Bearing capacity of Percut Sei Tuan clay stabilized with palm shell ash

Improvements to the bearing capacity of the soil have been carried out and developed at this time, one of which is the stabilization of clay soils. There are several alternatives to solve low soil bearing capacity, one of which is using geo-synthetic materials but has a weakness in terms of high cost. Another alternative is to add palm shell ash as a stabilizing agent. The effect of adding palm shell ash has not been thoroughly studied, so further research is needed. The material added is palm shell ash with a variation of 0%, 4%, 8%, 10%, and 12% in each test. The tests carried out in the laboratory were water content (w), specific gravity test (Gs), Atterberg limit test, sieve analysis (sieve analysis), soil compaction test, and CBR (California Bearing Ratio) test. The CBR test was carried out by curing the soil for 1, 3, 5, and 7 days with a mixture of palm shell ash before compaction. The soil in this study belongs to the A-7-5 group. The CBR (California bearing ratio) value increased with the increase in the palm shell ash percentage in the mixture after curing the soil. The highest CBR value was in the variation of 12% palm shell ash with a 7-day curing period of 6.92% with a soil bearing capacity of 5.06.


Introduction
The issue of bearing capacity becomes a top concern before construction work on clay soil.At the research site, the soil conditions are very unfavorable when the clay is used as a foundation and construction of other structures.A lot of damage is caused by unstable soil conditions, including damage to the walls of residents' houses and road access.Countermeasures often carried out when constructing construction on poor soil include using a foundation system or improving the condition of the soil layer if the area being burdened is quite large and thick, and the load is relatively the same as road construction [1].
Economically, the most appropriate alternative is to improve the clay soil to support the construction of the layer.Therefore, an effort is needed to improve the properties of the clay.The soil stabilization method is expected to improve soil properties.Soil stabilization was carried out using a mixture of palm shell ash.Oil palm shell ash has chemical compounds that play an active role in soil stabilization when reacting with soil and water [2].The chemical composition of palm shell ash, as shown in Table 1, is considered to affect the stabilized soil.This influence has an impact on changing the values of the parameters on physical and mechanical properties testing.In mechanical testing, the CBR value will be used to plan road construction or other construction to determine the value of the sub-grade bearing capacity [3].Based on the description that has been described above, the author will try to review the value of California Bearing Ratio (CBR) with several variations and ripening on clay soil from Percut Village, Percut Sei Tuan District [3].

Sampling Process
Soil samples used in this study were clay samples from Percut Village, Percut Sei Tuan District, Deli Serdang Regency.The original clay soil sample (undisturbed) was taken to test the clay's physical properties.In sampling the original clay soil, the mechanical properties of the soil must not change.Sampling is carried out at a depth of ± 1 meter from the original clay soil surface to maintain the authenticity of the soil.Clay soil samples were taken using a cylindrical tube with a certain diameter.After the tube was removed, it had to be tightly closed with plastic so as not to reduce the water content due to evaporation.The sampling basis is using a hand drill (hand auger boring).In contrast to taking disturbed clay soil, in disturbing clay soil samples, there is no need to protect the original clay soil.Plastic or rice can be used to store and bring soil from the research site to the laboratory [4].

Determination of Mixture Variation
The test material used in this study was a mixture of clay in Percut Village, Percut Sei Tuan District, Deli Serdang Regency, with palm shell ash.In this study, 6 types of mixed variations were made, namely 0%, 4%, 6%, 8%, 10%, and 12% with variations in curing time (1, 3, 5, and 7 days).The California Bearing Ratio (CBR) laboratory testing with variations in palm shell ash and curing time are shown in Table 2.

Preparation of Test Specimen
The sample used is clay soil which represents the soil sampling location.The number of test samples is shown in Table 3.The soil samples were taken to the laboratory for several tests on the soil's physical and mechanical properties.Based on Table 4 and the AASHTO classification system, it is known that the soil has passed sieve no.200 of 93.96% with the liquid limit (LL) is 50.43%,so the soil sample meets the minimum requirements to pass sieve no.200 of 36%, has a liquid limit (LL) of 41% and a plasticity index > 11% so that the soil sample can be classified as type A-7-5 as shown in Fig. 1 According to the USCS classification system, which obtained data in the form of a plasticity index value of 25.46% and a liquid limit value of 56.72%, a plot was made on the graph for determining the soil classification, which is shown in Fig. 2 from the plot results obtained soil including in the CL group, namely inorganic clays with low to moderate plasticity [1].The results of the sieve analysis are shown in Fig.

