Shaft construction

Shaft construction concerns the building of vertical openings such as Raises and Shafts. Shafts are vertical openings used for supplying equipment, personnel, and support systems to the horizontal tunnel where the pipeline is installed. They can be temporary or permanent, Which need large size excavations.(https://eservices.wsscwater.com/bcconnect/bicounty/BICOUNTY/FAQs/(R. Tatia 2005)

In this report we will addresses the different construction methods and different applications of shafts and raises, and during that we will also talk about the advantage and disadvantage of each method. In addition, we will talk about their impacts on surrounding infrastructures and environment, resource requirements, appropriate soil conditions, site layout requirements and finally we will have a rough cost estimation.

Definitions, applications, shapes

Raisings

Raisings are driven in the upward direction. They can be vertical or steeply inclined. During raising, gravity assists in drilling and mucking, thereby making the process faster and cheaper. (R. Tatia 2005)

hafts

Shafts are vertical openings which are driven downward. Decisions about the size, shape and positioning of shafts and raisings are taken based on the purpose they are intended to serve. (R. Tatia 2005)

Usually circular shafts are preferred in almost all situations because they are very stable. Also, when strata should be built, we can use the advantages of rectangular or elliptical shafts and use their cross sectional areas. (R. Tatia 2005)

Applications

According to (R. Tatia 2005) applications of raises and shafts are listed below:

Hydro-electric projects
* surge chamber
* ventilation shaft
* elevator shaft
* pressure shaft
* cable shaft

Water supply
* access or service shaft
* ventilation
* supply riser
* uptake or down-take shaft

Waste water shafts
* drop shafts

Tunnel projects
* ventilation
* accelerators housing
* access

Raise driving techniques

One classification for the raises is based on the application of explosives, that is to say with and without explosives while driving. (R. Tatia 2005)

The line diagram below shows a classification of raising techniques: (R. Tatia 2005)

Conventional methods

* the open rising technique is used in driving short raises which are less than 10 meters.
* Compartment method

Raising by mechanical climbers: Alimak raise climber

Alimak Company introduced this technique in 1957, and even today it is often used in driving blind raises which have long lengths.

The Alimak raise climber is designed to drive raises up to 100 m long, or more. There are several kinds of climbers available: pneumatic, electric and diesel (hydraulic driven).

The following are important features of this technique:
* it makes it possible to drive very long raises, vertical or inclined, straight or curved and mostly rectangular shape.
* The raise climber can be driven into a safe position using backward guardrails.
* Because of its features for blowing air and water at the face after blasting, risks of foul gases are eliminated, and the time required for ventilation is reduced.
* An additional extension piece can be connected to the platform

Blast hole techniques

* Long hole raising
* Drop rising

“Drop rising” technique is the advanced version of the “long hole raising” technique. This technique is based on the vertical carter retreat (VCR) concept. The crater has five holes, one of the holes is at the center and the other four are at the corners. In this method (DTH) drills, drill parallel holes in the raise direction. After that holes are blasted in stages. Raises of longer lengths, up to 150 m, can be drilled using this method.

Raising by application of raise borers

This technique can be used to drive a raise between 2 levels in the ground. Using this technique, Raises have been drilled successfully even in poor ground where the soil condition is not very good. A circular shape is obtained from this technique. In this technique, the machine is set up at the top and drills a hole of 225 to 250 mm diameter, to get to the lower level. After that a large reamer bit is put on at the bottom of the drill rod and then it reams up the raise.

We can execute the reverse procedure by the machine; however, this option is not very popular.

Raise borers can drive in soft ground and hard ground, and such units are useful to drive raises and shafts up to 6 m diameter,

This method has the advantages like, faster rates, better safety for working crews and least disturbance to the rock structure.

By using this method the holes by the following properties is driven before:Shaft length, 1000 m, Diameter .6 to 6 m (R. Tatia 2005)

haft sinking

Applications of Shafts: (R. Tatia 2005)

Shafts are usually used for the following purposes:“
* Mining mineral deposits
* Temporary storage and treatment of sewage
* Bridge and other deep foundations
* Hydraulic lift pits
* Wells
* In conjunction with a tunnelling system or network, for the purpose of lifts, escalators, stair and ladder ways, ventilation, conveyance of liquid, carrying pipes and cable in river crossing, drainage and pumping, particularly from sub aqueous tunnels.”

They also can be temporary or permanent,

(R. Tatia 2005) has classified the techniques which are used for sinking shafts:

Activities required for Shaft Sinking :

we can divide the operations for sinking a shaft into three parts: (R. Tatia 2005)

# Reaching up to the rock head
# Sinking through the rock
# Sinking through the abnormal difficult ground, if any, using special methods

A sinking cycle includes the following operations: (R. Tatia 2005)
* Drilling
* Blasting
* Mucking and hoisting
* Support or shaft lining
* Auxiliary operations
** Dewatering
** Ventilation
** Lightning or illumination
** Shaft centering

Drilling

We use sinkers to drill holes of 32-38 mm diameter ,The length of the holes vary between 1.5 to 5 meters.

There are three types of cuts
* Wedge cut
* Step cut
* Pyramid cut

1 and 2 are common drillings that are used and in rectangular shafts. Wedge cut is used most of the time. Pyramid cut is often used in the circular ones. Step cut is adopted if water is high and the shaft is of a large cross section.

