Open pit slope monitoring and instrumentation
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The document discusses various slope monitoring strategies employed by geotechnical engineers to assess and manage slope stability in different timeframes: short-term, medium-term, and long-term. It highlights the importance of monitoring for predicting potential slope failures and ensuring safety through automated systems and real-time data analysis. Different methodologies, including surface and sub-surface measurements, are explored along with their costs and effectiveness in different geological conditions.
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flaccelerometers, aligned so that they geological structures that rrray Itr'f!!
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^"urnie
the tilt of the probe in twomeasuie the tilt of the probe in two confirmed by other geotechnical Ittt'rttts.
mutually perpendicular directions. The From the seismic event locaticlrrs iuttl
probe is also equipped with a pair of sizes, itispossibletoinferrelativesurfat't'
wheels that run in the grooves in the movements resulting from this micrg-
casing and maintain the rotational seismicity. Surface movement is alstr
stabilityof theprobe. recorded by conventional surveying gf
prisms. Comparisons between these two
forms of data has revealed that the seismic
data may be able to indicate regions of
surface movement 30-45 days before these
movements are seen on the surface. This
delay would depend on rock properties
and the locations of the seismic events.
The usef ulness of micro-seismic
monitoring stems from the fact that cracks
are located wherever they occur, and so a
3-D picture of the rock mass is obtained.
Unlike the 2-D picture obtained with
conventional surf ace monitoring.
Real Time Monitoring: Real Timt'
Monitoring is a Mobile and global
monitoring system. Normally critical
Figure 6 : Inclinometer System at Rampura ,
Agucha LeadzincMirr"r, ]HZL slope surfaces are monitored real tin'tt'
basis. Its gives a real time warning of tlrt'
LongTermMonitoring: slope health and the risk factrrs
Micro-seismic monitoring gives an associated with it. the warning titrtt' ol
indication whether a particular known slope failure depends on a nul'trbt'rs ol
geological structure is seismological f actors including rock ty [-,.', t'ot'1,.
a ctive or not. If many seismic events occur weatherness, Presence of tl ist'o t t l i r r r r i l v
on or near the structure, then it is likely surfaces, persistency of thc t{ist'oltlitrttily,
lhat the structure is slipping. Indeed, inJill, ground water conclititttt, t'lt'. ( )vt'l'
planes of weakness definedby seismic 200 slope failure was atritlyzt'tl lry M/!1
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Open pit slope monitoring and instrumentation
- 1. Abrtrlct programs can be of value in managing ) (lltctt ttil s/rr1rr's ,tt(z)cs in aarying :t:p" hazards' and they provide rlr',gl'r'r'N tlttritty llttir ope rntion l'f'' ;t; information that is useful for the design of slrrlrl'5 slrtlr's tt tlttrtsi-stable state for a long remedialwork' tltt rttlitttt itt olltr'r lmnd some slopes fails after a slope monitoring strategy tttittrtr slo1tr tnouement' Slope monitoring Based on the slope design l,r(,5,'tttns can hetps the Geotechnic.al properties, its expected life, and risk !',ttgittrt'rs for understanding slope behaaior irrrrotrr"a the Slope monitoring strategy ltroltcrly. Short term, Medium term, Long framed. Figure-1 show four different Icrttt and Reql Time monitoring - these four types ofmonitoring strategy are strategi:i;;; ilffi"ffr::T,-fi #* ":lT:"fffrthe Geotechnical Engineers. Different tyyes,oJ monitoring strategy are strategized by the instrumentationusedfordffirentmonitoring Ceotechnical Engineers for Slope methods arebriefly describe in thispaper ' Movement Monitoring. Introduction Many rock slopes move to varying stli degrees during the course of their operational lives. Such movement T*trnr indicates that the slope is in a quasi-stable state, but this condition may continue for t*$n many years, or even centuries, without occurring of any failure. Slopes move to varying degrees during their operation ',.'... i * safely for years with moving slopes that itrc carefully monitored to warn of Figure L : Slope Movement Monitoring Strategy tlcteriorating stability conditions' I lowcver, in other cases, initial -"'o' short term monitoring- short Tem slope srunt' ,novcment mav be a precu"{i; ilfjilil:*fft;,1T,rffitilJ#";tf irr't't'lt'rittiltlS movement followed by area. Normally photometry is taken for t'rtllitPst'ttl'tlrt'slopc. this monitoring along with the visual llt't'iltlrt' ol' tlris unpredictability of inspection' Non-moving benches/ final nlgtrr, lrt.lrrrvlpt., llt()v(,ll'l(,ltt mon toring bench wall/slopes, matured' dumps (
