The effect of adding biopolymers on the physical properties of peat soils

. Indonesia's peatlands are concentrated in three major islands, namely Sumatra (35%), Kalimantan (32%), Papua (30%), and other islands (3%) of a total area of 21 million ha. Peat has a low carrying capacity. The carrying capacity of the soil is largely determined by the value of the water content contained in the peat. To overcome this problem, stabilization is carried out using a mixture of biopolymers to increase the carrying capacity of the soil. In this study, testing of the physical properties of peat soil was carried out in order to determine changes in the value of the physical properties of the soil that occurred after stabilization. The sampling location is in the area of Palangka Raya City. There were 5 variations of samples made for stabilizing peat soil with a mixture of 0.5%, 1%, 2%, 2.5%, and 3% biopolymer. The final results obtained after testing the physical properties of post-stabilization peat soil were a decrease in water content in the 3% biopolymer (395.13%) variation, the maximum decrease in fiber content in the 3% biopolymer (30.79%), and the maximum ash content obtained in the 3% biopolymer increasing the value of the bulk density at 3% bipolymer (1.64%), and increasing organic content (96.62%) at 3% biopolymer variation.


Introduction
The total area of peatlands in the world is 420 million hectares.there are around 30 to 45 million hectares of peatlands with tropical peat types.Indonesia is included in tropical peatlands with an area of 14.9 million hectares.Spread across several islands including the islands of Sumatra, Papua, and Kalimantan.The distribution of peat area on the island of Sumatra amounted to 43.18% or 6,436,649 Ha, peat area in Papua amounted to 24.72% or 3,690,921 Ha, and peat area on the island of Kalimantan amounted to 32.06% or 4,778,004 Ha. [1].
Peat soil is a highly organic material [2].Due to its water content and organic nature, peat soils can be deformed by loading.About 44.6% or 6.66 million hectares of the total peatland area in Indonesia is degraded because it is used for various purposes such as agriculture, forestry, plantations, and infrastructure development.
Peat soils also suffer from instability problems such as localized land sinking and slope collapse [3].Visually, peat soils are known as fibrous masses containing woodiness, usually dark in color and smell of decaying vegetation.KEMENKUMHAM [4] states that peat is an organic material formed naturally from decomposed plant remains.Peat soil is high in organic matter, easily compressible, has low shear strength, and has acidic properties that can damage building materials.[5].
The dry weight content of organic soils is very low, 0.2-0.3kN/m3.Mineral soils, on the other hand, have a dry weight of 1.25-1.45kN/m3.This is because, in its dry state, peat soil is very dry, this happens because of the organic nature of peat soil so that it undergoes advanced decomposition.
In addition, peat soil has a very high water retention capacity.Peat soil can hold 2-4 times its weight in water.On the other hand, mineral soils only hold ½ to 1/5 of their weight.Before decomposition, peat soil has the ability to hold water up to 12 to 20 times its dry weight.
One of the provinces with the largest tropical peatlands in Indonesia is located in in Kalampangan Village, Sebangau District, Palangka Raya City, Central Kalimantan Province.The research and sampling location is one of the areas where peatland is utilized in a variety of ways.The utilization of tropical peatland in this area has changed rapidly from peat forest to various types of land use.The land use in Kelurahan Kalampangan is used, for example, for oil palm plantations, secondary crop plantations, pineapple plantations, settlements, and infrastructure development.
To build infrastructure, one of which is a highway that is safe, stable, and can be used for a long time, it must overcome the problem and be able to find the right solution to build infrastructure on peat soil, one of which uses stabilization materials with Chitosan Biopolymer.Stabilization using biopolymers can affect the parameters of the physical properties of the soil in peat, resulting in changes in the physical properties of the soil in it.So, this research aims to determine the characteristics of tropical peatlands that have been stabilized for infrastructure development, the parameters of the physical properties of poststabilization peat soil include density, porosity, and water content.The samples were taken at a depth of 100 -150 cm, and the variation of stabilization materials was 0.5%, 1%, 2%, 2.5%, and 3%.

Research methods
This research was carried out in several stages, starting from a literature study which, among other things, aims to get an overview of research that discusses the physical properties of peat soil.

Location selection and peat soil sampling
The land criteria chosen in this study were plantation land in Kalampangan Village, Sebangau District, Palangka Raya City, Central Kalimantan Province at coordinates 2°27'24.23 "S 114°01'95.62"E.Soil sampling was undisturbed.Sampling was conducted at a depth of 100-150 cm.Sampling using cylindrical tubes ø 4 inches and 20 cm long and given a lid on the top and bottom.so that 10 cylindrical tubes are needed for undisturbed soil sampling.

Mixing peat soil sample with biopolymer
Methods of mixing peat soil and biopolymer at 0.5%, 1%, 2%, 2.5%, and 3% of wet soil specific gravity [6].When the peat soil was wet, it was mixed and stirred until it was evenly distributed.The mixture of peat soil with biopolymer that had been evenly distributed was left in an open this was done so that the peat soil could be maximally stabilized.The stabilized sample was then placed in a place protected from sunlight.This treatment process was carried out for 28 days.
The variations of biopolymer blends that should be added are: Peat soil weight = 4500 grams  The biopolymer used is chitosan biopolymer, which is produced from crab shell waste, which is processed to produce biopolymers in powder form.In the picture is the process of mixing peat soil with biopolymer stabilization material, then the stabilized soil must pass through a boiling period of 28 days

