What should I do if groundwater seepage occurs during the drilling process of the pile foundation?

During the drilling process of rotary bored pile engineering, if groundwater infiltration occurs and is not effectively controlled in time, it may cause a series of serious engineering problems and even lead to engineering accidents. The following are the possible effects of groundwater infiltration:

1. Instability of hole wall and hole collapse

- Hole wall collapse: Groundwater infiltration will scour the hole wall soil and destroy the stability of the soil structure, especially in the sand layer, silt layer or loose pebble layer, which is very easy to cause hole collapse, resulting in shrinkage or complete blockage of the pile hole.

- Slurry wall failure: The infiltrated water dilutes the wall mud, reduces its viscosity and specific gravity, weakens the lateral support of the mud on the hole wall, and increases the risk of hole wall instability.

- Pile body defects: After the hole collapses, the pile hole may become irregular, enlarged or necked, resulting in discontinuous pile body concrete, mud inclusion or broken pile after the pile is formed, which seriously affects the bearing capacity of the pile foundation.

2. Deterioration of concrete quality

- Concrete segregation: Groundwater infiltration into the pile hole will dilute the concrete slurry, resulting in cement slurry loss, aggregate sinking, resulting in reduced concrete strength and stratification.

- Voids and mud inclusions in the pile body: Seepage may carry mud and sand into the concrete, forming mud and sand inclusion defects; if the amount of seepage is too large, it may even disperse the concrete, forming a void or honeycomb structure.

- Insufficient pile top elevation: The influx of groundwater during the pouring process will raise the liquid level in the hole, resulting in insufficient actual concrete pouring volume, and the pile top elevation is lower than the design requirements, requiring subsequent pile connection or rework.

3. Construction safety risks

- Equipment overturning: The collapse of the hole may cause the soil under the drilling rig to suddenly lose, causing the equipment to tilt or overturn, endangering the safety of the operator.

- Ground subsidence: A large amount of groundwater seeping into the pile hole will carry away the surrounding soil particles, causing ground subsidence or collapse, affecting the safety of nearby buildings, pipelines and roads.

- Quicksand and pipe bursts: In high-permeability strata (such as sand layers and gravel layers), groundwater seepage may trigger quicksand phenomena and even form pipe burst channels, resulting in large-scale damage to the soil in the construction area.

4. Construction delay and cost increase

- Extended processing time: After the seepage causes the hole to collapse or the concrete quality problem, the work needs to be stopped for hole cleaning, backfilling and re-drilling or grouting reinforcement, which greatly extends the construction period.

- Material waste: After the hole collapses, concrete needs to be poured again, or a large amount of mud, plugging agent and other materials are consumed to plug the leak, which increases the project cost.

- Post-remediation costs: If the pile body is found to have defects (such as broken piles and mud inclusions) after the pile is tested, high-pressure grouting, pile replacement or even demolition and reconstruction are required, resulting in additional costs.

5. Environmental impact

- Decline in groundwater level: When continuous precipitation measures (such as well point precipitation) are adopted to control seepage, the groundwater level in the surrounding area may drop, affecting the growth of vegetation or the stability of the foundation of adjacent buildings.

- Mud pollution: Seepage carries the wall protection mud overflow, which may pollute the surrounding soil or groundwater, especially when chemical additives are used, the environmental risk is higher.

- Soil and water loss: Soil and water loss caused by infiltration may damage the site and the surrounding geological environment, exacerbating ecological problems.

So how to prevent and deal with groundwater leakage? Here are some systematic solutions:

1. Advance prevention and exploration

- Detailed geological survey: Before construction, the groundwater level, aquifer distribution and permeability coefficient are determined through geological exploration, and the wall protection scheme is designed in a targeted manner.

- Optimize the construction plan: For high permeability strata (such as sand layers and pebble layers), special plans are formulated in advance, and appropriate drilling tools and process parameters are selected.

2. Enhance the performance of mud wall protection - Adjust the mud parameters:

- Viscosity and specific gravity: Increase the mud viscosity (such as adding bentonite, CMC) and specific gravity (adding barite powder), increase the lateral pressure on the hole wall, and balance the groundwater penetration pressure.

- Colloid rate and pH value: Ensure that the mud colloid rate is ≥95%, the pH value is controlled at 8-10, and the wall protection stability is enhanced.

Dynamic monitoring: Real-time detection of mud liquid level. If the liquid level drops by more than 0.5m/h, it is necessary to immediately check the leakage point and fill the slurry.

3. Casing and casing technology

- Deeply buried casing: bury the steel casing into the impermeable layer (such as clay layer) for at least 1m, and compact and seal the outer side of the casing with clay in layers.

- Full casing follow-up: use a casing rotator with steel casing in the highly permeable formation, press while drilling, and isolate groundwater.

4. Local plugging and dewatering

- Quick plugging: Put plugging agents (such as sawdust + clay mixture, ultra-fine cement + water glass double liquid slurry) on the leakage point, or insert a catheter for grouting.

- Dewatering measures: 

Light well point dewatering: suitable for shallow diving, with a well point spacing of 1.5-2.5m, and continuous pumping until the concrete begins to set.

Tube well dewatering: for the confined water layer, the well depth penetrates the aquifer, and the single well pumping volume is determined based on the permeability coefficient.

5. Concrete pouring control

- Underwater pouring process: Use the tremie pipe method for continuous pouring. The first batch of concrete volume must meet the buried pipe ≥1m, and the pouring speed is higher than the seepage speed.

Add retarders or anti-dispersants (such as cellulose ether) to the concrete to ensure underwater strength development.

- Over-pouring control: The pile top elevation must be 0.8-1.0m higher than the design to ensure that the seepage affected section is eliminated.

6. Emergency and monitoring measures

- Emergency plan: Equipped with pumps, plugging materials and spare casings, and drainage ditches are set around the borehole to prevent water backflow.

- Real-time monitoring: Use ultrasonic drilling monitor or tester to check shrinkage and collapse, and backfill and re-drill in time if abnormalities are found.

7. Special situation handling

- Quicksand layer treatment: Use double-liquid grouting (cement + water glass) to pre-reinforce the stratum, or skip hole construction to reduce mutual interference.

- Pressure water treatment: Verify the risk of sudden surge at the bottom of the hole, increase the mud density or use high-pressure grouting to form a water-stop curtain when necessary.

Summary

Measures	Applicable conditions	Key technical parameters
Mud wall protection	General water seepage	Viscosity 25-30s, specific gravity 1.15-1.25
Full casing follow-up	Strong permeable layer, quicksand layer	Casing diameter is 100-200mm larger than the designed pile diameter
Well point dewatering	Phreatic layer, permeability coefficient 1-50m/d	Well point spacing 1.5m, vacuum ≥60kPa
Dual liquid grouting plugging	Centralized water gushing channel	Water-cement ratio 0.8:1, water glass modulus 2.8-3.4