2. Symmetrix Principle

SYMMETRIX THE SOLUTION IN OVERBURDEN DRILLING

Symmetrix Principle Drilled Casings – When using a drill casing, soil, rock and other debris is removed within the protection of a steel tube and brought to the surface. For foundations during the concreting process the pile support is transferred from the temporary drill casing, which is gradually withdrawn, to the concrete forming the pile shaft. Likewise, the casing may be left in place to be used as additional structural support and/or protection of the pile itself. For exploration and well drilling, the casing itself can become the conduit for bringing the bounty to the surface.

Rotex Symmetrix Principle The Symmetrix system is a casing advancing method for drilled casings able to be used in any and all ground conditions and at any angle to depths beyond 100 meters (300ft +). Casing sizes range from 76mm (3 inches) to 1220 mm (48 inches) OD. Systems are designed to work with DTH drilling however some smaller sizes are also available as top hammer versions. The 3 main components work together as a single effective unit. These consist of: a pilot bit with large internal flushing holes and external flushing grooves; symmetrical ring bit [reamer] with internal bayonet coupling; and a casing shoe for driving of casing.

1. Symmetrix STD

Symmetrix Advantages

• Straight holes always withoutdeviation due to changingground formations!

• Quick set-up and high productionrates !

• Less torque is required to drillthrough all formations than othermethods!

• Easy to unlock/ Easy to relock! • Drilling is easy at any angle! • Effective internal flushing! • Safe and controlled! • Significant economic savings! • Reaming for casing is done by

concentric ring bit with noeccentric components!

• Simple foolproof structure equalsno jamming and no lost bits!

How Symmetrix Works

The pilot bit is attached to the ring bit with abayonet coupling. Both rotate clockwise andtogether cut a hole, which is sufficiently largeenough to allow the casing shoe to pull down thecasing pipe. The ring bit rotates freely on thecasing shoe, which is welded to the casing.During drilling, the casing does not rotate. Casings can be added together as required todrill holes of more than 100 meters. The flushingair is ejected through the holes in the face of thepilot bit and returns immediately up wide groovesbetween the pilot bit and ring bit and the annulusbetween the casing and the drill string. Thisensures high flushing velocity with low holedegradation. When the hole is complete, the pilot bit isunlocked from the ring bit by a slightcounterclockwise motion and withdrawn upthrough the casing. The casing can then beeither left in place or retrieved from the hole.


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1. Symmetrix STD

• Pilot bit has two “shoulders”; one at the ring bit; one at the casing shoe • Has a wire or ring connection between the ring bit and the casing shoe • For drilling medium to deep holes when the casing is left permanently in the hole • For temporary casings it is used without the connection between the ring bit and the casing

shoe resulting in the ring bit to be left in the hole

Example 1, casing is used as a protective casing in the overburden part of the hole, after the overburden has been drilled through, the drilling is continued in bedrock without casing advancing. Using a normal rockbit (hammerbit).

Step 1: Casing is drilled through overburden and seated into bedrock. Step 2: The pilot bit is unlocked from the ring bit and withdrawn. Step 3: Drilling is continued with a smaller rock bit to complete the task (i.e. water wells, rock sockets, or rock anchors) – the casing and ring bit are left in place

Pilot Bit Ring Bit Casing Shoe


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Example 2. Casing is drilled through the overburden to the bedrock. Drilling is not continued but the casing is filled with concrete and or load bearing steel for piling purposes. Step 1: Casing is drilled through overburden and seated into bedrock Step 2: The pilot bit is unlocked from the ring bit and withdrawn Step 3: The casing, either a thick walled casing or thin walled with additional reinforcement, is filled with concrete to be used as a foundation pile. All Symmetrix systems include the pilot bit, casing shoe to pull the casing (except some shoeless models for double rotation rigs) and the reaming ring bit, which makes the space for the casing. The pilot bits are mainly done for DTH hammers but most small sizes are available also for top hammer drilling. All major shanks are provided according the make and the type of the DTH hammer.

