The electrokinetic stabilization (EKS) impact on soft soil (peat) stability towards its physical, mechanical and dynamic properties at Johor state, Peninsular Malaysia
Introduction
Soils plays a significant role in infrastructure and construction projects such as buildings, roads, dams, and other structural design developments. Ground enhancement is a fast-developing field because of the rapid devaluation of construction land. There are various types of soil used in construction projects; however, the use of soft soil (peat soil) has reportedly been problematic due to the extreme softness, unconsolidated, and possesses low shear strength, stiffness, and high-water content (Ghareh et al., 2020; Deboucha et al., 2008). This gives rise to serious issues such as excessive and long-term settlement during or after the construction and ultimately results in time and cost overruns in construction projects (Elufowoju, 2019).
Peat soil is recognized as soft soil having an excessive volume of natural matter (Kolay and Pui, 2010), and it is compressed to an extreme extent if a heavy load is applied to it. This is because of the deficient characteristics such as high porosity, excessive squeezability, high water volume, and low shear strength. Peat soil is formed due to the partial decomposition and disintegration of swamp, brushwood, trees, and plants that grow up in a humid condition in the absence of oxygen. (Kazemian et al., 2011). Peat is further classified into three different classes: fibric, hemic, and sapric based on the degree of decomposition. Based on fiber content, further peat is often reduced to three subclasses, including fibrous, semi-fibrous, and amorphous (Sutejo et al., 2017; Karthigeyan and Ramachandran, 2019).
This type of soil exists globally, almost covering about 8% of the Earth's land (Dehghanbanadaki et al., 2019). Mostly it's found in the tropical countries of the world (Abdel-Salam, 2018; Leng et al., 2019), where approximately 95.0% of peat exists in humid regions (north part of the hemisphere), covering about 4.24 million square kilometers, which make 4% of the world's land (Xu et al., 2018). The accurate volume of peat has yet to be exposed, but Rahgozar and Saberian (2015) stated that there are two countries around the globe having the highest sum of peatland, which is Canada with (170 million hectares) and Russia about (150 million hectares) as shown in Fig. 1. The worldwide distribution and the exact quantity of peatlands in several countries have been tabulated in Table 1.
Malaysia is located in the northern and eastern hemispheres and is considered a tropical country with the world's sixth-largest peat reservoirs. The peatland in this region is mostly used for plantations (palm oil, pineapple, and banana), cultivation land, and nominal economic value except for farming interests (Kolay and Pui, 2010; Mohamad, 2015). In Malaysia, the peatland is investigated as one of the most critical soil types covering about 3.0 million hectares (8.0%) of its terrestrial area. Mostly, peatlands are found in Peninsular Malaysia, while Sarawak states cover about 13.1% or 1.65 million hectares of peatland, which is considered substantial in the region (Moayedi and Nazir, 2018). Out of 3 million hectares, approximately 143974 ha of peatland are found in Johor state. Generally, 6301 ha are preserved in Pontian, Muar, and Batu Pahat areas in Johor state. The details of peat soil existence in Malaysia are presented in Table 2, whereas peat soil occurrences in Malaysia are shown in Fig. 2 (Hashim and Islam, 2008; Melling, 2016).
Soil's physical, mechanical, and dynamic properties such as strength, moisture content, liquid limit, and shear wave velocity play an actual appearance in developmental projects. Some significant characteristics of peat soil must be investigated during peat stabilization. In 1987, Hobbes expressed that some properties, such as; strength, color, organic content, water content, degree of humification, and bulk density, must be considered for the detailed explanation if any construction is projected on the peat (Huat et al., 2011).
The soil with more than 76.0% natural organic content & shear strength in between (5.0–20.0 kPa), with high compressibility and natural water content in between 250.0% and 985.41%, is considered as pure peat soil. When some infrastructure work is established on the peat accumulated area, it will continuously add to the complexity during or after construction (Mohd Razali, 2013). The Malaysian tropical peat soil is assessed as pure peat soil with organic content between 76.0% and 98.99% with weak physical and mechanical characteristics. The shear wave velocity of Malaysian peat soil is in the range of 26.02–95.89 m/s, as tabulated in Table 3 (Said and Jazlan, 2016; Wahab et al., 2018, 2020bib_Wahab_et_al_2018bib_Wahab_et_al_2020).
