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A Double Shield TBM consists of a rotating cutterhead mounted to the cutterhead support, followed by three shields: a telescopic shield (a smaller diameter inner shield which slides within the larger outer shield), a gripper shield and a tail shield.
In normal operation ("double shield mode"), the gripper shoes are energized, pushing against the tunnel walls to react the boring forces. The main propel cylinders are then extended to push the cutterhead support and cutterhead forward. The rotating cutterhead cuts the rock. The telescopic shield extends as the machine advances keeping everything in the machine under cover and protected from the ground surrounding it.
The gripper shield remains stationary during boring. A segment erector is fixed to the gripper shield allowing pre-cast concrete tunnel lining segments to be erected while the machine is boring. The segments are erected within the safety of the tail shield. It is the Double Shield's ability to erect the tunnel lining simultaneously with boring that allows it to achieve such high performance rates. The completely enclosed shielded design provides the safe working environment.
If the ground becomes too weak to support the gripper shoe pressure, the machine thrust must be reacted another way. In this situation, the machine can be operated in "single shield mode". Auxiliary thrust cylinders are located in the gripper shield. In single shield mode they transfer the thrust from the gripper shield to the tunnel lining. Since the thrust is transferred to the tunnel lining, it is not possible to erect the lining simultaneously with boring. In the single shield mode, tunnel boring and tunnel lining erection are sequential operations.
Regardless of the operating mode, working crews remain protected within the shields. Robbins Double Shield TBMs are capable of safely excavating a wide range of geologic conditions on a project. Our Double Shield TBMs are manufactured to suit your project requirements, in diameters from 1.6 m to 15 m (5 to 50 ft).
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Earth Pressure Balance Machines (EPBM)
EPBMs are used for high powered pipe jacking with precise control of earth pressure via operator control of the cutterhead with pressure sensors, jacking speed, screw conveyor operation and foam and bentonite slurry additive system for conditioning of spoils. Akkerman manufactures EPBMs for installation of pipe in the 96"-168" OD range.
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If the geology of your tunnel ranges from soft soils to weathered rock, then a Robbins Earth Pressure Balance Machine (EPBM) is the correct technical solution for your project. This is particularly true when your project is located in an urban environment and ground surface subsidence cannot be tolerated.
EPBMs are utilized in the construction of rail tunnels, metropolitan subway systems, highway tunnels, and other projects where the tunnel will be constructed either partly or completely in soft soil beneath the water table.
Robbins has integrated over 50 years of TBM design and jobsite experience into our EPBMs. Nobody has a wider range of experience designing innovative machinery to cope with difficult underground conditions. Our engineers will tailor your EPBM to handle the specific challenges of your project. From "Smooth Flow" cutterheads that reduce friction to super-reliable sealing systems and Variable Frequency Cutterhead Drives, Robbins has taken the traditional EPB design to the next level.
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A Robbins Main Beam TBM is complex in its design, yet relatively simple in concept. The front of the TBM is a rotating cutterhead that matches the diameter of the tunnel. The cutterhead holds disc cutters (ranging from 11" to 20" in diameter) which are positioned for optimal boring of the given rock type. As the cutterhead turns, hydraulic propel cylinders push the cutters into the rock. The transfer of this high thrust through the rolling disc cutters creates fractures in the rock causing chips to break away from the tunnel face. A unique floating gripper system pushes on the sidewalls and is locked in place while the propel cylinders extend, allowing the main beam to advance the TBM. The machine can be continuously steered while gripper shoes push on the sidewalls to react the machine's forward thrust. Buckets in the rotating cutterhead scoop up and deposit the muck on to a belt conveyor inside the main beam. The muck is then transferred to the rear of the machine for removal from the tunnel. At the end of a stroke the rear legs of the machine are lowered, the grippers and propel cylinders are retracted. The retraction of the propel cylinders repositions the gripper assembly for the next boring cycle. The grippers are extended, the rear legs lifted, and boring begins again.
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Robbins Small Boring Units (SBU-As)
The SBU-A is a small diameter rock cutting head (from 24"/600 mm to 72"/1.8 m) that can be used with any Auger Boring Machine (ABM) to excavate hard rock on drives less than 500 ft (150 m). The Robbins SBU-A has been proven on hundreds of jobs across the U.S. Over one hundred contractors in locations around the world have proven the SBU-A works better than any other method of excavating small diameter, hard rock bores.
Robbins Motorized Small Boring Units (SBU-Ms)
If you need to bore a small diameter tunnel in hard rock where line and grade are critical, Robbins offers Motorized Small Boring Units (SBU-Ms). These machines have been specifically designed for long bores (over 500 ft/150 m) with difficult ground conditions. They are offered in cutterhead diameters from 48"/1.2 m to 78"/2.0 m. If you are not familiar with SBU-As, we suggest you read about them before researching SBU-Ms.
