Comparative Study of Conventional Rotary and Rotary-Percussion Techniques in Grout Hole Drilling from the Perspectives of Time, Cost, and Quality

: A dam foundation structure is usually strengthened by grouting, which begins with grout hole drilling. This paper aims to examine a comparison between conventional rotary and rotary-percussion drilling techniques in a drilling case study of the Tugu Dam Project, from the perspective of time, cost, and quality comprehensively. Primary data was obtained from the field investigation and interviews. Secondary data was gathered from available project documents of the PT Wijaya Karya-APTA KSO Project Contractor. The findings have highlighted that the implementation of the rotary-percussion technique for grout hole drilling is better than conventional rotary drilling. There are 16 days of time-saving and 3.84% cost-savings for the rotary-percussion technique, as a result of faster rate of penetration. The quality of grouting work using the rotary-percussion drilling technique tends to be of better quality, although there is a shortcoming due to the limited drilling depth of only 5m particularly.


Introduction
Dams are civil engineering structures that cross the river as a barrier to the flow of river water which can raise the water level of the river to become a reservoir or lake.Dams have a very high risk because they have the potential to fail as a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water, spilling a very large volume of water downstream, in the event of a dam collapse, especially the collapse of the foundation structure.Thirty to fifty percent of dam failures [1] are caused by concentrated leaks from seepage through the dam and its foundation.Under pressure, water seeps through soil or rock's expanded cracks, causing progressive erosion.Cracks in soil or rock foundation are a significant issue for dam safety.A concentrated leak from the dam and its foundations can cause the dam to breach failure.In another case of the postconstruction period, grouting is one of the few ground improvement techniques that can be used for the restoration or retrofitting of structures.
For this reason, the dam foundation structure is usually reinforced with grouting, by injecting cement slurry into rock fractures inside grout holes.Thus, artificial underground impermeable grouting curtains can be formed, cutting off waterways, inhibiting water seepage through the foundation layer, and reducing structural failures or deficiencies in the dam [2].The grouting method has been widely applied to soil improvement and stability, including its consolidation ability, in the field of engineering geology, and is one of the most important techniques in anti-seepage and dam reinforcement [3].
The grouting work in the dam project begins with a drilling borehole which is the creation of a narrow, deep hole in the ground.In a typical drilling project for a dam, a drill bit is utilized to bore a hole in a circular cross-section of a deep hole in the earth's ground.Drilling work is the most resource-intensive aspect of grouting, which can give an immediate effect on the total cost of the whole grouting project [4], making it imperative to pay close attention to drilling techniques.In general, there are two primary drilling techniques: conventional rotary drilling and rotarypercussion drilling.The rotary drill works a high rotation and torque, the drill bit pressing, rotating rapidly at the end of the drill pipe, and boring the rocks, whereas the rotary-percussion drill utilizes the hammer impacts while simultaneously rotating the bit.
After the borehole drilling process is complete, the next step is to measure the average permeability of water in the borehole or first Lugeon test, which is expressed in terms of the Lugeon value.Lugeon value was obtained from an in-situ permeability test with a pressure of 1 MPa in the grouting hole.The Lugeon value [5] is the amount of water (liters) that enters or seeps into the 1-meter-long rock mass in the borehole in 1 minute (liters/minute/meter at a water pressure of 1 MPa).The first measurements of Lugeon values are considered Lugeon-I.Table 1 illustrates the conditions that are frequently linked with various Lugeon values, as well as the precision with which these values are typically reported.Due to the variability of rock and soil properties, the range of possible Lugeon values is alarmingly large among boreholes.< 1x10 -5  Very tight 1-5 1x10 -5 -6x10 -5 Tight 5-15 6x10 -5 -2x10 -4  Few partly open 15-50 2x10 -4 -6x10 -4  Some open 50-100 6x10 -4 -1x10 -3  Many open >100 > 1x10 -3  Open closely spaces or voids After the Lugeon-I values are obtained, the boreholes can be grouted completely.The grouting process is applying certain pressure to the grouting material in the form of liquid through a grouting pump into the borehole in order to increase the integrity of the rock and soil mass, as well as increase the seepage resistance of the dam foundation structure.After the whole boreholes have been grouted completely, there are second drilling works in order to make several new boreholes namely check holes, next to the boreholes that have been grouted.In these check holes, the water permeability test is also carried out for obtaining the second measurements of Lugeon value, namely Lugeon-II as verification of the grouting or plugging effect.The effectiveness of grouting work is measured by comparing the values of Lugeon-II and Lugeon-I, as indicators of the quality of grouting work.
