Spatial positioning of sidewall stations in a narrow tunnel environment: a safe alternative to traditional mine survey practice

5.5. Sidewall station observations

The first setup made in the test phase was at Hangingwall survey station UJ004, which point is on the flat section of the tunnel. Point SS03 had to be discarded as it was too close to the instrument so that focussing could not be achieved on the target. Please refer Figure .

Figure . Setup at UJ004


In order to compare the error vector obtained from each survey according to the requirements of the Mine Health and Safety Act, the shortest distance observed was used.
UJ004 Observation set 1. The instrument was placed directly under hangingwall control station UJ004 and the sidewall stations SS01 and SS02 were observed. The sidewall points are situated on the “first level” of the tunnel. The observations are tabulated below in Table :

Table . UJ004 Setup 1 using two known points

The error vector of the survey was calculated to be 5mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown in Figure

Figure . UJ004 Setup 1 using two observation rays

UJ004 Observation set 2. The instrument was placed directly under hangingwall control station UJ004 and the sidewall stations SS01, SS02 and SS04 were observed. The observations are tabulated below in Table :

Table . UJ004 Setup 2 using three known points

Figure . UJ004 Set-up 2 Observation rays
The error vector of the survey was calculated to be 3.6mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

UJ004 Observation set 3. The instrument was placed directly under hangingwall control station UJ004 and the sidewall stations SS01, SS02, SS07, SS08 and SS04 were observed. The observations are tabulated below in Table :

Table . UJ004. Setup 3 using five known points

The error vector of the survey was calculated to be 4.4mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ004. Setup 3 using five observation rays
UJ005 Observation set 1. The instrument was placed directly under hangingwall control station UJ005 on the second level of the tunnel and the sidewall station SS04 on the first level and SS05 close to the control point on the second level were observed. The observations are tabulated below in Table :

Table . UJ005 Setup Observation 1 using two known points

The error vector of the survey was calculated to be 4mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ005 Setup 1 using two observation rays
UJ005 Observation set 2. The instrument was placed directly under hangingwall control station UJ005 and the sidewall stations SS04, SS05 and SS07 were observed. The observations are tabulated below in Table :

Table . UJ005 Setup Observation 2 using three known points

The error vector of the survey was calculated to be 5mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ005 Setup 2 using three observation rays


UJ005 Observation set 3. The instrument was placed directly under hangingwall control station UJ005 and the sidewall stations SS04, SS05, SS08 and SS07 were observed. The observations are tabulated below in Table :

Table . UJ005 Setup Observation 3 using four known points

The error vector of the survey was calculated to be 5mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ005 Setup 3 using four observation rays


UJ005 Observation set 4. The instrument was placed directly under hangingwall control station UJ005 and the sidewall stations SS08 and SS07 were observed. The observations are tabulated below in Table :

Table . UJ005 Setup Observation 4 using two known points

The error vector of the survey was calculated to be 6mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . . UJ005 Setup 4 using two observation rays
UJ012 Observation set 1. The instrument was placed directly under hangingwall control station UJ012 and the sidewall stations SS17 and SS16 were observed. The observations are tabulated below in Table :

Table . UJ012 Setup 1 Observations using two known points

The error vector of the survey was calculated to be 4mm with the allowable Limit of Accuracy at 16mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ012 Setup 1 using two observation rays

UJ012 Observation set 2. The instrument was placed directly under hangingwall control station UJ012 and the sidewall stations SS11 and SS17 were observed. The observations are tabulated below in Table :

Table . UJ012 Setup 2 Observation using two known points

The error vector of the survey was calculated to be 9mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure . UJ012 Setup 2 using two observation rays




UJ012 Observation set 3. The instrument was placed directly under hangingwall control station UJ012 and the sidewall stations SS11 and SS12 were observed. The observations are tabulated in Table :

Table . UJ012 Setup 3 Observation using two known points

The error vector of the survey was calculated to be 13mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown in Figure :

Figure . UJ012 Setup 3 using two observation rays

UJ012 Observation set 4. The instrument was placed directly under hangingwall control station UJ012 and the sidewall stations SS09, SS10 and SS11 were observed. The observations are tabulated below in Table :

