INTRODUCTION Trenchless technology can be defined as “a family of methods, materials and equipment capable of being used for the installation of new or replacement or rehabilitation of existing underground infrastructure with minimal disruption to surface traffic, business and other activities” The difference between trenchless and other subsurface construction techniques depend on the size of passage under construction. If a subsurface construction does not permit human entry, it can be termed “trenchless”.
TRENCHLESS TECHNOLOGY METHODS NEW INSTALLATION REHABILITATION AND RENOVATION
NEW INSTALLATION MICROTUNNELING HORIZONTAL DIRECTIONAL DRILLING SHORT DRIVE SYSTEM GUIDED DRILLING
MICRO TUNNELING Only excavation required is for drive and reception shafts. Can be used in almost all types of ground conditions. First step, soil is converted in to slurry using water or betonies. Temporary steel tubes are jacked in and removed at next manhole position. Only indication on the surface is the presence of a control container with a hoist for lowering pipes in to the drive shafts. Noise levels and traffic disruption minimized.
HORIZONTAL DIRECTIONAL DRILLING These are nowadays widely used for installing pressure pipes under major obstacles such a motor way intersections, large rivers and airports runways. The first stage consists of drilling a small diameter pilot hole along the desired centre line of a proposed line. In the second stage, the pilot hole is enlarged to the desired diameter to accommodate the utility line and to pull the utility line through the enlarged hole. As the pilot hole is being drilled, bentonite-drilling mud is pumped down the center of the drill rods. The drill head consists of either a jetting head or drill bit. Before the start of back reaming the pipeline has to be positioned on rollers in line with the hole to minimize any axial load on the line.
ADVANTAGES Speed of installation combined with the minimum environmental and social impact. Method involves minimum surface damage Save a lot of time and expenses. Great importance in congested urban areas where the numbers of underground utilities are high often very little space is available. River crossings, the effect of buoyancy and danger of river bed erosion are eliminated as the utility can be installed.
DISADVANTAGES Special equipment and very high degree of operation skill is required. As the cost of the equipment and the operation are high, bore length should be sufficient in order for it to be economical. Mainly steel pipe is being installed by the method.
AUGER BORING Utilizes rotating head to excavate Head is recovered at an exit pit for the adjacent length of the pipe. Used in the range of 100-1000mm diameter Requires bore pits at both entry and exit points. Pipe size from 100-1500 mm and avg bore length btwn 53-68 m Major advantage is casing is installed at same time as bore hole excavation. Requires different sized cutting heads and auger sizes. Difficult to use in soils containing large boulders.
IMPACTMOLING Pipe size is generally limited to 6 inches or less. The span lengths were limited to 60 feet (18 meter) with 40 feet being optimum. Any type of pipe or cable can be installed. Applicable in most ground conditions.
ADVANTAGES Rapid, economical and effective method for installing small diameter lines Any type of utility line can be installed using this method. Stability of soil around the borehole is increased due to compaction Investment in equipment is minimum.
DISADVANTAGES Compaction methods are limited in length by reliability because basic systems are unintelligent Unguided tools tend to bury themselves, surfaces in the middle of road or damage existing utility lines.
ROD PUSHINGA bore of diameter 50 mm is formed by displacement. Rod is advanced by a straight hydraulic push and pilot hole may be back reamed to required size. Used for installation of pipes and conduits up to 15mm dia over lengths of 30-40 mm
PIPE RAMMING & THRUST BORING Suitable for most soil types except solid rock formations. Cost saving alternative to open trenching, pipe jacking methods. Pipes up to 2000mm dia can be laid using this technique.
GUIDED DRILLING Itemploys an excavation or soil displacement with compact light weight rig for rapid mobilization.
PNEUMATIC PIPE BURSTING Air powered hammer mounted inside bursting head. Constant tension winch designed to facilitate extraction of burst head. Excavation cost reduced. Bursting head bursts damaged pipeline and new pipe is pulled in. Lubricants used for larger and longer bursts. HDPE pipe is used.
STATIC PIPE BURSTING Preferable in clayey soils . Existing pipelines can be replaced without opening up ground. Mole is used as bursting head. Small power source is used to drive mole .
PIPE EATING Based on micro tunneling. Defective pipe excavated together with surrounding ground. Consists of micro tunneling shield. Shield has larger diameter than existing pipe. Pipe fragment can be removed by 2 methods1. Vacuum excavation2. Slurry pumping
Contd.. Pipe eating shield is pushed forward using hydraulic jacks. Replacement pipes are connected to the back of tunneling shield. This technique can be used to replace clayware,concrete,asbestos pipe etc.
CURED-IN-PLACE LINING Fabric impregnated with polyester or epoxy resin is inserted in to defective pipe & inflated against pipe wall. Cured by hot water, steam or UV light. The lining adjusts to variations in pipe size. Used for the rehabilitation of gravity sewers etc. Usually results in no loss of capacity.
CLOSE-FIT LININGS It is deformed through a swage a metal dye) or manufactured in folded state. Spirally wound liners are a form of close-fit. Useful for emergency repairs and for strengthening weak pipes.
SLIP-LINING Involves putting a pipe within a pipe and grouting the resulting annulus between the pipes. Causes reduction in capacity. Modifications are introduced to reduce thickness of liner and size of annulus.
