The equipment utilized by ACT is second to none in the grouting industry. As a result of the specialized nature of our business, we routinely innovate and customize our equipment to facilitate our needs, as well as the needs of our customers. We have a complete line of computer monitoring, grouting batching, and drilling equipment to suit almost any site conditions we encounter. Some of our more technologically innovations are listed below:
Cubex Water Actuated DTH Hammer Drills
ACT was awarded the Chicagoland Underflow Plan (CUP) McCook Reservoir Grout Test project by the Chicago District, USACE, in 2003. The Specifications required that both “Rotary drilling or rock coring shall only use water as circulating fluid. Percussion drilling shall use water in addition to air as the circulating fluid. Other drilling methods for this portion of the work may be proposed by the Contractor in the RFP for approval by the Government.” After thoroughly review the available Down-the-hole (DTH) drilling techniques, ACT proposed the use of water DTH (W) hammer, the first time adoption and application in the drilling and grouting industry in North American.
1.0 Technical Background
There are three basic methods available for drilling grout holes: rotary drilling systems, percussion drilling systems utilizing a top hole hammer, and DTH systems. Within each basic method available, there are multiple variations that can be used. All have been used for drilling grout holes at one time or another.
Hole quality is critical for effective rock grouting. The three primary elements with respect to quality are adequate alignment tolerance for the depth of grouting; maintaining intercepted fractures in as clean a condition as possible to allow free entry of the grout; and utilizing drilling methods that do not routinely risk introducing high pressures into the formation that might result in hydro-fracturing or lifting after grouting has been completed in prior hole sequences. Provided below is a synthesis of information that represents the technical consensus of various drilling methods with respect to best practice in drilling grout holes. The primary references for this information are Construction and Design of Cement Grouting (Houlsby 1990), Dam Foundation Grouting (Weaver 1991), Dam Foundation Grouting (Weaver & Bruce, 2007), and Grouting in Geotechnical Engineering (ASCE – Various Authors 1982).
1.1 Rotary drilling, using diamond bits (coring or non-coring) or non-diamond bits as appropriate for the materials being drilled, produce high quality grout holes. Rotary drilled holes produces clean, groutable holes; smooth-walled holes of uniform diameter, facilitating setting and sealing of packers; and holes with good alignment. Holes can be drilled to great depth with rotary drilling equipment. Copious amounts of relatively low pressure water as the flushing medium is a key element of the quality that results. The only disadvantage of rotary drilled holes is cost, which may be several times the cost of other alternative methods.
1.2 Top hole percussion drilling, utilizing water as the sole flushing medium has become the standard method of drilling grout holes when grouting depths are less than about 200 feet. The top hole percussion hammer is powered by high pressure air or hydraulics, but only water is injected into the hole. Advantages of this system are high production efficiency; low operating costs; and extensive experience that has shown that a hole of similar cleanliness and equal groutability as a rotary drilled hole will result provided that only water is used the flushing medium. The importance of using water as the sole flushing medium is strongly emphasized by numerous expert sources:
“It is essential to drill ‘wet’ with grout holes. In other forms of drilling such as blasting work, air can be used for flushing instead of water, but the insistence on use of water for grout holes is to make sure that there is minimal chance for cuttings to be forced into cracks. Air can tend to do this, particularly in work below the water table, where it may produce a foamy slurry. Another objection to air flushing is that any interruptions to the return of cuttings, such as a buildup of temporary balling or plugging in the hole can result in compressed air entering foundation cracks and possibly penetrating them rapidly and extensively.” (Houlsby 1990, p. 114-115).
“Diamond drilling with rotary equipment has long been favored for drilling grout holes, as it has been thought to produce a cleaner, more groutable hole than does percussion equipment. However, as this has proven not to be the case if water circulation is used for percussion drilling, the greater speed and economy of the latter method has led to its increasing use. ……… Water circulation is always preferred. However, air circulation may be permitted when drilling deep holes with down-hole hammers in saturated rock in which air circulation causes the formation to produce water sufficient to keep the hole clean. Nonetheless, this is poor practice in rock that contains weathered, clayey, or silty materials. Where those materials are present, air percussion drilling tends to clog groutable openings and may damage the foundation by injection of high-pressure air.” (Weaver 1991 p. 62-64).