Table . UJ012 Setup 4 Observation using three known points

The error vector of the survey was calculated to be 7mm with the allowable Limit of Accuracy at 15mm. The geometry of the rays observed are shown here in Figure :

Figure .. UJ012 Setup 4 using three observation rays

UJ014 Observation set 1. The instrument was placed directly under hangingwall control station UJ014 and the sidewall stations SS09 and SS10 were observed. The observations are tabulated below in Table :

Table . UJ014 Setup 1 Observation, using two known points

The error vector of the survey was calculated to be 286mm with the allowable Limit of Accuracy at 16mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed is shown here in Figure :

Figure . UJ014 Setup 1 using two observation rays.

UJ014 Observation set 2. The instrument was placed directly under hangingwall control station UJ014 and the sidewall stations SS09, SS10 and SS12 were observed. The observations are tabulated below in Table :

Table . UJ014 Setup 2 Observation, using three known points

The error vector of the survey was calculated to be 13mm with the allowable Limit of Accuracy at 16mm is within the required minimum standards of accuracy. The geometry of the rays observed are shown here in Figure :

Figure . UJ014 Setup 2 using three observation rays

UJ014 Observation set 3. The instrument was placed directly under hangingwall control station UJ014 and the sidewall stations SS17, SS16, SS14FS and SS15FS were observed. The observations are tabulated below in Table :

Table . UJ014 Set up 3 Observation, using four known points

The error vector of the survey was calculated to be 5mm with the allowable Limit of Accuracy at 15mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown here in Figure :

Figure . UJ014 Setup 3 using four observation rays


UJ015 Observation set 1. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS09 and SS10 were observed. The observations are tabulated in Table :

Table . UJ015 Setup 1 Observation, using two known points

The error vector of the survey was calculated to be 740mm with the allowable Limit of Accuracy at 19mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . UJ015 Setup 1 using two observation rays

UJ015 Observation set 2. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS09, SS12 and SS10 were observed. The observations are tabulated below in Table :

Table . UJ015 Set up 2 Observation, using three known points

The error vector of the survey was calculated to be 62mm with the allowable Limit of Accuracy at 18mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed are shown here in Figure :

Figure . UJ015 Set up 2 using three observation rays

UJ015 Observation set 3. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS14FS2, SS15FS2, SS16FS2 and SS17FS2 were observed. The observations are tabulated in Table :

Table . UJ015 Setup 3 Observation, using four known points

The error vector of the survey was calculated to be 7mm with the allowable Limit of Accuracy at 17mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . UJ015 Setup 3 using four observation rays

UJ015 Observation set 4. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS16FS2 and SS14FS2, surveyed from the UJ014 Freestation, were observed. The observations are tabulated in Table :

Table . UJ015 Setup 4 Observation, using two known points

The error vector of the survey was calculated to be 11mm with the allowable Limit of Accuracy at 17mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . UJ015 Setup 4 using two observation rays

UJ015 Observation set 5. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS15FS2 and SS17FS2 , surveyed from the UJ014 Freestation, were observed. The observations are tabulated in Table :

Table . UJ015 Setup 5 Observation using two known points

The error vector of the survey was calculated to be 34mm with the allowable Limit of Accuracy at 17mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed are shown in

..

Figure . UJ015 Setup 5 using two observation rays

UJ015 Observation set 6. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS15FS2 and SS14FS2, surveyed from the UJ014 Freestation, were observed. The observations are tabulated in Table :

Table . UJ015 Setup 6 Observations using two known points

The error vector of the survey was calculated to be 1mm with the allowable Limit of Accuracy at 17mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . UJ015 Setup 6 using two observation rays

UJ015 Observation set 7. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS16FS2 and SS17FS2, surveyed from the UJ014 Freestation, were observed. The observations are tabulated in Table :

Table . UJ015 Setup 7 Observation using two known points

The error vector of the survey was calculated to be 29mm with the allowable Limit of Accuracy at 17mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure

