Documentation of the Construction of the Underground Subway at Welham Girls’ School, Dehradun

Proposed By:

Riwayat Katia, Class 12,

Welham Girls’ School.

Date of completion: 20th September, 2018

Acknowledgements:

This work would not have been possible without the support of Mrs. Padmini Sambasivam, the Principal of Welham Girls’ School. I am especially indebted to Group Captain SK Singh, Mr. Nitin Bansal, the school engineer, and Ms. Shefali Thapliyal who have been supportive of my career goals and who have worked actively to provide me with the protected academic time to pursue these goals. Ms. Deepshikha Walia has provided me extensive personal and professional guidance and taught me a great deal about writing and compiling research papers and formal documents along with guiding my art classes. Mrs. Neera Kapoor has always encouraged me to proceed with the concept of Architecture that I have in my mind and often discussed its various aspects with me. She has provided me with unending inspiration. I further extend my gratitude to Mrs. Reema Pant. As a teacher and mentor, she has taught me more than I could ever give her credit for. She has shown me by her example where curiosity and an inquisitive mind can take you.

Abstract:

Tunnel construction, structural diaphragms, and debris from quarry exploitation require careful consideration of the soil management, as this involves environmental, economic and legal requirements. In this paper, a primary research on the methods of constructing the underground subway at Welham Girls’ School is detailed. The project of underground construction was initiated in August, 2013 and completed in March, 2018. This paper gives indications about the required treatments as well as soil tests that were performed to ensure the stability of the structure. The main issue that has been addressed in the paper is the overcoming of the problem of monsoon rains and earthquake tremors of 2017. Physical parameters and technological features of the materials were assessed, according to their valorization potential, for determining the methods to deal with these problems. The methodology proved to be effective and the team of the structural engineers was able to work some way through every situation.

Methodology:

Research permission was taken from Mrs. Sambasivam. Semi-structured interviews were conducted

with Group Captain SK Singh and Mr. Nitin Bansal. A questionnaire was submitted to the school engineer following a basic introduction to the construction undertaken. Additional data was gathered through the study of other research papers on the methods used in the construction of the underground subway. The questionnaire proposed is as follows:

a) Why was the Subway Constructed?

i) What was the purpose of this project? When was it first initiated?

b) How was the Subway Constructed?

i) What were the surveys that were conducted before drilling in the ground?

ii) After the soli-testing had been done, what method was preferred and why? What was the

structure of the soil and of the ground?

iii) What was the depth of the launch shaft? How was the stability and the shape of the tunnel drive

ensured? How was the live and dead load balanced? Please mention the methods, techniques

and the structures that were used.

iv) What was done to protect the workers from the exposure to the air contaminants and the hazards

of fire and explosion? Were the acoustic sheds placed to minimize the noise, light and dust

impacts on the local community?

c) What were the problems faced during the construction?

i) How were the major problems of an underground construction dealt with, such as:

Groundwater seepage and water flow

Compressed Air

Rock Face Fall Out

Underground pipeline breakages

ii) How was the earthquake that took place in February, 2017 dealt with?

iii) Why was the digging done from the main campus if it had already been initiated from the other

side-The Senior School? Were there any problems in connecting the two sides of the tunnel

drive?

iv) What has been done to protect the subway from the heavy showers during the months of July

and August.

Through the course of this research paper, each of these questions will be addressed, as answered by the respective professionals.

Introduction:

The girls and the faculty members used to cross the Circular Road to go to the No. 6 (Senior School)

Campus from the No. 12 (Main) Campus which certainly caused inconvenience to whoever used to

pass by since they had to be stopped. Furthermore, the commuters used to travel at a very high speed

causing the road to be extremely unsafe for the school members. Thus, for safety and security purposes, the project of constructing an Underground Subway was proposed in 2013.

