- Email: [email protected]
Weak zone characterization using full drilling analysis of rotary-percussive instrumented drilling
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
Contents lists available at ScienceDirect
International Journal of Rock Mechanics Mining Sciences journal homepage: www.elsevier.com/locate/ijrmms
crossmark
Weak zone characterization using full drilling analysis of rotary-percussive instrumented drilling ⁎
J. Chena, , Z.Q. Yueb a b
China Harbour Engineering Company, Beijing, China Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
A R T I C L E I N F O Keywords: Weak zone characterization DPM Full drilling analysis Rock mass characterization
1. Introduction Weathered rock masses often contain weak zones. The behavior of weathered rock masses is strongly affected by the presence of the weak zones such as joints, fissures, fractures, faults and cavities. How to detect and describe the characteristics of weak zones has become one of the important subjects in geology, geophysics, mining engineering, petroleum engineering, hydrology and waste disposal. The continuous growth in capabilities and reliability of computers, combined with the development of technical and managerial software packages, has inspired use of instrumented drilling monitoring in the geological industry to characterize weak zones both from lab tests and from field tests. Barr and Brown1 performed core drilling tests through an assemblage of concrete blocks having various cement/water ratios and aggregate types. The blocks were arranged to simulate changes in lithology, variations in strength, fissures of various aperture and orientation with and without infilling material associated with faults. They concluded that the special behaviors of pressures and drilling rate would occur when drilling through joint zone. They also pointed out when the fissure was in-filled; the net effect was to dampen the response of the drilling variables, often to the extent that no variation occurred. In the lab test, drilling responses were recorded corresponding to different kinds of weak zones. This provided a good foundation for weak zone characterization in site. Scoble and Peck2 discussed and summarized the characterization of drill performance parameters: thrust, rotary speed, circulating fluid flow rate, operating pressure, drilling rate, torque and drilling fluid pressure. They also combined the laboratory study with the in-situ
⁎
study to estimate drilling rate. They applied drilling rate log to detect shale bands. Upon comparison with the fractures logged from core, 60% of these were also indicated by a corresponding drilling rate peak. Because the most important parameter, drilling rate, was estimated by a pre-selected depth advancement increment, different pre-selected increments could result in different drilling rate variations with depth for the same ground geological conditions3. This undermined the application of this system for weak zone characterization. Pfister4 described the recorded shapes of curves for silly surface deposits, clay layers, alluvium, empty cavity, unfilled fracture, plain massive limestone and fractured zone filled with clay and summarized three steps to analyze the raw data obtained from Enpasol recorder. He tried to characterize different rock and soil structures with drilling parameters. However, because the data were recorded by depth increments, the recorded data did not include the pushing-in actions and pulling-back actions which is important to characterize weak zones. The accuracy of weak zone characterization was reduced. Garassino and Schinelli5 used the Papero system for monitoring of a number of tricone drillholes to detect cavities in a power plant project in Italy. They adopted an optimized drilling rig pressures and kept them as constant as possible during drilling. The accuracy was also affected by the sizes of cavities and depth increment for recording. Cheetham and Inett6 designed an experimental drilling rig for testing the performance of percussive drilling machines and for investigating the factors affecting percussive drilling of rocks, such as lubrication of a rock drill and effect of cuttings flush. They also summarized the relations between drilling parameters such as thrust, rotation and drill speed. This provided a good idea to normalize the insitu drilling data.
Corresponding author. E-mail address: [email protected] (J. Chen).
http://dx.doi.org/10.1016/j.ijrmms.2016.09.012 Received 22 October 2015; Received in revised form 17 May 2016; Accepted 20 September 2016 1365-1609/ © 2016 Elsevier Ltd. All rights reserved.
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Schunnesson7 suggested a data analysis method for separating rock dependent variation from other influences on the monitoring drilling parameters. Furthermore, he separated the drill response into two independent signals, one representing the hardness of the rock and one representing the inhomogeneity (fracturing) of the rock. These research efforts supplied a new idea for characterizing weak zones. But the drill response to weak zones could not be separated from those to different kinds of breaking actions because of the intrinsic problem of depth-sampling based instrumented drilling methodology3. For weak zone characterization, instrumented percussive drilling has not become a standard method in spite of great efforts made both in the field of drill monitoring hardware and in analysis method over the last decades. One of the major reasons is that past studies apply depth-sampling based instrumented drilling devices to record drilling parameters from the total time that is used for a pre-selected depth advancement increment. To overcome above obstacles, this article has applied drilling process monitoring (DPM) methodology to record drilling process in real time series. We have conducted full drilling analysis to divide full drilling process into many actions (such as pushing-in action, pullingback action and drilling action). The criteria for characterizing weak zones were built and two kinds of weak zones in percussive drilling are summarized based on the new DPM based full drilling analysis.
