microtunnling

ADVANCE CONSRUCTION PRACTICE

1 INTRODUCTION

1.1 General Introduction Microtunneling is a underground method of constructing pipelines using a

sophisticated, remotely controlled, laser guided, steerable boring machine. In Mocrotunnling, the pipe is installed using pipe jacking method by pushing pipe

section through the ground with the hydraulic jacks from a shaft excavation is called jacking pit to another shaft is called receiving pit.

Excavation is carried out by the microtunnling machine in front of the lead pipe section as the pipe line pushed forward from the jacking pit.

It is used for networks with diameters generally ranging from 500 to 1500 mm and which can go up to 2000 mm

1.2 History Techniques are relatively recent; the first boring machines were used in Japan

during the 1970s. In US it is used in 1984 in Miami ,Florida In France, the first site was constructed in 1989 in the Val –de-Marne department

at the instigation of the water and sanitary drainage services. In India Michigan Engineers has been the first Indian company to execute a

micro-tunneling project in Kolkatta 1997 for relocation of sewer lines at Ghariahat Junction. In Mumbai, Aject (Saudi-based) company had executed a project ('97-'99)

Manish Patel (CP1209) of 23


2 TECHINIQUES AND THEORY OF OPRATION

Microtunnling Process1) Thrust Pipe2) Crane3) Control Container4) Injection Pump5) Decantation Container6) Jacking Shaft7) Receiving Shaft8) Thrust frame9) Pipes10) AVN Cutting head11) Generator

2.1 DIFFERENT FUCTION OF MICROTUNNLING

All types of boring machine have the following function in common: Mechanized ground excavation and stabilization of the face Disposal of rubble (or mucking) Monitoring and correction of trajectory Installation of pipelines by jacking


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2 34 5

6 7

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10

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2.2 DIFFERENT PARTS OF MICROTUNNLING

for sandy- gravely soil for coherent soil

for rock



3 PARAMETERS AFFECTING WORK AT SITE

3.1 Rate of Penetration

Duration of Pipe jackingTotal pipeline = 1838mCohesive Soil = 507mFine Sand = 855mSand and Gavel = 476m

Average jacking time for pipe (2m)

Total duration of the cycle (installation/connection/jacking/maintenance)

Clay 70min 120min

Fine Sand 16min 60min

Sand and Gravel 38min 90min

3.2 Alignment of deviation



3.3 Frictional Forces Pipe friction is an important consideration in microtunneling as it affects a number

of key the issues that have direct impact on the success of installing the pipe (i.e. completing the drive) and also the cost of the project.

When jacking a pipe through the ground the friction generated along the pipe is the fundamental factor as it determines the total jacking force required to install the pipe.

The magnitude of the jacking force affects the pipe strength requirements, capacity of the main jacking system, maximum possible drive length, number of shafts required, the need for intermediate jacking stations, and the capacity of the thrust wall to provide a reaction for the main jacks.

All of these factors will influence the feasibility, construction plans, and/or cost of the project.

Frictional forces depend upon… Pipe materials Type of Soil Depth of Boring Type and amount of lubricant Details of microtunneling equipment and methods

3.3.1 Pipe materials Reinforced Concrete Steel Fibreglass Polymer Concrete Clay



Ductile Iron

Advance materials for Pipe jacking

One new pipe that has been used for several recent projects in California is polymer concrete jacking pipe made in Germany (Bloomfield, 1994). Polymer concrete pipe is constructed using polyester resin instead of cement as a bonding agent. It has high strength (typically 12,000 psi or higher) and is inherently resistant to corrosion due to chemical attack. In addition to its high strength, this pipe has numerous advantages for microtunneling, including a smooth pipe surface and very consistent and physical dimensions (i.e. tight tolerances). Both of these advantages minimize pipe friction and the high strength reduces the potential for damaging the pipe during installation. This is a very good pipe for sewer pipelines due to the excellent corrosion resistance of this pipe material.

A new type of steel pipe manufactured in the US that could be used as a casing is called Permalok. This pipe has a mechanical joint that does not require welding, and is much easier and faster to install than a steel casing with welded joints (Argent et al. 1995). Permalok is also easier to steer than a welded steel casing because it is less rigid at the joints. The manufacturer is working on developing a pressure joint design that is designed to be an acceptable carrier pipe in a low-pressure application

3.3.2 Type of Soil

The project involved the installation 42inch ID polymer pipe in clay soil ranging in strength from soft to stiff jacking force range from o.oo7 to o.o34 tsf for six drives



3.3.3 Depth of Boring

L

F= f*3.14*D*dl

0F = Frictional forcesf = dynamic frictionD = Depth of Boring

As per equation as depth of boring increase frictional force also increase.

