Biotechnical Ground Improvement

• The future of ground improvement will involve new equipment and improved existing equipment using computer controls and sensors.
• Artificial intelligence is expected to assist field engineers in decision-making.
• Advancements in instrumentation for performance monitoring and quality control are anticipated.
• New materials and material combinations will lead to improved ground performance in terms of strength, compressibility, permeability, bearing capacity, settlement, and liquefaction resistance.
• Biological methods, such as microbial induced calcite precipitation, may be used to enhance strength and reduce compressibility/permeability of sandy soils.

Biotechnical Ground Improvement (Microbial Geotechnology)

• Biogeotechnical ground improvement combines biological processes and geochemistry to enhance soil properties.
• Bio-mediated processes including mineral precipitation, biopolymer generation, mineral transformation, and gas production have potential in ground improvement.
• Mineral precipitation can improve bearing capacity, reduce settling, and improve liquefaction resistance.
• Biopolymer generation (biofilm growth) can reduce permeability for hydraulic barriers and underground seepage control.
• Mineral transformation can reduce soil expansion and improve slope stability.
• Gas production from microbes can reduce liquefaction potential.
• Engineered biogeotechnical systems can harness natural processes for beneficial use.
• There are billions of bacteria per gram of soil that participate in biogeochemical reactions.
• Engineers can learn from natural processes that change soil properties, like carbonate cementation of sand and mineral transformation of clays.
• Detrimental processes like mineral scaling of piping and bioclogging of drainage systems should be avoided.

Biocementation

• Biocementation is defined as the biological production of materials that bind soil grains together, increasing shear strength and reducing compressibility.
• Microorganisms induce calcium carbonate precipitation (biomineralization) to bind soil particles, increasing strength, stiffness, and liquefaction resistance while reducing permeability.
• Microbial Induced Calcite Precipitation (MICP) bacteria, such as Sporosarcina Pastueurii, break down nutrients like urea by hydrolysis, increasing pH and precipitating calcium carbonate.
• Precipitates bond particles at contact points and within voids, increasing density and reducing permeability.
• Biogeotechnical ground improvement methods are projected to be cost-effective and sustainable.
• Research is focused on managing complex biological, hydrological, and geochemical processes, and avoiding unintended side effects.
• MICP can be produced through multiple processes, with varying end products and undesirable side effects.
• The formation of gas, an undesirable attribute, has been shown to reduce pore pressure during earthquake loading, improving liquefaction resistance.
• Calcium carbonate concentrations greater than 60 kg/m³ improves peak compressive strength.
• The threshold calcium carbonate content of 60 kg/m³ corresponds to 3.6% cement by weight.

Bioclogging

• Bioclogging is the biological production of materials that reduce effective porosity and hydraulic conductivity.
• Slime, biomass, and biogenic gas bubbles accumulate in soil pores reducing the ability to transmit water.
• Microbial processes that lead to bioclogging are the result of different organisms and various mechanisms.
• Each bacteria type requires specific conditions (light, nutrients, oxygen, salts, urea) to produce bioclogging.

New Materials for Ground Improvement

• Ground improvement methods incorporate ordinary portland cement (OPC) to increase strength, reduce compressibility, and reduce hydraulic conductivity.
• Examples include vertical barriers, deep soil mixing, jet grouting, stabilization/solidification, and vibratory concrete columns.
• Shrinkage is inevitable with cementitious mixtures and can reduce stress and cause cracking in structures, such as vertical barriers.
• Magnesia (MgO) can be used as a shrinkage compensating additive without detrimentally affecting other properties.
• Samples containing MgO experience expansion both initially and throughout the curing period.
• Effects of MgO on hydraulic conductivity and strength are being studied.

Polymers

• Water-soluble polymers saw increasing use starting in the 1990s.
• Early polymers were biodegradable natural polymers such as guar gum, used for slurry trenching and subsurface drain installation.
• Synthetic polymers are increasingly used.
• Polymer support fluids will find increasing usage in ground improvement applications as polymer science advances and bentonite availability decreases.

Smart and Self Healing Materials

• Smart materials adapt in response to changes in their environment.
• A smart structure is a system with components that can sense, control, and respond to environmental changes.
• Piezoceramic actuators can be used for vibration suppression in structures.
• Smart materials include piezoelectric materials, shape-memory alloys, and photomechanical materials.
• Temperature-responsive materials can aid closure in ground freezing walls.
• Self-healing materials can repair cracking that may occur in barrier walls.
• Self-healing is taken from living systems and is termed biomimetics.
• Self-healing of concrete occurs as cracks fill with white crystals of calcium carbonate.
• Microbes that convert nutrients into limestone can be embedded for self-healing.
• Acid producing bacteria used for self-healing of cracks, can remain viable for over 200 years under dry conditions.
• Self-healing for ground improvement represents a future development.