Well-known studies on dam safety using Lugeon values mentioned the Tapin dam [6], the Nipah dam [7], and the Sirikit dam [1].However, a detailed study is still limited to using the Lugeon value to measure project quality based on grouting work effectiveness [6], to calculate the composition of grouting material [7], and to explore cracking mechanism due to hydraulic fracturing [1].In fact, major project goals are not only the quality of the project but also time and cost considerations as a key direction process for managing risks in construction projects.Generally, the construction dam projects are complex in nature and limited resources, thus it is important to consider three primary objectives in a project, in terms of time, cost, and quality [8][9].Time reflects the amount of time available to complete the project, cost represents the amount of money or resources available, and quality accords to the fit-to-purpose that the project must achieve in order to be successful.For example, in order to reduce both cost and time, the drilling equipment must be able to be rapidly moved and transported from one hole to the next.According to the grout hole drilling, the need for an optimal decision to choose the best techniques for drilling, either conventional rotary drilling or rotary-percussion drilling has arisen due to huge competition in the drilling dam construction project.
One of the major dam projects in Indonesia was the Tugu Dam Project, located in Trenggalek Regency.
The Tugu Dam was one of the 65 large dams in the strategic plan of the Indonesian Ministry of Public Work [10].The project started with the ground breaking on January 29 2014 and was inaugurated on November 30 2021.This project took a long time, namely 7 years, due to land acquisition problems.
Grouting hole drilling work began on May 8, 2017.
The tight schedule for this project dictated that the grouting work had to be completed immediately first because the successor tasks, namely the core embankment work, was urged to be completed before entering the rainy season.In the early stage of grouting work, project manager decided to carry out the drilling work in the blanket section of the right abutment using five conventional rotary drilling machines.Based on the daily project work progress report, the performance and progress of conventional rotary drilling work did not satisfy the planned project schedule.In order to achieve the pre-determined targets for the project, the project manager had implemented effective risk management by accelerating drilling work.It was decided to add another drilling technique, namely rotary-percussion technique which generally had faster rate of drilling penetration.This rotary-percussion technique was to drill the grouting boreholes in the blanket section of the left abutment.Therefore, the drilling works in the right and left abutments had been carried out simultaneously.Unfortunately, there has been no in-depth study previously of the selection of these two drilling techniques from the perspective of time, cost, and quality comprehensively.
The current paper attempts to examine the comparison between conventional rotary and rotarypercussion drilling techniques in drilling work for grouting boreholes in a case study of the Tugu Dam Development Project, which includes a detailed comparative assessment of time, cost, and quality comprehensively.This research is very important in order to choose the right construction technique for drilling a grouting borehole because many dams are still in the planning stages in Indonesia for improving more resilient and sustainable community life [10].
The significance and potential impact of the reported work will make the implementation of dam construction more efficient due to the limited resources faced by the Indonesian government, and other similar countries.

Research Methods
This study has utilized primary and secondary data in accordance with the grout hole drilling on Tugu dam project as a case study.Primary data was obtained from the field investigation.Recording of cycle time data was carried out directly on-site, then synchronized with project weekly reports.Interviews were employed to collect qualitative data about time, cost, and quality of work performed and its progress.Secondary data was obtained from available project reports and documents on the PT Wijaya Karya-APTA KSO Project Contractor, such as grouting layout, borehole drilling work volume, Lugeon value, and the actual cost of work performed.The project implemented 5 drilling machines each for conventional rotary technique (right side abutment) and rotary-percussion technique (left side abutment) respectively.
There were 2 abutments, left and right sides, in the Tugu dam project and there were 3 grouting sections on each abutment: the blanket grouting, L=5m deep, the sub-curtain grouting, L=15m deep, and the curtain grouting, L=25~40m deep.This study was only focus on drilling work of blanket grouting, all with 5 metres deep.Grout holes of about 75 mm were drilled using a particular drilling method.An example of schematic layout of the grouting section in the right abutment is presented in Figure 1.