Different shanks and bit designs for different hammers


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Symmetrix STD in Well Drilling

The development of Symmetrix occurred due tothe requirements from well drillers to have aneasier and more reliable overburden drillingsystem. Today well drillers are one of the mainusers of Symmetrix worldwide. Typical wells are referred to as “screen wells”whereby a fairly large diameter casing is drilled topenetrate the water table; a sand packer and wellscreen are installed inside the casing; a pumpshaft is installed; and finally the temporary casingis pulled out.

Symmetrix Method of Well Drilling

Screen Well

Well Drilling in Alberta, Canada Using Symmetrix Method

Withdrawing the Pilot Bit

In Symmetrix well drilling, the wells have either steel orPVC casing drilled through the overburden layers. Thepilot bit is then unlocked from the ring bit and withdrawn.The casing is then grouted to seal it to the bedrock thuspreventing surface water from contaminating the well.The lower part of the well is then drilled with standardrock bits and drilling methods. The Symmetrix Method has been extremely well receivedby well drillers worldwide who, thanks to Rotex andSymmetrix, can considerably shorten the work timenecessary for overburden drilling.


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Symmetrix STD in Piling

With the development of the Symmetrix System,drilling contractors and design engineers have quicklycome to realize that the used of drilled casings asfoundation piles were becoming more economical. With the Symmetrix System the installation of largecasings with relatively small drill rigs is possible – thishas lead to wide spread increases in the use ofdrilled casings especially in across Scandinavia andother parts of Europe.

Klemm KR 807 drilling 16 inchpermanent casings for a railway bridge inFinland

Piling with drilled casing is a fairly common practicein most parts of the world. The selection between friction piles and end bearingpiles as well as best methodology and constructiontechnique will depend on the local ground conditions. In areas with varying ground conditions, boulders,extreme hard ground or the need for rock sockets,Symmetrix Casing Advancing System will prove to bethe quickest and most economical tool.

Retaining wall with soldierpiles (casings) drilled intobedrock

Operators of small drill rigs really appreciate theease of drilling and the small torque required whenusing Symmetrix. A small drill rig can easily matchthe productions of larger drill rigs with the samefeed length when Symmetrix is used – and getproductions of 200% or more in comparison toother methods.

Small drill rig usingSymmetrix does the work ofa big rig in Hong Kong


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Symmetrix STD in Underpinning Underpinning in non-homogeneous conditions has always been a problem especially in areas where till, boulders, and hard rock formations are encountered. Due to penetration problems, piles have been left on unstable layers, later settling and causing damage to the structure it was meant to support. Only through the use of Symmetrix in underpinning can consecutive penetration through cemented sands, hard clays, boulders and till be possible.

Symmetrix STD as an Alternative to Driven Piles In areas where vibrations from pile driving may have caused damage to nearby structures, Symmetrix has been the economical alternative. Symmetrix drilling does not cause lateral movement or soil displacement making it ideal in such sensitive areas.

When underpinning in conditions where the existingfoundation has been damaged, the work must be performedwith the least obtrusive method in order to prevent stress tothe foundation, With the Symmetrix System, piles can be drilled through allobstructions to the required depth without disturbingsurrounding structures.

Three additional floors were excavatedbelow an old building after underpinningusing Symmetrix

This is very evident in railway workswhere quick non-obtrusive methodsare a must. Here, at a railway realignment projectin the UK, 1860 steel casings weredrilled through overburden and voids(including old mines) to bedrock to anew railway track foundation.


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Symmetrix W – Ring Bit with Integrated Casing Shoe The W version was originally developed to maximize the drill through diameter in order to allow a 6 inch hammer with 7 inch casing. This was possible by integrating the casing shoe and the ring bit together. W153, the original system for 7 inch casings, is very popular with water well driller. W140, for 6 5/8 inch casings, was also created for well drillers. Today W190, for 8 5/8 inch casings, and W240 are available as W versions with the ability to develop W versions from any Symmetrix size. W versions have proven very reliable in drilling deep casings with holes of 740 feet deep already having been cased with the W version. New W-systems have longer casing shoe sleeves over the casing to allow better guidance and the use of additional plug welds.

