Tunneling & Excavation Engineering (CEP)

Here we will discuss different tunneling and excavation methods to solve a complex engineering problem.

Complex Engineering Problem

Abstract

This complex engineering is in accordance with the course of tunnel engineering and shaft sinking. Tunnel is basically a horizontal pathway having both ends open.

They are used for different purposes like transportation, subways, water ways, railways etc. First, we do site investigation of the area upon which tunnel is to be excavated. We have to see different aspects, including seepage, roof heaving, soft ground conditions, hard ground conditions, faults, folds and other different lithologies.

Tunnels can be excavated either by drilling and blasting or by using mechanical excavators. Tunnels come in different shapes including circular, horseshoe, oval, cathedral arch etc. For a specific type of a tunnel there is a specific blast design which is to be followed to achieve that shape. Tunnels are designed according to the standards by AASHTO green book which gives details of different types of tunnels.

Thus, we have to design tunnel according to all the standards and blasting material to be used so that it can be used for transportation purposes.

Introduction

Tunnels

A tunnel is a long passage which has been made under the ground, usually through a hill or under the sea. A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in tunnel.

Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.

Types of tunnels

The different types of tunnels are as follows:

• Mine tunnels

These tunnels are used during ore extraction, enabling laborers or equipment to access mineral and metal deposits deep inside the earth.

• Public works tunnels

They carry water, sewage or gas lines across great distances. The earliest tunnels were used to transport water to, and sewage away from, heavily populated regions.

• Transportation tunnels

They are artificial waterways used for travel, shipping or irrigation. Just like railways and roadways today, canals usually ran above ground, but many required tunnels to pass efficiently through an obstacle, such as a mountain.

Site investigation

A site investigation simply is the process of the collection of information, the appraisal of data, assessment, and reporting without which the hazards in the ground beneath the site cannot be known.

Site investigation is carried out in order to enable a geotechnical and geo-environmental assessment of the ground conditions and analysis of the engineering and environmental considerations related to the proposed development.

Adequate investment in geological engineering investigation may account for as much as 3% of the estimated cost of the construction work.

This cost depends on factors such as: geological complexity, tunnel length and overburden thickness.

Below 3%, the number of tunnels where problems occur increases, while above it, unforeseen events are kept to a minimum.

Preliminary studies

Preliminary study is an initial exploration of issues related to a proposed quality review or evaluation. Preliminary studies do not happen in all systems, but they may be used to identify key features to be addressed in a quality process.

Blasting

Process of reducing a solid body, such as rock, to fragments by using an explosive. Conventional blasting operations includes:

1. Drilling holes,
2. Placing a charge and detonator in each hole,
3. Detonating the charge,
4. Clearing away the broken material.

Blast designs

A common case is of the conventional drill and blast technique, it is defined as follows:

The technique of rock breakage using explosives involves drilling blast holes by percussion or rotary-percussive means, loading the boreholes with explosives and then detonating the explosive in each explosive and then detonating the explosive in each hole in sequence according to the blast design.

Blast pattern design

One of the basic principles of designing the configuration and sequential detonation of blast holes in a one blast, is the presence of a free face parallel or sub-parallel to the blast holes, as detonation occurs. In some cases, these free faces may already be present benches in an open pit cases, these free faces may already be present but in other cases may need to be created by the blast itself.

Figures (1) and (2) below, demonstrate some common blast patterns.

Blasting techniques

During blasting, the explosive damage may not only occur according to the blasting round design, but there may also be extra rock damage behind the excavation boundary. to minimize damage to the rock a presplit blast (surface excavation) or smooth wall blast rock, a pre-split blast (surface excavation) or smooth-wall blast (underground) may be used to create the final excavation surface. These techniques include:

1. Pre-splitting.
2. Smooth wall blasting.
3. By using explosives.

Drill and blast summary

Drill and blast summary then show that there are some of the parameters which are controllable while some parameters are non-controllable, so we have to take a look over all the scenarios before drilling and blasting so that the tunnel we made does not cause any problem in future. Figure (3) shows a pictorial representation of the drill and blast summary.

Tunnel cross-sections

For road tunnels the cross-sectional shape is typically rectangular or circular. However, this may vary depending on the following factors:

1. Method of construction.
2. Geological setting.
3. Use of the tunnel.
4. Tunnel specifications (length and dimensions etc.)