From a construction perspective, peat soil is reflected as the most challenging soil, and construction engineers consider it hard to develop any project on peat soil without proper treatment. The construction of road embankments on peat soil becomes more complex, where a differential settlement of the substrate, slope failures, globe instabilities, and long-term settlement occurs during or after construction. To build reliable and durable highways, high-rise buildings, and railway tracks on peat soil, its critically essential to strengthen its properties (Razali et al., 2013). Peat soil is one of the most exciting materials for construction engineers due to its weak properties. The challenges such as excessive settlement and local drowning occur when the advanced load is subjected (Abdel-Salam, 2018).
In West Malaysia, generally, peat is found in the seaside areas, especially in the west parts such as Pontian, Batu Pahat, Kuantan, Pekan, West Selangor, and Perak state. Major construction activities and economic developments focus on the coastal area, which comprises problematic soil. In Malaysia, the construction projects, including coastal high-rise buildings and roads, face instability problems that are frequently supported by soils having low stability, high water content, and high compressibility. One of the critical issues faced by geotechnical engineers in Malaysia is establishing the peat groundwork for construction projects such as building and railway tracks. However, when a street road was built on un-stabilized peat, the depression and cracks were observed due to low strength and high permeability, as shown in Fig. 3. To ensure these issues are at least reduce with electrokinetic stabilization technique, which easily enhances the weak properties and decreases its negative effect on the construction industry (Hua et al., 2016).
Electrokinetic stabilization (EKS) is a newly developing technique especially acknowledged for strengthening low permeable soil. The electric potentials are applied to fluid transport in porous media and physical and chemical transport of charged particles (Mosavat et al., 2012; Ossai et al., 2020). It refers to applying a low direct current (DC) or (pulsed electric fields) connected through a pair of electrodes. The electrodes are injected vertically into the soil, and during the electric current exerting, the electroosmosis, electromigration, and electrophoresis phenomena occur, and the ions move towards the electrodes, as shown in Fig. 4 (Wen et al., 2020; Cameselle et al., 2013).
This technique is mostly applicable to apply for both in-situ and ex-situ low permeable soil stabilization by using low electric potential difference or direct current to both anode and cathode electrodes. This method inspires researchers in understanding to enhance the engineering properties, including slope instability, unstable embankments, backfill strengthening, soil drainage, remediation of salt-affected soils, recycling of contaminated soil, assisting pile driving, dewatering of sludges, groundwater lowering, and treatment of dispersive soil (Tang et al., 2021; Razali et al., 2013).
Many other methods are used for soil stabilization, such as stabilization, using different admixture, lime, cement, fly ash, thermal, geo-textile, and fabrics stabilization Hozatlıoğlu and Yılmaz (2020). Compared to the method mentioned above, there are numerous advantages to using the EKS method in terms of cost and operation duration. It can appropriate both in-situ and ex-situ with having rapid installation, silent operation, and easy to operate (Mosavat et al., 2012).
Previously, several researchers such as (Keykha et al., 2014) performed a laboratory-based electrokinetic stabilization experiment to enhance soft soil properties, including strength and moisture content. They used two graphite laminates as electrodes, while CaCO3 was used as electrolyte solutions. An electric current of 60 V was practiced for ten days. The study results showed that the moisture content was reduced, and shear strength was increased from 7 kPa to 61 kPa.
Askin and Turer (2016) observed electrokinetic stabilization laboratory-based experiments to strengthen the soft clay. The samples were taken from Ankara city, Turkey. They used a circular experimental setup with several electrodes, and calcium chloride was used as an electrolyte solution with an electric current of 110 V for 240 h. The results indicated that the shear strength showed a remarkable improvement up to 36, 50, 58, and 85 kPa, respectively, in different experiment phases.