Figure 1. Schematic Grouting Layout of the Right Abutment
This study described 91 grout boreholes and 3 check holes on the blanket section of the right abutment using conventional rotary drilling, namely R.1 -R.91.
In addition, there were 91 grout boreholes and 4 check holes on the blanket section of the left abutment using rotary-percussion drilling, namely P.1 -P.91 (Figures 2 and 3).The sub-curtain and curtain drillings were not discussed further in this study because the Project cost was measured by direct and indirect costs [13].Direct costs were collected from the actual cost of work performed, while indirect costs were collected from the project overhead costs, summarized from the interview with five competent drilling person in the project.Overhead costs included employee salaries, general needs, electricity, water, etc.
The quality of the grouting work was measured by the magnitude of the effectiveness of the grouting work, based on Lugeon-II value in the check hole against the Lugeon-I value in the boreholes, expressed in %.The value of the effectiveness of the grouting work is calculated by Equation 2and also presented in Table 2.
Where: Efs = grouting effectiveness in percent (%); KG = Lugeon-II value in the check hole; and K = average Lugeon-I value in the three boreholes next to the check hole before they are grouted

Case Study Project
Grout hole drilling work in the Tugu Mini Hydropower Dam project was used in the current case study.The dam is located in Trenggalek district, East Java province Indonesia (Figure 4).The Tugu dam is located in the regional geology of volcanic breccia, andesite, and some other tuffaceous sandstone, with whitish-gray to yellowish-yellow in color.The Tugu dam has a total water storage capacity of 12.14 million m 3 with an inundation area of 41.74 Ha.The benefits of the construction of the Tugu dam include mini hydro-power, irrigation water, raw drinking water, and flood control.This ambitious aim for

Drilling Techniques
Drilling is a cutting operation in which a drill bit is used to create a circular hole in a solid material.In a dam project, borehole drilling is the creation of a narrow (diameter of about 75 mm), deep hole in the ground known as a borehole.A borehole is bored beneath the ground during the course of a Geotechnical evaluation and improvement of foundation conditions.In Tugu dam project, there were two most common drilling techniques i.e. conventional rotary drilling and rotary-percussion drilling.Both were portable drilling machines, hand-held operations, and locally manufactured machines in Indonesia, as described in Figure 5. Schematic drawings of two types of drill are presented in Figure 6.The speed of rotations and their high frequency make rotary drilling an effective means of carving through hard and soft rock formations.This is driven by a hydraulic motor with the manual gear change, providing fully controlled power and rotational speeds in forward or reverse [14].This equipment uses water circulation to clear out the borehole, cool the drill bit, and reduce friction so that it can be operated optimally.The circulating water carries the crushed rock to the surface, so that drilling is continuous until the bit wears out.Rotary drilling rigs keep the job site clean with low environmental pollution.They generate smaller vibrations and operate with less noise.
Rotary drilling is a common drilling technique used by Indonesian people due to the cheap initial equipment cost.It is usually used in water well drilling by the Indonesian community.Water well drilling is the hole drilling process through the earth's surface for the purpose of accessing a groundwater source.Perhaps the least expensive method of drilling, the conventional rotary technique is by far the simplest and also requires low-skilled workers.Common rotary drilling techniques have enabled boreholes to be drilled to depths of about 150 meters.
The rotary drilling machine has a diesel engine as the driving force and it is attached to the main body of the rotary drilling equipment.The equipment's main body consists of a base, column, table, radial arm, and drill head.In the Tugu Dam Project, the weight of the diesel engine and the main body of the drilling machine was about 100 kg and 150 kg respectively.Because the layout of the Tugu dam project in the abutment section had a slope of about 40 degrees, there were difficulties to move the drilling equipment from one hole to the next.Due to the difficult site contour and limited budget, rotary drilling operators handled the equipment manually.For safety purposes every time during this movement, the diesel engine was released from the main body of the drilling equipment.The diesel engine were then be assembled on the main body again when the drilling equipment began to operate to the new next drilling position.This type of work process was time-consuming and required four to five worker or operators.
On the other hand, rotary-percussion drilling has widely been acknowledged for its potential to drill faster in rock due to the advantage of the hammering action, in comparison to conventional rotary drilling methods.This capability becomes apparent when drilling in heavy-stony formations such as granites, sandstones, dolomites, and limestones.Test results are clear that the rate of penetration (ROP) in hard formations when the rotary-percussion drilling method is applied, is significantly bigger.According to the drilling data with drilled formations were sandstones, limestone, and anhydrite in Tarim Basin, People's Republic of China, conventional rotary drillings were carried out with a relatively low ROP, achieving 1.67 m/hour on average, whereas rotary percussion drillings provided ROP of 4.74 m/hour on average.Rotary-percussion drilling was about 3 times faster than that of conventional rotary drilling [15].
The main problem of this type of drill was no possibility of drilling in loose formations.
In the current project site, rotary-percussion drilling had a slime/drilling residue removal system using compressed air.The depth of the drill hole with this machine was maximum only for about 5 m because the slime material in the form of soil grains and rock fragments was not easy to remove from the drill hole using only air pressure from the air compressor machine.The rotary-percussion drilling machine consisted of three components i.e. main body, electrical generator set, and air compressor machine, and they were connected either by hose or cable to each other.This modular design made the drilling machines easy to install and relocate, in turn, allowing greater operational flexibility to move it to the new next drilling position.As the machine dimensions were smaller than rotary machines, the operation and movement to the next drill only required 2-3 workers or operators.The project managers were gaining its convenience to this method in terms of saving time significantly.However, this percussion method required a high initial equipment cost.Also, it needed high durability of the drilling bits, during long runs of the drilling work.All made the process of percussion drilling increased the total cost but save time.
This case study focuses on the 5-meter-deep hole drilled in the blanket section, for which both conventional rotary and rotary-percussion drilling machines may be employed.Choosing a drilling machine in the grouting work for the dam project is a big challenge for engineers.All of the described problems generate relevant extra costs and time, which is the reason to compare the results of drilling technique when conventional rotary and rotary-percussion drilling methods are applied.Therefore it is urgent to take consideration of time, cost, and quality as the main objectives for a successful grout hole drill project.