3.3.4 Type and amount of Lubricant Utilizing an effective pipe lubrication system can minimize pipe friction.

Minimizing pipe friction and jacking loads has a number of important benefits such as promoting longer drive lengths, minimizing the number of shafts, and reducing the risk of pipe damage during installation.

An effective pipe lubrication system involves providing adequate overcut to create annular space outside the pipe, use of appropriate pipe lubricants, and injecting lubricants continuously under pressure as the pipe is advanced. The quantity of lubricant injected should at least be equal to the theoretical volume of the overcut. When effective lubrication procedures are implemented jacking forces can be reduced by up to 50 %.

Because of the importance of minimizing pipe friction there is a considerable interest in utilizing appropriate pipe lubricants. As well as reducing pipe friction, pipe lubricants provide another important function, which is to stabilize the annular void created by the overcut around the pipe.

Clay soils may swell around the pipe and gradually reduce the annular void, eventually contacting the pipe. Coarse-grained sands and gravels will collapse onto the pipe eliminating the overcut, unless the pipe lubricants injected outside the pipe can stabilize the soils and maintain the annular void. If the annular void is lost, pipe lubricants cannot be effectively injected around the pipe and jacking forces will increase considerably.

Pipe lubricants typically employed include bentonite, polymers, and bentonite/polymer mixtures. The choice of the proper lubricant depends on the type of soil. Bentonite, which has traditionally been used for lubrication in all soils, is considered to be most effective for coarse-grained sands and gravels. In these soils, it is important to stabilize the annular void with the lubricant and sometimes additives are used to create a thick lubricating paste that will support the soil. For fine-grained cohesive soils, polymers are believed to provide better



lubrication characteristics. These polymers can also be beneficial in stiff, high plasticity clays as they can reduce the swelling characteristics of the soil by maintaining the clay at its natural moisture content. For intermediate soil classifications, e.g. mixtures of fine- and coarse-grained materials, bentonite/polymer mixes are sometimes used. Polymers include a wide variety of organic and semi-synthetic materials. Most polymers are bio-degradable and environmentally benign. A number of different polymers have been introduced into the market in the last few years in an effort to develop polymers with improved lubrication characteristics.

3.4 Overcut Overcut defined as an annular space between the pipes and soil for the reduction

of the friction. Small diameters pipe small overcut Generally ranges from 10mm to 30mm

3.5 Main hitches at site

3.5.1 Blocking of the Machine Due to…..

Various boulders and obstaclesExcessive frictionAbrasiveness of the soilSticking of clay

3.5.2 Damaged PipesThe drive thrust is no more center of the axis of the pipe and the distribution of the load is no more uniform, which lead to a concentration of stresses and cause damage the pipe.

3.5.3 Surface Distribution Due to…

Closing of annular spacesImproper balancing of pressure at the face,Excessively high injection pressure of lubricant

3.5.4 Excessive rollRoll is the rotation of the entire boring machine with respect to its longitudinal axis. To limit the roll, the trailing tube of the machine is usually equipped with “fine” that help stabilized the machine body. A large torque or premature



lubrication may favor roll. A Large roll can be cause the rupture of cable connections on the machine.

4 GUIDELINES FOR INVESTIGATION

4.1 Data to be acquired Geological configuration of the site Hydrogeological condition Geotechnical characteristics of the ground Cavities and artificial obstacles Environmental Condition

4.2 Geophysical Method



Method Area of application

Advantages Drawbacks

Geological radar Detection of interfaces, various networks and obstacles

Rapid, Not very cumbersome

Tricky implementation and interpretation

RMT (radio-magnetotellurgy)

Geological identification of soil and buried obstacles

Continuous profile, very rapid, Good lateral resolution

Investigation depth not controlled, Disrupted by metallic networks

Electromagnetic method

Geological identification

Easy to implement and efficient

Discontinues profile, Frequent interference

Seismic refraction

Looking for a dimension of a substratum

Rapid method, Continuous profile

Preferable to work at night, under water

Seismic surface waves (SASAW)

Identification of hard and loosed spots.

Assumed stratified ground

5 PIPE JACKING PROCESS



6 SHAFT CONSTRUCTION

Some of the new developments in shaft construction involve the use of jet grouting and ground freezing methods for groundwater control and excavation support. These approaches may be necessary when dewatering cannot be allowed because of cost reasons such as where groundwater contamination is present, or where shafts are in close proximity to structures that could be damaged if settlement was to occur as a result of dewatering.