Robbins Rockhead (SBU-RHSS or SBU-RHDS)
If line and grade are critical and you have a longer bore (over 1000 ft/300 m in length) for your next project, you should consider the Robbins Rockhead. The diameter range is available between 54" (1.35 m) and 78" (2.0 m). The Robbins Rockhead is a powerful mid-sized tunneling machine available in both Single Shield and Double Shield models.
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Microtunneling is the best pipe jacking method for wet and unstable ground conditions or contaminated soils. Microtunneling is generally defined as remotely controlled pipejacking (personnel-entry is not required) whereby the soils at the cutter face are controlled to maintain balance. Some examples of microtunneling applications are crossings under existing utilities, busy highways, railroads, levees, waterways and sensitive wetlands or shaft-to-shaft pipeline installation. An Akkerman microtunneling system is made up of several pieces of machinery that function together, controlled by an operator who monitors and controls the tunneling operations from a console inside a control container on the surface. Akkerman manufactures MTBMs for installation of pipe in the 30" -96" OD range.
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Pipejacking Systems are used to hydraulically install underground pipelines within strict alignment and grade tolerances where personnel-entry (i.e. operator located inside the boring machine and/or on the haul cart) is permissible. Akkerman manufactures TBMs for installation of pipe in the 44 "-168" OD range.
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Robbins Single Shield TBMs protect workers from broken rock until the tunnel lining can be safely installed. The body of the machine is enclosed in a shield that is marginally smaller than the diameter of the tunnel. The flat, low-profile cutterhead minimizes disturbance of the face as it bores, and prevents large blocks from collapsing and causing excessive boring stresses. The front of the TBM is a rotating cutterhead that matches the diameter of the tunnel. As the cutterhead turns, a ring of hydraulic cylinders provides forward thrust through shoes that push against the tunnel lining. The cutterhead holds disc cutters (ranging from 11" to 20" in diameter) positioned for optimal boring. The transfer of high thrust through the rolling disc cutters creates fractures in the rock, causing chips to break away from the face. Boring and lining installation are performed sequentially. To steer, cylinders orient the articulated cutterhead in the required direction.
Robbins Single Shield TBMs are available in diameters from 1.6 to 15 m (5 to 50 ft). All Single Shields are equipped with high-speed segment erectors for rapid tunnel lining installation. To steer the machine, the cutterhead is articulated. The short shield length enables a small turning radius and minimizes exposure to squeezing ground forces that could potentially trap the machine.
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This type of boring machine is used for tunneling in stable to unstable rock for the excavation of traffic tunnels (road and rail), supply tunnels (water, gas and electricity) and other special applications.
The main elements in the construction of the shield tunnel boring machine are the shield which gives the machine its name, a construction like a steel tube in which all other components of the machine are embedded, the cutter head and its drive housing, the advance mechanism and the robot-like device for installation of the tunnel lining, the so-called erector. The tunnel lining, usually consisting of prefabricated concrete sections, is installed with the erector, protected by the rear shield mantle, the so-called tail shield.
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Earth pressure balance tunnel boring machines
Historically, EPBs were developed in order to do away with the mucking system and the reprocessing of boring slurry. To do this, the soil must ideally consist of fine elements (clay and silt) and natural water. This type of mix is rare, which is why foams were developed.
Basic principle
The earth pressure balance tunnel boring machine or EPB consists of a cutting chamber located behind the cutterhead. This chamber is used to mix the soil + water foam. It is maintained under pressure by the mucking system. The system consists of a screw conveyor whose speed is controlled so that constant pressure inside the chamber is guaranteed. The material exits the screw conveyor via a hatch that can be closed when the TBM is shut down. The material is then removed by a belt conveyor and/or train cars circulating in the tunnel.
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This type of boring machine is suitable for driving in stable rock and is used for the excavation of traffic tunnels (road and rail), supply tunnels (water, gas and electricity), pressure water utility tunnels for hydroelectric plants, tunnels for cable cars high in the mountains, tunnels for geological investigations and other special applications.
The main elements in the construction of the open tunnel boring machine are the cutter head with its associated drive housing, the support construction (the so-called gripper) and the advance mechanism.
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WIRTH has been involved in tunneling and mining for over 100 years, producing the largest, most powerful machines in the world. But within the last 25 years the growing demand for trenchless technology as a means for installing underground utilities, has made WIRTH develop a range of equipment to provide trenchless solutions.
At WIRTH we believe that a combination of a high installed power & superior engineering means the user is on to a winning formula. Unlike large diameter TBMs which are made project specific, microtunneling machines are modular and can be adapted to suit a variation in ground conditions and product pipe sizes. This means that a contractor having a system is able to be versatile in the work that he can compete in by either increasing the diameter of his machine, or renting the head he requires for this project. Or maybe he just needs to change the configuration of the machine for use in a harder ground formation by getting a rock head for his existing machine.
