Water Control, Drainages and Grouting
India is on the verge of becoming a global super power, which necessitates a robust and reliable infrastructure. The varied terrain and geology of the nation poses difficult challenges to undertake swift and smooth developmental activities.
1.Underground excavation, especially in the treacherous Himalayan region needs special attention as the unpredictable geology leads to hazardous and sluggish working conditions.
During Underground excavation, heavy water inrush, weak shear zones, rock falls and tunnel squeezing are a major concern for designers and site engineers. Groundwater acts as a detrimental agent for rocks and soils as it drastically reduces their shear strength due to generation of porewater pressure, which eventually leads to excessive deformation, collapses and failures .
2. Mechanically, the lower effective stress due to water, lowers the fracture strength, while chemically, it has been observedthat the presence of water leads to a greater strain rate sensitivity of failure stress, which is greater at higher confining pressures.
3. Moreover, not just water soluble rocks, water reacts with silicate to breaks the Si-O bond and, fluids can have a profound chemical effect on the physical properties ofsilicate rocks too.
4.Hence, it is crucial to protect the excavation form excess water in order to minimize the deformation. In India, conventionalwater remedial systems in tunnels are implemented on a regular basis, however, they have proven to be less effective and uneconomical in the long run. In the Himalayan regions, where the ground is erratic, with high water pressure, time and efficacy of the stabilisation and control measure is of prime importance. Grout injection with micro fine cements has shown to be rather unproductive at places with high water volume and pressure.
In these scenarios, high competence is demonstrated by chemical injections, which have a low viscosity, quick setting time and high strength.
DrucHyd-2C, is one such polyurethane (PU) based two component resin and a proprietary product of GCPL, which has shown tremendous densification and water sealing capabilities in excavations through fractured/sheared water laden Himalayan rockmass.DrucHyd-2C is a customized PU resin which can be tailored according to the site requirements. The reaction time can be lowered to a few seconds to up to minutes.
Figure 1: Sheared/fragmented rock mass at Tunnel 5 of the USBRL railway tunnel, J&K, India
One such of experience where GCPL has demonstrated its state-of-the-art grouting execution skills using the DrucHyd2C resin for controlling the heavy water ingress situation was at USBRL project. A thick shear band on the left crown of the excavation was encountered at Tunnel 5 of the USBRL project (Chainage KM 44/520). The dolomitic rocks belonged to Trikuta formation. The shear zone had made further excavation difficult due to accompanying high water pressure (Figure 1). There was an accumulation of approximately 6000 m3 of muck on the face due to heavy water ingress of about 200 litre/minute and subsequently a cavity had also been developed (figure 1).
Unsuccessfully, cement grouting was conducted at the location to stabilize the rocks, where refusal was as high as 80%. Afterwards, it was proposed to undertake pre-excavation grouting using DrucHyd-2C to consolidate the shear zone and facilitate the further excavation . The resin grouting was carried out using perforated self-drilling anchors, spaced at a distance of 1m.
Due to its supreme consolidation properties and seep through even the finest of void, DrucHyd-2C was successful in consolidating the ground, while working against high water pressure (figure 2). The consolidation improved the ground, enabling further excavation.
Figure 2: Consolidated lump of sheared/fragmented rock mass by DrucHyd-2C at railway tunnel, J&K, India.
Similarly, for the micro tunnel oh outer diameter of 1400mm in Pipavav, Gujrat for protected from water ingress using DrucHyd-2C (figure 3).
Figure 3: Water ingress in a micro tunnel in Pipavav, Gujrat, India.
The micro tunnel was 50 m away from the sea line and the exact location of the ingress was not known. GCPL suggested the resin grouting for the water stoppage from inside of the tunnel using the manualdrilling method. The task was completed with two injection points located at 900 and 2700to the mirco tunnel and very nearby surface wall (figure 4).
Figure 4: Contained water ingress after the resin injection at micro tunnel in Pipavav, Gujrat, India.
The success of the resin injection is a testament to the advent of innovative technology which are more reliable than the traditional techniques of grouting and water control.
References: A Kainthola, 2015, Tunnelling Challenges and Solutions – Indian Scenario, Tunnelling Association of India, vol. 4 (2), pp.89  S Panthee, PK Singh, Ashutosh Kainthola, R Das & TN Singh, 2016, Comparative study of the deformation modulus of rock mass, Bulletin of Engineering Geology and the Environment, DOI: 10.1007/s10064-016-0974-3  K Masuda, 2001, Effects of water on rock strength in a brittle regime, Journal of structural geology, vol. 23, pp. 1653-1657  A D Lockner, 195, Room temperature creep in saturated granite, Journal of GeophysicalResearch, vol. 98, pp. 475-487  N Madhubabu, A Kainthola & T N Singh, 2016, Use of DrucHyd-2C (Polyurethane) Grout in HimalayanTunnelling, 416-427,Proceedings 6thINDOROCK 2016, IIT Bombay, Mumbai (17-18th June 2016)