Jet grouting involves pressure-injecting a water/cement grout into the ground and mixing it with the soil using rotating jet pipes under an extremely high pressure (typically 4,000 to 6,000 psi). This technique creates a mix of grout and soil that hardens to provide a compressive strength typically ranging from about 100 to 300 psi or more. Usually, the jet grout holes treat a 3- to 4- foot-diameter zone of soil and the holes are overlapped to stabilize a certain volume of soil. With proper use, jet grouting creates a relatively strong and homogeneous material with increased strength and reduced permeability. Jet grouting methods are applicable to almost all types of soils (Welsh, 1992). Usually a grid pattern is used to provide for overlap of the jet grout columns both at the base and/or along the sides of the shaft excavation. The Nimitz Highway Reconstructed Sewer microtunneling project in Honolulu used jet grouting extensively to provide a groundwater cutoff at the bottom of sheet pile supported shafts.

Ground freezing is used to form a solid wall of frozen ground in unconsolidated water-bearing strata around the perimeter of a shaft excavation. Typically, freeze pipes through which brine is to be circulated are placed around the perimeter of a shaft excavation and the freezing proceeds outward from each pipe until the frozen zones around adjacent pipes overlap. This forms a continuous cylinder of frozen ground, which protects the area to be excavated from groundwater inflows and stabilizes of the excavation walls. Shaft excavation does not proceed until the freezing is complete, a period which may range from a few weeks to several months. In the US, ground freezing has usually been regarded as a last resort, as a remedial measure, or employed where dewatering or grouting either was not feasible or failed to provide adequate groundwater control. This is probably due to the relatively high cost and the specialized nature of this technique. Ground freezing was used for groundwater control in shaft excavations for the Duwamish River crossing located near Seattle that was constructed using microtunneling methods in 1994 (Post, 1997) and also for a recent project in Santa Monica, California

7 RESEARCH PAPER

GEOPHYSICAL TECHNIQUES FOR IDENTIFYING OBSTRUCTIONS

By: Steve Klein

University of NevadaManish Patel (CP1209) of 23


Las Vegas

Obstructions are objects that conflict with the planned pipeline alignment and are capable of preventing the forward progress of the microtunneling machine. Typically, such obstacles may consist of boulders, cobbles, trees, and construction debris such as timber piles, sheetpiles, abandoned utilities, concrete, timber, bricks, and metal objects.

Identifying such obstructions is important because of the serious consequences of encountering one with a microtunneling machine. It is potentially a fatal flaw if surface access is not available to recover the machine or remove the obstruction.

It may be necessary to modify the pipeline alignment, require special machine provisions, have a provision for recovery shafts, or other contingency measures. In order to be able to adopt the proper approach it is critical to evaluate the possibility of encountering obstructions and, if it is not possible to avoid the obstructions at least determine the nature and sizes of the obstructions.

Due to the difficulty in being able to locate obstructions with conventional small-diameter boreholes, there is a considerable amount of interest in two geophysical investigation techniques that may be able to locate obstructions more effectively.

One of these is a new seismic technique known as seismic imaging or the Site Uniformity Borehole Seismic (SUBS) method (Clark et al., 1995). This method has been used on some recent microtunneling projects on the West Coast.

The SUBS method produces a seismic topographic image of the seismic velocity distribution of materials around a borehole. This is achieved with detectors placed down a borehole at several depths, which record the response due to a surface energy source applied at various distances from the collar of the borehole.

This recorded image allows subsurface features, such as obstructions to be identified at distances from the borehole of up to about three times the borehole depth.



SUBS Concept for Detecting an Obstruction

Ground penetrating radar (GPR) uses the principle of the reflection of electromagnetic signals to locate buried objects. This technique has also been used for identifying voids near the ground surface and for locating underground utilities.

When the signals encounter a material with different dielectric properties a portion of the signal energy is reflected back to the surface. In order to be detectable an object must have sufficient electrical contrast with the surrounding ground.

Therefore, metallic objects are generally easily detectable whereas wood or concrete may not have sufficient contrast to be detected.

GPR measurements are obtained by towing an antenna over the ground surface. If the electromagnetic wave hits a buried object, it is reflected back to the ground surface and the signal is captured and recorded.

One disadvantage of this technique is that the effective depth of a GPR survey can be limited. At some projects, the observed penetration in wet sand was about 30 feet, but in clay the penetration was only about 6 feet (Miller, 1996). Small amounts of clay in the formation or groundwater can quickly attenuate the signal.



GPR Survey Concept for Locating Obstructions

GPR surveys were conducted for the Tanner Creek Stream Diversion Project in Portland, Oregon to help address the potential for encountering obstructions in a 500-foot section of the 72-inch pipeline to be installed using microtunneling/pipe jacking methods where man-made fill materials with buried debris was known to be present.

Three antennas were used for the survey at frequencies of 25, 50, 100 MHz. Ten potential obstructions, 2- to 12-foot wide, were identified at depths of 10 to 33 feet but only three at the depth of the proposed pipeline. The nature of these potential obstructions is unknown and pipeline could not be relocated to avoid these features, therefore provisions for obstruction removal shafts (sometimes called recovery or “911” shafts) were included in the contract documents.