Table (1) shows typical tunnel cross-sections along with their tunneling methods and some info.

Type of cross-section	Tunneling Method	Comments
Circular	Tunnel Boring Machine (TBM)	Recently extended in Japan for rectangular cross section
Rectangular	Immersed tube tunnel	In USA, circular cross sections are common
Rectangular	Cut and cover tunnel	Precast technology sometimes leads to circular cross sections above the carriageway
Horse-shoe	Blasting	Applied in hard rock
Circular crown and elliptical invert	Excavation sustainment methods	In hard rock, horse-shoe shapes are usual

Problem statement

The task assigned to students relates to their Tunneling and Excavation Engineering course. Each student needs to propose a tunnel for a specific application and then perform all the design and construction related research and calculations.

He/she is then to present those findings in the form of a report that he/she will submit to the course instructor. This will involve all aspects covered in the scope of this course and beyond. 

Scope

The tunnel proposed in this report is a road tunnel that will connect the residents of Islamabad with Khanpur Dam and its surrounding areas. The main advantages of this proposal are as follows:

• Promotion of tourism.

Those who have been to Khanpur Dam are fully aware of the recreational activities it provides such as boating, jet skis and barbeque points. Islamabad being the capital of Pakistan, gets tons of tourists from around the world and many of which would love to visit Khanpur Dam, thus bringing revenue into the country and promoting trade. 

• Shorter travel time to the target location.

The current route from Islamabad towards Khanpur Dam is quite long and time consuming. The most common route taken starts from Islamabad, Marvi Road, GT Road, Taxila and then ends at the Khanpur Dam Viewpoint. It’s approximately a 52.9 km drive and the average time taken on this route is 1 hour and 3 minutes in ideal traffic conditions. However, by construction of this tunnel, the time is reduced to under 40 minutes.

• Shorter travel time to surrounding localities.

This tunnel will also help those travelling to surrounding areas like Haripur and Abbotabad by reducing their travel times.

• The provision of a simpler route.

The straightforward route will make traveling far easier and a pleasant experience.

• Reduction of stress on current roads and pathways to target location.

The establishment of a newer more dedicated route to Khanpur Dam will no doubt reduce the traffic and commotion on other routes. Thus, avoiding unnecessary traffic jams and accidents etc.

Location

The proposed tunnel is to be 8.47 km in length. It is to be constructed in such a manner that it cuts through the Margalla hills that border Islamabad and exits directly at the road leading to Khanpur dam.

The tunnel will be a two-way tunnel and will have two access portals, portal A will be near Islamabad (33 ° 43’05” N and 72 ° 56’21” E) at the Margalla hill boundary and portal B will be near Khanpur Dam (33 ° 47’42” N and 72 ° 55’15” E) . Figure (4) below shows a map with the current route used in purple and the proposed route in black.

Literature Review

Geologic Information

The following formations are encountered throughout the tunnel:

• Hangu Formation

It consists of Laterite, lateritic claystone and sandstone with minor siltstone. Sandstone is reddish brown, weathers dark rusty brown, fine to coarse grained, pisolitic and ferruginous. These are exposed in Mountains situated in the north part of Main Boundary Thrust (MBT). The main part of the Hills are composed of these rocks.

Precambrian rocks consist of shale with intercalation of  limestone  layers.  Paleozoic rocks    consist of sandstone, shale, conglomerate, limestone and dolomite.

• Lockhart Formation

It is well-developed formation in the area. It consists of predominantly marine limestone and subordinate marl and shale. Limestone is pale gray to dark gray, medium grained, thick bedded, in part nodular, hard, bituminous, and fossiliferous. Marl is grayish black amid fossiliferous. 

The shale is olive, gray to greenish gray and has weakly developed cleavage. Thickness ranges from 70 to 280 m. Limestone has an average Los Angels Abrasion Test Value of 22.79 percent loss for 500 revolutions.  The average apparent specific gravity of the crushed rock is 2.69 and average absorption is 0.625. 

These are exposed in Hazara and Margala hills occupying the northern to central part of the area. They are in general black, hard and compact shale that are highly eroded along the bedding planes. The main part of the Haro River basin consists of these layers.

