Heavy rainfall events are increasing in frequency and intensity across many regions. While surface flooding is visible, the more critical damage often occurs below ground. Water infiltrates rapidly into the soil, triggering internal erosion, loss of fines, and the formation of voids.
Over time, this leads to:
Reduced soil density and stiffness
Loss of bearing capacity
Differential settlement of foundations and slabs
Cracking and structural instability
This process is gradual, often unnoticed, and typically only identified once damage has already occurred.
Voiding due to soil washout below boundary wall foundations
Settlement of slab on grade
During heavy rainfall or flooding, water rapidly infiltrates the ground, leading to an increase in pore water pressure (u) within the soil mass.
According to Terzaghi’s effective stress principle (σ′ = σ − u), this rise in pore pressure directly reduces the effective stress carried by the soil skeleton.
In terms of Mohr’s circle, this is represented by a horizontal shift of the circle towards lower effective normal stresses (to the left), while the radius remains unchanged because total stresses are constant.
As the circle moves closer to the Mohr–Coulomb failure envelope, the available shear strength decreases, increasing the likelihood of instability, settlement, or even failure.
This explains why soils subjected to intense rainfall often experience softening, loss of bearing capacity, and deformation. Once the excess pore pressures dissipate over time, the Mohr circle shifts back to the right, restoring effective stress and stability.
Effect of water pore pressure on soil shear strength
Conventional approaches to address erosion-induced settlement typically involve:
These methods are often:
A more advanced approach involves the use of expanding geopolymer injections to stabilize the ground in place.
This method works by injecting a two-component material into the soil, which reacts and expands rapidly. As it expands, it (in granular soil):
The expansion process induces controlled ground improvement through densification and stress redistribution, leading to measurable increases in soil resistance and performance.
Geobear process
Geobear Ground improvement soil injections
One of the key advantages of Geobear's soil injection solution is its effectiveness in wet or saturated ground conditions.
This makes it particularly suitable for post-rainfall stabilization and erosion repair.
From an engineering principles prospective, heavy rainfall increases pore water pressure, which reduces effective stress and shifts the Mohr circle to the left without changing its size, bringing the stress state closer to the original Mohr–Coulomb failure envelope and reducing shear strength.
This is shown in the graph below by the movement from the blue circle (dry condition) to the dashed orange circle (after rainfall), indicating a loss of stability.
Geopolymer soil injection then improves the situation through two mechanisms: it partially restores effective stress (shifting the circle back to the right by ) and, more importantly, increases the soil’s angle of friction (φ′) through densification, which rotates the failure envelope upward (from the red line to the steeper purple line).
As a result, even if pore pressures remain elevated, the distance between the Mohr circle and the failure envelope increases, meaning higher available shear strength and improved stability.
Effect of Geobear ground improvement solution on soil shear strength
Time is critical when addressing rainfall-induced ground damage. Our Geopolymer injection offers:
The result is a stabilized ground system achieved without removing or replacing soil:
Heavy rainfall does not just affect the surface—it fundamentally alters ground behavior.
If left unaddressed, soil erosion and washout can compromise the integrity of infrastructure. However, with targeted, non-invasive ground improvement techniques, these risks can be mitigated quickly and effectively.
If you are concerned about heavy rainfall affecting the ground under your assets, or need emergency repairs, contact us today to discuss and schedule an inspection.