“Normally, it is Corps practice to require water as a drilling fluid rather than air. In some instances, however, water causes problems such as hole caving, erosion, or blinding of the bit, and in these cases, air or some other agent is required for best results. Air may also be used to evacuate cuttings when water circulation cannot be achieved. Rotary drilling methods are specified for many grouting applications, but recent years have seen greater acceptance of percussion drilled grout holes using water. Percussion drilling in fine materials such as shale or percussion drilling with air can cause premature plugging of fine fractures and joints. The clay slurry or rock flour, if forced into fine fractures, or if not completely cleaned from the hole, can either plug fractures or mix with the initial grout causing a reduction in the water-cement ratio and instant plugging of the fractures.” (Cement Grouting Practices - U.S. Army Corps of Engineers by John A. Albritton, published in Grouting in Geotechnical Engineering, ASCE, 1982).
The only disadvantages of top hole percussion with a water flush are limitations on hole depth, which is in the range of 200 feet depending on size of equipment, and hole deviation, which may be on the order of 5-15% depending on equipment, methods, and depth. However, since grout hole depths for most projects are normally well within the effective drilling depth of top hole percussion systems, top hole percussion drilling with water flush is essentially standard practice for drilling grout holes.
1.3 DTH Systems. Conventional DTH systems use a hammer powered by high volume pressure air systems placed down the hole on top of the bit, thereby increasing the energy at the point of drilling. DTH systems, in general require the continuous use of petroleum based lubricants, have minimum effective drill hole diameter of 4.5 inches, can economically drill to greater depths and produce straighter holes. High pressure air is the flushing medium in conventional DTH systems. Above the water table, small amounts of water may be added to assist with dust control. A significant concern exists regarding the risks of injecting high pressure air into the formation if momentary clogging occurs. Additional concerns have been expressed (Houlsby 1990) regarding the effects of air flushing below the water table due to the creation of a foamy slurry that can clog fractures.
2.0 Current DTH Technologies
At the time the ACT’s McCook Reservoir project, four DTH technology variations were identified:
2.1 Direct Circulation (DC) DTH Systems, which is conventional DTH technology. DC systems utilize an air flush and result in the air/cuttings discharge stream in direct contact with the hole sidewalls throughout the entire drilling process. This system produces a high potential for clogging of fractures by the flush discharge stream, as well as potential for clogging of the system during drilling, thereby subjecting the formation to high pressure air and possible damage.
2.2 Reverse Circulation (RC) DTH Systems utilize an air flush, but the system incorporates dual drilling pipes and a deflector system to feed the majority of the air flush and cuttings upward through the inner rod. At any given moment, only the portion of the hole sidewalls between the bit and the top of the hammer are exposed to 100 % of the air flush and cuttings. In contrast to DC systems, the entire length of the hole is not continually exposed to the flush and cuttings throughout the entire duration of drilling. Therefore, it reduces the potential for clogging of fractures and clogging of the hole. If clogging were to occur either within the inner rod or at the entrance point to the inner rod, high pressure air would be injected into the rock formation.
2.3 Dual Fluid (DFS) DTH Systems are a relatively new development in DTH technology. It utilizes an air powered hammer but a center tube that allows a 100% water flush. The configuration of the system is such that it virtually recreates same conditions within the hole during drilling as the top hole percussion with water flush method that is the accepted standard for drilling at lesser depths.