8 CASE STUDY

Waste Water Pipeline Project in Poland

Project in Poland's capital Warsaw is expected to be completed mid summer 2008: To relieve the down-town sewer collector and to transport wastewater to the new treatment plant "Czajka," astounding 3.3 km large diameter (up to OD 2160 mm) HOBAS CC-GRP Jacking Pipes are installed by remote controlled jacking (microtunneling) and were literally driven around several bends.

These projects along with project requirements such as installation depths up to 10.6 m

Established up to 2 m below groundwater level.

Waste water pipe project in Poland's capital Warsaw is expected to be completed mid summer 2008: To relieve the down-town sewer collector and to transport wastewater to the new treatment plant "Czajka," astounding 3.3 km large diameter (up to OD 2160 mm) HOBAS CC-GRP Jacking Pipes are installed by remote controlled jacking (microtunneling) and were literally driven around several bends.

Trenchless technologies are the most convenient and reasonable way to install a pipeline in a city where traffic and buildings above ground but also dense infrastructure below ground need to be considered. Numerous microtunneling projects have been successfully implemented with HOBAS CC-GRP Jacking Pipe Systems in Warsaw before. These projects along with project requirements such as installation depths up to 10.6 m convinced the municipality, waterworks and designer to once again opt for a trenchless solution. Furthermore, the installation method per se saved on pumping costs as the line was partly established up to 2 m below groundwater level.

The competition was tight and material prices for sure did not speak for GRP. HOBAS undoubtedly convinced in different respects such as offering extensive experience, know-how and reliability in curvilinear jacking. As so often, a second more thorough glance showed that the higher material costs were considerably outweighed by savings through, for instance, a 30% reduction of extracted soil thanks to smaller consistent outer diameters of the comparably thin walled CC-GRP Pipes. Construction sites and construction equipment could be kept small and to a minimum, for pipe size and weight surely mattered also in this case. Fast assembly and small curve radii were further cost saving advantages that spoke for



HOBAS, not to mention the high corrosion resistance, long life expectancy of the products, low maintenance costs, etc.

The 3.3 km line runs in 4.7 and 10.6 m depth and includes 6 curves with 200, 300 and 600 m radii, the longest curve being 124 m at an average gradient of 0.063%. Sand and clay are the main soil components on the route and a part of the pipeline is assembled below groundwater level.

HOBAS Poland delivered CC-GRP Jacking Pipes in 1 m, 1.5 m and 3 m lengths for the different radii and straight sections. Since the absolutely leak-tight flush HOBAS Couplings incorporate a certain angular deflection, smaller curve radii are achieved by utilizing shorter pipe sections. Although not absolutely necessary, HOBAS Experts recommended the use of wooden rings between the pipes in curved sections in order to guarantee a perfect fit. An intermediate station that was run in the curve was a novelty that required a special design for the consequent station as for the steel pipe of the intermediate station itself.

Challenges of the Project Clearance of only 0.6 m between the pipeline and subway were easily overcome. Precise planning and the relatively small outer diameter of HOBAS Pipes were

imperative for this remote controlled jacking project. A single jacking drive over 500 m was the technical highlight of the project. No

wonder: The close and well functioning cooperation between HOBAS Organizations is indispensable in every regard and allows drawing from a large pool of technical expertise for top quality customer solutions.


Jacking Shaft



Laser Detector and Monitor

Different Types of Joint



Intermediate Jacks

Control Cabin


9 COST AND ENVIRONMENT IMPACT

The total cost of a pipeline rehabilitation/renewal project can be divided into components as shown in the following table.

Cost estimates can be obtained from a wide range of sources including



9.1 Direct Cost

Direct Costs are borne by the utility owner and usually include:A. Planning, Design and Supervision. B. Payments to contractors and suppliers. C. Diversion of flows and/or provision of temporary service. D. Permanent reinstatement of excavations.

Direct costs are the most easily measured and compared component of overall costs.

9.2 Indirect CostThese generally include any additional costs associated with a contract which are borne by the utility. Typical examples are:

A. Compensation for damages paid to other utilities and the owners of property and land. B. Compensation to businesses for loss of profits. C. Compensation to customers for any excessive service interruptions.

9.3 Social CostSocial cost related to construction work is numerous. The case histories reported in the paper considered the following six social cost categories:



10 REFERENCES

1) Microtunnling and Horizontal DrillingBy FSTT

2) 2001Klain_NewmicrotuntechUniversity of NevadaLas Vegas

3) TRC Guidelines

4) [email protected]

5) mtsprefecto_micro tunneling system.htm.


mailto:[email protected]

microtunnling

Documents

thrust pipe

jacking shaft

pipe line

jacking pit

lead pipe section

total jacking force

pipe strength requirements

advance consruction