Time Aspect
Site investigation has been carried out for cycle time data collection.Based on field observation on 20 boreholes, the cycle time data obtained for the conventionnal rotary drilling and the rotary-percussion technique are shown in Table 3 and 4 respectively as follows.
Each blanket borehole had a depth of 5m, and each technique operated for 91 boreholes; therefore, the total volume of work (or total depth of drill holes) for each technique was 5m x 91 boreholes = 455m.Based on Table 3 and 4, the average: cycle time (Ct), drilling speed (V), and work duration are formulated in Table 5, as follows.
It is clear that the work duration of the rotarypercussion technique is faster than the rotary and there are 16 days time-saving due to the faster ROP of rotary-percussion technique.

Cost Aspect
The contractor of PT Wijaya Karya which implemented the drilling work for both right and left abutment of blanket section had construction contract price of IDR 284,500,000 and 22 working calendar days.
According to the requirements of the project, only certified drilling operators or technicians could operate the drilling equipment.These technicians were in charge of operating drilling equipment.They had a comprehensive comprehension of safety procedures, as well as the equipment and its operation.In addition, they were capable of resolving any mechanical or technical issues that may have arisen during drilling.These included reduced downtime resulting from equipment malfunctions and enhanced safety on the job site.
According to the project drilling cost consideration, several interviews to the competent drilling supervisors in the Tugu dam project have been carried out in order to get the actual cost of work performed for the two techniques.Some emerging data of direct cost have been revealed including: cost components, quantities, unit price per components, and amount per components.As a consequence of employing a certified operators, the unit cost of labour was greater than that of an ordinary technician, as measured by hourly wage.Detail of unit prices for the two method are described in Tables 6 and 7 for conventional rotary and rotary-percussion drilling techniques respectively.Labour cost of conventional rotary method is about two times higher than that of rotary-percussion method.Contrary, equipment cost for conventional rotary method is almost two times lower than that of rotary-percussion method.
Based on the analysis of unit prices in Tables 6 and 7, the unit prices of the rotary drilling is IDR 245,022 and the rotary-percussion drilling is IDR 245,076.
There are no significance difference on unit prices between the two techniques.The total direct cost of rotary drilling is 455 m x IDR 245,022 = IDR 111,485,010.Whereas, the total direct cost of the rotary-percussion drilling is 455 m x IDR 245,076 = IDR 111,509,580.
According to the work duration, there were 20 working days for rotary drilling technique and 4 working days for rotary-percussion drilling technique.The total cost of work performed (direct + indirect cost) of rotary drilling technique was = IDR 111,485,010 + 20