Blasting

In practice, at the bottom of shaft is usually full of water during sinking. therefore, high density, water-resistant explosives are used.

Lashing and mucking

Lashing is made for the loading of muck into a conveyance for its disposal.This activity is a time consuming activity due to Presence of water, limited space.

upport or shaft lining

There are two types of lining,
* Temporary
* Permanent

The type of water and strength of the rock and soil layer where sinking operation is done determine which option to select. Therefore, in some cases, temporary support is not adopted, while in others it becomes essential to protect the crew and equipment from any side fall.

The permanent lining can be made of bricks, concrete blocks, monolithic concrete , shotcrete and cast iron tubing.

Auxiliary operations

* Dewatering: When the shaft is reached to the water table or beyond it, water inflows inside it, to remove this water usually face or sinking pumps are used.(tatiana) Removing water can also be done by driving deep wells or well point systems around the shaft, that results in lowering the water table around the shaft.(zhou)
* Ventilation: Fresh air, supplied by a forcing fan installed at the surface, which can be provided by rigid ventilation ducts for below 6 m depth or flexible ones for more than 6 m depth.
* Illumination: A pneumatically operated light , is used to provide illumination at the working face during construction work.
* Shaft centering: Using the reference points, which are fixed before , to fix the shaft center. The shaft center is checked from time to time by the use of centering device installed at the surface.

pecial methods for shaft sinking.

In the process of shaft sinking , it becomes necessary to adopt a special method if the ground through which the shaft is sunk is loose or unstable such as in sand , mud, gravel, or alluvium, or when an excessive amount of water is encountered, which cannot be dealt with by sinking pumps. In some situations , both sets of these conditions my be encountered. Listed below are special methods that can be used to deal with the situations outlined above:

# piling system
# cementation
# freezing method
# grouting
# shotcrete

1. Piling system (Soldier pile):

These piles are driven and after installing the steel beams can be concreted .Piling method and the spaces between piles depend on the soil conditions. (Fangyi Zhou, 2006)

3. Freezing method

”Sometimes when we can’t control the groundwater by pumping, we may use freezing or grouting. This procedure consists of sinking pipes around the area to be excavated and circulating and circulating a cold brine solution through the pipes, thereby freezing a wall of soil, this process needs 2 months to complete,” . (Fangyi Zhou, 2006)

4. Grouting:

In this method we drill rows of grout holes around the shaft perimeter, then inject grout into them, but freezing is more reliable comparing to this,

5. Shotcrete:

Shotcrete is sprayed concrete can be applied immediately to freshly excavated rock

Impact on surrounding infrastructures

Shaft sinking can have the following impacts on the infrastructure and environment around it:
* blocking the streets and causing traffic in the area around it
* making noise and dust which can bother the people around the construction area
* bad effects on soil because of making vibrations in the ground while construction
* cutting some trees and clearing the area for construction site

(https://eservices.wsscwater.com/bcconnect/bicounty/BICOUNTY/FAQs/Tunneling+Impacts/)

Appropriate soil conditions

The appropriate soil condition For each method is mentioned during the construction method, and if the soil is not strong, we should use piles and temporary linings to take care of that The space between columns depends on the soil conditions and amount of ground water existing, piles can be close to each other or have the appropriate distance.

However, strong and consolidated soil is the most appropriate soil for driving shafts.(class lectures)

ite layout requirements

Tommelein (1989) defines Construction site layout and its benefits as below:

blockquote
“ identifying the facilities that are temporary needed to support construction operation on a project but that do not form apart of the of the furnished structure: determining the size and shape of these facilities; positioning them within the boundaries of the available on-site or remote areas” (Fangyi Zhou, 2006)

blockquote
“the so called temporary facilities usually remain on site for a period ranging from a few days to several months or even years, a time period that ranges from duration of a construction activity to the duration of a major phase of the entire construction period”(Fangyi Zhou, 2006)

blockquote
“ a well-organized site facilities inventory control , cuts travel times, reduces noise and dust, prevents obstructions and interference, increases safety and security, and improves site access” (Fangyi Zhou, 2006)

According to Fangyi Zhou, considerations affecting the site layout are shown below:

Efficiently using site space to accommodate resources throughout a construction project is fundamenta to success of project.

So optimizing the construction site layout using models such as physical and computational is the interest of many researchers.

(Fangyi Zhou,2006)

Site Layout has a great effect on project costs, therefore, models are used to simulate the different site layouts and choose the best one. (Fangyi Zhou,2006)

Resources required: (cost estimation for shaft, City of Edmonton,2005)

Human resources

Equipment operators, labourers and workers, foremen, supervisors

Equipments and machines

* Drill rig, compressor, excavators, explosives
* Cranes, hoists, trucks
* Welding truck
* Lumbers (laggings), liners, ribs, tie rods, support beams, tie wire
* General purpose concrete, concrete forms, concrete pump, rebars
* Water pumps
* Illumination and electrical equipment
* Communication systems
* Personal protective equipment
* Ventilation System
* Instrumentation to determine the concentration of flammable gases

References

Tatiya, Ratan. (2005) Civil excavations and tunnelling: a practical guide, Thomas Telford ; London , Reston, VA : Distributed in the USA by ASCE Press.

Zhou Fangyi (2006). “an integrated framework for tunnel shaft construction and site layout optimization” Master Thesis, University of Alberta, Edmonton

External links


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