Peat soil is formed by the buildup and decomposition of organic elements (derived from plant residues) in an oxygen-deficient, wet environment, making it one of the most challenging soils in the fields of civil and environmental engineering.
In general, soils are considered to be organic if they contain more organic matter than 20%, however peat soils are characterized as having more organic matter than 75%. Plant remnants in peat can be found in a variety of phases of decomposition, from undecomposed to highly decomposed, therefore the soil frequently has a dark brown to black color, is spongy, and has a characteristic smell.
Nearly 5%–8% of the Earth’s land surface is reported to be covered by peat deposits, which are found to be dispersed throughout numerous nations. According to a recent study on peatland mapping, there are 4.23 million km2 of peatland in total. Peatlands are widely distributed, especially in the northern hemisphere.
In comparison to other soil types, peat soils are significantly weaker and more compressible, necessitating unique considerations when supplementing deposits to make them acceptable for engineering uses and long-term preservation. The main drawbacks of peat and the problems they cause are succinctly described below.
- Inadequate Strength and Sustainability
- High Water Content
- Higher Acidic Condition
- Contamination of Humus
Peatlands were traditionally thought to be unsuitable for construction operations because of the aforementioned sensitive qualities; access to peatlands, in particular, was extremely difficult for engineers. However, avoidance is no longer an option because there are fewer and fewer suitable sites for infrastructure expansion and construction. As a result, there is currently more focus on improving the peatlands to meet engineering standards. The most often used techniques involved excavating peat layers and/or replacing them with hard materials like sand, but their application is more likely to be appropriate for peatlands with shallow distributions.
In some cases, piles of buildings were pushed through peaty soil layers to the bedrock. The infrastructures nonetheless experienced differential settlements and tilting, despite the pile supports’ best efforts to reduce the settlement problems. While this was going on, numerous studies were conducted to better understand the complexity of peat soils. With the expertise and knowledge obtained from these studies, technologies were also created to speed up the consolidation process, enhancing the load-bearing capabilities of peat grounds.
The use of prefabricated vertical drains, sand rains, and preloading are only a few of the regularly used methods that are intended to improve drainage capacity and speed up the settlement process. However, the majority of the aforementioned methods use a lot of mechanical energy, demand expensive, high-performance equipment systems, and were not always easily affordable.
On the other hand, chemical-based cementation techniques have been frequently proposed in the past and are seen to be a potential route for organic and peaty soil stabilization. Several cementitious materials have been researched up until this point, including lime, fly ash, blast-furnace slag, bentonite, and gypsum. OPC is a commonly used peat stabilizer, and research suggests that it may be superior to other binders in terms of enhancing peat’s usability. The mechanism entails the hydration procedure that takes place when the peat’s pore water reacts with OPC.
The porous cement gel, which is made up of calcium silica hydrates, ettringite, hydrated lime, and other materials, progressively forms inside the pore voids throughout the hydration. This gel serves as a glue for the neighboring particles and eventually hardens to create stabilized peat. Despite their effectiveness, the majority of cement-based binders and the production methods used to create them are environmentally harmful. For instance, it has been observed that the synthesis of OPC results in a sizable release of carbon dioxide, one of the main greenhouse gases. Additionally, the burning methods that produce the ash-derived binders (such as fly ash) are said to produce toxic pollutants and environmental damage. Because traditional cementitious materials have negative environmental effects, alternative technologies are required.
Foundation Design on Peat Soil
Peat soil is a major problem in the location where we plan to build the foundation. Peaty soil is a very fragile soil with a very poor load capacity, as we previously described. Further, the foundation suffers severe settlement as a result of its compressible nature.
Unless there is a specific need for a deep foundation, we often build small buildings on shallow foundations. Even a single-story building might not be able to build if peat is discovered; ground improvement may be required. We will have to build it on deep foundations if the structure has relatively large axial loads.
The design of deep foundations with peat soil is also challenging due to the following reasons.
- Even if we rest the piles on the rock or hard soil layers, peat soil induces negative skin friction due to its compressible nature.
- Lack of lateral restraint to the piles. Piles having high axial loads could buckle due to the small lateral restraints compared to the other types of soils. Therefore, during the design, these shall be considered.