ing, removing, push downward and connecting will be carried out until the hammer rod is retrieved from the drillhole. Then, the drilling machine is relocated to next drillhole position. Steps 1–3 are repeated. 3. Full drilling analysis Full drilling analysis is to divide full drilling process into many actions and study the relations between drill parameters in these actions. A total of six kinds of actions can be determined: Drilling action, Pulling-back action, Pushing-in action, Tightening action, Untightening action, and Stoppage action. Only the first three actions are related to the rock mass characterization. The analysis to drilling action is called as net drilling analysis3. Especially, the pushing-in action and pulling-back action can be taken as drilling or retrieving in the air. Because there are no variations in “drilled material”, the relations between drill parameters in these two actions are very useful for weak zone characterization and calibration of drilling machine. It is further noted that above information of drilling without penetrating new geomaterial has not been recorded in existing devices for depth-sampling based instrumented drilling. They recorded the relevant drilling parameters corresponding to the drilling process for drill bit deeper advancement at a pre-selected depth advancement increment4,5,7,9–17.
2. Full drilling process
4. Weak zone characterization with full drilling analysis
Full drilling process includes all actions of air-driven rotary percussive drilling from beginning to end recorded by seven DPM transducers (position transducer, five pressure transducers and rotation transducer). It can be briefly described as the following main steps in a time sequence8. The sampling rate is 2.
4.1. Weak zone without infilling Drilling in weak zone without infilling is the process of drilling in air because no geomaterial exist. It is included in the net drilling process and is same as pushing-in actions. The drilling rate at the weak zone is only determined by the downward thrust pressure. Fig. 1 shows the full drilling process of a soil nail hole including weak zone without infilling. To detect weak zone without infilling, full drilling analysis is used to divide full drilling process into many actions and study the relations in net drilling actions and pushing-in actions.. A breaking action based zoning analysis3 has been applied to divide the net drilling process into a series of breaking actions. Adjacent breaking actions with similar drilling speed were combined into one zone. Thus, the net drilling process is finally divided into fourteen zones in Fig. 2. The zone drilling rates are listed correspondingly. Among them, the drilling rate of zone 10 is 23.52 m/min and is much higher than other zone drilling rates. It may indicate the weak zone without infilling but need to be confirmed with subsequent comparison.. A pushing-in process analysis has been carried out focusing all pushing-in actions. In these actions, the drill bit is moving forward in a drill hole that has been drilled already. There is no influence of the soil and/or rock resistance. The downward thrust pressure is the only factor to determine the pushing-in rate. A relation between pushing-in rates and downward thrust pressures has been built and is compared with zone drilling rates with their associated downward thrust pressures in Fig. 3. At same downward thrust pressure level, the drilling rate of zone 10 (23.52 m/min) is higher than the pushing-in rate. This means that there is no geomaterials to dampen the drill bit speed. The difference between the pushing-in rate and the drilling rate of the weak zone is caused by the sampling rate. It may be not enough to capture the positions of high speed drill bit accurately. Some systematic variations will be involved..
Step 1: Initial drilling The control panel is used to install the down-the-hole hammer onto the swivel drill chuck via its shank adaptor. The hammer bottom end is fixed with a drill bit. The control panel is used again to move the drill bit touching the surface of the ground to be drilled. The control panel is further used to commence the drilling with the actions of percussion, rotation and thrust. The drilling work will be stopped once a majority of the hammer length is advanced into the ground. Step 2: Subsequent drill runs by adding extension rods After completion of the initial hammer advancement, the swivel drill chuck will be disconnected with the hammer at the shank adaptor. The chuck will be pulled back for adding the first extension rod onto the shank adaptor and the upper hammer end. Then the drilling will be advanced again until the first extension rod is in the ground. The first extension rod and hammer system will be disconnected with the chuck at the shank adaptor. The chuck will be pulled back for space to add the second extension rod. Similarly, the second extension rod will be connected with the shank adaptor and the upper end of the first extension rod. Such operations of drilling, disconnecting, adding and connecting and drilling will be repeated until the hammer bit is advanced to the designed depth in the ground. Step 3: Dismounting the drilling by retrieving extension rods and hammer After the completion of Step 3, the control panel is used again to pull back the last added extension rod back to the ground surface. This last rod is then disconnected with the shank adaptor and the remaining extension rods in the hole. The chuck is pushed downward again to connect the shank adaptor with the upper end of the remaining extension rods. Then the above operations of pulling back, disconnect-
4.2. Weak zone with infilling This kind of weak zone can be subdivided based on the sequence of infilling collapse. 228
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Fig. 1. Full drilling process of a soil nail hole with weak zone without infilling: (a) drill bit position versus full drilling time; (b) associated downward thrust pressure; (c) associated upward thrust pressure; (d) associated forward rotation pressure; (e) associated reverse rotation pressure; (f) associated percussion pressure.