Physical properties of Palangka Raya peat soil
The results of laboratory analysis of peat soil samples Kalampangan Village, Sebangau District, Palangka Raya City, Central Kalimantan Province are shown in Table 2. Table 2 is a test of the physical properties of the soil, including the water content in peat soil of 779.87%, while according to the parameters of peat soil [7] the average natural moisture content of peat soil in Indonesia is 750% -1500%.
The organic content of the soil in Palangka Raya was 97.38%, and the peat soil parameters showed an average value of organic content in peat soil of 95 -99%.
The specific gravity value of the soil in Palangka Raya is 1.13, while the average specific gravity value of peat soil in Indonesia is 0.95 -1.25.
The value of soil fiber content in Palangka Raya is 61.14 while in peat soil parameters the average value of the specific gravity of peat soil in Indonesia is 39.5 -61.3.
The ash content of the soil in Palangka Raya is 2.62, while the average specific gravity of peat soil in Indonesia is 1-5.
The pore number of the soil in Palangka Raya is 9.93, while the average pore number for peat soil parameters is 6.89 -11.09.
From these indications, it can be concluded that the soil in this Palangka Raya location is categorized as peat soil.

Relationship between biopolymer addition and physical properties of Palangka Raya peat soil
Stabilization carried out on peat soils with the addition of biopolymers and a boiling period of 28 days, obtained optimum results compared to the reference value, the results of testing the physical properties of peat soil as shown in the table below: Table 3 is a test of the physical properties of the soil, including a decrease in the optimum water content in peat soil with additional biopolymer blending material of 395.13%, while according to peat soil parameters [7] the average natural moisture content of peat soil in Indonesia is 750% -1500%.Testing the moisture content of peat soil was carried out based on standard testing as shown in Figure 7. From the test results in Figure 7, it can be seen that the tendency for moisture content to decrease along with the variation of biopolymer blending materials with a 28-day holding period.This is because the cementation reaction between peat and stabilization material requires water, so the longer the curing period, the more the stabilization material reacts to absorb the water [8].In Figure 8. Testing the organic content of the soil in Palangka Raya after stabilization shows that 96.62% occurs in the 3% biopolymer variation, and the peat soil parameters show the average value of organic content in peat soil which is 95 -99%.
The post-stabilization specific gravity of the soil in Palangka Raya was 1.64 in the 3% biopolymer variation.Whereas in peat soil parameters, the average value of specific gravity of peat soil in Indonesia is 0.95 -1.25 as shown in Table 3.The content weight of the poststabilization soil increased with the increase of the soaking period.This is because the cementation process between the peat and the stabilization material is getting harder and harder so that the peat soil becomes denser.
The Fibre Content value of the soil in Palangka Raya after stabilization was 30.79, while the average specific gravity value of peat soil in Indonesia is 39.5 -61.3.This may be due to the drying process that has occurred so that the behavior is closer to inorganic soil because the peat fibers have dried.In addition, it is also because with the 28-day soaking period, there is continuous damage to the soil fibers and the value of the soil fiber content decreases from its initial condition.The post-stabilization soil ash content value in Palangka Raya was 2.04, which occurred in the 2.5% biopolymer variation.While in the parameters of peat soil, the average value of the specific gravity of peat soil in Indonesia is 1-5.
The pore number of the soil in Palangka Raya is 5.22 while in the peat soil parameter the average pore number value is 6.89 -11.09.From all the testing processes, it can be indicated that there is a decrease in the soil that has been stabilized using biopolymers.The value of the pore number of peat soil, especially fibrous peat, can reach a value of 25 [9].In other studies, the value of Indonesian peat soils has a pore number between 5-11 [7].In this research, the number value was obtained from the correlation of the Gs test.Table 3 shows that the pore number value tends to decrease with the increase of stabilization material variation.This is because, as is the case in the discussion of volume weight, the longer the cementation process hardens and the pores of the peat soil are increasingly covered by the cementation results.

Conclusion
Based on laboratory testing and analysis of calculations in the study of the physical properties of peat soil before stabilization, it was found that Palangka Raya peat soil had physical properties including: moisture content = 779.87%,while the addition of stabilization materials in the form of biopolymers as much as 0.5%, 1%, 2%, 2.5%, and 3% in Palangka Raya peat soil tended to reduce the moisture content of Palangka Raya peat soil with the highest value of 395.13% in the 3% biopolymer mixture.The wet weight (γ) of Palangka Raya peat tended to increase the wet weight (γ) by 1.64 gr/cm 3 at 3% biopolymer blend.The organic content of Palangka Raya peat soil obtained the highest value of 96.62 g/kg.The maximum fiber content (%) of Palangka Raya peat soil averaged 30.79% at 3% biopolymer blend.The maximum ash content (%) of Palangka Raya peat soil was 2.24%.The pore number (e) of Palangka Raya peat soil obtained a maximum value of 5.22.This is because, as in the discussion of volume weight, the longer the cementation process, the harder it becomes and the more the pores of the peat soil are covered by the cementation.

Fig. 6 .
Fig. 6.Burial Period of Peat Soil with Variation of Chitosan Biopolymer The next test of the physical properties of the soil was carried out at the Laboratorium Mekanika Tanah Politeknik Negeri Bandung.In this test, the researchers conducted several tests including: a) Water content, b) Content Weight (Density), c) Fiber content, d) Fiber Size Distribution, e) Ash content

Table 1 .
Variation of chitosan biopolymer blend in peat soil.

Table 2 .
Test results of physical properties of peat soil before stabilization.

Table 3 .
Test Results of physical properties of post-stabilization peat soil.