• Patala Formation

It comprises sandstone and shale.  Sandstone is grayish green to dark yellowish green, glauconitic, massive hard. Shale is greenish black, thin bedded and fissile.

These sequences cover the southern part of the area. The rocks in this category consist of alternation of shale and sandstone. This series can be divided into two groups.

One is Murree group of Miocene age and other is Siwalik group of Pliocene age. Rocks in these groups are generally weak, highly weathered and not able to endure erosion well. Among them, the shale is highly sheared and has turned into very weak red clay. The Soan river basin is composed of these layers.

Rock Conditions

The bedrocks in the study area are highly folded, faulted and over thrusted because of Himalayan uplift during Pliocene epoch. The deformational axes are running in ENE- WSW direction. Among the many deformational units, MBT is the major fault. It has considerably wide fractured zone accompanied with many derivative faults.

Tectonic Information

Some epicenters of earthquake have concentrated along certain part of this fault. The faults given below are present in the near vicinity of the Margalla Hills.

1. Main Boundary Thrust (M.B.T.) in ENE-WSW trend
2. The Main Boundary Thrust (MBT) is a long feature extending for several hundred kilometres (about 270 km) along the Himalayan front.  West of the Hazara-Kashmir syntaxes, it takes several bends and is concealed under the alluvial sediments at many places and therefore its structural continuity cannot be established. It passes at a closest Distance of about 1 km from Margala hills.
3. Margalla Fault in ENE-WSW trend
4. Hazara Thrust

The three branches of the Hazara thrust fault system are present in the Margala hills. The nearest trace of this fault is at a distance of about 15 km from the area. These are active Tectonic features.

• Panjal Thrust
• Jhelum Fault in N-S trend
• Manshera Thrust
• Murree Thrust

Hydrological Information

There is water in the lower part of the mountain but at such a high point where the tunnel is being excavated, at 600 m height, there is no or very little water that is negligible.

Conclusion

1. Major Boundary Thrust works the base of this area. 
2. Rocks present here are of different lithology and are mostly from Precambrian, Paleozoic, Mesozoic, Pliocene. Here Jurassic formation is older then Miocene.
3. Major structure is anticline in this area.
4. Minor structure under compression effect of MBT is reverse Fault
5. Water Conditions are favorable in this vicinity.

Site Investigation

Site investigation was done using Aerial Photography and Borehole Drilling. Figures (5) and (6) below are the images obtained from aerial photography:

Furthermore, several boreholes were drilled through the length of the tunnel in the formations at different target locations. They are shown below in Figure (7).

Geology

The borehole logs are shown below in Figure (8). They show the lithology that will be encountered while progressing through the hills. They also shed some light on the condition of rocks to be encountered.

Inferences

It is evident from the above borehole that the major formation to be encountered here is limestone containing a little bit shale. Also, we can see that the formations form a sort of anticlinal structure. Therefore, such a tunnel shape is to be selected that can withstand this problem along with the stresses from the faults and be able to survive earthquakes.

Tunnel Cross Section Design

Tunnel Dimensions

Size of the tunnel face depends upon the maximum width and height of the vehicle that has to pass through the tunnel.

Tunnel Width

The total width of the tunnel face is 45 ft. Out of this 45 ft 24 ft is left for two lanes, 8 ft for shoulder on each side and 2.5 ft for the walkway.

Tunnel Height

Vertical clearance should be selected as economical as possible consistent with the vehicle size. The 5th Edition of AASHTO Green Book (2004) recommends that the minimum vertical clearance to be 16 feet (4.9 m) for highways and 14 feet (4.3 m) for other roads and streets.

Note that the minimum clear height should not be less than the maximum height of load that is legal in a particular state The total height is 26 ft out of which 18 ft is for the traffic envelope and the 2 ft is for the pavement thickness. The rest of the height is for the ventilation and lightening purposes.

The vertical clearance shall also take into consideration for future resurfacing of the roadway. Although it is recommended to resurface roadways in tunnels only after the previous surface has been removed, it is prudent to provide limited allowances for resurfacing once without removal of the old pavement.