Rotex Oy has patentedthe manufacturingmethod of the Wsystems – a methodallowing the models tobe made in largequantities

Integrated ring bit andcasing shoe of theW153


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2. Symmetrix Econ Symmetrix Econ is used for the same purposes as STD. The only obvious difference is that the ring bit (reamer) is not attached to the casing shoe with wire locking but instead is locked to the pilot bit only.

• The pilot bit is the same as in the STD System • The ring bit and casing shoe are not mechanically connected • Designed especially for shallow holes with permanent or temporary casings

Symmetrix Econ Principle Step 1: Casing is drilled through overburden into sufficiently firm till or seated in bedrock Step 2: The pilot bit is unlocked from the ring bit and withdrawn Step 3: The casing is filled with concrete and, if needed, with reinforcement

Econ Set

STD Set


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When a large number of piles is needed to be installed in fair to medium-difficult conditions, Symmetrix Econ is the right tool. Easy drilling, fast hole-to-hole movements and adaptation of new casing are the elements of efficiency in the Econ bit.

Drilling with Rotary Head/Drill Table Machines There are several double head units developed for anchoring works whereby the casings are pushed or rotated consecutively with the drilling action. The Symmetrix system is easily adapted to work with these machines by eliminating the casing shoe striking shoulder (as in the STD SL pilot). In this case the pilot bit and ring bit do all the actual drilling work and do not restrict the action of the casing rotator.

Symmetrix Econ can also be used fortemporary casings, especially where it isdifficult to pull out the casing. The casing isdrilled through the overburden and seatedinto bedrock or to the designed tipelevation. The pilot bit is unlocked from thering bit and withdrawn. Rebar or astructural beam is inserted with concrete toform a pile. The casing is then extractedleaving the ring bit behind.

Rotary table machines, which push and rotate thecasing simultaneously while drilling with a DTHhammer inside have difficulties when facing hardrock conditions. Symmetrix SL versions, which have no casingshoe and pilot shoulders, can solve this problem. The pilot bit breaks up the center of the drill holeand the attached ring bit clears the way for thecasing, which is maneuvered into place by therotary table. As the impact energy of both the pilot bit and ringbit is combined, hard rock formations can bedrilled easily and quickly with no additionalassistance. With the use of the Symmetrix STD-SL versionthe drilling time is cut considerably withcomparative studies showing that the Symmetrixsystem is 3 to 8 times more productive thanrotary head/drill table machines alone.


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3. Symmetrix SE Symmetrix SE is a new ring bit design made especially where there is no need to continue drilling beyond the bottom of the casing. When the ring bit ID is not a critical concern, strong shoulders can be built into the pilot bit and ring bit.

SE Set Principle: Simple casing shoe and ring bit are very economical yet still strong enough for deep holes and difficult rock conditions. The ring bit thickness is the same as the pilot bit groove width with a deep striking shoulder giving it excellent wear resistance and long pilot bit life. This system is perfect for drilled foundations where the casing is brought to the bottom of a rock socket (in which case additional drill through is not necessary).

The SE type is specified according tothe casing OD as in SE applicationsthe drill through diameter is regardedas insignificant.


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• SE is designed to be the most cost-effective solution for single-use drilling allowing the casing to be drilled to the bottom of the rock socket

• SE is designed for drilled foundations where there will be no additional drilling beyond the tip of the casing

• SE system consists of the SE pilot bit, SE ring bit, and SE casing shoe

• SE type is specified according to the casing OD as the drill through diameter is insignificant

• The ring bit thickness is the same as the pilot bit groove width

• The impact shoulder is deep giving excellent wear resistance and long pilot bit life

• Simple ring bit and casing shoe are strong enough for deep holes and difficult rock conditions

• Maintenance welding of worn impact shoulders is easy to perform when necessary

Symmetrix SE is a family of products designed for applications where drilling is not necessary beyond the tip of the casing.


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4. Symmetrix N System Symmetrix N Version is designed for temporary casings. The ring bit is integrated with the casing shoe and designed to allow the casing to be pulled out from great depths.

