Soft ground conditions can need reinforcement for deep foundations and to maintain safety on drilling sites. There are a variety of in situ methods for improving the performance of the soil by compacting, reinforcing, and fixing particles and soil masses to deliver site conditions that can support significant loads and maintain structural integrity for civil projects as well as commercial development.
This process should be completed following a professional soil boring and lab analysis followed by an engineering plan based on empirical data and environmental controls. In some cases, specialty foundation drilling equipment may be needed to compact loose soils to ensure proper conditions for pile driving or drilling deep foundations.
These techniques can present unavoidable dangers, and rig operators should take all necessary precautions to maintain crew safety, and they should be completed by experienced operators following strict guidance from engineering and geotechnical analyses.
Soft Ground Conditions: Different Types of Compaction
These are the most common methods for achieving stable soft ground conditions that can support deep foundations and provide a sturdy base for significant loads.
Dynamic
This method utilizes pile driving hammers to repetitively apply force on loose soils to compact and condense them to provide support for significant loads. Dynamic compaction is an effective option in granular, permeable soils because cohesive soils can limit the effect by absorbing the impact.
Vibro
By lowering vibratory equipment into loose, granular soils, load-bearing capacity can be increased and reduce settlement. This method is most effective in soils that are free draining and located under the water table.
Compaction begins at the bottom of a treatment depth and can rearrange granular soils, increasing density by 70%-85%. At the surface level, sand is added to adjust and compensate for the value reduction which occurs during compaction.
Grouting
This technique utilizes drilled or driven pipes that inject low slump, low mobility grout into free draining and low sensitivity soils. This method will increase shear strength and reduce settlement though it is not typically used for soil improvement. It’s also an effective solution for safeguarding against sinkholes.
The process begins at the bottom of the treatment zone and moves upwards, and is effective at targeting specific zones at depth. Penetration tests can be used to verify the improvement of the soil’s load-bearing capabilities.
Surcharge
By placing soil fill on existing soil, improvements can be made by compressing the soil, and increasing stiffness and shear strength. Soft, fine-grained soil conditions are often improved with surcharging, where fill material brought in by dump truck is moved into place with dozers. These mounds improve the amount of load capacity the soil can handle significantly.
Reinforcement Methods
By constructing a reinforcement element into the soil, load-bearing capacity can be improved without changing the surrounding soil conditions. This can require rig operators to utilize specialized equipment that may not be part of their existing fleet. Drilling rig rental offers a dynamic solution for improving soil conditions without maintaining expensive equipment which will sit idle in the following phases of the project.
Columns
Compacted gravel is constructed in a vertical column and compacted with a vibroflot. This method increases the density of the surrounding granular soil to improve soft site conditions and provide a stiff, high shear column. A post-treatment penetration test and load test measure the improvements and are compared to specific engineering requirements.
Concrete Reinforcement
These are installed in situ and constructed using a bottom-fed vibroflot that densities granular soil and transfers load through soft soils. Concrete is pumped until it penetrates and expands the base densifying the surrounding soil.
Soil Nails
Another in situ solution that is often utilized to stabilize, reinforce, and provide retention for excavations. Weathered rock or cohesive soil is required to install this type of reinforcement as it needs a near-vertical face as nails are installed. A drill rig is used to install the nails at three to six-foot intervals. After installation, tension tests can be performed to confirm load-bearing capacity is met.
Micro Piling
These are a common solution to stabilizing soft soil, and advances in drilling rig technology have brought load capacities to over three hundred tons and diameters of more than ten inches.
Micropiles are best suited to areas with clearance restrictions as they can be driven with side clamp vibratory hammers or smaller drilling rigs.
Fractured Grouting
The primary benefit of fracture grouting is that it can be performed in any soil conditions, and it is often used to reduce or mitigate previous settlement. It can also prevent settlement where tunnels or other subsurface features have been installed.
With the right equipment and proper planning, even the softest soil conditions can be improved to match robust load-bearing requirements.
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