Consideration should also be given for potential truck mounting on the barrier in the tunnel or on low sidewalk and measures shall be used to prevent such mounting from damaging the tunnel ceiling or tunnel system components mounted on the ceiling or the walls. The designer must follow the latest edition of the Green Book

Tunnel Profile

Shape of the tunnel depends on the following factors:

1. In-Situ Stresses
2. Type of Formations
3. Direction of Stresses
4. Life of Tunnel
5. Ventilation
6. Risk Management
7. Maintenance
8. Avoidance of Claustrophobia 

The choice of profile helps in improving the performance requirements and also minimizes the bending moments in the linings. Here, I am using the mouth profile. A mouth profile is composed of circular sections. The ratio of adjacent curvature radiuses should not exceed 5. The minimum radius should not be lower than 1.5 m. Following formulae apply for the calculation of the mouth profile:

Figures (9) and (10), show the different parameters in play in our calculations.

Calculations:

Drill Selection

Based on our formation’s parameters such as abrasion, penetration, blasting factor etc. we determine the number of drills needed to drill the holes in a much effective method. Following are the conditions in the proposed tunnel that help us in making our calculations.

Area = 2449.5 ft²

Rock = Limestone

Drill Bit = 32mm       

Penetration Rate = 45 in/min

Blasting Factor = 7.4 ft²/hole

Depth of Hole = 20 ft

Drill rounds/shift = 4

Delay Time = 3 min

Allowable drilling time/round = 4 hours

Tonnage Factor = 14 ft3 / ton

The drillability of Limestone from table is given as 1.22. So,

Penetration Rate = 1.22 x 45 = 54.9 in/min

Required No. of Holes = 2449.5 / 7.4 = 331 holes.

Net Drilling Time = 4.37 min/hole

Gross Drilling time = Net + Delay = 7.37 min/hole

Capacity / Drill = 4×60/7.37 = 32.56 = 33 holes

Required Drills = 331/33 = 10

Total hole length/round = 331 x 20 = 6620 ft/roung

Volume = Area x depth = 48990 ft3/round

Weight = Volume / T.F = 3499.3 ton /round

Drilling Factor = D.F= Length/Weight

D.F = 1.89 ft/ton

So, it shows that 10 drills are needed for better advance in rock excavation.

Drill and Blast-Tunneling and Excavation Methods

The Drill and Blast Cycle

It is an old and mostly used methods for tunneling excavation. It is a kind of cyclic process of continuous nature. For each round we have to follow the same steps, no doubts exceptions are there for abnormal conditions. This method is slow and less safe. By using different machines, such as “Jumbo Drill Machine”, rate of excavation can be increased. The following is known as the drill and blast cycle.

Survey

Prior to the excavation of any stretch of tunnel, tunnel profile is marked by surveyor as per given coordinates. After completing each round of tunnel excavation surveyor’s mark, the length of excavated stretch and mark the profile again for next blast as well as for under/over excavation.

• The points are marked around face periphery to keep the tunnel alignment as per design at designed elevation.
  • Surveyor also confirms the round length of blast.
  • At lot C2, laser theodolites are being used for this purpose.
  • Surveyor also gives the points for drilling.

Drilling

After completion of the survey work drilling for specified length (4m generally) and number (104) holes required for blasting.

• It normally takes about 03 to 04 hours’ time.
• Drilling is being done with hand held Air-leg drill machines.
• Jumbo machine also being used.
• It is better to drill holes with the drilling Jumbos which has very much precision as regards angle and direction of the hole.
• V- Cut hole (to give free face), and perimeter holes are drilled for blasting.

Charging

Process of loading the drilled holes with explosive, is called charging.

• Delay for each hole according to the approved blast design is ensured.
• What we observed at downstream of A3 site, 80% wabox, which is a dynamite, WahNobel manufactured, Explosive of class 3, div-1, is being used.
• Explosive accessories are also from WahNobel.
• None-electric initiation system is opted for blasting purpose.
• In each charging request or report, powder factor, charge weight, burden, time etc. is mentioned.

Blasting

The process involved in initiating the explosive, while keeping the safety of workers in account, is called blasting.

• After completion of charging, loader, displaces the charging or drilling platform.
• A siren is blown to warn the workers to shift to the safe places/distances.
• To ensure safety a safety man is also present there, which ensures that workers should be at least 200m away from the tunnel face.
• Then blasting is done by detonating the explosives.

Ventilation

Process of removing the after-blast dust, gas fumes (polluted air) from the tunnel and at the same time intake of fresh air, is called ventilation.

