Introduction to MICP and Sample preparationZeal ZCOER
In India the increase in population and industrialization, there is a much need for the soil to be used for various activities. There is a need to improve the properties of soil, if the soil at any particular locality is unsuited, wholly or partially selected for the construction. With increasing awareness of environmental issues, there has been a remarkable shift toward “green” and sustainable technologies. In view of these attempt is made to study the new sustainable method of biogeochemical techniques to improve the soil properties.
Dam is a solid barrier constructed at a proper location across a river valley to store flowing water. Earth Dams are mainly built with clay, sand and gravel, hence they are also known as Earth fill dam or Rock fills Dam. They are trapezoidal in shape. They are built where the foundation or core material or rocks are weak to support the masonry dam. Earthen dams are comparatively smaller in height and broad at the base. Earth Dams are less rigid and hence more vulnerable to failure. Earth Dams may fail, like other engineering structures, due to inappropriate designs, faulty considerations, lack of maintenance etc. The various causes leading to the failure of earth dams can be grouped into three categories i.e. Hydraulic failure, Seepage failure and Structural failure. Uncontrolled or concentrated seepage through the dam body or through its foundation may lead to piping or sloughing and the subsequent failure of the dam. More than 1/3rd of the earth dams have failed because of these reasons. Various remedial measures has been suggested for controlling dam failures. This includes treatment of control of excessive seepage, structural defects failure and non-structural defects failure. This study focuses on reducing the seepage losses by injecting the soil containing MICP Bacteria in the impermeable membrane of dam.
In India nearly there are 3200 major/ medium dams in which most common dam is an earthen dam. All dams have seepage as the hold water seeks paths of least resistance through the dam and its foundation. Seepage becomes concern if it carries a material with it. The hearting of earthen dams are made up of black cotton soil and seepage through this is a major concern. In this project we are trying to control the excess seepage and losses through the hearting of dams. MICP will increase the bonding between the soil my calcite precipitation produced by bacteria reducing the permeability and seepage.
Most embankments exhibit some seepage. However, this seepage must be measuredin velocity and quantity. Seepage occurs through the earthen embankment or dike and/or through its foundation. Seepage, if uncontrolled, can erode fine soil material from the downstream slope or foundation and continue moving towards the upstream slope to form a pipe or cavity to the pond or lake often leading to a complete failure of the embankment. This action is known as “piping.” Seepage failures account for approximately 40 percent of all embankments or dyke failures. Seepage can also cause slope failures by saturating the slope material, thereby weakening the adhesive properties of the soil and its stability. Burrows or holes created by animals such as theGround hog, woodchuck, or muskrat create voids in the embankment or dyke, which weaken the structure and may serve as a pathway for seepage. Tree roots can provide a smooth surface for seepage to travel along. When trees die, their decaying roots may leave passageways for seepage to concentrate in. Pipes through the embankment may also provide smooth surfaces for seepage to concentrate along as well.
In the past few years before soil stabilization technique using MICP was introduced, chemical grouting method was applied to stabilize soil. The process of chemical grouting technique is achieved by adding variety of additives which is very toxic such as Portland cement, lime, asphalt, sodium silicate, acrylate, lignin, urethane, and resins in order to strengthen the soil. Many researchers had proved that these additives will modify the pH of soil and contaminate the groundwater and soil and chemical grouting is becoming very popular due to its economic benefits but nowadays with the increasing awareness of environmental issues, it is likely to introduce a more sustainable method in stabilization of soil such as MICP method.
Several problems of tropical residual soil condition such as low strength, high compressibility, softening due to infiltration on raining season had caused many geotechnical engineering problems such as settlement of embankment or foundation, debris flow, landslide and others Natural 238 disaster such as landslides has increased and become the major concerns of engineering geologists and geotechnical engineers.The conventional soil stabilization method such as grouting method had applied in order to strengthen the soil. Stated that chemical used in grouting method such as Portland cement, lime, asphalt and others are toxic and hazardous. Applying this method to strengthen the soil are not environmental friendly because chemical in the soil will change the pH of the soil and contaminate groundwater and due to environmental concerned, previous study about soil stabilization by using chemical grouting method are not suitable because it may cause soil and water pollution. MICP is a relatively green and sustainable soil stabilization technique which utilizes biochemical process that exists naturally in soil to improve the engineering properties of soil. Hence, there is a need of study on new green technologies, MICP method which is more environmental friendly to stabilize soil.
Hence a study is carried out to validate the idea behind “Microbial Induced Calcite Precipitation (MICP)” is to provide comparatively clean and sustainable technique in the field of ground improvement.Improve the shear strength of soil.To study the feasibility of Bacillus Megaterium in MICP treatment of black cotton soil.To reduce the seepage losses through the dam.For the improvement of behavior of soil, various ground improvement methods are available example chemical stabilization, cement stabilization etc. The inherent drawbacks of these methodare not new to the industry. MICP promises to provide a solution for the existing problem like repair work of roads, tunnels, canals, etc. This method is eco-friendly and economical technique compared to other soil stabilization technique. The availability of bacteria as well as its cultivation can be done in huge amount.
- Converting lyophilized bacterial strain into active liquid form
0.65gm nutrient broth powder is added in 50ml distilled water. Then sample is kept in autoclave for sterilization. The pressure in autoclave is maintained to 15kg/cm2. When the pressure reaches 15kg/cm2 the temperature is about 121oc. sterilization is done to remove or to kill the biological agents or bacteria’s which are already present in the solution due to broth powder. Autoclave is done for 15min then solution is taken out and it is allowed to get cooled to room temperature. Then with the help of sterile loop(it is a small stick which is used to remove strain from test tube) the strain is taken out and dipped in the sterilized medium and kept for 24hrs for the growth of bacteria.
- Sample preparation and vane shear test:
We conducted vane shear test on PVC pipes filled with black cotton soil and bacteria. For vane shear test the required L/D ratio is in the range between 2 to 3 so we selected pipe of internal diameter 2.6cm and length 7.8cm.
Total 8 samples were prepared for the test and each specimen is filled with black cotton soil and stain about 2.5ml was injected with the help of sterilized dropper. Vane shear test is performed on 0, 1st, 2nd day and results were taken.
MICP is a microbial process which greatly depends on temperature, pH, calcium concentration. This makes it a complex and time consuming process in comparison to the chemical process under standard environmental conditions.
The economic limitation makes MICP less industrially friendly, as laboratory grade sources needs to be used. Since there’s a potential of inefficient MICP when using non-laboratory grade chemical reagents. Although alternative inexpensive nutrient sources for MICP such as lactose mother liquor have been implemented, consideration of a wider range of alternative sources would provide a better assessment of its cost effectiveness.
In addition to this limitation, application of in-situ MICP would require the generation of substantial volumes of chemical reagents and microbial solutions.