The Physical Properties of Clay Soil with Stabilizers
The physical properties of the clay soil that has been mixed with palm shell ash are shown in Table 5.The correlation between water content and palm shell ash is shown in Fig. 4. From the results of the tests that have been carried out, it was found that the test results for disturbed clay with a mixture of palm shell ash decreased the water content value as the percentage of palm shell ash increased.It is due to the reaction of potassium, magnesium, calcium, and silica in palm shell ash which can cause heat in the soil so that the water content in the soil decreases [5].

Fig. 4 Correlation between the water content with the CSA/PSA mixture variation
The correlation between specific gravity and palm shell ash is shown in Fig. 5.The results of the tests that have been carried out show a tendency to decrease the value of specific gravity and increase the percentage of palm shell ash.The cementation process on the soil and palm shell ash cause clumping that bind between soil particles [6].The correlation between sieve analysis and palm shell ash is shown in Fig. 6.The percentage of soil from the test results of sieve analysis shows that the percentage of passing sieve no.200 on the original clay soil is 95.72%.In the variation of CS/PSA4, the percentage of passing sieves is 96.06%, in the CS/PSA6, the percentage of palm shell ash passing sieves is 96.13%, in the CS/PSA8, the palm shell ash the percentage passing sieves is 96.15%, in the CS/PSA10, the palm shell ash the percentage yield passed sieves by 96.25%, in the CS/PSA12, the palm shell ash the percentage that passed sieves was 96.33% [7].The correlation between Atterberg and CSA/PSA mixture is shown in Fig. 7.The results obtained in the test and the picture above show that the CS/PSA mixture ash affects the increase in the plastic limit of the original clay soil, which was originally 25.08%.The higher the palm shell ash percentage, the increased limit value plasticity.The highest value was 37.75% for a mixture of 12% palm shell ash.Meanwhile, the plasticity index value decreased due to palm shell ash, which can fill voids and bind water between soil grains [8].In the standard soil compaction test on the original soil, the optimum moisture content (Wopt) value was 24.16%, and the maximum dry weight value (γd max) was 1.29 gr/cm 3 .In laboratory CBR testing on native soil, the penetration value of 0.1 "is 3.22% and the penetration value of 0.2" is 3.45 g/cm 3 .

The Mechanical Properties of Clay Soil with Stabilizers
Based on the results of the soil mechanical properties test carried out on the original clay soil sample, the results of the clay soil compaction test and CBR laboratory test were obtained as listed in Table 6.8 shows that the dry density value continued to increase in all variations of the mixture with palm shell ash.There was an increase in dry density because the added stabilizer filled the pore spaces in the soil.In the original soil conditions, the pore cavities are filled with water and air, with stabilizers filling the soil cavities, causing the percentage of water contained in the soil to decrease.The increase in the number of solid particles in the soil impacts its dry density compared to the original soil condition [9].Fig. 8 Correlation between dry weights with the CS/PSA mixture variation The results obtained from the study of the optimum water content in the original soil are equal 24.16%.In a mixture of 3% palm shell ash, the optimum water content increases and then decreases for each addition of the percentage of variation in the mixture of stabilizers.This decrease in optimum water content is due to the stabilizer material urging water out of the soil pores.The cavities in the soil containing water will be replaced by stabilizing agents so that water cannot re-enter the soil micropores.As a result, the percentage of water contained in the soil is reduced.The cause of the decrease in optimum water content is because the stabilizer material for palm shell ash causes the soil to become hot, so the mixture requires more water content to bond together.It can be seen in Fig. 9.The results of the CBR test on the original soil and the mixture of palm shell ash according to the percentages of 0%, 4%, 6%, 8%, 10%, and 12% are shown in Fig. 10.On the CBR value, it can be concluded that a mixture of palm shell ash from 0% to 12% is good for use as a soil stabilizing agent.The largest CBR value was obtained in the variation of the mixture of 10% palm shell ash, which was 5.61%.Furthermore, in the variation of 12%, adding palm shell ash decreased the CBR value to 5.35% due to a large number of stabilizers present in each test sample.