• N-type pilot bit • Designed for applications where casings are retrieved and the same ring set is used

multiple times • N-type multi-use ring sets; ring bit and casing shoe are connected by a strong mechanism • System also suitable for thick wall casings

Symmetrix N System Principle Step 1: Casing is drilled through overburden to the required depth Step 2: The pilot bit is unlocked from the ring bit and extracted Step 3: Reinforcement, in the form of a rebar cage or structural beam, and concrete is place in the casing Step 4: The casing is extracted (even from great depths) leaving a suitable friction pile


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Symmetrix N352 for 406 mm (16”) casing pulled out to be used again

Symmetrix N in Anchoring A typical application for the Symmetrix N-system is in the construction of ground anchors. Temporary casings with the Symmetrix N-system are extracted after the anchors have been completed. Quick and economical installation of ground anchors is possible especially in the case where the anchor length is working as the bonding unit.

Seismic Retrofit with N131; Vancouver, Canada

Different anchor applications, such as groundanchors and rock anchors, have different bondinglengths. Both anchors can easily be installed withthe N-system.

The Öresund Bridgebetween Denmark andSweden required theSymmetrix N109 to drill2200 anchors.


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Symmetrix Drill-Through Systems: N-DT and W-DT The Symmetrix system also includes two models where the drilling can be continued with the pilot bit beyond the tip of the casing by passing through the ring bit. Typical applications for the Drill-Through Systems include most anchoring applications and foundations where sufficient skin friction for uplift is not available and a rock socket is necessary.

The use of drill-through in piling operations where a separate rock socket is required brings about tremendous savings in cost and time by avoiding the need of an additional drill rig and/or the use of a crane for handling additional tools and switching out the hammer and drill strings. The reduction of time equals an increase of 100% over methods in which the rock socket is drilled separately. Anchoring is another application for Symmetrix DT systems as a separate rock bit is no longer needed for the rock socket saving both time and cost.

DT in normal drilling mode – drilling through the ring bit and being retrieved though the ring bit

N-DT W-DT


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5. Applications for Symmetrix STD, Econ, SE, N & DT Versions The use of drilled casings is becoming increasingly popular worldwide primarily due to the expansion of building and infrastructure growth to areas that are less than perfect for their construction. In complex ground conditions the use of driven piles, CFA and other displaced or bored pile types becomes either physically or economically infeasible. Pile driving in dense urban conditions can disturb surrounding structures or utilities and is often difficult to estimate its costs in areas with sloping or changing bedrock. Additionally undue problems such as settlement, soil compaction and lateral soil displacement/heaving can occur. For these reasons, most designers and owners have turned to drilled casings to overcome the potential problems and liability. DTH drilling is the only drilling method that can drill through all ground conditions, boulders and hard solid rock. The Symmetrix system is the most advanced system for drilling casings with DTH hammers due to its vast array of applications and noted field experience.

Piling Applications There are numerous ways to apply the Symmetrix system to foundation piling ensuring that the right tool is available for every possible project.

For end bearing piles: the casing isdrilled through overburden to therequired elevation; the pilot bit isunlocked from the ring bit andwithdrawn: the casing is filled withconcrete (and when necessaryadditional steel reinforcement). Inmost cases the casing, typically thickwalled, is left in place and acts solelyor, along with the steelreinforcement, partially as the loadbearing member.

If stable bedrock is not withinfeasible piling depth, the casing itselfmay be used only as additionalcorrosion protection or as a liner tokeep the hole open. The main load isthen carried out by an internalcasing, pile or beam installed insidethe drilled casing. The internal loadbearing element would require alength for bonding the pile to theground through a rock socket. Drilling with N532 DT at

Hong Kong Airport


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Thick Wall Casings Used as End Bearing Piles Permanent thick wall casings can be included in the structural makeup of a pile whereby the casing is not only used for corrosion resistance but also as a load bearing member as well.

Rebar cage inside drilled casingbefore concrete pumping

Work phases of drilled bridgefoundations seated in bedrock

End bearing piles for this bridgewere installed prior to rockexcavation (accomplished bydrilling and blasting)

In the case where the pile is requiredto have a designated capacity in bothbearing and tension, the casing pilewill typically require a rock socketwith friction pin to take the tensionloads.


