Study of 3-D information Prediction on GeologicalDisasters During Tunnel Construction in Fractured Rock Mass" of national natural scienceproject(40272117) and excellent junior instructors' project of "A Study on the Mechanics Modelof 3-D Network Structural Rock Masses in Engineering geology casualty"(120413133)sponsored by Education Department. On the basis of full rock fractures information investigationand research, against Baolilinyu community project's lithologic slope in Guangzhou, digital closerange photogrammetry is used in the rapid acquisition and the application research ofdiscontinuities information .The main purpose of the article is to discuss possibility, accuracy andwork pattern to acquire fractures information with digital close range photogrammetry. In theresearch, digital photogrammetric workstation and DLT programme is adopted respectively totransact data & images and acquire 3-D spatial coordinates of fractures typical characteristic,coupled with the research of orientation calculating model of rock mass fracture to obtain itsorientations based on 3-D control survey with total station instrument and digital photographwith common digital camera. Consequently, it is easy to get the information of 3-D traces andorientations and further draw trace chart of fracture by displaying model. The article dividesdominating fracture groups and analyzes stability with stereographic projection to offer safegrading angle in the project of Baolilinyu community lithologic slope strengthening based on thestatistical analysis of fractures information. Above all, the results can be listed as follows:1.3-D control survey method is developed with total station instrument and themathematical model of differentical height of two instruments with only a tripod leg is proposedin response to high lithologic slope. Furthermore, 3-D spatial coordinate system to use magneticnorth as direct-axis is developed in combination with compass surveying on the spot.2.Common digital camera calibration is developed in photogrammetry. In response to closerange photograph, grid square method of practical camera deformation calibration is put forwardand is done. In response to long range photograph(e.g.high lithologic slope),calibration and datatransaction are simultaneously completed. Baolilinyu community project uses this method.3.Using digital photogrammetric workstation transact the images and data. Acquiringmethod, workflow and notices of fracture information are developed with digitalphotogrammetric workstation. Thus a new study direction is developed in rapid acquiring rockmass fractures information. On the condition of control point accuracy 1cm and approximationstraightness photograph of photograph distance 70m, photograph baseline 10m, baselinedirection paralleled to the trend of lithologic slope, fractures data of the north slope of ballast pitin Baolilinyu Ccommuity is interpreted. The fit mean deviation of the result of interpretationorientation compared with compass measuring data is below 6°.4.DLT programme and DLT with reservation are designed with Matlab to acquire workflowand method of fracture information with DLT programme. To solve the problem of acquiringquantity of image element axis, the acquiring method with ArcGIS is developed.5.In order to directly reflect trace length and its distribution of rock mass fractures, themathematical model of 3-D coordination projected on lithologic slope of fractures terminationpoint is developed in response to acquired 3-D coordination.6.The mathematical model of calculating orientation of fractures based on normal vector isdeveloped in response to acquired characteristic information.7.Accuracy analysis of acquired spatical points by ways of digital photogrammetricworkstation and DLT programme is conducted. Analysis shows that: On the condition of controlpoint accuracy 1cm and approximation atraightness photograph of photograph distance 70m,photograph baseline 10m, baseline direction paralleled to the trend of lithologic slope, theaccuracy of two approaches is corresponding. The accuracy of 6cm may be acquired whentaking 10 and above control points, whereas the accuracy of 8cm may be acquired when taking 8control points.The accuracy of 14cm may be acquired when taking 6 control points and theaccuracy drops dramatically.8.Statistical analysis of orientation accuracy of compass measuring is conducted. The resultindicates that mean error of dip measuring at a time of man-made compass on the spot is 4°,dipangle is 3°, so the limitation difference of dip is 12°and dip angle is 9°. The above limitationdifference serves as standard to contrast digital close range photogrammetry and compassmeasuring.9.Statistical analysis of acquired orientation accuracy of digital close range photogrammetryis conducted. From diverse methods of transacting images & data, different cameradistinguishability, different photograph distance and different control points distribution andquantity, Acquired orientation accuracy of digital close range photogrammetry is developed.1)The acquired orientation accuracy with digital photogrammetric workstation and DLTprogramme is corresponding. The fit mean deviation is below 6°, but by the contrast ofefficiency, the method of digital photogrammetric workstation make the judgement of fracturesaccurately and the whole process is swift because of reproducing 3-D model.2)Acquired orientation accuracy of using digital camera of 350 myriad image element can'tmeet the requirement. Acquired orientation accuracy of using digital camera of 800 myriadimage element meet fundamentally the requirement and the fit mean deviation of the result ofinterpretation orientations compared with compass measuring data is below 6°.3)Acquired orientation accuracy meets fundamentally the requirement when measuredobject is surrounded by control points and 8 and above control points are taken. Acquiredorientations accuracy can't ensure to meet the requirement when measured object isn'tsurrounded by control points.Analysis mentioned above is obtained On the condition of control point accuracy 1cm andapproximation straightness photograph of photograph distance 70m, photograph baseline 10m,baseline direction paralleled to the trend of lithologic slope.4)On the condition of control point accuracy 1cm and approximation straightnessphotograph of photograph baseline 10～15m, baseline direction paralleled to the trend oflithologic slope, interpreted orientation accuracy can't meet the requirement when photographdistance is 100m. interpreted orientation accuracy meets fundamentally the requirement whenphotograph distance is 70m and fit mean deviation the result of interpretation orientationcompared with compass measuring data is below 6°.10.Application analysis is conducted by interpreted fractures information of Baolilinyucommunity, including division of dominating fractures groups and stability analyzing withstereographic projection to offer safe grading angle . Analysis shows that the safe dip angle ofN-slope is 65°and it is greater than N-slope's actual dip angle, so N-slope is comparativelystable;the safe dip angle of E-slope is 45°and it is less than E-slope's actual dip angle, soE-slope exists potential instability;the safe dip angle of designed-slope of 7c-5Ⅰdistrict is 65°and it is greater than designed-slope of 7c-5Ⅰdistrict's designed dip angle, so dip angle ofdesigned-slope of 7c-5Ⅰdistrict can be more steeper. With the same theory, other safe dip angleof designed slope can be calculated. Accordingly, it offers standard of design to the project ofslope strengthening.