Construction of Budhwarpeth Underground Metro Station, Pune

Urban areas are characterized by a scarcity of land, making it a highly valuable commodity. As the population in these areas continues to grow, the demand for land resources to support infrastructure development becomes increasingly significant. One solution to this challenge is the utilization of underground spaces for infrastructure development. This approach allows for accommodating urban growth without disrupting existing land use patterns and has the added benefit of causing minimal environmental impact.

Underground metro systems provide commuter convenience while minimizing their impact on the urban environment. The use of sub-surface space allows for a holistic urban planning benefiting from the three-dimensional space with required integration of the spaces above and below the surface creating opportunities for more efficient use of the urban land.

An underground metro system not only provides commuters with a convenient transportation option, but also minimizes its overall impact on the urban environment. However, it's important to note that conventional underground metro stations have traditionally been designed using the Cut-and-Cover methodology, which can be land-intensive during construction.

In situations where space is limited, such as in densely populated urban areas, underground stations must be strategically placed within the confines of available land parcels. This often necessitates a collaborative approach to construction planning, involving careful consideration and the utilization of various construction techniques to address the spatial constraints effectively. This approach allows for the continued expansion and enhancement of underground metro systems while working within the limitations of urban land availability.

Planning & Executing Metro Stations in Urban Areas

The planning of metro stations involves careful consideration of factors such as their catchment area, connectivity to business districts, integration with existing transportation modes, and potential for future urban development. Metro alignments often pass through densely populated areas where open land for station construction is scarce. In such situations, planners typically look to existing roads and the few available land parcels adjacent to them as potential station locations. This approach allows the metro alignment to follow existing road networks as closely as possible.

However, the roads in densely populated areas often have buildings lining their sides. This presents a significant challenge in planning and placing metro stations within the limited road carriage width or available land parcels without causing disruption or inconvenience to nearby residents. In some cases, this may also lead to the construction of stations close to existing heritage structures, bridges, and sensitive facilities like schools, hospitals, and places of worship.

Innovative construction techniques of Pune’s underground metro networks

To address the above stated challenges, while safeguarding the interests of the general public and planning for future growth, Pune’s underground metro networks have adopted innovative construction techniques. Two of five underground metro stations are constructed using a combination of Cut-and-Cover and NATM (New Austrian Tunneling Method) construction techniques. In this approach, a cut-and-cover box is excavated below ground level vertically up to shaft level using an earth-retaining system, while adjacent platform tunnels are constructed horizontally using the NATM technique. This dual-method approach allows for efficient station construction in densely populated urban areas while minimizing disruptions to existing structures and infrastructure.

Phase-1 of Pune Metro project which includes five underground metro stations, encountered a unique challenge, specially the Budhwarpeth underground station. This station is situated in an area characterized by a dense population, which posed significant constraints and necessitated alterations in the initial design and planning.

Location & Alignment Challenges

Budhwarpeth station is proposed in a densely populated residential area near Kasabapeth, which is the oldest residential area of Pune established in 5th century and also called the “heart of Pune city”. It is in the vicinity of the famous Shaniwarwada, Lal Mahal, Kasba Ganapati, Somwarpeth, Sat Toti Police Chowki, Raviwarpeth etc. The narrow lanes of Kasbapeth are surrounded by old residential houses made of wooden pillars and structural elements known as ‘wadas’.

The dense population in the vicinity of the Budhwarpeth station meant that there was limited available land for conventional cut-and cover station construction. The station was also required to be used for retrieval of TBMs of UGC01 and UGC02 contracts and C&C portion is proposed in the center of the station. Numerous options were worked for C&C box based on potential land availability. The construction of the station requires significant land take at these locations which involves relocation of over 150 affected residents and demolition and reconstruction of surrounding structures falling in the severe zone of construction.

As relocation, demolition and reconstruction will take immoderate time, the possibility of constructing the station in a timely manner at this location appears remote. Thus, it was decided to realign the station with some modifications in the station design and with careful planning.

Station Planning

Site Assessment: A thorough assessment of the site was conducted to understand the specific challenges and constraints posed by the dense population and limited land availability. The original station location near Phadake Haud chowk posed significant challenges due to the presence of deteriorating buildings and narrow roads. Moreover, it required an extensive effort in terms of Relocation and Rehabilitation (R&R), displacement of over 150 residents, and reconstruction of housing for all those affected by the project.