229
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Fig. 2. Results of the DPM methodology in identifying the zones of constant drilling rates along the soil nail hole. 35
4.2.1. Infilling collapse after drilling action A weak zone with infilling collapse after drilling action is quite difficult to be detected in drilling process, because the corresponding drill responses to infilling are same to other parts. There is no collapsed infilling to dampen drill bit speed during drilling process. In Fig. 4, drill bit positions in net drilling process of Hole No. TN281, together with the associated pressures, are presented in time series. No abnormal zones can be located in this net drilling process. Fig. 5 shows the drill bit positions in full drilling process. Stages B, C and E are stages of pushing or retrieving rods. In stages B and E, the pullingback speed of drill bit in the zone with drill bit position between 4 m and 6 m is much lower than that of other parts, even though the downward thrust pressure keep in a constant level. Because the infilling collapses after the drilling action, collapsed chippings reduce the drill
30 y = 10.325ln(x) + 30.667
Unit: m/min
25 Weak zone without infilling
20 15
Pushing-in rate
10 Drilling rate 5 0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Downward thrust pressure (MPa)
Fig. 3. The drilling rates and the pushing-in rates with respect to their associated downward pressures for the soil nail hole with weak zone without infilling.
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International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue 0
3
4
6
7
8
9
14.69m
Drilling rate : 0.16m/min
5
Drilling rate : 0.93m/min
Drilling rate : 1.13m/min
2
Drilling rate : 1.55m/min Drilling rate : 0.55m/min
1
Drilling rate : 1.31m/min
0
9.53m 10.50m 11.59m 12.13m 12.93m 14.22m
Drilling rate : 0.98m/min
25
Drilling rate : 0.96m/min
20
Drilling rate : 1.35m/min
15
Drilling rate : 0.58m/min Drilling rate : 1.09m/min
10
Drilling rate : 0.73m/min
Net drilling depth (m)
7.86m
Drilling rate : 0.51m/min
5.62m 5.79m 6.95m
5
Drilling rate : 0.97m/min
4.28m
22.40m 21.70m
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Net drilling time (Min)
Downward thrust pressure (MPa)
1.0 0.8 0.6 0.4 0.2
Forward rotation pressure (MPa)
0.0 1.0 0.8 0.6 0.4 0.2
Percussion pressure (MPa)
0.0 1.0 0.8 0.6 0.4 0.2 0.0
Fig. 4. Results of the DPM methodology in identifying the zones of constant drilling rates along the soil nail hole (TN28-1).
and percussion pressure is not well built up. Its average value of weak zone is lower than that of other parts. Higher forward rotation pressure is needed to remove more chippings. Total five of this kind of weak zones can be located based on the special drilling responses in Fig. 7. The drill responses to this kind of weak zone are in accordance with many researchers’ observation1,2,4,5,7,9..
bit speed during retrieving rods stage. However, this kind of weak zone cannot be located by adding rods and pushing in stage, because percussion pressure is applied in this stage to remove chippings off (Fig. 6).... 4.2.2. Infilling collapse during drilling action In this kind of weak zone, hole collapse occurs during drilling action. The collapsed geomaterial makes the net drilling responses different with those to other parts. Before drilling the weak zone, drill bit has good contact with drilled geomaterial. The percussion pressure at the interface between the bit and the geomaterial is steadily built up. The corresponding forward rotation pressure and downward thrust pressure are also steady to remove chippings and keep drill bit contact with drilled geomaterial. When drill bit drills the weak zone, infilling collapses. The collapsing process makes pressures change frequently. Many generated chippings separate drill bit from drilled geomaterial
5. Grouting tests for weak zones determined by DPM methodology 5.1. Test slope The test slope is a 14 m high fill slope. It has a length of approximately 75 m along the crest at an average face angle of 35°. It comprises a layer of fill (Fill), overlying successively completely decomposed granite (CDG) and highly decomposed granite (HDG). It is 231
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Drill bit position (m)
0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
10
20
30
40
Full drilling time (Min) 50 60
70
80
90
100
110
Weak zone with infilling
A
B
C
D
E
Stage A, and D: Adding rods and drilling Stage B and E: Retrieving rods Stage C: Adding rods and pushing in Fig. 5. Drill bit positions of Hole No. TN28-1 in full drilling process. Stage A, and D: Adding rods and drilling, Stage B and E: Retrieving rods, Stage C: Adding rods and pushing in.
Fig. 6. Drill bit drills the weak zone with infilling collapse in drilling action.
results of the two holes. The theoretical volume of grouting can be calculated by
situated in the subtropical zone and experiences a hot and humid climate with seasonal heavy rainfalls. Such a seasonal environment promotes chemical weathering of the rocks and has resulted in a weathered mantle of varying thickness and decomposition that covers fresh granite rocks. Such chemically decomposed granites generally have much less shear strength than those associated with the parent fresh solid granites. The higher the decomposition, the lower the weathered volcanic strengths.
v = α π r 2L
(1)
where v is the theoretical volume of grouting, r is the radius of soil nail hole, L is the length of soil nail hole, and a is the factor considering the cement loss during the grouting, normally, it is taken as 1.2. The net grout volumes of the two holes are much greater than the theoretical calculation. Especially for Hole TN28-2, the net grout volume is two times the theoretical volume. This suggests the wider spatial distribution of its weak zones.