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Friction Piles When there is no composite material such as bedrock to seat an end bearing pile, a friction pile is utilized. Casings are typically used when the ground conditions will not allow the hole to stay open and the integrity of the hole and the drilling tools themselves must be protected. When working in areas where the ground conditions require the use of a DTH hammer, Symmetrix N, Econ or SE with temporary casings is the best choice. Typically the N-system is the prescribed system however if the ground has numerous boulders or the casing is drilled deep through hard rock layers then the use of Econ or SE systems may be more feasible. Sometimes the foundation design for friction piles calls for rock sockets to extend beyond weathered or fractured rock for additional uplift capacity. In such cases a rock socket must be drilled beyond the tip of the casing and the load transfer is based on the bond between the socket element, such as an H pile, and the grouted rock interface.

Friction bars are sometimes weldedalong the rock socket length of the Hpile for extra gripping surface Drawing of installing H piles with Symmetrix N532DT


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N-system used for grout columns When working in alluvial riverbeds and valleys jet grouting can be very problematic as rotary drilling through and within hard boulders is not possible. Percussive drilling is required for drilling. In such situation predrilling with casings is required to drill through strata with stones and boulders. Depending on the depth and ground, either N-system of Econ is used with temporary casings.

Jet grouting works going on through grout columns done with drilled casings, Sikkim

Phase 1 Phase 2 Phase 3 Phase 4 Phase 5 Phase 1 Casing is drilled with Symmetrix N or Econ system Phase 2 Symmetrix System is lifted out and hole straightness checked Phase 3 Casing is filled with grout in 4-5 meter intervals lifting the casing simultaneously or with packers while casing is lifted out Phase 4, Jet-grouting rods are drilled in to required depth Phase 5, Jet grouting is done


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Secant Pile Wall with Drilled Casings Secant pile walls are commonly used in the construction industry for retaining walls in support of excavation. Using Symmetrix in their construction gives them significant advantages over slurry diaphragm walls typically constructed by grabs or hydromills – among these are the ability to work in all ground conditions without changing the methodology or changing tools. Production time and scheduling can be accurately predicted and exact budgeting feasible. Symmetrix is especially suitable in ground conditions with boulders or when a footing in bedrock is required and/or advantageous. Primary piles (1) are drilled and rock socketed consecutively. After a suitable number of casings have been installed, the casings are filled with concrete then extracted Secondary piles (2) are then drilled down to tip elevation. Rebar or other reinforcement is set into the casings, the casings filled with concrete and then the casings are extracted. A fully stable rock socketed and reinforced wall is now ready.

A secant pile wall requireswhat appears to be anexcessive amount of drilledlength however the resultingcost is certainly much lessexpensive than a grab or millconstructed wall whensignificant boulders areencountered or when thebottom of the wall must beconstructed into solid bedrock.


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Using N-System with Leader Machines As the Symmetrix system requires only a minimal amount of torque it ideally suited to gravity fed drilling without a drill rig or leader – only a crane is needed. This methodology, in use by several contractors, is the perfect solution for construction of temporary work trestles, temporary bridge foundations or in limited access situation where alternative methods would be costly due to the need for access and/or special equipment.

The Symmetrix N-version is ideally suitedto be used with leader type machines.The rotary head is raised and lowered bya cable network giving it the ability to pullback or give sufficient crowd whenneeded. In regular drilling operations when drillingdeep, the drilling operation must bestopped to add additional drill string andcasing. With this type of machine, the mastlength can often be extended by addingadditional segments or by lifting the footoff the ground – this allows for drilling ofthe casing in a single pass. This type of machine allows for quickdrilling of multiple holes without having tomove the base of the machine equalingeven greater productions (the reachdependent on the capacity of the craneand the weight of the operation).