- 2. flslopes need to monitor regularly for short safe access to the site. Optitllts I'ot' 'j term monitoring. Surface cracks, monitoring equipment inclutlt' f displacement of slope surface etc are automaticallycollectingmeasurernentsnl noticed during short term monitoring. pre-set intervals on data loggers, trtltl Short term monitoring gives a reasonable using telemetry to transmit these results fair idea on the slope stability; however it to another location for analysis ancl requires experts Geotechnical Engineers plotting. These systems can also for proper error free inspection of the incorporate alarms that are triggered if Slopesurfaceforanearlywarning. pre-set movement thresholds are Medium Term Monitoring: Medium exceeded' An important aspect of such Term Monitoring includes Surface automated systems is the cost of Monitoring and Sub-lateral Movement installatiorUandparticularlymaintenance' Monitoring. Crackwidthmonitors Surfacemonitoring Since tension cracks are an almost universal feature of slope movement,Surface monitoring can only be used where the surface movement accurately represents the overall movement of the slope. It would not be appropriate to make surface measurements where loose blocks of rock on the surface were toppling and rotating independently of the main slide movement. Monitoring of the surface of a slope is less costly to set up and maintain than sub-surface measurements that will require drilling holes to install the instruments. Other factors to consider in the selection of a monitoring system include the time available to set up the instruments, the rate of movement and crack width measurements are often a reliable and inexpensive means of monitoring movement. The simplest procedure is to install a pair of pins/ wooden pegs on either side of the crack and measure the distance between them with a steel tape. If there are two pins on either side of the crack, then the diagonal distance can also be measured to check the transverse displacement. Crack meters with displacement sensor are also used for this monitoring. The maximum practical distance between the pins is probably2rn. Figure 2: Crack meter
- 3. ()tr litrgc slides where access to the skrpc is hitzitrclous and/or there is a need to makt'frt'tlutlnt and Precise measurctncnts ilttcl rapit'lly analyze the Figure 3 : Slope Monitoring system at Kiriburu Iron Ore Mines
- 4. Figure 4 : Automatic Theodilite
- 5. l*;llll, l;'l:;'1,,,i*,lll::;"il; ;l: ;;ff:;'#;il ;;: can be l'wered Pt.ritlt|s,witltrrtr,....,.|t.,sctupreferencedownthehole,andinthiswayboththe lltritttrrtllt|ltt,grtlutrtl.However,Sometopandbottomoftheslideplanecanbe lirtritirtiotrs ol' thc tcchnique are that the located' l'r('(lll('11('y ttl' the measurements are The ad'vantages of the probe are the 11ttvt.rttt,t|tlytheintervalbetweensatellitelowcostandsimplicity,butitwillprovide rrrbits ovcr the site, which is about once little inf ormation on the rate of ('v(iry 24-35 days, and the proces^sing of movement' thc data can take another 35-40 days' Also, movement is most accuratelY monitored' in the vertical direction' Sub-surf ace monitoring metho ds Sub-surface measurement of sloPe movement is often a useful component ot a monitoring program in order to provide a more complete picture of the slope behavior. In cases where surf ace monitoring is not feasible' then sub-surface Fieure 5 : Inclinometer system- measuremt nts is only measu ements working principal available. The main purpose c f these Inclino eters ;"ffi::',''j;;':"ffi:1"'J:' fJT,., ^'1:' inometer ; are instruments movemenu in some,ases the ,"J;;i 'i:,1iH;:"tl:" i'"tffil"firilffi: used for monitoring t oth move rent and orr", it, "r'rtir" l".rgth. By making a series of waterpre sures' readings over time it is also possible to Boreholeyrobes monitor the rate ol movement' The c)ne of the simplest sub-surface compo nts of the inclino eter are a rrrr.it.ringmethodsistheborehoreprobe prastic casing with four longitudinal c.rrr'risirrg a lcngth of reinforcing steel gloovescutinthe rsidewall'andaprobe abtlttl 2ttt lotrg t'hat is lowered r own the that is lowered d lwn the casing on an drilr rrrrt, '' ir lt.rrgth .f rope. If the hole electric il cable with graduated depth - ^^,tqit.rc IIAIO illril:; ,,";,;;;; ;,il-io,,", the hore markings. rhe probe co^rtains two