Redesign: Based on the assessment, the station's design and layout has been re-evaluated and modified. This includes changes to the station's footprint, depth, and layout to make the best use of the space available.

Innovative Construction Techniques: Given the constraints of limited available land and a densely populated area, innovative construction techniques have been utilized. These methods involve a combination of part cut-and-cover and part on both sides of the Cut-and-Cover section. This approach aims to minimize the station's physical footprint at ground level while effectively addressing the challenges posed by the urban environment.


Community Engagement: Engaging with the local community was crucial to ensure that the altered station design and construction process did not unduly disrupt the lives of nearby residents. This involved communication, addressing concerns, and possibly even adjusting construction schedules to minimize inconvenience to the public.


Safety Measures: Comprehensive safety measures, including advanced instrumentation and monitoring systems, were meticulously implemented to protect both construction workers and the nearby community during the altered construction process. These comprehensive safety measures were augmented by the deployment of advanced instrumentation and monitoring systems. Environmental monitoring tracked air quality and noise levels for swift detection of any adverse environmental impacts. Continuous monitoring ensured the structural integrity of the station and surrounding structures. Additionally, efficient traffic and road safety measures safeguarded commuters and residents.

Station Re-Alignment & Design Modification

A site survey was carried out to identify an alternative land parcel in the vicinity to minimize private acquisition. A PMC plot housing a non-functional school building (Dadoji Kondadev School) was identified by Maha Metro close to Phadake Haud chowk. Since this land will become available without any private R&R, feasibility of re-routing the alignment through Dadoji Konddeo School premises was studied.


An approximate land area of 2925 sqm (about 45M x 65M) was available within the school premises. The area was adequate for constructing the retrieval shafts of the TBMs. However, as a result of the alignment passing through the plot diagonally, additional land take would be required to accommodate the station’s entry/exit. This proposed re-routing will result in a reduction in the alignment. Revised alignment has reduced the overall tunnel length by about 370M.


The alignment, however, is not parallel to either side of the plot identified, thus creating a construction and design challenge, resulting in a fairly small cut and cover shaft. The cut and cover box contains all vertical circulation, shaft transfers from the platform to equipment rooms, other operational facilities, and vice-versa.

The station layout developed at Dadoji Kondadev school site houses facilities within the identified plot. Keeping the constraints in mind, the station has been designed with a unique configuration. The small cut and cover shaft contains vertical circulations and various ventilation and system shafts. All major equipment rooms like ASS, TVS etc. have been shifted above grade, which are typically planned close to platform level in typical underground stations.


A wider mezzanine 1 has been created to allow for paid unpaid circulation as concourse. Most of the system rooms are placed on the ground and first floor above the ground which provides ease of access for maintenance. System rooms such as the signaling room and the telecom room are combined with smaller size requirement. Typically, two ASS rooms are provided in an underground metro station, however, only one ASS is provided at ground level without compromising the functional requirements. TOM and EFO have been combined into one space for optimal design. This option would significantly minimize displacement of residents and any distress to the properties.

As the station box is located in a dense residential area without major road connectivity, it is vital that the station visibility and catchment be enhanced by connecting the station to the nearest wider roads and landmarks. A subway has been proposed to serve this purpose. To augment the catchment in nearby areas, a knockout wall has been designed with the subways. This will provide an extension to the nearby Kamla Nehru hospital. The proposal reduces R&R and also reduces the overall tunnel length, without further compromising the station’s functionality.

Construction Sequence

Geology: The ground conditions at these locations are generally fresh to highly weathered basalt rock with overburden consisting of soil cover of around 0-9 m (0-3 m filled soil, 3-9 m sandy to silt clay). Highly weathered tock for following 9-11 m, moderately weathered rock between 11- 15 m and below that slightly weathered rock to hard ballistic rock is available.