The Construction of the Subway

Before drilling in the ground, there had to be a number of surveys done to check all the services under the road: Manholes, Water and Sewage Lines, Electric Poles etc. to check if the construction of the Subway was feasible. It was all done with the help of a Digital Survey and the obstructions to the

construction were marked so that the Architect, Ms. Malvika Ahuja and the Structural Engineer, Mr.

Nitin Bansal could work out the complete project. Apart from this, the soil-testing was also conducted since it plays a major role in determining what methods and materials have to be used while going underground to ensure the structure’s stability. The soil is tested for strength, density, compaction, contamination, organics and sand content, to assess its impact on the construction project. The results of the structure and the ground are as follows:

Layer 1: Exactly Silty sand (Non-Plastic Fines) with Clay (Plastic fines) till 1.8 meters.

Layer 2: Sandy Gravel with Plastic Fines GP till 2.5 meters. (GP means clean gravel <5% smaller than No.200 Sieve; poorly graded gravel-Uniform Particle Sizes.)

Layer 3: Silty Clay with medium plasticity CI till 8m. (CL means Clay with Low Plasticity)

Layer 4: Gravelly Silty Sand with Clay (Plastic Fines) till 10 meters.

The Unified Soil Classification System (USCS) [1] was used. This is a soil classification system used in Engineering and Geology to describe the texture and grain size of a soil. The depth of the launch shaft was 7.5 meters. In order to push the 4m mild steel pipe across the road, the Hydraulic Jack System was used. Mild Steel, also known as Plain-Carbon Steel and Low-Carbon Steel, is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications. In the Hydraulic Jack System, an Earth Pit approximately 8m wide, 10m long and 7.5m deep was dug. It had to be done in steps to ensure that there is no problem of Rock Face Fall Out due to loose earth and coarse sand. To support loads during construction, Propping was used which is a system of structural members used temporarily. The forces arising from these loads must be fully resolved, using props or columns to provide all the support needed for the work under construction, such as beams, formwork, etc.

Along with Propping,[2] Scaffolding[3] was also used which is a temporary structure used to support a work crew and materials to aid in the construction, maintenance and repair of buildings, bridges and all other man-made structures. Scaffolds are widely used on site to get access to heights and areas that

would be otherwise hard to get to. These were the two main methods that were used to keep the

stability and shape of the tunnel drive in place. The Live Load (people and vehicles) had to be stopped while the Mild Steel Pipe was being pushed in.

Thus, the road had to be blocked for a few days after the school had been permitted to do so by certain departments. The Dead Load of the road and the layers of the soil above were taken care of with the help of the 4m mild steel pipe which was 25mm thick. After the completion of the Tunnel Drive, the lines with heavy grade R.C.C were inserted with Short-Crete Method[4] [5]to ensure that the Tunnel Drive does not collapse. The project was structurally designed with the help of the expert consultants, ‘Syal and Associates’ from Chandigarh, to ensure the structural stability of the Subway. Certain measures were taken to protect the workers from the hazards of underground construction. As the Mild Steel Pipe was pushed through the soil, the provisions for proper ventilation were made. The acoustic sheds[6]were placed to minimize the noise, light and dust impacts on the local community-the students and faculty of the school. In most of the underground constructions, workers have to be protected from the exposure of air-contaminants and hazards of fire and explosion as well but fortunately there were no such problems faced.

The Problems Faced During the Construction

The major problems of an underground construction are Groundwater Seepage and Water Flow, Rock

Face Fall Out and Underground Pipe Line Breakages. [7] In order to prevent the Groundwater Seepage and Water Flow, temporary drains and pits were made to collect and pump out ground water with the help of the Dewatering Pumps. The Dewatering Pumps provide the required force to push out the water from the area under construction. There was no problem of compressed air. Sand bags were placed on the face of the Subway for Rock Face Stabilization which means to prevent loose earth, boulders, and unwanted material to fall in the tunnel drive that has already been constructed.

