Ground Improvement

Soil/Ground Improvement Design methods have been used to solve many ground condition problems and improve desired engineering properties of available soils.

The soil can be improved by adapting certain soil/ground improvement design and techniques. We have been providing Soil/Ground Improvement design and consulting services including evaluating various options, designing and supervising the implementation on site.

Beta Design Consultants provides soil/ground improvement design services for the following methods:

• Stone Columns
• Deep Soil Mixing
• Jet & Super Jet Grouting
• Chemical Grouting
• Soil Stabilization
• Prefabricated Drains (PVD)
• Rapid Impact Compaction (RIC)

Soil/Ground Improvement Design: Stone Columns Method

• Define: The stone columns method is a ground improvement technique that reinforces the soil with a network of stone compacted columns.

• Benefit: Stone columns are used to reduce settlement and increase load-bearing capacity. They also accelerate soil consolidation as a result of the drainage capacity of the granular material within the columns, which act as pore or water pressure evacuation points. Stone columns are particularly effective in improving slope stability and preventing liquefaction by increasing shear strength within a soil.

• Execution: The technique uses a vibrating probe which penetrates the soft soils to the necessary depth and to compact the material incorporated. There are a wide variety of construction methods (dry and wet, vibrating probes in the top or bottom of the tool, pendulum or mast-guided system) and methods for incorporating the materials (bottom feed / top feed) that can be used in combination to meet the project requirements and specifications.

Soil/Ground Improvement Design: Deep Soil Mixing

• Define: Soil Mixing is a ground improvement technique that reinforces the soil by mixing in situ a network of cement and soil columns.

• Benefit: Soil Mixing is a ground improvement technique that is used for a wide variety of applications: controlling and reducing settlement under structures, increasing the bearing capacity of the soil, ensuring stability, reducing liquefaction risk, mass stabilization, reducing earth pressure behind retaining structures, blocking ground water, and increasing lateral reaction around foundation piles.

• Execution:
• The Soil Mixing machine is fitted with single or multiple mixing tools (auger, blades, rotary head) to directly inject the binder into the mixing zones. The stabilization agent is combined with the soil to be treated and robustly mixed by the mixing blades. The binder dosage and mixing parameters are adopted based on the soil strength and the desired specifications or performance required.

Soil/Ground Improvement Design: Jet Grouting

• Define: Jet grouting is a ground reinforcement technique. One or several jets of fluid with high kinetic energy are used to break apart and mix the ground with a liquid cement slurry so as to form a column of “soil concrete”.

• Benefit: Jet grouting is a soil reinforcement technique used as a targeted treatment for a wide range of applications: control and reduce settlement under structures, increase of bearing capacity, create impervious cut-off wall or impervious bottom for deep excavation, install retaining walls, underpin existing structures, reinforce soils with existing utilities lines and burred structures, operate in areas that are difficult to access (limited headroom or cramped spaces).

• Execution: The equipment consists of a fixed grout production plant (silos, grout mixer, high pressure pump) attached to a drilling rig with high pressure grout lines. Once in place, the rig drills a small diameter hole (70 to 120 mm) through the layer of soil requiring treatment. Grout (which is often a cement slurry) is then pumped through the rod with a very high flow (200 to 400 L/min) and high velocity using a high-pressure pump and exits through one or several small diameter injection nozzles (1 to 10 mm). The tool is then withdrawn to form column (with rod rotation) or panel (with no rod rotation).

Soil/Ground Improvement Design: Chemical Grouting

• Define: Chemical grouting is a ground improvement technique that densifies the soil by grouting under pressure a network of inclusions.

• Benefit: Chemical grouting is a ground improvement technique used to stabilize and densify compressible soils, and for liquefaction mitigation.

• Execution: The treatment involves the injection of a mortar, generally with high viscosity, under pressure and at a controlled flow rate, which displaces the soil around the drilling tool and subsequently compacts it. Compaction ratios for this technique can be quite high and are generally in the range of 6-10%.

Soil/Ground Improvement Design: Soil Stabilization

• Define: Soil stabilization is a process by which a soils physical properties are transformed to provide long-term permanent strength gains.

• Benefit: Stabilized soils provide a strong working platform, the foundation for all other parts of projects. After stabilization techniques, weak soils can be transformed by the formation of permanent pozzolanic reactions. Meaning that soils are not liable to leaching and have drastically reduced permeability resulting in reduced shrink/swell potential and increased freeze thaw resistance. In addition, soils that have been stabilized have also undergone some modification. In other words, the soil has physically changed making compaction easier and reducing plasticity. Easier compaction makes achieving maximum dry density easier. Plasticity index is an important geotechnical measure that involves the critical water contents of soils. Any time plasticity in soils is reduced, the soils are more friable and workable.

• Execution: Stabilization methods involve the use of chemicals to improve soil properties for engineering a better working platform for construction. Lime increases the pH of a soil, solubilizing silica and alumina that are naturally present in soils containing any amount of clay. Silica and alumina react with the calcium from the lime and water present in the soil to produce calcium-silicate-hydrates (CSH) and calcium-aluminate-hydrates (CAH). CSH and CAH are the same interactions that are present when working with cement. They form long-term, permanent bonds that drastically improve the bearing capacity of a soil. Co-products of the lime manufacturing process can be valuable as clay content decreases in the soil.

Soil/Ground Improvement Design: Prefabricated Drains (PVD)

• Define: Vertical drains, also known as prefabricated vertical drains or wick drains, are made up of a plastic core surrounded by a geotextile that acts as a filter to prevent clogging.

• Benefit: When a load is applied on saturated cohesive compressible soils (clays, silts), the structure can settle for a long period of time (up to 10 to 20 years). Prefabricated vertical drains, also known as wick drains, are a technique which is used to control long term residual settlement in these type of soils within acceptable limits. The installation of a network of drains creates a preferred path for the water. The combination of vertical drains with the placement of preloading or a surcharge programme accelerates the consolidation period.

• Execution: Vertical drains are made up of a plastic core surrounded by a geotextile that acts as a filter to prevent clogging. There are various types of vertical drains (round and flat) and various sizes. Networks of drains are designed according to the type of ground and the degree of consolidation targeted. Depending on the ground, static, dynamic or static-dynamic installation methods are employed. The machines used can conventionally install drains up to depths of about 50 meters. The mandrel is attached to a sliding mast, which is attached to the arm of an excavator or a crane.

Soil/Ground Improvement Design: Rapid Impact Compaction (RIC)

• Define: Rapid Impact Compaction is a ground improvement technique that densifies the soil by pounding it at high frequency with a medium sized pounder.

• Benefit: RIC is a high-frequency, controlled energy, soil compaction technique used to densify surface layers of soils (to a depth of 5 to 7 meters in most cases) with minimum impact on the immediate worksite environment. Rapid Impact Compaction is widely used to densify loose granular soils (sand or gravel) as well as loam fill and industrial brownfield sites for surface compaction, foundations and floor slab support, liquefaction mitigation and waste stabilization.

• Execution: A compaction plate is placed on the ground to be treated. A hydraulic hammer, generally weighing less than 10 to 15 tonnes, is fitted to an excavator and used to transmit compaction energy to the soil via repeated impact. Without specific site precautions, a safe working distance to sensitive structures can usually be defined on the order of 8 to 10 m, as a distance of 5 to 6 m can usually be adopted for classical structures. At that distance, noise levels are lower than 90 dBA.