5.2. Test result Two soil nail holes Nos. TN28-1 and TN28-2 are grouted and measured to indirectly verify different kinds of weak zones determined by DPM methodology. The DPM analysis results of the two holes are shown in Figs. 4, 5 and 7 respectively. Table 1 shows the grouting
6. Concluding remarks Full drilling analysis for identifying weak zones in rock mass from 232
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
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Fig. 7. Results of the DPM methodology in identifying the zones of constant drilling along the soil nail hole (TN28-2).
Table 1 Grouting volumes for Trial Nail Nos. TN28/1 and TN28/218. Measurement method
Non-Mechanical Digital Flow Meter Theoretical Calculation
Total Grouting Volume (litre)
Grout Loss Percentage (%)
Grouting Time (s)
TN28-1
TN28-2
TN28-1
TN28-2
TN28-1
TN28-2
358.8 329 215.6
787.5 801
66.4 52.6 N/A
265.3 275.7
675 675
1500 1500
Grouting Rate (litre/min)
17 to 60 24 to 32
Net Grout volume used (litre) TN28-1
TN28-2
292.4 276.4
522.2 525.3
the corresponding net drill responses are hard to be distinguished from those to breaking actions of percussive drilling. However, it can be located by analysis to retrieving rods stage based on full drilling analysis. Grouting tests for soil nail holes in this article have shown that the grouting volumes of soil nail holes with weak zones detected by DPM methodology are greater than the theoretical volumes. This indicates the validity of DPM methodology for locating weak zones of rock mass. This article propose an efficient method to characterize weak zones with and without infilling. This provide a good foundation to determine important parameters of rock mass characterization system by drilling process monitoring, such as joint spacing and joint condition. Together
automatic monitoring of pneumatic rotary-percussive drilling process for production holes in soil nail construction was presented in this paper. Three kinds of weak zones are classified based on full drilling analysis. The weak zone without infilling can be identified based on the comparison between drilling rates and pushing-in rates with respect to their associated downward pressures. Weak zone with infilling collapse during drilling action can be characterized by net drilling analysis. Because of infilling dampening, the drilling rate of this kind of weak zone is not high but its net drilling responses of air pressures are different compared with others. Weak zone with infilling collapse after drilling action cannot be characterized by net drilling analysis because 233
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
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Sci. 1998;35(6):711–725. 8 Yue ZQ, Lee CF, Law KT, Tham LG. Automatic monitoring of rotary-percussive drilling for ground characterization-illustrated by a case example in Hong Kong. Int J Rock Mech Min Sci. 2004;41:573–612. 9 GuiMWSogaKBoltonMDHamelinJPHassGBurgessNButlerAP. Instrumented borehole drilling using ENPASOL system. In: Proceedings of the Fifth International Symposium on Field Measurements in Geomechanics. Singapore. p. 577-581; 1999. 10 Gui MW, Soga K, Bolton MD, Hamelin JP. Instrumented borehole drilling for subsurface investigation. J Geotech Geoenviron Eng. 2002;128(4):283–291. 11 SmithHJ. New approach for determination of rock and rock mass properties at dredging sites. In: Proceedings of the Second International Conference on Dredging and Dredged Materials Placement. Florida. p. 259-268; 1994. 12 PazukiADoranSR. Soil investigation for cross passages. In: Proceedings of the XI European Conference on Soil Mechanics and Foundation Engineering. Copenhagen, Denmark 5. p. 63–72; 1995. 13 PeckJVynneJF. Current status and future trends of monitoring technology for drills. In: Proceedings of the International Mining Geology Conference. Kalgoorlie, Australia. p. 311–325; 1993. 14 FortunatiFPellegrinoG. The use of electronics in the management of site investigation and soil improvement works: principles and applications, Geotechnical Site Characterization. 1st International Conference on Site Characterization (ISC 98), Atlanta, GA; 19–22 April; 1998. 15 Suzuki Y, Sasao H, Nishi K, Takesue K. Ground exploration system using seismic cone and rotary percussion drill. J Tech Des. 1995;1:180–184. 16 NishiKSuzukiYSasaoH. Estimation of soil resistance using rotary percussion drill. 1st International Conference on Site Characterization (ISC 98), Atlanta, GA; 19–22 April. p. 393–398; 1998. 17 Ghosh R, Schunnesson H, Kumar U. Evaluation of rock mass characteristics using measurement while drilling in Boliden Minerals Aitik copper mine. Mine Plan Equip Sel. 2014:81–91. 18 OveArup. & Partners Hong Kong Ltd. Stage 3 Study Report for Feature No. 11SE-C/ FR22 Opposite Mount Butler Road. Near Lamp Post No. 22805. Tai Hang Road; 2005.