Quality Aspect
Quality of grouting work can be measured by the value of the effectiveness of grouting work, as stated in Table 2.According to the effectiveness of grouting work, there were data of Lugeon-I values and also Lugeon-II values (KG) obtained from the check hole value.As described in Figure 2, there are three triangled boreholes as check holes for the rotary technique and Figure 3 describes four triangled boreholes as check holes for the rotary-percussion technique.These Lugeon values are mentioned in Tables 9 and 10.The value of the effectiveness of grouting work, which is based on Equation 2, can be used to determine the quality of grouting work.Based on Tables 9 and 10, the effectiveness of grouting work is summarised in Table 11, as follows.
From the results above, the effectiveness of grouting work relevant to The results of grouting effectiveness are at the range 83.89% -97.49%, so the effect of grouting is in good and very good categories.
The effectiveness of grouting work using rotary-percussion drilling technique tends to be in a better quality, but need a further investigation on rock formation and characteristics.
licensed operators.Therefore, the implementation of the drilling techniques has to be explored comprehensively, as a part of a conceptual effort to the engineer, to more rational and economic design.Summary of the results of comparative study of conventional rotary and rotary-percussion techniques in blanket grout hole drilling from the perspectives of time, cost, and quality is presented in Table 12.

Conclusions
These findings highlighted that the conventional rotary drilling technique required the work duration of 20 days with a drilling speed of 0.588 m/hour.The total costs of the rotary drilling were IDR 116,916,374.Also, it produced quality results with the effectiveness of grouting at 60-90%, and the effectiveness of grouting work is included in the category of good.Whereas, the rotary-percussion technique took 4 days with a drilling speed of 3.74 m/hour.The total costs were IDR 112,595,853.There are 16 days time saving and 3.84% cost saving for rotary-percussion technique, as a result of faster ROP and also reduction of indirect costs.The effectiveness of grouting work performed by rotary-percussion drilling tends to be of higher quality, but the heterogeneity of rock formation requires further investigation.Although the implementation of rotary-percussion drilling technique is the correct decision of the project manager in order to accelerate drilling work, this application is limited to a drilling depth of only 5m in blanket section only, due to the rotary-percussion machine characteristics mentioned above.For drilling boreholes deeper than 5 metres, the conventional rotary method is the only viable option.

Figure 2 . 1 )
Figure 2. The Layout of Ninety-One Grouting Work and Three Check Holes on the Blanket Section of the Right Abutment using Conventional Rotary Drilling Technique (R.1 -R.91)

Figure 3 .
Figure 3.The Layout of Ninety-One Grouting Work and Four Check Holes on the Blanket Section of the Left Abutment using Rotary-percussion Drilling Technique (P.1 -P.91)

Table 3 .
Cycle Time Data for Rotary Technique

Table 4 .
Cycle Time Data for Rotary-Percussion Technique

Table 5 .
Formulation of Cycle Time (Ct), Drilling Speed (V), and Work Duration of Both Drilling Techniques

Table 6 .
Unit Prices for 1 m Drilling Depth for Conventional Rotary Technique

Table 9 .
Lugeon-II Value on Check Holes and Lugeon-I on Boreholes for Rotary Technique

Table 10 .
Lugeon-II Value on Check Hole and Lugeon-I on Boreholes for Rotary-Percussion Technique

Table 7 .
Unit Prices for 1 m Drilling Depth for Rotary-Percussion Technique

Table 8 .
Total Cost of Work Performed and Their Savings

Table 11 .
The Effectiveness of Grouting Work

Table 12 .
Summary of the Results