Main purpose of this project is to improve earthquake liquefaction risk mitigation planning, design and execution with reference to an innovative and environmentally friendly Ground Improvement (GI) technology named Induced Partial Saturation (IPS).

By introducing a certain amount of air or gas into the voids of the soil, partial saturation can be increased and so that resistance to liquefaction susceptibility will also increase. Induced partial saturation can increase the compressibility of the pore fluid. So, during earthquake loading, the pore pressure build-up is reduced, and it leads to an increase in the soil cyclic resistance, without affecting any nearby structure. Some researchers have found that an initially saturated sand can experience relevant effect even if there is a small reduction of the degree of saturation.

The research team is very keen to developing IPS implementation because India being a highly seismic country with many areas at risk of liquefaction, and also having the goal to implement environmentally friendly technologies. This method is being a carbon free technology, it has the potential of beating more conventional mitigation techniques, that often rely on the injection of cement/lime in the soil. The development of the technology readiness level of IPS technique to show the way of important opportunities in the national and international markets of economically sustainable methodologies for the mitigation of liquefaction effect.

Mechanism of IPS

In general, the terms “unsaturated,” “partially saturated,” and “fully saturated” soil can be used to describe different soil conditions. Continuous air phases inside the soil aggregates will ultimately disappear, and the matric suction would decrease, leading to a phase transition from unsaturation to partial saturation. Despite their ability to change the compressibility of pore water, these air bubbles, which are largely present in pore water, will not interact significantly with soil aggregates. The mechanism behind IPS is that the presence of air bubbles lowers the bulk modulus of the pore fluid, enabling the soil to conserve energy by decreasing its volume while preventing the development of further pore pressure due to cyclic loading. Because of the low volumetric stiffness of gases, the fluid bulk modulus is extremely sensitive to the presence of gas. Even tiny amounts of gas greatly reduce the fluid bulk modulus, which causes the production of excess pore water.

Advantages of this technique:

1. Environmentally friendly
2. Economical
3. Applicable without affecting any nearby structure.
4. Applicable under existing structures

Planned work flow:

1st method of IPS – Microbial Induced partial saturation (MIPS)

1. In the biological process of denitrification, nitrate (NO3) is gradually converted to nitrogen gas (N2). A wide variety of bacteria, including Pseudomonas, Paracoccus, Flavobacterium, Alcaligenes, and Bacillus spp., participate in heterotrophic denitrification, which employs an organic carbon electron donor like methanol, ethanol, or acetic acid (Mieczyslaw Blaszczyk 1993; Park and Yoo 2009).
2. Nitrogen gas (N2) is neither flammable nor a greenhouse gas, which is one of its many advantages that are pertinent to this investigation. The most significant characteristic is its extremely low solubility, which is 0.014 l of gas per liter of water at 250°C and atmospheric pressure (He and Chu, 2014).
3. Knowing the principles and limiting variables of the microbial denitrification process, Pseudomonas stutzeri was chosen to perform the soil desaturation experiment. Dry powdered Pseudomonas stutzeri (MTCC 863) was purchased and grown on a petri dish stabilized with nutrient agar.
4. Preliminary Microbial batch test on sand sample to confirm nitrate reductase, to determine optimum nitrate content, pH and different temperature effect.
5. Modification was done for this application method to the typical triaxial configuration
6. Series of Cyclic traxial test were performed with different relative density, confining pressure, and cyclic stress ratio (CSR) which has computed according to Earthquake magnitude of moderate to major.

2nd IPS method – Direct air injection

1. The triaxial facility was altered to include an air compressor line that was linked to the base of the sample in order to facilitate and precisely maintain the air injection pressure.
2. Series of cyclic triaxial test were performed with different relative density, confining pressure, and cyclic stress ratio which has computed according to Earthquake magnitude of moderate to major.
3. Development of air injection setup and test series were performed with different set of air injection pressure, duration and different overburden for developing relation between air injection pressure and degree of saturation ,duration without creating crack in sample.
4. The factor of safety (Fliq) against the liquefaction of saturated and desaturated sand at various degrees of saturation is determined against several earthquakes ranging from strong to major magnitude by converting lab (Cyclic resistance ratio) CRR to field CRR.

Visible desaturated zone after air injection process in fully saturated sand samples.

In micribial induced partial saturation(MIPS) study , partial saturation generated by denitrifying bacteria metabolism has been
evaluated, as well as the liquefaction behaviour of the treated sample. The desaturation test
proved that the microbial denitrification process may create nitrogen (N2) gas in sand, resulting
in the sand desaturation. By changing the nitrate content of the soil, a saturation level of
less than 80% can be reached. The cyclic triaxial test reveals that reducing the saturation level
of sand from 100 % to 90% can greatly reduce its liquefaction potential. Saturated sands lose
their stiffness much more rapidly than partially saturated sands when subjected to cyclic loading,
as evidenced by the less number of cycles necessary to produce early liquefaction in the
saturated samples. After inducing partial saturation with the MIPS approach, the soil’s resistance
to liquefaction increases rapidly. This suggests that induce partial saturation of sand by
this technique can be a highly effective countermeasure against liquefaction.