with the weathering grades characterization by DPM net drilling analysis, we propose a new methodology for rock mass characterization based on DPM monitoring. Acknowledgements The author thanks the financial supports from China Natural Science Foundation (CNSF No. 41372336) and Research Grants Council (RGC) of Hong Kong SAR Government (GRF No. 27204415). The authors also thank some in-kind supports from the National Natural Science Foundation (Project No. 51208023). The first author also thanks HKU for his PhD studies. References 1 BarrMVBrownET. Instrumented horizontal drilling trials. Final report. Cracking; 1984. 2 Scoble MJ, Peck J, Hendricks C. Correlation between rotary drill performance parameters and borehole geophysical logging. Min Sci Tech. 1987;8(3):301–312. 3 Chen J, Yue ZQ. Ground characterization using breaking-action-based zoning analysis of rotary-percussive instrumented drilling. Int J Rock Mech Min Sci. 2015;75:33–43. 4 Pfister P. Recording drilling parameters in ground engineering. J Ground Eng. 1985;18(3):16–21. 5 GarassinoALSchinelliML. Detection of cavities by monitored borehole drilling (TMD). 1st International Conference on Site Characterization (ISC 98), Atlanta, GA; 19-22 April; 1998. 6 Cheetham WR, Inett EW. Factors affecting the performance of percussive drills. Trans Inst Min Met. 1953;63:45–74. 7 Schunnesson H. Rock characterization using percussive drilling. Int J Rock Mech Min
234
Contents lists available at ScienceDirect
International Journal of Rock Mechanics Mining Sciences journal homepage: www.elsevier.com/locate/ijrmms
crossmark
Weak zone characterization using full drilling analysis of rotary-percussive instrumented drilling ⁎
J. Chena, , Z.Q. Yueb a b
China Harbour Engineering Company, Beijing, China Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
A R T I C L E I N F O Keywords: Weak zone characterization DPM Full drilling analysis Rock mass characterization
1. Introduction Weathered rock masses often contain weak zones. The behavior of weathered rock masses is strongly affected by the presence of the weak zones such as joints, fissures, fractures, faults and cavities. How to detect and describe the characteristics of weak zones has become one of the important subjects in geology, geophysics, mining engineering, petroleum engineering, hydrology and waste disposal. The continuous growth in capabilities and reliability of computers, combined with the development of technical and managerial software packages, has inspired use of instrumented drilling monitoring in the geological industry to characterize weak zones both from lab tests and from field tests. Barr and Brown1 performed core drilling tests through an assemblage of concrete blocks having various cement/water ratios and aggregate types. The blocks were arranged to simulate changes in lithology, variations in strength, fissures of various aperture and orientation with and without infilling material associated with faults. They concluded that the special behaviors of pressures and drilling rate would occur when drilling through joint zone. They also pointed out when the fissure was in-filled; the net effect was to dampen the response of the drilling variables, often to the extent that no variation occurred. In the lab test, drilling responses were recorded corresponding to different kinds of weak zones. This provided a good foundation for weak zone characterization in site. Scoble and Peck2 discussed and summarized the characterization of drill performance parameters: thrust, rotary speed, circulating fluid flow rate, operating pressure, drilling rate, torque and drilling fluid pressure. They also combined the laboratory study with the in-situ
⁎
study to estimate drilling rate. They applied drilling rate log to detect shale bands. Upon comparison with the fractures logged from core, 60% of these were also indicated by a corresponding drilling rate peak. Because the most important parameter, drilling rate, was estimated by a pre-selected depth advancement increment, different pre-selected increments could result in different drilling rate variations with depth for the same ground geological conditions3. This undermined the application of this system for weak zone characterization. Pfister4 described the recorded shapes of curves for silly surface deposits, clay layers, alluvium, empty cavity, unfilled fracture, plain massive limestone and fractured zone filled with clay and summarized three steps to analyze the raw data obtained from Enpasol recorder. He tried to characterize different rock and soil structures with drilling parameters. However, because the data were recorded by depth increments, the recorded data did not include the pushing-in actions and pulling-back actions which is important to characterize weak zones. The accuracy of weak zone characterization was reduced. Garassino and Schinelli5 used the Papero system for monitoring of a number of tricone drillholes to detect cavities in a power plant project in Italy. They adopted an optimized drilling rig pressures and kept them as constant as possible during drilling. The accuracy was also affected by the sizes of cavities and depth increment for recording. Cheetham and Inett6 designed an experimental drilling rig for testing the performance of percussive drilling machines and for investigating the factors affecting percussive drilling of rocks, such as lubrication of a rock drill and effect of cuttings flush. They also summarized the relations between drilling parameters such as thrust, rotation and drill speed. This provided a good idea to normalize the insitu drilling data.
Corresponding author. E-mail address: [email protected] (J. Chen).
http://dx.doi.org/10.1016/j.ijrmms.2016.09.012 Received 22 October 2015; Received in revised form 17 May 2016; Accepted 20 September 2016 1365-1609/ © 2016 Elsevier Ltd. All rights reserved.