2.4 Water DTH Systems, the most recent DTH technology, utilizes a single fluid, water, for both powering the hammer and for flushing during drilling. These systems operate in a manner similar to DC systems, with the exception of the fluid used for power and flushing. The Water DTH systems, utilizing high pressure low volume water, are more energy efficient than air DTH systems and can achieve twice the penetration rate with a lower energy input in smaller diameter hammers. The flow rate in the system is on the order of 80 gpm, which produces an upflow velocity on the order of 3 ft/sec. The combination of flow volume and upflow velocity is the mechanism that maintains the hole in a clean condition and greatly reduces the potential for clogging and overpressuring of the formation.
3.0 Water DTH System
In comparison with other DTH systems, the Water DTH has the following advantages:
In contrast to the RC system, the Water DTH will never expose any of the hole to an air flush. The hole sidewalls will be constantly subjected to a strong upflow of water, which will result in drilling and maintaining a cleaner hole. This is consistent with preferred and recommended standard practice for drilling grout holes.
Clogging of the system, which could result in exposing the formations to high air pressure, would not occur with the Water DTH. Clogging of air flush systems is a relatively common occurrence. Clogging of water flush systems, by comparison, is highly rare. The high water velocities in combination with the large annular space between the drill steel and the hole sidewalls significantly reduces the potential for system clogging during drilling. Therefore, even though significantly higher pressures are present internally in the Water DTH system, external flushing pressure is only the water head pressure plus 2 or 3 atmospheres. It is ACT’s opinion that the risk of formation damage is dramatically less for the Water DTH system than the currently approved RC system especially in consideration of the water table.
The overall economics, both for the test section and later for construction of the full grouting program, strongly favor use of the Water DTH. The economic factors that must be combined in this assessment include the cost of furnishing and maintaining tooling and support equipment, overburden drilling diameters and excessive annular space, the production rate of the equipment, and other savings that will occur such as reduced time spent on hole washing. The Dual Fluid System (DFS), while providing an excellent technical solution, requires special tooling and furnishing and maintaining air and water systems at the same time. The economics of the DFS technology are severely compromised by the fact that the production rates are the lowest of any of the DTH systems. The Water DTH also requires special tooling in the form of the hammer and the high pressure pumps, but it does not require furnishing and maintaining air and water systems at the same time. Further, the production rates for the Water DTH are the highest of any of the systems and are on the order of 2 – 2.5 times the production rate of the RC DTH system. At the same time, it produces a very clean hole that minimizes the time and cost of pressure washing as a separate operation.
The Wassara system has been proven to be both reliable and effective.
The Water DTH is a technically superior drilling system with respect to drilling grout holes. The system operates in a manner that is considerably more consistent with best drilling practices for grout holes than the currently approved DTH system.
The Water DTH drilling system can be operated with conventional rotary drill rigs.
The Water DTH drilling system was only used to drill grout holes for the Kentucky Lock Grout Curtain project for the USACE Nashville District.
Wassara Water DTH system was successfully utilized for the Chicagoland Underflow Plan (CUP) McCook Reservoir Grout Test project for the Chicago District, USACE. This was the first major grouting project utilizing the Water DTH system.
Since first introducing the water actuated DTH to the USACE, Chicago District, on the McCook Reservoir Grout Test, we have successfully drilled over 600,000 lineal feet using water DTH hammers over the past decade and installed grout holes reaching 650 feet deep at a Mine located in Sudbury, Ontario in Canada. We have used the water DTH hammer to drill grout holes on the Clearwater Dam Exploratory Drilling and Grouting – Phase 1B (DSAC 1 Dam), Wolf Creek Dam Grout Curtain (DSAC 1 Dam), and Center Hill Dam Foundation Grouting (DSAC 1 Dam) projects. These projects are presented in Tab II of our proposal. In addition, we have also completed the following projects using a water actuated DTH hammer to drill the grout holes: Clearwater Dam Exploratory Drilling and Grouting – Phase 1 (DSAC 1 Dam), Clearwater Dam Exploratory Drilling and Grouting – Sinkhole Repair (DSAC 1 Dam), and the Totten Mine Grout Curtain.
The Water TDH drilling system has been exclusively specified by the USACE for its dam drilling and grouting projects.