Foundation Strengthening

Foundation Strengthening, specifically focusing on the two techniques you mentioned: Micro Piling and Soil Stabilization.

These methods are typically used when a building is settling (sinking), showing cracks, or when you need to add more floors to an existing structure.

Technique 1: Micro Piling

Best for: Transferring the building’s weight past weak soil to a deeper, stronger layer of rock or hard soil. This is effectively “bypassing” the weak foundation.

Phase 1: Drilling & Access

1. Site Access: Small, specialized drill rigs are brought in. Unlike massive piling rigs, these can fit inside basements or tight alleyways (low headroom).

2. Boring the Hole: The rig drills a small-diameter hole (usually 100mm to 300mm wide) through the existing foundation and down into the soil.

3. Casing Installation (Optional): If the soil is very loose and keeps collapsing, a steel casing (pipe) is drilled down simultaneously to keep the hole open.

Phase 2: Reinforcement & Grouting

1. Insert Steel Core: A high-strength steel bar (often threaded) is lowered into the drilled hole. This acts as the “spine” of the new pile.

2. Grout Injection: Cement grout is pumped into the hole from the bottom up.

   • Pressurized Grouting: The grout is often injected under high pressure. This forces the cement into the surrounding soil, bonding the pile tightly to the ground (friction).

3. Top Up: As the grout settles, more is added to ensure the hole is filled completely to the top.

Phase 3: Connection (The “Bracket”)

1. Capping: Once the grout cures (hardens), a steel plate or concrete cap is installed on top of the pile.

2. Bonding to Building: This cap is chemically bolted or concreted into the existing building foundation. The weight of the building is now effectively resting on these new steel-and-cement needles.

Technique 2: Soil Stabilization (Injection Grouting)

Best for: “Densifying” or solidifying loose soil directly beneath the house without installing deep steel piles. This alters the soil properties as you requested.

Phase 1: Survey & Detection

1. Drill Test Holes: Small holes (penny-sized) are drilled through the floor slab or around the perimeter.

2. Soil Testing: A penetrometer is often used to find exactly where the soil is weak (e.g., is the void at 3 feet deep or 10 feet deep?).

Phase 2: Injection Process

1. Insert Injection Ports: Metal tubes are inserted into the drilled holes to the depth of the weak soil.

2. Inject Material: Two common materials are used:

   • Cementitious Grout (Compaction Grouting): A thick, low-slump cement mix is pumped in under pressure. It forms a “bulb” that pushes the soil outward, compacting it and making it dense.

   • Polyurethane Resin (Chemical Grouting): A liquid resin is injected. It reacts with the soil and expands (foams) rapidly, filling voids and hardening immediately.

3. Monitor Lift: Laser levels are placed inside the house. As the injected material expands and strengthens the soil, it can actually lift the sunken floor back to its original level.

Phase 3: Cleanup

1. Seal Holes: The injection ports are removed, and the small drill holes are patched with concrete.

2. Curing: Unlike concrete, chemical resins cure in minutes; cement grouts may take a day or two.

Summary Difference:

• Micro Piles are like putting your house on stilts that reach deep underground.

• Soil Stabilization is like injecting filler into the ground to make the sponge-like soil hard as a rock.