• After blasting about 30 to 45 min times is required for ventilation.
• The air is taken by ventilation ducts inside the tunnel through jet fans.

Mucking

Mucking is the activity of dumping all the blasted material form the face to muck disposal area. An advantage of cuttings is that hard rock cuttings (sand stone SS1, SS2) may be crushed again to the required size so that they can be used in Shortcrete mixture as an aggregate. Different machines i.e., Jack Hammer, and also some explosives are used for this purpose.

• It takes about 04 hours to shift the spoil material from the tunnel face.
• For this purpose, powerful loader and dumpers are used.
• Different spoil places have been selected for dumping purpose. E.g. spoil near the C2 residence camp.

Scaling

Scaling is the first step of supporting the excavated tunnel stretch. Removal of loose rock blocks/pices from the crown and walls, so that masonry and mechanical support can be installed is called scaling.

• Scaling is being done through chain excavators etc.
• It is necessary to remove the loose material and to provide safety for the workers.

Geological Mapping and Support Recommendation

During mapping photos of the face, crown, left/right wall are taken and then mapping is done by drawing joints on the mapping template dip/dip direction are recorded for each joint. Mapping is done by NJC’s geologists and geological engineers.

After completion of mapping of the face, Crown and wall Q value of the rock mass is assessed. On the basis of observation, different parameters are observed, these parameters are then used in q- system for tunnels support. This system gives us idea about the quality of rock and support to be installed accordingly.

Following is the general range of Q values:

            Q1 =    Q value above 40

            Q2 =    Q value 10 to 40

            Q3 =    Q value 04 to 10

            Q4 =    Q value 01 to 04

            Q5 =    Q value below 01

Support design drawings are given to engineers and geologists, on the basis of rock quality type, and their visual observation, they recommend support to contractors.

If rock Q value is in the transition of any two-rock type, say Q2 andQ3, then for first round we install support for Q3, if in next round we encounter the same Q value, then we will go for Q2 support design.

Support pattern

In D&B excavation method, first of all, first layer shotcrete, then rock bolts installation, then wire mesh is installed, and at the end 2nd layer shotcrete to reach the required thickness. If conditions are not good, then third layer of shotcrete can also be done.

Calculations for Drill and Blast

I kept the advance at 94% and the hole depth at 4.3 m. From the graph, the diameter of empty hole came out to be 152 mm or 0.152 m. The blast hole diameter is kept at 39mm or 0.039 m.

1^st square:

The distance from the center of the large hole to the center of the closest blast hole is

a = 1.5 x Φ

   = 1.5 x 152 = 228 mm = 0.228 m

The width of the 1^st square is

W₁ = a x (2)^0.5 = 0.228 x (2)^0.5 = 0.322 m

The requisite charge concentration for the holes in the 1^st square is 0.45 kg/m of Emulite 150. For practical reasons, Emulite in 25 x 200 mm cartridges are used giving a charge concentration of 0.55 kg/m. An overburden of this magnitude does not cause any inconvenience. The uncharged party of the hole is equal to the C-C distance: a=h_o. The charge of the hole is the length of the charge (H-h_o) times the actual charge concentrations.

Figure (11) shows the 1^st square diagram.

Q = I_c x (H-h_o)

    = 0.55 x (4.3 – 0.228)

    = 2.2396 kg

Key data for the 1^st square

a = 0.228 m

W₁ = 0.322 m

Q = 2.2396 kg

2^nd square

The burden in the 2^nd square is equal to the width of the opening created in the previous step.

B₁=W₁

B₁ = 0.322 m

a= 1.5 W₁ = 0.483 m

W₂ = 1.5 x W₁ (2)^0.5 = 0.683 m

The requisite charge concentration for the holes in the 2^nd square is less than 0.55 kg/m.

Emulite 150 in 25 x 200 mm paper cartridges is used making the practical charge concentration of 0.55kg/m. Figure (12) shows the 2^nd square diagram.

The uncharged part of the hole is 0.5 x B.

Q = I_c x (H – h_o)  

    = 0.55 x (4.3 – 0.161)

Q = 2.276 kg

Key data for the 2^nd square

a = 0.483 m

B = 0.322 m

W₂ = 0.683 m

Q = 2.276 kg

3^rd square

The opening has now a width, W = 0.683 m. the burden B is equal to W₂.

