Common Problems and Solutions in the Construction Process Using HDD Machines

Problems and solutions related to geological conditions

1. Unfavorable formations (such as loose sand layers, pebble layers, gravel and mud layers)

These formations are unstable in structure, easy to flow and collapse when encountering water, easy to deviate the drilling tools, the hole wall cannot be effectively maintained, and it is easy to "collapse" or "drill stuck".

 

Solutions:

Use special formation drill bits (such as roller cutter bits, eccentric reamer) to improve drilling capacity.

Use high-density mud to enhance the formation support.

If necessary, use casing wall protection or introduce freezing method to deal with the collapse-prone section.

 

2. Sudden formation changes (such as sudden changes from sand layers to gravel layers, rock layers)

When the drill bit suddenly enters the hard layer from the soft formation, the drill bit may shake violently, deviate, or even damage the equipment, which may lead to failure of crossing in severe cases.

 

Solution:

Detailed geological exploration, combined with multi-point sampling to establish layered profiles.

In the transition section of the formation, reduce the advancement speed and gradually adapt to different formations.

Arrange experienced operators to monitor the drilling pressure, rotation speed and mud changes in real time and make timely adjustments.

 

3. High water content formations or shallow groundwater

High water levels or abundant groundwater may cause mud dilution, loss, hole collapse, and even surface bulges or slurry accidents.

 

Solution:

Adjust the mud formula to increase density and thixotropy, and enhance the ability to block water flow.

Add a mud circulation and replenishment system to ensure constant pressure.

If necessary, surface interception ditches or drainage wells can be laid to control the groundwater level.

 

Equipment and construction technology problems and solutions

1. Insufficient accuracy of the guidance system

In cities or areas where metal pipelines are concentrated, the magnetic field interference is serious, which can easily lead to the accumulation of guidance instrument errors and trajectory deviation.

 

Solution:

Use a dual guidance system (magnetic permeability + gyroscope) to improve anti-interference ability.

Plan the best drilling path through geomagnetic interference test points before construction.

Set up relay wells or inspection wells during construction to facilitate guidance correction.

 

2. Wear, breakage or stuck drill

Drill bits or drill rods may break due to long-term drilling or impact with hard rocks, and drill bits stuck in the hole will cause significant downtime losses.

 

Solution:

Perform non-destructive testing and life assessment of drill bits regularly.

Select higher strength materials (such as alloy steel and carbide heads) for hard formations.

When stuck drills occur, use a combination of reverse vibration + extraction + mud flushing to unblock.

 

3. Improper back-expansion control

If the back-expansion aperture is too large or the operation is too hasty, it will cause channel collapse, mud backflow difficulties, and drill bit deviation.

 

Solution:

Adopt staged hole expansion, and control the increase of hole diameter in each stage to 1.3~1.5 times.

Control the hole expansion speed (usually no more than 8 meters/hour).

Use a spiral hole expander with strong stability and self-cleaning function.

 

Mud system problems and solutions

1. Mud performance does not meet the requirements

The mud is too thin to protect the wall, and too thick will block the reflux. improper viscosity will reduce the cooling effect or prevent the chips from being discharged.

 

Solution:

Develop a dynamic mud formula table and adjust it in real time according to the formation and drilling depth.

Add multifunctional additives such as modified bentonite, PAC, CMC, lubricants, etc..

Implement an on-site mud testing system to test viscosity, density, and pH value every 2 hours.

 

2. Mud leakage or loss

Gravel layers, rock layers with developed cracks, or old pipeline landfill layers are prone to large-scale mud infiltration and loss, causing pressure loss and hole collapse in the hole.

 

Solution:

Use plugging materials (such as polymer gel, cotton fiber) for local plugging.

Pre-add anti-water loss agent in mud.

Based on geological prediction, slow down drilling in advance and strengthen mud circulation in leaky layers.

 

3. Poor backflow or blockage

After back-expansion, there are too many chips in the channel, and the mud flow rate is insufficient, resulting in the accumulation of drill cuttings, which eventually leads to the blockage of mud circulation.

 

Solution:

Control the drilling footage and the return slurry rate.

Clean the hole before expansion, and stop briefly every 10 meters during the back-expansion process.

Configure high-power mud pumps and solid control equipment (such as vibrating screens, desanders) to ensure mud cleanliness.

 

Environmental and management issues and solutions

1. Small construction site

Working on urban roads, under bridges or in densely built areas, it is difficult to arrange drilling rigs and the working surface is crowded, which may affect construction efficiency and safety.

 

Solution:

Use small or modular drilling system.

Optimize the layout drawings and set up equipment, mud pools, and expansion areas in different areas.

Coordinate with local transportation and urban construction management to apply for night construction permits to relieve space pressure.

 

2. Noise pollution and nuisance

Drilling rig operation, mud pumps, high-pressure water pumps, etc. generate noise, which can easily cause dissatisfaction or complaints from surrounding residents.

 

Solution:

Use low-noise equipment (select silent pumps and noise reduction covers).

Set up soundproof enclosures and lay shock-absorbing pads.

Avoid residents' rest time at night and arrange work hours reasonably.

 

3. Underground facility conflict

The risk of conflict with existing water supply, gas, communication, cable and other pipelines is high, which can easily cause third-party damage.

 

Solution:

Entrust professional units to conduct underground pipeline detection before construction.

Track real-time guidance to ensure crossing trajectory avoidance.

Establish a linkage mechanism with each right-holding unit and formulate an emergency response plan.

 

Safety and emergency issues and solutions

1. Drilling stuck

Drilling tools are stuck underground due to accumulation of drill cuttings, closure of the hole wall or sudden breakage, and cannot be pushed or withdrawn.

 

Solution:

Use forward and reverse rotation + vibration + mud flushing to loosen the drilling tools.

If it still does not work, try to cut the stuck section and replace the rear section of the drilling tools.

Increase the mud flow rate during construction to ensure that the hole is clean and free of accumulation.

 

2. Crossing failure

Large guiding deviation, closure or collapse of the hole make it impossible to lay pipelines, and even re-drilling is required, causing huge economic losses.

 

Solution:

Preliminary 3D crossing design simulation to check each turning radius and depth change.

Set relay points or auxiliary wells to improve the controllability of crossing.

Arrange alternative construction plans (Plan B) for high-risk areas.

 

3. Mud leakage causes environmental accidents

Untreated mud flows into water bodies, cultivated land or residential areas, causing environmental problems and even triggering legal liability.

 

Solution:

Build a temporary mud storage tank and a secondary sedimentation tank.

Equip with emergency plugging tools and collection equipment.

Separate mud and water before all slurry discharges, and discharge after meeting the standards.