Figure . UJ015 Setup 7 using two observation rays



UJ015 Observation set 8. The instrument was placed directly under hangingwall control station UJ015 and the sidewall stations SS09 and SS10 , surveyed from the UJ014 Freestation, were observed. The observations are tabulated in Table :

Table . UJ015 Setup 8 Observation using two known points

The error vector of the survey was calculated to be 731mm with the allowable Limit of Accuracy at 19mm which exceeds the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . UJ015 Setup 8 using two observation rays
GH832 Observation set 1. The instrument was placed directly under hangingwall control station GH832 and the sidewall stations SS21 and SS22, were observed. The observations are tabulated in Table :

Table . GH832 Set up 1 Observation using two known points

The error vector of the survey was calculated to be 2mm with the allowable Limit of Accuracy at 15mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure :

Figure . GH832 Set up 1 using two observation rays


GH832 Observation set 2. The instrument was placed directly under hangingwall control station GH832 and the sidewall stations SS26 and SS27, were observed. The observations are tabulated in Table :

Table . GH832 Setup 2 Observation using two known points

The error vector of the survey was calculated to be 9mm with the allowable Limit of Accuracy at 16mm which is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure

Figure . GH832 Set up 2 using two observation rays

GH832 Observation set 3. The instrument was placed directly under hangingwall control station GH832 and the sidewall stations SS21, SS22, SS26 and SS27 , were observed. The observations are tabulated in Table :

Table . GH832 Setup 3 Observation using four known points

The error vector of the survey was calculated to be 3mm with the allowable Limit of Accuracy at 15mm this is within the required minimum standards of accuracy. The geometry of the rays observed are shown in Figure .

Figure . GH832 Setup 3 using four observation rays

From the results a number of issues have been highlighted. A tabulation will show that a minimum angle of 2 degrees and a maximum distance of 42metres provided acceptable results in the fixing of a point, given the forced poor triangular geometry (refer to Table . Two point freestations) . The accuracy improves as the geometry of the triangle increases in the angle at the observation point, and in such cases distance does not become a problem. The grade peg configuration provides an accurate fix only if more than two points are observed. Poor fixes on the y- and x co-ordinates were in all cases the result of a two peg only resection.

The minimum standards of accuracy as stated by the MHSA do not provide for the accuracy achieved using the resection method of surveying. The principle of using the shortest sighting distance to calculate the error figure appears to be the correct principle. However the minimum Limit of error determined by the MHSA is 15mm. In most cases this accuracy should be acceptable in the mining industry but for high accuracy applications like tunnelling and shaft sinking a 15mm limit of error may not be sufficient to meet the tolerances required by such a project.
The freestation method using two points only, has indicated that it may not be possible to identify if a point is “out of tolerance”, it is not clear if the instrument software will be able to identify any such “out of tolerance” points if only two points are used. In the case of where more than two points are used, it is possible to identify an “out of tolerance point” and remove such point from the observation file before the final fix is determined.
During the observations made in the tunnel it became apparent that on one specific setup, the tolerances were outside the expected tolerances. Through a process of elimination SS17FS2 was identified as being outside the acceptable tolerance as all observations that included observations to SS17FS2 displayed an error. The error on the positional fixes using SS17FS2 displayed on the y co-ordinate bears out this argument. This underlines the importance of ensuring that the sidewall station numbers and identification are correct as well as displaying the importance of using more than two reference points in the observation fix. Refer to Appendix 7.

From UJ015 Observation Setup 3 using SS14FS2, SS15FS2, SS16FS2 and SS17FS2 an error of 7mm was obtained. This would indicate that the additional fourth reference point was able to correct the geometry of the setup to a point where an acceptable result could be achieved. The exercise indicated that a control point could be transferred forward from a freestation setup provided that the freestation setup complied with the constraints of a maximum of 42m ahead of the last survey control point with a minimum angle of 2 degrees. From the results it is evident that a position fix using two points only did not provide an acceptable accuracy on the elevation of the forward surveyed point. It was determined that the large errors in the elevation of some points were the result of the instrument software not being specifically setup to deal with the negative instrument height and positive target height as used in the traditional underground setup. A practical solution used in industry is to leave both the target and instrument heights at 0.000m.

6.