B₂ = W₂ = 0.683

a = 1.5 x W₂ = 1.025 m

W₃ = 1.5x W₂ (2)^0.5 = 1.45 m

The requisite charge concentrated is approx. 0.65 kg/m. now the 25 x 200 mm cartridges do not provide sufficient charge concentration to ensure breakage. A large dimension of Emulite 150 must be used unless the cartridges are temped.

Emulite 29 x 200 mm in paper cartridges give a charge concentration of 0.90 kg/m. The hole will thus be overcharged. Figure (13) shows the 3^rd square diagram.

The uncharged part of the hole is 0.5 x B.

Q = I_c x (H – h_o)

    = 0.90 x (4.3 – 0.341)

    = 3.56 kg

Key data

a = 1.025 m

B   = 0.683 m

W₃ = 1.45 m

Q = 3.56 kg

4^th Square

Like before, the previous width is the burden for this square hole.

B = W₃ = 1.45

From graph, we see that for a 39mm diameter blast hole,

B_b = 1.02

I_b = 1.42

As B > B_b, so,

h_b = H/3 = 1.433

Q_b = I_b x h_b = 2.035 kg

Now

I_c = 0.5 x I_b = 0.71 kg/m

As it is closer to 0.55 than to 0.9, so in the next equation we will use 0.55 kg/m i.e. Emulite 25 x 200

h_o = 0.5 x B = 0.51

h_c = H – h_b – h_o = 2.357 m

Q_c = I­­_c x h_c = 1.296 kg

Total charge = Q_T = Q_c + Q_b = 3.331 kg

Floor Holes

For floor holes,

Burden = B = 1.02 m

Spacing = S = 1.1 x B = 1.122 m

Bottom charge

I_b = 1.42 kg/m

H_b = 1/3 x 4.3 = 1.433

Q_b = I_b x h_b = 2.035 kg

Column charge

I_c = I_b= 1.42 kg/m

Stemming = h_o = 0.2 x B = 0.204 m

h_c = H – h_b – h_o = 2.663 m

Q_c = I_c x h_c = 3.78 kg

Total charge = Q_b + Q_c = 5.81 kg

Key data for floor holes

B = 1.02 m

S = 1.122 m

Q = 5.81 kg

Wall Holes

Following calculations are for wall holes:

Burden = 0.9 x B = 0.918 m

Spacing = S = 1.1 x B = 1.0098 m

Bottom charge

I_b = 1.42 kg/m

h_b = 1/6 x H = 0.72 m

Q_b = I_b x h_b = 1.017 kg

Column charge

I_c = 0.4 x I_b= 0.568 kg /m

Stemming = h_o = 0.5 x B = 0.459 m

h_c = H – h_b – h_o = 3.121 m

Q_c = I_c x h_c = 1.77 kg

Total charge = Q_b + Q_c = 2.789 kg

Roof Holes

Now, for roof holes

Burden = 0.9 x B = 0.918 m

Spacing = S = 1.1 x B = 1.0098 m

Bottom charge

I_b = 1.42 kg/m

h_b = 1/6 x H = 0.72 m

Q_b = I_b x h_b = 1.017 kg

Column charge

I_c = 0.3 x I_b= 0.426 kg /m

Stemming = h_o = 0.5 x B = 0.459 m

h_c = H – h_b – h_o = 3.121 m

Q_c = I_c x h_c = 1.329 kg

Total charge = Q_b + Q_c = 2.347 kg

Stopping Holes (Upward and Horizontal)

In stopping holes, less explosive is required.

For stopping holes upward and horizontal,

Burden = B = 1.02 m

Spacing = S = 1.1 x B = 1.122 m

Bottom charge

I_b = 1.42 kg/m

h_b = 1/3 x 4.3 = 1.433 m

Q_b = I_b x h_b = 2.035 kg

Column charge

I_c = 0.5 x I_b= 0.71 kg /m

Stemming = h_o = 0.5 x B = 0.51 m

h_c = H – h_b – h_o = 2.357 m

Q_c = I_c x h_c = 1.67 kg

Total charge = Q_b + Q_c = 3.708 kg

Stopping Holes (Downward)

For stopping holes (Downward),

Burden = B = 1.02 m

Spacing = S = 1.2 x B = 1.224 m

Bottom charge

I_b = 1.42 kg/m

h_b = 1/3 x 4.3 = 1.433 m

Q_b = I_b x h_b = 2.035 kg

Column charge

I_c = 0.5 x I_b= 0.71 kg /m

Stemming = h_o = 0.5 x B = 0.51 m

h_c = H – h_b – h_o = 2.357 m

Q_c = I_c x h_c = 1.67 kg

Total charge = Q_b + Q_c = 3.708 kg

Below in Figure (14) is the complete profile with blast holes located in it.