Building Condition survey & corrective measures: Many structures in the area are quite old and constructed with spread footing and load bearing walls with metal sheds and old wooden structures. Major modifications and additions to these structures have taken place. However, a detailed survey has been carried out for the structures along the alignment in the influence zone of construction for the purpose of assessment of the health of these structures. Based on the types and severity of defects and damage, the building condition has been categorized as slight, moderate, severe, and very severe. Approximately more than 15 buildings are identified as severe/very severe along the proposed alignment. Proper remedial measures have been taken during the construction stage like TBM tunnel excavation in semi-close to close mode, NATM tunnels by controlled blasting, proper instrumentation work done in buildings, tunnels, and on ground, to know the settlement and deformation. Severe buildings after the structural survey to be protected by using the propping.

Space utilization for construction: Due to limited workspace, sacrificial piles were introduced in such a way that the vertical shaft can be excavated below the ground level and the extended portion above mezzanine-1 level will be utilized as workspace for resource stacking and machinery operation. Once the shaft structure construction using bottom-up will be done till ground level, further work of extended portion will be taken up by utilizing plinth slab as workspace.


Excavation near Severe Category/Heritage structures: The excavation work was taken in phases. Filled material up to a depth of 9 meters was excavated using crane bucket. Highly weathered rock up to 11 meters was excavated through a breaking mechanism. Moderately weathered to hard ballistic rock from 11 to 30 meters was excavated by using controlled drill & blast technique. The main objective of blasting is fragmentation of the hard rock mass using chemical energy in the form of explosives. Ground vibrations may cause damage to the nearby structures and inconvenience to the residents in the vicinity if the intensity of the blast is above the threshold limits. Other significant problems during blasting are ground vibrations above threshold limit, generation of fly rock, and noise. Control blasting technique is adopted to control the blast induced vibrations. Many trial blasts were carried out before commencement of controlled blasting on a daily basis.

Rock flying during blasting is a major concern as the shaft is surrounded by residential buildings. So muffing arrangement was done using rubber blast mat to control the flying rock pieces. Each blast is monitored with minimate-plus blast vibrations for ground vibration and noise at specific locations on a daily basis.


NATM Excavation by controlled drilling & blasting: Platform tunnels adjacent to cut-and-cover box are constructed horizontally using the NATM technique. NATM tunnel is proposed on both sides of cut & cover boxes spanning a length of 120 meters. Cross sectional area of the NATM is 215 sqm and it is one of the biggest NATM platform tunnels proposed in an underground station.

NATM tunnel excavation is divided into four parts: 3 top headings and 1 bench/invert. The NATM tunnel was excavated by using controlled drill & blast technique due to hard ballistic rock. Before commencing the excavation of tunnel, the face/portal below berm level were supported by shotcrete of 100 mm thickness with one layer of wire mesh, rock bolts (25mm dia., 6m long & 2x2m C/C staggered NATM tunnel/station interface wall) and fore polling (32mm dia. 6m length & 400mm spaced) around periphery of the crown for stability. The minimum trailing distance between the faces is required to prevent interference of the disturbance zone.

Conclusion

Budhwarpeth underground metro station in Pune Metro Rail project had numerous challenges like land constraints, relocation and rehabilitation requirement, potential demolition & reconstruction of surrounding severe structures, lack of open space and road access during construction, noise and vibration issues for nearby residents. However, with innovative design and construction solutions and through meticulous project planning, this proposal not only eliminates permanent relocation and rehabilitation (R&R) of private residents, but also reduces construction footprint, overall construction area of station, and shortens the overall tunnel length, while maintaining the functionality for smooth operations of the metro station.

Acknowledgements

Authors are thankful to the management of MAHA Metro & M/s. Gulermak-TATA Projects Ltd for providing the necessary support to carry out the work.

References

Austrian Society for Geomechanics (2010): Guideline for the Geotechnical Design of Underground Structures with Conventional Excavation, 2010

Design Manual for NATM Crossover & Cross Passages – UGC01 (B01), P4B01- GUT-TN-BAS-P4-00- 00-DBR-0003.

Geological Interpretative Report - Part – V, Civil Court Station (Chainage 12600m to Chainage 12950m), P4B01-GUT-GTBAS-CVC-00-00-DCL-004

Maha Metro/ Pune Metro Tender Documents- UGC 02- Section VII- outline design specification

Maha Metro/ Pune Metro Tender Documents- UGC 02- Section VIII- outline construction specification Maha Metro/ Pune Metro Tender Documents- UGC 02- Section IX- Tender drawing.