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Tunneling systems for mixed ground
Dual mode - two process technologies in one
As the term 'dual mode' indicates, two process technologies are combined in these machines.
Shield machines
These machines are externally similar to shield machines and combine the functional features of a hard-rock shield tunnel boring machine and, optionally, of a slurry shield or a hydroshield machine (Bentonair, slurry shield). They are always used when tunnels have to be driven alternately in stable and unstable sections.
New style machines
Dual-mode tunnel boring machines are still a new type of machines and have been developed to meet the requirements of complex projects in strongly varying geologies. Where conventional tunneling techniques had to be used formerly, these machines now open the way to lower-risk and lower-cost tunneling in difficult geological conditions
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This type of boring machine is used for tunneling in stable to unstable rock for the excavation of traffic tunnels (road and rail), supply tunnels (water, gas and electricity) and other special applications.
The main elements in the construction of the shield tunnel boring machine are the shield which gives the machine its name, a construction like a steel tube in which all other components of the machine are embedded, the cutter head and its drive housing, the advance mechanism and the robot-like device for installation of the tunnel lining, the so-called erector. The tunnel lining, usually consisting of prefabricated concrete sections, is installed with the erector, protected by the rear shield mantle, the so-called tail shield.
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Slurry shield tunnel boring machines
Bentonite slurry, consisting of a specific clay and water mixture is universally used in boring and digging operations. The slurry has numerous properties: sealing of the cutting face, reduced friction on the TBM's structure, and transport of cuttings to the separation plant outside the tunnel.
The basic principle of this TBM is to maintain the tunnel's cutting face during the excavation phase by filling the working chamber, located behind the cutterhead, with slurry.
Slurry pressure is carefully controlled by a large air bubble which is maintained by a separately-controlled air supply system. This air bubble acts as a damper by absorbing sudden variations in mucking output.
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Double - or Telescopic - Shields unite the principles of the Gripper and the Single Shield TBM, enabling fast excavation even in varying rock formations.
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Herrenknecht Earth Pressure Balance (EPB) Shields are in their element in soft ground. Cohesive and incohesive soils with high clay or silt content and low water permeability provide the ideal conditions for EPB tunnelling.
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For use in solid rock, the principle of the gripper is both the most simple and most effective technique. The single gripper machine braces itself against the rock using two gripper plates. Then, hydraulic cylinders push the cutterhead into the tunnel face at high pressure, grinding it with cutter rings. Double gripper machines work according to the same principle, using four hydraulically operated gripper plates.
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Worldwide, more than 600 Herrenknecht Utility Tunnelling Machines (Ø < 4.20m) excavate modern supply and disposal tunnels and renovate existing systems. Whether our project engineers can help our customers to implement a project successfully largely depends how well the machinery is adapted to the prevalent geological conditions (permeability and grain distribution). It is a good job that Herrenknecht is able to offer the entire range of Utility Machinery and collaborates with site teams to implement successful projects.
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Fluid-supported Mixshields are specialists for multi-layered, complex geologies, particularly those with a high water content, and are a patented trademark of Herrenknecht. This functioning principle is particularly well-adapted to heterogeneous soils: Thanks to the center-free drive with the floating bearing of the cutting wheel and the modular structure of the machine, the operating mode can be altered to suit the soil conditions in the tunnel.
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Single Shield TBMs are the right choice for brittle or soft rock. In shield tunnelling, the tunnel is lined with concrete segments. To tunnel forward, the hydraulic thrust cylinders of the Single Shield TBM push against the last installed lining ring.
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An Auger Boring Machine (ABM) is used to bore horizontally through soil or rock with a cutting head and auger. The majority of ABMs are used to install pipe casing under railroads, highways, airport runways, creeks or any area of ground that cannot be open cut or disturbed in any way.
There are many types of cutting attachments for this machine. They range from Backhoe Teeth cutters for cutting through soil to the Robbins Small Boring Unit for boring hard rock.
Initially the ABM is set up in the starting pit on a predetermined length of track. A backing plate, usually steel or reinforced concrete block, is installed in the wall opposite of the boring to withstand the thrust exerted by the boring machine. The machine bores through the earth with a cutting head and the jacking force is provided by the hydraulic thrust. The pipe casing and auger sections are added as the machine advances. Spoil is removed from the auger through the casing to a door located on the side of the machine.
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The Guided Boring method (also know as pilot tube microtunneling) installs small diameter pipes with grade and alignment precision. The pipe installation involves a three-step process where launch and reception shafts are strategically located to minimize surface disruption. Three robust jacking frame configurations are available to meet contractor's needs. Akkerman GBMs are used in conjunction with a theodolite guidance system to provide accurate pipe installation. Our GBM is extremely versatile and our customers continually surprise us with new applications. Akkerman manufactures GBMs for installation of pipe in the 4" - 48" OD range in displaceable soil under 50 blow count.
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