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Schunnesson7 suggested a data analysis method for separating rock dependent variation from other influences on the monitoring drilling parameters. Furthermore, he separated the drill response into two independent signals, one representing the hardness of the rock and one representing the inhomogeneity (fracturing) of the rock. These research efforts supplied a new idea for characterizing weak zones. But the drill response to weak zones could not be separated from those to different kinds of breaking actions because of the intrinsic problem of depth-sampling based instrumented drilling methodology3. For weak zone characterization, instrumented percussive drilling has not become a standard method in spite of great efforts made both in the field of drill monitoring hardware and in analysis method over the last decades. One of the major reasons is that past studies apply depth-sampling based instrumented drilling devices to record drilling parameters from the total time that is used for a pre-selected depth advancement increment. To overcome above obstacles, this article has applied drilling process monitoring (DPM) methodology to record drilling process in real time series. We have conducted full drilling analysis to divide full drilling process into many actions (such as pushing-in action, pullingback action and drilling action). The criteria for characterizing weak zones were built and two kinds of weak zones in percussive drilling are summarized based on the new DPM based full drilling analysis.
ing, removing, push downward and connecting will be carried out until the hammer rod is retrieved from the drillhole. Then, the drilling machine is relocated to next drillhole position. Steps 1–3 are repeated. 3. Full drilling analysis Full drilling analysis is to divide full drilling process into many actions and study the relations between drill parameters in these actions. A total of six kinds of actions can be determined: Drilling action, Pulling-back action, Pushing-in action, Tightening action, Untightening action, and Stoppage action. Only the first three actions are related to the rock mass characterization. The analysis to drilling action is called as net drilling analysis3. Especially, the pushing-in action and pulling-back action can be taken as drilling or retrieving in the air. Because there are no variations in “drilled material”, the relations between drill parameters in these two actions are very useful for weak zone characterization and calibration of drilling machine. It is further noted that above information of drilling without penetrating new geomaterial has not been recorded in existing devices for depth-sampling based instrumented drilling. They recorded the relevant drilling parameters corresponding to the drilling process for drill bit deeper advancement at a pre-selected depth advancement increment4,5,7,9–17.
2. Full drilling process
4. Weak zone characterization with full drilling analysis
Full drilling process includes all actions of air-driven rotary percussive drilling from beginning to end recorded by seven DPM transducers (position transducer, five pressure transducers and rotation transducer). It can be briefly described as the following main steps in a time sequence8. The sampling rate is 2.
4.1. Weak zone without infilling Drilling in weak zone without infilling is the process of drilling in air because no geomaterial exist. It is included in the net drilling process and is same as pushing-in actions. The drilling rate at the weak zone is only determined by the downward thrust pressure. Fig. 1 shows the full drilling process of a soil nail hole including weak zone without infilling. To detect weak zone without infilling, full drilling analysis is used to divide full drilling process into many actions and study the relations in net drilling actions and pushing-in actions.. A breaking action based zoning analysis3 has been applied to divide the net drilling process into a series of breaking actions. Adjacent breaking actions with similar drilling speed were combined into one zone. Thus, the net drilling process is finally divided into fourteen zones in Fig. 2. The zone drilling rates are listed correspondingly. Among them, the drilling rate of zone 10 is 23.52 m/min and is much higher than other zone drilling rates. It may indicate the weak zone without infilling but need to be confirmed with subsequent comparison.. A pushing-in process analysis has been carried out focusing all pushing-in actions. In these actions, the drill bit is moving forward in a drill hole that has been drilled already. There is no influence of the soil and/or rock resistance. The downward thrust pressure is the only factor to determine the pushing-in rate. A relation between pushing-in rates and downward thrust pressures has been built and is compared with zone drilling rates with their associated downward thrust pressures in Fig. 3. At same downward thrust pressure level, the drilling rate of zone 10 (23.52 m/min) is higher than the pushing-in rate. This means that there is no geomaterials to dampen the drill bit speed. The difference between the pushing-in rate and the drilling rate of the weak zone is caused by the sampling rate. It may be not enough to capture the positions of high speed drill bit accurately. Some systematic variations will be involved..
Step 1: Initial drilling The control panel is used to install the down-the-hole hammer onto the swivel drill chuck via its shank adaptor. The hammer bottom end is fixed with a drill bit. The control panel is used again to move the drill bit touching the surface of the ground to be drilled. The control panel is further used to commence the drilling with the actions of percussion, rotation and thrust. The drilling work will be stopped once a majority of the hammer length is advanced into the ground. Step 2: Subsequent drill runs by adding extension rods After completion of the initial hammer advancement, the swivel drill chuck will be disconnected with the hammer at the shank adaptor. The chuck will be pulled back for adding the first extension rod onto the shank adaptor and the upper hammer end. Then the drilling will be advanced again until the first extension rod is in the ground. The first extension rod and hammer system will be disconnected with the chuck at the shank adaptor. The chuck will be pulled back for space to add the second extension rod. Similarly, the second extension rod will be connected with the shank adaptor and the upper end of the first extension rod. Such operations of drilling, disconnecting, adding and connecting and drilling will be repeated until the hammer bit is advanced to the designed depth in the ground. Step 3: Dismounting the drilling by retrieving extension rods and hammer After the completion of Step 3, the control panel is used again to pull back the last added extension rod back to the ground surface. This last rod is then disconnected with the shank adaptor and the remaining extension rods in the hole. The chuck is pushed downward again to connect the shank adaptor with the upper end of the remaining extension rods. Then the above operations of pulling back, disconnect-
4.2. Weak zone with infilling This kind of weak zone can be subdivided based on the sequence of infilling collapse. 228
International Journal of Rock Mechanics & Mining Sciences 89 (2016) 227–234
J. Chen, Z.Q. Yue
Fig. 1. Full drilling process of a soil nail hole with weak zone without infilling: (a) drill bit position versus full drilling time; (b) associated downward thrust pressure; (c) associated upward thrust pressure; (d) associated forward rotation pressure; (e) associated reverse rotation pressure; (f) associated percussion pressure.