Virtually any crane can be adapted for DTHdrilling – Nova Scotia, Canada


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Bulk Sampling and “Rat Hole” Drilling Bulk sampling and “rat hole” drilling are typical applications for the use of large diameter casings. Traditionally these have been done with rotary rigs however as modernization has caught on with this industry the realization that the traditional methods are both time consuming and expensive (due to the need for large expensive drill rigs) has resulted in many drillers to turn to the Symmetrix system. A starter casing drilled with the Symmetrix casing advancing system is 4 to 5 times faster than traditional rotary systems – making a tremendous impact in total productivity and cost. The Symmetrix system also allows for the use of smaller and lighter equipment – highly regarded when transporting across rough terrain.

Underwater Drilling and Blasting

Bulk sampling with 28 inchSymmetrix system Drilling is done with dual stage drillrod with cuttings directed to acontainer

Underwater drilling and blasting operationscan be sped up through the use oftemporary drilled casings as chargingtubes.


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6. Symmetrix Horizon Symmetrix Horizon is designed for situations where long horizontal drilling must occur. Due to the high friction levels experienced in horizontal drilling, the impact shoulders have been designed as heavy duty. Because the ring bit is collected from the receiving pit, there is no requirement for drill through and thus there is no limit to the contact surface size and the striking surfaces can be made thick and strong.

• Designed for long horizontal holes when casing is left permanently in the hole (or for very deep vertical holes)

• Strong ring bit and casing shoe to guarantee long borings in any soil or rock conditions

Symmetrix Horizon Principle The casing is drilled through the overburden with HZ version pilot bit and separate reamer with several striking shoulders for extra strength. Typical work for Symmetrix Horizon is for horizontal underpasses (i.e. for utility conduits), which may 200 meters or more in length. The reamer and casing shoe are recovered from the receiving pit.

Although the HZ system is designedfor “break through” drilling it can alsobe used for drilling extremely deep ordifficult holes where the ring bit is leftin the hole.

HZ type pilot bit usedfor deep vertical holes


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In horizontal drilling, the casing may require pushing in addition to the pulling action of the casing shoe in order to overcome the tremendous friction. Flushing is therefore critical and the use of augers may be necessary to bring out cuttings from the casing.

Horizontal Drilling for Utility Lines Horizontal drilling is a common practice for locating utility lines under active roads and railways. Today trenching activities are becoming increasingly unpopular even though improvements to infrastructure require the addition or relocation of new water mains, sewer lines, electrical or telephone conduits. With Symmetrix HZ horizontal drilling system a passage up to 1 meter in diameter can be drilled regardless of the geological conditions faced.

A horizontal drilling rig ready for action

609mm drill bit and casing breakingthrough after 240 meters of drilling inItaly

44 meters of horizontal drilling, Sweden


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Horizontal Drilling for Pipe Roofs Pipe roofs are a method of building tunnels through overburden or weak rock formations where a cut and cover method would not be suitable due to existing buildings, roadways or other obstacles.

Pipe roof constructed for a metro line in Hong Kong (preserving park and trees)

Examples of Pipe Roof Designs

Sometimes interlocked casings are used toallow the casings to form an ideal shape. Theexample in Hong Kong on the right showswhere not only the roof but also the walls wereconstructed using drilled casings interlocked tokeep the structure aligned and deviation to aminimum.

Construction of pipe roof for a horizontal underpass, Hong Kong


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7. Symmetrix T-System The Symmetrix T-system is designed for small diameter casings used with both top hammer (drifter) and DTH hammer use. The driving shoulders are designed very strong which means a long pilot bit lifetime even through difficult conditions. The drill through passage is small however these bits were not designed to be drilled beyond the casing tip. A standard Symmetrix design ensures that only a small amount of torque is needed allowing these bits to be used with standard tunneling “jumbos” which have very limited torque.

• Primarily designed for forepoling in tunnel construction • Robust, concentric construction for drilling in fractured and variable hard rock formations • Available for both top-hammer and DTH drilling

Symmetrix T-System Principle

The Symmetrix T-system was made forforepoling with injection casings. The casings are drilling into the requiredpenetration; the drill rod and pilot bit arewithdrawn and injection material ispumped into the casing allowing it to flowout through the casing holes. The groundimmediately around the casing becomespermeated with the injected substanceas the material is packed in causing it tobecome more stable. Both cement slurries and chemicals areused depending on the nature of theground.


