Ground improvement — increasing bearing capacity of waterlogged soils When a site suffers from high groundwater (waterlogged conditions) that reduces bearing capacity, which of the following methods may be used to improve the soil so it can safely support loads?

Introduction / Context:
Waterlogged soils exhibit low effective stresses, leading to reduced shear strength and bearing capacity. Improving such soils can involve changing water conditions, modifying soil structure, or adding binders. The best solution depends on soil type, depth, and project constraints.

Given Data / Assumptions:

• Shallow foundations affected by high groundwater.
• Soil type ranges from cohesionless to cohesive deposits.
• Objective is to improve bearing capacity and reduce settlements.

Concept / Approach:

Lowering the groundwater level via drainage increases effective stress, directly improving bearing capacity. Compaction densifies granular soils, raising friction angle and stiffness. Grouting fills voids and bonds particles in coarse soils; chemical stabilization (lime, cement, other reagents) alters plasticity and strength particularly in fine-grained soils. Often, a combination is used for best results.

Step-by-Step Solution:

Verification / Alternative check:

Case histories show significant bearing capacity increases after dewatering and compaction; lime/cement treatment of clays improves unconfined compressive strength and reduces settlement.

Why Other Options Are Wrong:

• They are not wrong individually; all listed methods can be appropriate depending on the soil and project.

Common Pitfalls:

• Attempting compaction in saturated clays without prior drainage or stabilization.
• Ignoring environmental impacts of chemical additives or grout migration.

Final Answer:

All of these.