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Fig. 2. Results of the DPM methodology in identifying the zones of constant drilling rates along the soil nail hole. 35
4.2.1. Infilling collapse after drilling action A weak zone with infilling collapse after drilling action is quite difficult to be detected in drilling process, because the corresponding drill responses to infilling are same to other parts. There is no collapsed infilling to dampen drill bit speed during drilling process. In Fig. 4, drill bit positions in net drilling process of Hole No. TN281, together with the associated pressures, are presented in time series. No abnormal zones can be located in this net drilling process. Fig. 5 shows the drill bit positions in full drilling process. Stages B, C and E are stages of pushing or retrieving rods. In stages B and E, the pullingback speed of drill bit in the zone with drill bit position between 4 m and 6 m is much lower than that of other parts, even though the downward thrust pressure keep in a constant level. Because the infilling collapses after the drilling action, collapsed chippings reduce the drill
30 y = 10.325ln(x) + 30.667
Unit: m/min
25 Weak zone without infilling
20 15
Pushing-in rate
10 Drilling rate 5 0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Downward thrust pressure (MPa)
Fig. 3. The drilling rates and the pushing-in rates with respect to their associated downward pressures for the soil nail hole with weak zone without infilling.
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J. Chen, Z.Q. Yue 0
3
4
6
7
8
9
14.69m
Drilling rate : 0.16m/min
5
Drilling rate : 0.93m/min
Drilling rate : 1.13m/min
2
Drilling rate : 1.55m/min Drilling rate : 0.55m/min
1
Drilling rate : 1.31m/min
0
9.53m 10.50m 11.59m 12.13m 12.93m 14.22m
Drilling rate : 0.98m/min
25
Drilling rate : 0.96m/min
20
Drilling rate : 1.35m/min
15
Drilling rate : 0.58m/min Drilling rate : 1.09m/min
10
Drilling rate : 0.73m/min
Net drilling depth (m)
7.86m
Drilling rate : 0.51m/min
5.62m 5.79m 6.95m
5
Drilling rate : 0.97m/min
4.28m
22.40m 21.70m
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Net drilling time (Min)
Downward thrust pressure (MPa)
1.0 0.8 0.6 0.4 0.2
Forward rotation pressure (MPa)
0.0 1.0 0.8 0.6 0.4 0.2
Percussion pressure (MPa)
0.0 1.0 0.8 0.6 0.4 0.2 0.0
Fig. 4. Results of the DPM methodology in identifying the zones of constant drilling rates along the soil nail hole (TN28-1).
and percussion pressure is not well built up. Its average value of weak zone is lower than that of other parts. Higher forward rotation pressure is needed to remove more chippings. Total five of this kind of weak zones can be located based on the special drilling responses in Fig. 7. The drill responses to this kind of weak zone are in accordance with many researchers’ observation1,2,4,5,7,9..
bit speed during retrieving rods stage. However, this kind of weak zone cannot be located by adding rods and pushing in stage, because percussion pressure is applied in this stage to remove chippings off (Fig. 6).... 4.2.2. Infilling collapse during drilling action In this kind of weak zone, hole collapse occurs during drilling action. The collapsed geomaterial makes the net drilling responses different with those to other parts. Before drilling the weak zone, drill bit has good contact with drilled geomaterial. The percussion pressure at the interface between the bit and the geomaterial is steadily built up. The corresponding forward rotation pressure and downward thrust pressure are also steady to remove chippings and keep drill bit contact with drilled geomaterial. When drill bit drills the weak zone, infilling collapses. The collapsing process makes pressures change frequently. Many generated chippings separate drill bit from drilled geomaterial
5. Grouting tests for weak zones determined by DPM methodology 5.1. Test slope The test slope is a 14 m high fill slope. It has a length of approximately 75 m along the crest at an average face angle of 35°. It comprises a layer of fill (Fill), overlying successively completely decomposed granite (CDG) and highly decomposed granite (HDG). It is 231
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Drill bit position (m)
0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
10
20
30
40
Full drilling time (Min) 50 60
70
80
90
100
110
Weak zone with infilling
A
B
C
D
E
Stage A, and D: Adding rods and drilling Stage B and E: Retrieving rods Stage C: Adding rods and pushing in Fig. 5. Drill bit positions of Hole No. TN28-1 in full drilling process. Stage A, and D: Adding rods and drilling, Stage B and E: Retrieving rods, Stage C: Adding rods and pushing in.