Tajudin et al. (2016) practiced the electrokinetic stabilization technique in two phases to improve Batu Pahat marine clay. The author applied a constant voltage gradient of (50 V/m) through stainless steel electrode for 21 days. Two reactors were used as an electrolyte solution, including 1.0 M of calcium chloride (CaCl2) and sodium silicate (Na2SiO3). His results concluded an excellent improvement in the soil properties after electrokinetic stabilization treatment.
Wahab et al. (2018) performed an EK experiment to intensify peat soil's low characteristics. The samples were collected from different Parit Botak areas, Batu Pahat District, Johor, Malaysia. The load of 50 kg was subjected to peat samples before operating the electric current. The electric gradient of 110 V was used through an aluminum electrode on both cathode and anode for 3 h. The authors' findings demonstrated that shear-strength was enhanced from 8.8 kPa to 75 kPa and 9.9 kPa–69 kPa for different peat samples. The moisture contents were detected to be condensed from 568.248% to 309.274% and from 502.595% to 284.73% in various phases.
Accordingly, Wahab et al. (2020) applied the electrokinetic stabilization technique to soft soil. The peat sample was collected from Parit Lapis Kadir, Batu Pahat, Johor. The electric gradient of 110 V was applied for 3 h with a subjected load of 50 kg. The results indicated that shear strength was improved up to 64 kPa, the water content was decreased from 478.849 to 306.384%, and the liquid limit was also improved effectively.
Estabragh et al. (2021) performed a laboratory electrokinetic stabilization technique for clay strength improvement. The experiment was conducted under constant voltage and time, and calcium chloride (CaCl2) or magnesium chloride (MgCl2) was used as an electrolyte solution with different concentrations. His results reported an outstanding improvement in strengthening the soil properties.
Therefore, in this study, further investigation on the effect of electrokinetic stabilization (EKS) for this soft soil (peat) toward its physical, mechanical, and dynamic is performed. This study concentrated on three objectives, and the first is to measure the in-situ shear strength of peat in twenty different locations. The second objective is to examine the physical, chemical, and dynamic peat properties of treated soil. In contrast, the last objective is to enhance the physical, chemical, and dynamic properties by using the electrokinetic stabilization technique and compared untreated and treated soil properties between pre and post EK stabilization.
An electrokinetic cell was designed to achieve these objectives, and a series of laboratory experiments were examined for both untreated and treated soil specimens, including shear strength and moisture content: liquid limit and density test. The test parameters were repeatedly examined five times for all collected samples, which led to an excellent stabilization result for this study.
Section snippets
Method and materials
In this study's scope, the peat samples were taken from various locations in the Parit Botak surroundings area. According to the EK cell size, the in-situ shear strength was measured for 20 multiple locations at a depth of 10, 20, and 40 cm. Furthermore, three-peat soil samples were collected from three sites as shown in Fig. 5, Parit Haji Ali, Parit Nipah, and Parit Lapis Kadir based on low shear strength, the GPS coordination is tabulated in Table 4. The collected samples were transferred in
Peat soil properties (Pre-EK)
Peat soil's physical, mechanical, and dynamic properties were studied for all three samples that show the original properties without additional treatment. The shear strength of unstable peat soil is shown in Fig. 7, while the dynamic properties of un-treated peat soil have been presented in Fig. 8, Fig. 9, Fig. 10. The discussed properties for untreated peat are tabulated in Table 5.
Peat soil properties (post-EK)
Peat soil characteristics were analyzed for post electrokinetic treatment, where the voltage of 150 V was
Conclusions
The study has analyzed that peat soil properties such as shear strength, moisture content, liquid limit, and dynamic properties (shear wave velocity) were improved by exercising the EKS treatment; the following conclusions were drawn from this study:
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Significant improvement was observed in the shear strength of peat soil. It was concluded that strength was enhanced up to 55 kPa (65%) for Parit Haji Ali, 48 kPa (48%) for Parit Nipah, and 58 kPa (54%) for Parit Lapis Kadir peat soil with a voltage
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors would like to thank the financial support by FRGS (Vot: 0836) provided by University Tun Hussein Onn Malaysia.
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