- 6. )1O r gd5;- 5 7 t f Annu a [ 9vt.in e s s dfe ti'(ie e Q c e [e 6 rat io n- 2 0 t I -:3${! flaccelerometers, aligned so that they geological structures that rrray Itr'f!! 'i ^"urnie the tilt of the probe in twomeasuie the tilt of the probe in two confirmed by other geotechnical Ittt'rttts. mutually perpendicular directions. The From the seismic event locaticlrrs iuttl probe is also equipped with a pair of sizes, itispossibletoinferrelativesurfat't' wheels that run in the grooves in the movements resulting from this micrg- casing and maintain the rotational seismicity. Surface movement is alstr stabilityof theprobe. recorded by conventional surveying gf prisms. Comparisons between these two forms of data has revealed that the seismic data may be able to indicate regions of surface movement 30-45 days before these movements are seen on the surface. This delay would depend on rock properties and the locations of the seismic events. The usef ulness of micro-seismic monitoring stems from the fact that cracks are located wherever they occur, and so a 3-D picture of the rock mass is obtained. Unlike the 2-D picture obtained with conventional surf ace monitoring. Real Time Monitoring: Real Timt' Monitoring is a Mobile and global monitoring system. Normally critical Figure 6 : Inclinometer System at Rampura , Agucha LeadzincMirr"r, ]HZL slope surfaces are monitored real tin'tt' basis. Its gives a real time warning of tlrt' LongTermMonitoring: slope health and the risk factrrs Micro-seismic monitoring gives an associated with it. the warning titrtt' ol indication whether a particular known slope failure depends on a nul'trbt'rs ol geological structure is seismological f actors including rock ty [-,.', t'ot'1,. a ctive or not. If many seismic events occur weatherness, Presence of tl ist'o t t l i r r r r i l v on or near the structure, then it is likely surfaces, persistency of thc t{ist'oltlitrttily, lhat the structure is slipping. Indeed, inJill, ground water conclititttt, t'lt'. ( )vt'l' planes of weakness definedby seismic 200 slope failure was atritlyzt'tl lry M/!1 t'ventsmayindicatepreviouslyunknown Ground Probe, Australiir itttrl il hr lilttltrl :S ;,e Ie of to ne a ral ,be an rth wo
- 7. .l7t li )4 rttttul':M ina's sdIety 'l'leefrcefe6ration-2019 that orrly l'h of lht' slolrt' Inils with a wrtntittlq lltttt' lt'nn lltltt l-'r tttitrtttcs. That tn('|rltlH rtll tttttril ('v('ry slitlt' I'itilure mencan rrrtft'ly ('vll('llitl(' tltt' l'nilurc area. 1'6% frtllrtrr' (x'('ltt's witlr it warning time 5 Figure 8: SSR SYstem For Real Time Monitoring SYstem Slope Monitoring Radar of M/S Ground Probe, Australia and The Movement and SurveYing Radar (MSR Figure 7: Warning Time Histogram analysis by ld/S GroundProbe, Australia for over 200 Slope Failure minutes to L hour. It means except these 83% cases men and machinery can'safely evacuated the failure areas when real time monitoring are used to monitoring the slope surface. asaaE.ctai _r^-Cin:idrNe Figure 9: MSR SYstem 200) another real time monitoring instrument by M/S Reutech Mining, South Africa are used for this monitoring. t Ut asirre TE Ea Htstogram
- 8. ffi s 7tn Annuar totines safery T:':::ration- 20 1 e '- There are several well-documented cases of slope monitoring at open pits where mining continued for several months below the moving slope. Eventually the rate of movement increased rapidly indicating that stability conditions were deteriorating and operations were halted shortly before the slopefailed. It is considered that where there is a significant risk to lives and property, remediation is preferred to medium term and long-term monitoring. The instrumentations for different types of monitoring may be chosen based on the working principal of the instruments, working condition, location and accessibility of the slope and risk ranking. Biswas Rdthin & Sarkar Priyaranjary 2009, "SLOPE STABILITY RADAR- AN ADVANCED SLOPE MOVEMENT MONITORING SYSTEM" 23'o Mines Safety Week- 2009, Ajmer Region, Available at https: / / www. slideshare.net/ rathin mining/ssr-paper Bye Alan, & Little Megan, 2005, " SLOPE STABILITY RISK MANAGEMENT AT ANGLO PLATINUM'S SANDSLOOT OPEN PIT" 36.N ANNUAL CONFERENCE & EXHIBITION, Birchwood Conference Centre, Gauteng DGMS Circtilar Tech (S&T) 2 of 200 Noon Rabort, 2012, Slope Stability Radar WyllieDuncanC&Mah Christopher W, 1981.., "Rock Slope Engineering" 4'n Edition, Spon Press a a Rathin Biswas Sr, Mnnngcr (Mining), ltMD Training Centre, Klrlburu lron Ort' Mitrcs, I{aw Materials Division, Stccl Authority of India Limited I E