SPRAY LINING Cement or resin is used. Cost effective. Ease of transport Mobilization of equipment.
COATINGS Used to repair cracks To protect from corrosion ,mechanical abrasion. Manual coating possible for pipes with a minimum of 1.21 m diameter. No extra work or equipment needed.
CEMENT MORTAR Applied to concrete, steel or iron pipes. Service life extended up to 50 yrs. Made of 1 part sulphate resistant cement to 2 parts sand. Cannot be applied in pipe networks with many bends, or in very cold regions.
REINFORCED GUNITE Also referred as “SHOTCRETE” Mixture of cement, sand and water. Steel reinforcing mesh attached inside pipe. Improves structural integrity of system. Can be used on varying cross-sectional profiles. It reduces internal diameter of original pipe. Reduces coefficient of friction. Application restricted to pipes of dia greater than 4ft.
RESINS Coating are made of polyurethane, phenol epoxy or poly urea. Can solve problems of corrosion and erosion. Can be applied to steel or concrete pipes. Excellent adhesion and impermeability.
GROUT Grout is a variety of materials used to fill voids, stabilize soil, hold bricks in place, coat cement & prevent infiltration. Used here to seal the joints between segmented concrete pipes. Used to seal off ground water infiltration in non pressure pipelines. Adapts well to irregular surface.
LIMITATION & ADVANTAGES OF GROUT Limitations AdvantagesNot a structural repair Stops groundwater from leaking inRequires highly skilled operators Stabilizes soilDifficult to seal actively infiltrating Fills void around pipe jointsPacker will not seal properly in badly Is a long-term, inexpensive trench less corroded pipe technologyNot for small- or large-diameter pipe Well suited to 10- to 15-in. pipeCan make small cracks biggerPipe must be thoroughly cleaned and in good condition (no protruding taps or broken sections)
TRENCHLESS TECHNOLOGY ININDIA Brihan Mumbai Municipal Corporation for the construction of 3m dia. Tunnel by micro tunneling. MTNL in Delhi, kolkata installing large telephone cables by T.T.in Delhi 185 k.m line is made by this. Pipe line laying below river bed is impossible by open trench method, pipe line laying below Hoogly river by this technique is sufficient to say its importance In Varanasi(u.p) an urgent repair for brick sewers is successfully done by this In kolkata 700m length and .762 dia. Iron pipe was repaired which started leakage. Laying of 18’ dia. Pipe of HBJ across yamuna river is accomplished by this technique 1719m gas pipeline was laid 35mbelow gautam-godavari river in 1994 3 underground crossing of 24’ dia. And 350 long pipes were completed by Indian Oil Corporation for panipat refinery.
NEED FOR TRENCHLESSTECHNOLOGY The disadvantages and difficulties encountered in conventional trenching methods have resulted in thinking of the need for trench less technology. The advantages of the no-dig technology are also responsible for the need of this technology to be adopted in mainly urban areas
OPEN TRENCH METHOD – As the open trench is going to create obstruction roads, busy areas, diversions have to be provided before start of any digging word. – As the obstruction is created, the traffic has to be rerouted causing traffic jams. – Original users of the road have to undergo hardships in the form of additional mileage as well as time. – Many a time, while cutting deep trenches in congested areas appear in the adjacent buildings. – Another difficulty, which is encountered very often is the damage caused to other service lines or cables present underground, providing temporary supports to these lines during the construction is cumbersome and costly affair. – Trenches left open overnight should be fenced and barricaded. Hand of mechanical signs should be used where necessary.
CONTD.. – While cutting open trenches, trees, shrubs, gardens etc. may have to be destroyed damaging the environment. – If any rehabilitation or renovation is required, the trenches once cut and refilled should again be cut through out and refilled causing difficulties to the public; that is, cutting and refilling is required at frequent times
ADVANTAGES OF NO-DIGTECHNOLOGY It reduces damages of valuable surface. It reduces the danger of improperly compacted excavations. It saves resources. It is accident free. It avoids traffic jam. It makes the use of the line (track) of the old pipe possible. It saves underground space (pipe busting). It reduces the impact on the environment. It provides the hassle-free road surface. It is possible to lay service lines across railway track, narrow lanes etc. When open trenching is impossible. Presence of a canal, pond, river etc. across the root poses no problems to the trench less technology systems. Without disturbing the traffic and life on the surface, the lines can be laid below ground in a much shorter time by using this technology. For replacement, repair and rehabilitation of old water and sewer lines in cities, it is very helpful to use trench less technology without disturbing the normal life on the surface.
CONCLUSIONPlanners need to understand the opportunities that the alternative TT has tooffer. Designer must design with the knowledge that a wide range of TT andtechniques are already available with continuing economic advantages.Likewise with trench less installation, refurbishment and rehabilitationtechniques, a wide range of social technical and economical advantages willalso be readily available. High level strategies within the utilities to utilize theavailable technology must be encouraged. This implies developing anunderstanding of the value of the application of technology and linking thisclosely with asset management strategies already in place. Once there isgreater awareness of the impressive state of development that T.T industryhas achieved when advantage is taken of the range of technique equipmentand material that already exist and when the traffic authorities and utilitiesrecognize the need for and advantage of T.T then the true potential of no-digtechniques will start to be realized.