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Symmetrix T-Version in Tunneling For underground infrastructure construction in urban areas, which have typically poor ground conditions or for any underground construction in weak or disturbed soils, modern tunneling engineers have developed a face stabilization and protection system called “Forepoling”. This method is based on the use of drilled poles (casings) in advance of the tunnel excavation. Rotex was one of the first to develop Symmetrix drilling accessories for this type of work. Symmetrix product ranges cover all forepoling and roof piping application wherever drilling is required. Forepoling is constructed either with standard tunneling “jumbos” with short 3~4 meter feeds and threaded casings or as a single pass drilling operation with specialty forepoling rigs with long feeds. Forepoling is a ground stabilization technique where the support structure of a tunnel sector is placed ahead of the excavation. The supporting mechanism provided by the forepoling technique stabilizes the tunnel face area in both transverse and longitudinal directions by an arch-like reinforced zone. The Spiling method consists of four different parts:

• Drilled steel pipe • Grout inside the pipes and in voids outside • Treated ground by permeation or fracture grouting • Steel arch supports (with foot piles when necessary)


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Injection is the crucial part of this system in order to form the arch-like structure. For cement or chemical grouting, perforated casings are used; holes are either open or fitted with one-way valves for double packer grouting.

Weak and/or wet conditions may require fiberglass casings at the face of the tunnel for stabilization and longer drainage casings with Sidra/Sidrex systems.

Sidrex Simultaneous Drainage In forepoling, the ground around the casings is treated by permeation or compaction grouting through the casing holes with packers. A high water content will complicate the work resulting in the need to have special drainage casings drilled in for dewatering. Standard forepoling casings can now be utilized for simultaneous drainage with the new Sidrex System. Dewatering slots are protected with a water soluble material and they open automatically within 12 hours after drilling. A patented packing seal located on the outer surface of the drainage element prevents grout from blocking the slots. Symmetrix and Sidra are patented trademarks.

Casing shoe and thread Fiberglass system

Some forepoling casings have an added1.5 to 6 meter element with slots fordraining water. The slots openautomatically after drilling. The outsidepacker prevents the grout from blockingthe slots.


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8. Special Symmetrix Systems

Enhanced flushing by Symmetrix RC Reverse circulation drilling was originally designed to collect chip samplings for geological exploration. This required the use of special two stage (or two way) drill rods and an RC hammer with a collection inlet. Later, RC hammers were also used in the construction industry to drill in locations where exhaust air escape through the collection inlet helped to cope with high backpressures. This assisted in reducing the worry of volumes of air being introduced to the ground and a control of the material washed out. To overcome the most common problems experienced with this method, Rotex developed a new pilot bit. The new RC bit does not require the use of double wall or two stage drill rods or a special RC hammer – yet it allows proper flushing without risk of over-flushing to be gained through the superior design:

• Air flushing (water and foam if added) cleans the bit face and directs the flow back inside the casing through the center holes

• The amount of face cleaning air is controlled through a nozzle in the other air passage opening in the casing

• By controlling the second passage we can balance the flushing without over flushing

The RC design is available for all Symmetrix Systems


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Rotex DRC Systems Rotex Oy has developed a system with fluid flushing. This system is based on the Symmetrix RC version bit and the use of a RC hammer where the collection tube is used as a conduit for the flushing media, normally water or water/bentonite slurry.

Ports Open Ports Closed


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SimGrout Simultaneous Grouting Method Sometimes simultaneous grouting is a requirement either in rock sockets for a solid anchor or along the whole casing before the drilled casing can be accepted as a permanent pile. All Symmetrix STD bits can be used with the new SimGrout system developed by Rotex Oy.

SimGrout • Simultaneous grout injection • Available for all Symmetrix

STD pilot bits • Three injection holes • Grout volume and pressure

selected according to theapplication and availablegrouting equipment

• Modifications to adopt themethod can be made at thework site

Grouting is done eitherthrough standard plasticgrouting hoses (if double walldrill rods are used) orthrough steel hosing (waterpipes) with simpleoverlapping joints. Centralizers are not rotatingbut fixed to the casing andretrieved when the hammerand pilot bit are extracted.


