A Study on the Different Types of Biochar on the Geotechnical Behaviour of Locally Available Soils

Soil is a foundational material in civil engineering, especially for infrastructure like roads, embankments, and foundations. However, many natural soils, particularly clayey and silty types, are weak in strength, highly compressible, and susceptible to moisture variation. Stabilizing such soils is necessary to ensure long-term structural stability and load-bearing performance. Traditionally, soil stabilization has relied on chemical additives like cement and lime. Although effective, these materials are energy-intensive, expensive, and contribute significantly to environmental degradation through carbon emissions. In recent years, attention has shifted toward sustainable alternatives, especially those derived from waste materials. Biochar, a carbon-rich byproduct obtained from the pyrolysis of organic waste under limited oxygen, has emerged as a promising eco-friendly stabilizer. Its porous structure, lightweight nature, and chemical stability make it suitable for improving the physical and mechanical behavior of soils. Biochar is known to improve water retention, reduce swelling, enhance compaction characteristics, and increase the strength of treated soils. This study explores the geotechnical impact of three locally available biochars—Water Hyacinth Biochar (WHB), Rice Husk Biochar (RHB), and Sugarcane Waste Biochar (SWB)—on silty and clayey soils collected from Golaghat, Assam. The objective is to assess how the addition of these biochars influences Atterberg limits, compaction properties, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS) of soils. The findings are expected to promote the use of agricultural waste for soil improvement and encourage sustainable construction practices, particularly in rural and low- cost infrastructure projects

LITERATUREREVIEW:

Hagemann et al. (2017) studied the impact of biochar on soil structure under drought conditions. The authors found that biochar improved soil aggregation and water retention, leading to enhanced soil stability and greater plant resilience. Their work emphasized biochar’s potential role in climate change adaptation within agriculture and land restoration practices.

Ahmad et al. (2014) examined the performance of biochar-lime combinations for stabilizing tropical benefits, especially in acidic or degraded soils.

Beesleyetal. (2011) investigated the role of biochar in reducing the mobility of toxic metals such as lead (Pb) and cadmium (Cd) in contaminated urban soils. The study showed that biochar immobilized these heavy metals, significantly reducing their bioavailability and thereby minimizing environmental and health hazards.

Cao et al. (2009) focused on dairy-manure-derived biochar and its ability to immobilize lead in polluted soils. The findings confirmed that biochar reduced Pb leaching effectively through mechanism such as surface complexation and precipitation.

Ghosh et al. (2020) evaluated the use of biochar in sewage sludge stabilization. Their research demonstrated that biochar additions reduced the leachability of heavy metals and improved nutrient retention, making treated sludge more viable for land application.

Mohan et al. (2014) explored the stabilization of industrial waste using biochar. The results indicated that biochar improved handling properties, minimized environmental risks, and facilitated the immobilization of harmful elements, emphasizing its role in sustainable waste management.

Tan etal.(2021) assessed the integration of biochar into cementitious materials. Their study found that while thermal insulation and sustainability improved, as light decrease in compressive strength was observed, suggesting the need for optimized formulations when using biochar in concrete composites. Despite these promising studies, few have compared the geotechnical impacts of different types of biochar - such as Water Hyacinth, Rice Husk, and Sugarcane Waste - on different soil types under uniform testing conditions. This study addresses this gap by systematically evaluating the effect of three locally available biochars on the geotechnical behavior of clayey and silty soils.

MATERIALS AND METHODS:

MATERIALS:

Two types of locally available fine-grained soils were selected for the experimental program. The first, a clayey soil (Soil1), was collected from Sumoni, Golaghat, Assam, at a depth of approximately1meter.Thesecond, asiltysoil(Soil 2), was obtained from the campus of Golaghat Engineering College from a similar depth. Bothsoils were air-dried, crushed, and sieved through a 4.75 mm IS sieve prior to testing. Three types of biochar were used in this study: Water Hyacinth Biochar (WHB), Rice Husk Biochar (RHB), and Sugarcane Waste Biochar (SWB). All biochars were prepared locally using controlled pyrolysis methods.

• WHB was produced by drying water hyacinth hand burning it in a partially sealed pit with restricted oxygen supply to retain carbon content.
• RHB was obtained from a local rice mill where rice husks were slowly burned in a sealed tin chamber to preserve silica content.
• SWB was derived from dry sugarcane bagasse burned in a trench kilnand covered with moist fabric to control combustion.

Each type of biochar was cooled, ground, and sieved to pass through a 425-micron sieve. The processed biochar was stored in airtight containers until use.

METHODS:

Pyrolysis: It is the process of breakdown of organic waste in the absence of oxygen to obtain product like biochar, biogas, tar etc.

Fig.1: California Bearing Ratio Test

Fig.2: Unconfined Compression Test

RESULTS AND DISCUSSION:

Proctor Test:

The results from the proctor test shows that Optimum Moisture Content (OMC) and Maximum Dry Density of the soil sample. We have taken two Types of soil samples i.e; soil sample1and soil sample 2 which is clayey and silty soil respestively As per ISCS classification of soil.

Fig.3: Proctor Test Result Soil1

Fig.4: Proctor Test Result Soil 2

California Bearing Ratio Test:

The collected soil sample were tested under California Bearing Ratio (CBR) machine at 0%biochar and treating with soil at 5% biochar respectively for both soil. The results of the soil were given below:

Fig.5:CBR Test Result Comparison

Fig.6:CBR Test Result Comparison

Unconfined Compression Test:

The unconfined compression test (UCS)were carried

out on soil sample 1 and 2 with the combination of 0%biocharand5%biochar. Soil mix were prepared Soil + 5% biochar + OMC for treatred soil sample.

Fig.7: UCS Test Result Comparison

Fig.8: UCS Test Result Comparison

DISCUSSION:

For CBR Test:

Table.1:CBR test result comparision for soil1

Table.2:CBR test result comparision for soil2

For UCS Test:

Table.3:CBR test result comparision for soil1

Table.4:CBR test result comparision for soil2