Support Method

It is common practice to apply concrete lining in such highway tunnels. Also, a 5 – 6 inch layer of concrete is applied for support but this is just hypothetical. The real support will be decided when watching the actual conditions of groundwater flow and joints and fractures etc.

Ventilation

The ventilation system of a tunnel operates to maintain acceptable air quality levels for short-term exposure within the tunnel. The design may be driven either by fire/safety considerations or by air quality; which one governs depends upon many factors including traffic, size and length of the tunnel, and any special features such as underground interchanges.

Ventilation requirements in a highway tunnel are determined using two primary criteria, the handling of noxious emissions from vehicles using the tunnel and the handling of smoke during a fire. Computational fluid dynamics (CFD) analyses are often used to establish an appropriate design for the ventilation under fire conditions.

An air quality analysis should also be conducted to determine whether air quality might govern the design. Air quality monitoring points in the tunnel should be provided and the ventilation should be adjusted based on the traffic volume to accommodate the required air quality.

Environmental impacts and air quality may affect the locations of ventilation structures/buildings, shafts and portals. Analyses should take into account current and future development, ground levels, the heights and distances of sensitive receptors near such locations and the locations of operable windows and terraces of adjacent buildings to minimize impacts.

Ventilation buildings have also been located below grade and exhaust stacks hidden within other structures.

The two main ventilation system options used for tunnels are longitudinal ventilation and transverse ventilation. A longitudinal ventilation system introduces air into, or removes air from a road tunnel, with the longitudinal flow of traffic, at a limited number of points such as a ventilation shaft or a portal. It can be sub-classified as either using a jet fan system or a central fan system with a high-velocity (Saccardo) nozzle.

The use of jet fan based longitudinal system was approved by the FHWA in 1995 based on the results of the Memorial Tunnel Fire Ventilation Test Program (NCHRP, 2006). Generally, it includes a series of axial, high-velocity jet fans mounted at the ceiling level of the road tunnel to induce a longitudinal air-flow through the length of the tunnel as shown in Figure (15).

Lighting

Lighting in tunnels assists the driver in identifying hazards or disabled vehicles within the tunnel while at a sufficient distance to safely react or stop. High light levels (Portal light zone) are usually required at the beginning of the tunnel during the daytime to compensate for the “Black Hole Effect” that occurs by the tunnel structure shadowing the roadway.

These high light levels will be used only during daytime. Tunnel light fixtures are usually located in the ceiling or mounted on the walls near the ceiling. Tunnel lighting methods and guidelines are not within the scope of this manual. However, the location, size, type, and number of light fixtures impact the geometrical requirements of the tunnel and should be taken into consideration.

References

Analytic Quality Glossary. (2018)

Figure 2f from: Irimia R, Gottschling M (2016) Taxonomic revision of Rochefortia Sw. (Ehretiaceae, Boraginales). Biodiversity Data Journal 4: E7720.

http://www.fhwa.dot.gov/bridge/tunnel/pubs/nhi09010/08a.cfm.

http://www.fhwa.dot.gov/bridge/tunnel/tunres2.cfm.

http://www.fhwa.dot.gov/bridge/tunnel/pubs/nhi09010/02a.cfm

King, H. (2018). Schist: Metamorphic Rock – Pictures, Definition & More. Retrieved from https://geology.com/rocks/schist.shtml

Kolymbas Dimitrois (2005) Tunneling and Tunnel Mechanics, PP {7-9}

Zare, S., & Bruland, A. (2006). Comparison of tunnel blast design models. Tunnelling And Underground Space Technology, 21(5), 533-541. doi: 10.1016/j.tust.2005.09.001

Also, study Geotechnical Engineering CEP.

Explore different Tunnels in Pakistan