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Drilling with Water Hammer Rotex Oy is the supplier of Wassara’s W-Rex casing drilling product line.

The Wassara water hammer has many advantages over standard air powered hammers. They can be used in areas with a high ground water pressure; they keep their efficiency in long holes; and drilling with water consumes only 1/3 the energy used in standard DTH drilling.

Drilling with Rotary and DTH in the Same Hole Due to Symmetrix’s unique locking system it is possible to drill with a tri-cone bit or drag bit and with a DTH hammer in the same hole. A special ring bit adapter is used when drilling with the tri-cone or drag bit in order to rotate the ring bit. When DTH drilling is required, the drill string is lifted out and the DTH hammer with Symmetrix pilot bit is locked into the ring bit.

W-Rex casing advancing systems


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9. System Requirements Drilling requires: a suitable DTH hammer applicable to the task at hand: compressors to run the hammer; drill rods; and a Symmetrix pilot bit with sets of reamers

Drill String Principle Drill rods conduct the air required by the DTH hammer downward; exhaust air and the cuttings return between the drill rod and the casing wall. The bailing velocity depends on the compressor used and the annulus area between the rod and casing. Air speed should exceed 15 m/sec (3000 fpm). With large casing sizes this typically means drill rods that are about 60~80mm (2~3 ½ inches) smaller in diameter than the casing size. If hexagonal joint rods are used, a man cage or mast lift will be required to assemble and disassemble the locking pins on the drill head spindle.

Hexagonal joint drill rod for 610mm casing

The DTH hammer requires a certain feed force to workproperly. Ensure that you have a feed force between8~10 kg/mm of bit diameter (450~560 lb/inch). DTH hammers require lubrication. An adjustable positivereplacement pump ensures adequate lubrication at alltimes.


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Another possibility is to utilize the reverse circulation principle with dual wall drill pipes. Two swivels, one for compressed air and the other for exhaust air with cuttings and soil need to be installed. One must ensure that the hollow spindle of the rotary head has a passage equal to the inner diameter of the RC pipe. Reverse Circulation Drilling Principle: Cuttings are collected; same rod can be used for several different casing sizes by only changing the rubber liner seal; suitable for sensitive drilling conditions. The diverter directs the return flushing air into the inner pipe of the dual wall drill rod and up through the rotary head into the collection pit. In all DTH drilling remember:

• Grind the casing shoe and casing surfaces before welding • Use a proper root weld • Ensure you have enough flushing velocity; especially in deep holes (over 30 m) slow flushing

increases back pressure thus causing slow penetration and possible shoe breakage • Use stabilizers • Use air valve to reduce the stress on casing shoe/reamer shoulders after breaking through

boulders • Maintain your pilot bits • Use foam when necessary

Rubber liner keeps cuttings from traveling up the casing


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Welding of Reamer Set to the Casing As the casing shoes conduct the impact energy and pulling force to the casing and must come up with the casing when it is extracted, care should be taken that the weld is competent to take the load. The casing shoe and casing should have a minimum 2~2.5 mm gap prior to welding to ensure full weld penetration. This also applied to the buttwelded N-version.

Maintenance

When large diameter N versions arewelded the first root weld is donefrom inside with the weld groundsmooth from both sides.Subsequently the weld should beinspected and then filled fromoutside with two or three runs(depending on the type and size ofthe electrodes and the casingdiameter)

When doing repair welds, usehard welding rods and grind thesurfaces back to originalstandards. Keep buttons grinded. Grindthem before 1/3 of the button isflat. Especially watch gaugebuttons. Good welding rods for hardwelding the worn shoulders are:Esab OK 84.58


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10. Exceptional Casing Shoe Designs Symmetrix STD135 version B will adapt to any casing wall thickness

Symmetrix STD155 Symmetrix STD165

Symmetrix W versions W140 and W153 look today as follows:

Old short shoe sleeve New design allows plus welding

2. Symmetrix Principle

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