There was an earthquake in this region in February 2017 which was one of the major reasons why the

completion of this particular project got delayed. The service lines that were running underground at

that time broke. The Tunnel Drive was completely filled with water and sewage up till 2m. The water

had to be pumped out which took a lot of efforts and human resources. But with the help of the planned drainage system and Dewatering Pumps, the problem of water flow was resolved. But, since the sewage and water supply lines running underground were dislodged, the face of the tunnel drive got completely blocked with heavy mud and earth residue. It was not at all possible to continue the construction from the No. 6 (Senior School) Campus. Therefore, the Engineers and the Architect took the decision to continue the construction of the tunnel drive from the No.12 (Main) Campus. The Mild Steel Pipe was pushed through after the launch shaft had been dug in August 2017. When the distance between the two parts of the Subway was 3 meters, the mild steel pipes were welded together. Before this, the digital survey had to be repeated to get the center line of the Subway in exactly the right place. This task was done with extreme precision and accuracy which is why the Subway stands before us.

The Subway was inaugurated in March, 2018. But in August 2018, certain measures had to be taken to protect the subway from the heavy showers during the months of July and August. Thus, the

construction was again undertaken. A proper CGI Sheet Shed was installed over the steel framework

of the Subway. The CGI Sheet Shed also played a major role during the construction that was initiated on the main campus in August 2018. It protected the trenches of the Tunnel Drive from collapsing due to the rain.

Conclusion:

Underground development is an important tool in developing and reshaping urban areas to meet the

challenges of the future. Placement of infrastructure and other facilities underground presents an

opportunity for realizing new functions in urban areas without negatively impacting the surface

environment, and at the same time brings opportunities for long-term improvements in the

environmental impact of cities and more efficient use of space and resources. In this small set it can be observed that the construction of the subway has not only helped improve multiple of the problems faced in urban development-traffic congestion- but also helped protect the school students and the staff.

Reference:

[1] https://en.wikipedia.org/wiki/Unified_Soil_Classification_System

[2] www.planete-tp.com/en/propping-a995.html

[3]https://en.wikipedia.org/wiki/Scaffolding

[4]http://www.google.co.in/url?

sa=t&rct=j&q=&esrc=s&source=web&cd=18&ved=2ahUKEwiR8u6O_8PdAhUFMI8KHTX0BDQQFjARegQIBRAB&url=http%3A%2F%2Fengineeringindia.tradeindia.com%2Fshort-creting-and-soil-nailing-1160849.html&usg=AOvVaw1IMZH1FpH6a0Jd_5RfTPfH

[5]https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&cad=rja&uact=8&ved=2ahUKEwjuseakzIfdAhWBso8KHSFfDmkQFjAMegQICRAC&url=https%3A%2F%2Fcan.sika.com%2Fdms%2Fgetdocument.get%2Fffadc352-e3dd-3b85-b844-bd98660f3af3%2FShotecrete%2520in%2520Tunnel%

2520Construction.pdf&usg=AOvVaw2VptNyggvxarGeYPpT318z

[6]https://metrotunnel.vic.gov.au/construction/construction-impacts/acoustic-sheds

[7]https://graduatedegrees.online.njit.edu/.../top-5-challenges-in-tunnel-construction

Glossary of terms:

Manholes-Steel covers can contain gas, electric, or sewer storm lines and plastic or composite (green

or gray) communications.

Mild Steel Pipe-Iron containing a small percentage of carbon, strong and tough but not readily 

tempered.

R.C.C-Reinforced Cement Concrete, a material used in construction.

Short-Crete Method-The dry mix method involves placing the dry ingredients into a hopper and then conveying them pneumatically through a hose to the nozzle.

Acoustic Sheds-commonly used during construction of tunnels to minimize noise, light and dust spill

on the local community during 24-hour tunneling activities.

Rock Face Fall Out-Rock face fall-out refers to when rocks fall from the construction face as a result of weakening ground and support conditions.

CGI Sheet Shed- corrugated sheets of metal with some of the highest strength-to-weight ratios of

almost any construction material. The corrugated grooves also increase the metal sheets'

water-shedding properties, making it desirable for both roof and siding applications.