In tunnel lining works, high-pressure grouting is generally resorted to when the rock mass is highly fissured, of poor quality, or likely to permit water seepage. Which case(s) typically justify high-pressure grouting before concreting the lining?

Difficulty: Easy

When the rock is highly fissured
When the rock quality is poor
When the rock is likely to permit water seepage
All of the above.
None of the above

Correct Answer: All of the above.

Explanation:

Introduction / Context:
Pre-lining grouting in tunnels is a key ground improvement and water-control measure. By injecting grout under pressure, engineers reduce permeability, fill joints and fissures, and improve the rock mass prior to placing the permanent concrete lining. This question checks when high-pressure grouting is typically warranted in practice.

Given Data / Assumptions:

Context: rock tunnels requiring durable, watertight linings.
Potential issues: fissures/joints, poor rock mass quality, and water inflow risk.
Goal: stabilize ground and reduce leakage paths before concreting.

Concept / Approach:
High-pressure grouting aims to seal discontinuities (joints, bedding planes, cracks) and to strengthen weak zones. Where the rock is highly fissured or of poor quality, grout penetrates and creates a more competent composite mass. If seepage is likely, pre-lining grouting reduces inflow, improving placement quality and long-term performance of the lining. The combined effect is reduced overbreak, minimized washout or laitance, and enhanced durability.

Step-by-Step Solution:

Assess rock conditions via mapping/borings to identify fissuring and poor quality.Estimate groundwater conditions to anticipate seepage pathways.Select high-pressure grouting where any of the above conditions exist to seal and strengthen before lining.

Verification / Alternative check:

Post-grouting Lugeon/packer tests often show reduced permeability, confirming the effectiveness of the treatment before concreting.

Why Other Options Are Wrong:

Options a–c each capture individual triggers; in practice, any or all justify grouting, hence the comprehensive answer is “All of the above.”“None of the above” contradicts standard tunnelling practice.

Common Pitfalls:

Confusing low-pressure contact grouting (post-lining) with high-pressure pre-lining grouting—both exist, but triggers here match high-pressure pre-treatment.Underestimating seepage impacts on lining quality, leading to honeycombing or cold joints.

Final Answer:

All of the above.

Discussion & Comments

No comments yet. Be the first to comment!

In tunnel lining works, high-pressure grouting is generally resorted to when the rock mass is highly fissured, of poor quality, or likely to permit water seepage. Which case(s) typically justify high-pressure grouting before concreting the lining?

More Questions from Tunnelling

Discussion & Comments