Tunnel Design And Construction Challenges

Water and its effects on Strength

Faults, shear zones, weak rock, problematic soil, water, high in-situ stress

  1. Difficult to quantify and uncertain
  2. Limited working access to mitigate
  3. High risks during construction
  4. Great uncertainties with high risks for Long and deep tunnels

Water inrush

  1. Hampers the construction activities inside.
  2. Escalation of project costs and delays.
  3. Reduction in shear strength of rock mass leading to failure of rock mass occurs from the crown and above spring level. flowing ground condition.
  4. The high pore water pressure behind the tunnel periphery adversely affects the support system resulting to distress.

Once water finds its way into our workplace (shaft, gallery, tunnel, etc.) it can be complicated to stop it.

As soon as we plugged one leak, the water will find another gap and a new leak will appear in a formerly dry point. The key thing is the effective stoppage is water inrush, i.e. minimum danger to the excavation

DrucHyd 2-C

Resins are very interesting compounds both in the field of structural renovation as well as in new constructions. Some of their most important uses apply to anchoring, sealing, cavity filling, rock stabilization and crack injection.

There are many different resins for injection, each suitable to specific circumstances and conditions. The selection of the right one, for an especially problem, has proved to be a decisive question. Therefore we can find a wide range of products in the market.

The main advantages of the resins are:

  • Set can be very quick, but can also be retarded
  • Approved for contact with potable water
  • Very good resistance to corrosive and aggressive environments.

Major benefits of DrucHyd-2C

  • Reduced groundwater movements and control
  • Increased geomaterial strength and rigidity
  • Safety against collapse of rocks and soils
  • Settlements
  • Utilities damage
  • Tunnel run-ins Predictable degree of improvement

Geotechnical considerations

  • The in-situ vertical stress in the treatment stratum must be sufficient to enable the grout to occupy fractures
  • The grout injection rate should be slow enough to allow pore pressure dissipation. Pore pressure dissipation should also be considered in hole spacing sequencing
  • Sequencing of grout injection is critical.
  • Distribution and characteristic of discontinuities
  • Greater displacement in weaker strata
  • Rate of tunnel advance and tunneling method

Effectiveness of grouting operations

  • Success rate of Pre-excavation grouting operations is 70-90% higher than post grouting.
  • Quantum of geotechnical data increases the effectiveness of grouting works.
  • Onus of successful grouting operation primarily lies on the execution of grout design.

Issues with Cement grouting:

  • Poor injection ability (penetration into tiny fractures and silty sand layers is difficult)
  • Fragility of the solid
  • Poor ductility
  • High water pressure

Major advantages

  • The major difference between particulate grouts and chemical grouts is in the penetrability.
  • Chemical grouts can penetrate into fine-grained rocks and soils.
  • The penetrability for chemical grouts is a function of the solution viscosity,
  • whereas the penetrability for particulate grouts is a function of particle size.
  • Flexibility after solidification.

Major advantage Contd.

  • Chemical grouts have been frequently used for stabilizing or for increasing the loadbearing capacity of fine-grained materials in foundations and for the control of water in mine shafts, tunnels, trenches, and other excavations.
  • Chemical grouts have also been used in conjunction with other void-filling materials for curtain grouting under dams constructed over permeable alluvium and for other treatments such as area grouting or joint grouting.

Major Advantages of DrucHyd‐2C

  • High Penetrability
  • Quick setting time
  • Lower Viscosity
  • Longer life
  • Lower unit weight/Doesn’t increase the static load above the excavation
  • Higher effectiveness Improving rock mass strength parameters
  • Chances of success are 60-70% higher as compared to Cement grout for the Himalayan regions

Issues with Cement grouting

  • Poor injection ability (penetration into tiny fractures and silty sand layers is difficult)
  • Fragility of the solid
  • Poor ductility
  • High water pressure

Workshop on Tunnel Design and Construction Challenges by Geo Constech findings will help you get the most suitable solutions for your underground construction projects.

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