Fig. 6. Drill bit drills the weak zone with infilling collapse in drilling action.
results of the two holes. The theoretical volume of grouting can be calculated by
situated in the subtropical zone and experiences a hot and humid climate with seasonal heavy rainfalls. Such a seasonal environment promotes chemical weathering of the rocks and has resulted in a weathered mantle of varying thickness and decomposition that covers fresh granite rocks. Such chemically decomposed granites generally have much less shear strength than those associated with the parent fresh solid granites. The higher the decomposition, the lower the weathered volcanic strengths.
v = α π r 2L
(1)
where v is the theoretical volume of grouting, r is the radius of soil nail hole, L is the length of soil nail hole, and a is the factor considering the cement loss during the grouting, normally, it is taken as 1.2. The net grout volumes of the two holes are much greater than the theoretical calculation. Especially for Hole TN28-2, the net grout volume is two times the theoretical volume. This suggests the wider spatial distribution of its weak zones.
5.2. Test result Two soil nail holes Nos. TN28-1 and TN28-2 are grouted and measured to indirectly verify different kinds of weak zones determined by DPM methodology. The DPM analysis results of the two holes are shown in Figs. 4, 5 and 7 respectively. Table 1 shows the grouting
6. Concluding remarks Full drilling analysis for identifying weak zones in rock mass from 232
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Fig. 7. Results of the DPM methodology in identifying the zones of constant drilling along the soil nail hole (TN28-2).
Table 1 Grouting volumes for Trial Nail Nos. TN28/1 and TN28/218. Measurement method
Non-Mechanical Digital Flow Meter Theoretical Calculation
Total Grouting Volume (litre)
Grout Loss Percentage (%)
Grouting Time (s)
TN28-1
TN28-2
TN28-1
TN28-2
TN28-1
TN28-2
358.8 329 215.6
787.5 801
66.4 52.6 N/A
265.3 275.7
675 675
1500 1500
Grouting Rate (litre/min)
17 to 60 24 to 32
Net Grout volume used (litre) TN28-1
TN28-2
292.4 276.4
522.2 525.3
the corresponding net drill responses are hard to be distinguished from those to breaking actions of percussive drilling. However, it can be located by analysis to retrieving rods stage based on full drilling analysis. Grouting tests for soil nail holes in this article have shown that the grouting volumes of soil nail holes with weak zones detected by DPM methodology are greater than the theoretical volumes. This indicates the validity of DPM methodology for locating weak zones of rock mass. This article propose an efficient method to characterize weak zones with and without infilling. This provide a good foundation to determine important parameters of rock mass characterization system by drilling process monitoring, such as joint spacing and joint condition. Together
automatic monitoring of pneumatic rotary-percussive drilling process for production holes in soil nail construction was presented in this paper. Three kinds of weak zones are classified based on full drilling analysis. The weak zone without infilling can be identified based on the comparison between drilling rates and pushing-in rates with respect to their associated downward pressures. Weak zone with infilling collapse during drilling action can be characterized by net drilling analysis. Because of infilling dampening, the drilling rate of this kind of weak zone is not high but its net drilling responses of air pressures are different compared with others. Weak zone with infilling collapse after drilling action cannot be characterized by net drilling analysis because 233
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with the weathering grades characterization by DPM net drilling analysis, we propose a new methodology for rock mass characterization based on DPM monitoring. Acknowledgements The author thanks the financial supports from China Natural Science Foundation (CNSF No. 41372336) and Research Grants Council (RGC) of Hong Kong SAR Government (GRF No. 27204415). The authors also thank some in-kind supports from the National Natural Science Foundation (Project No. 51208023). The first author also thanks HKU for his PhD studies. References 1 BarrMVBrownET. Instrumented horizontal drilling trials. Final report. Cracking; 1984. 2 Scoble MJ, Peck J, Hendricks C. Correlation between rotary drill performance parameters and borehole geophysical logging. Min Sci Tech. 1987;8(3):301–312. 3 Chen J, Yue ZQ. Ground characterization using breaking-action-based zoning analysis of rotary-percussive instrumented drilling. Int J Rock Mech Min Sci. 2015;75:33–43. 4 Pfister P. Recording drilling parameters in ground engineering. J Ground Eng. 1985;18(3):16–21. 5 GarassinoALSchinelliML. Detection of cavities by monitored borehole drilling (TMD). 1st International Conference on Site Characterization (ISC 98), Atlanta, GA; 19-22 April; 1998. 6 Cheetham WR, Inett EW. Factors affecting the performance of percussive drills. Trans Inst Min Met. 1953;63:45–74. 7 Schunnesson H. Rock characterization using percussive drilling. Int J Rock Mech Min
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