The Effect of Palm Shell Ash Adding on CBR Value of Curing
In this test, clay was stabilized by palm shell ash by curing the sample for 1, 3, 5, and 7 days according to the percentage of mixture variation.In this test, the test sample that passed filter no.40 was prepared, approximately 5.5 kg for each sample.The sample was mixed with palm shell ash according to the additional variation and then entered the optimum water content obtained from the soil compaction test.Furthermore, stir the sample soil with palm shell ash with optimum water until evenly distributed.Then curing is done according to the predetermined time before compaction is carried out.
The test results can be seen in Table 7.Based on the results of the CBR values above, the CBR value with the addition of palm shell ash to curing can be seen in Fig. 11 below: From the curve obtained from the laboratory CBR test results, the highest CBR value was achieved at the percentage of palm shell ash at 12% with a curing period of 7 days.As the curing period increased, the CBR value tended to increase.The highest CBR value is 6.92%.The increase in the CBR value in the soil is due to the condition of the soil experiencing a decrease in the water content (Wopt) value as the ripening period increases.It directly increases the density of the soil so that the CBR value in the soil will increase [10].Based on the correlation value above results, the correlation value can be entered in the graph in Fig. 12.

Fig. 12 Correlation between CBR values of clay soil with stabilizer againts SBC
Based on SKBI-2.3.26.1987, the soil's bearing capacity value is determined from the lowest CBR value, namely at 0.1" penetration.Based on the analysis of the CBR value of 3.22%, the original soil bearing capacity value is 3.88.The value of the bearing capacity of the soil can also be determined based on the correlation graph between the CBR values of the subgrade.From the graph, it can be seen that the higher the value of a soil CBR, the value of the bearing capacity of the soil also increases.

Correlation of Curing CBR Value with stabilizer againts SBC
Based on the analysis results, the correlation of the curing CBR value added with stabilizers with the carrying capacity of the soil is shown in Table 9.Based on SKBI-2.3.26.1987, the value of soil bearing capacity is determined from the lowest CBR value, 0.1" penetration.The graph shows that the higher the value of a soil CBR, the greater the value of the soil's carrying capacity also increases [11].

Conclusion
Based on the research that has been done on improving the bearing capacity of clay stabilized with palm shell ash, it can be concluded that the clay soil of Percut Village, Percut Sei Tuan District, has a high water content (w) of 87.81%, specific gravity (Gs) of 2.64, and sieve analysis of 95.72%.Clay, according to AASHTO, belongs to group A-7-5.Furthermore, according to USCS, it is included in the CL type, namely inorganic clay with low to moderate plasticity.The clay soil that is not good or bad as a subgrade.The carrying capacity of the soil has increased, as evidenced by the results of the laboratory CBR test carried out on the original soil.The CBR value is 3.45%.After being mixed with a predetermined variation, the laboratory CBR value increased to a variation of 12% palm shell ash mixture of 5.61% with a soil carrying capacity of 4.92.The CBR test resulted in the optimum variation in 12% of the palm shell ash mixture, which was 5.61%.The length of curing time greatly affects the water content and CBR value so that the water content value will decrease while the CBR value will increase.From the results of the largest test, namely the variation of a mixture of 12% palm shell ash with 7 days curing of 6.92% with soil carrying capacity of 5.06.From the results of the tests that have been carried out, the improvement of the bearing capacity of the soil stabilized using palm shell ash can be said to be quite good in increasing the bearing capacity of the soil.

Fig. 5 Fig. 6 Fig. 7
Fig. 5 Correlation between the specific gravity with the CS/PSA mixture variation

Fig. 9
Fig. 9 Correlation between moisture content with the CS/PSA mixture variation

Fig. 10
Fig. 10 Correlation between CBR values with the CS/PSA mixture variation

Fig. 11
Fig. 11 Correlation between CBR laboratory values with the CS/PSA mixture variation against curing

Table 1 .
Composition of palm shell ash

Table 2 .
The mixture of clay and palm shell ash with variations in curing time of 1, 3, 5, and 7 days

Table 3 .
Soil testing sample

Table 2 .
The soil samples were taken to the laboratory for several tests on the soil's physical and mechanical properties.After testing the clay's physical and mechanical properties, the clay soil test results are shown in Table4.

Table 4 .
The physical and mechanical properties of the clay soil

Table 5 .
The physical properties of the clay soil with palm shell ash variation

Table 6 .
The mechanical properties of the clay soil with palm shell ash variations

Table 7 .
CBR test results with curing on the sample

Table 8 .
Soil bearing capacity (SBC) is a scale used in the pavement thickness determination monogram to express the strength of the subgrade.Meanwhile, it is recommended to base the bearing capacity of the subgrade only on the measurement of the CBR value.The bearing capacity of the soil can be calculated graphically and analytically.The value of the bearing capacity of the soil is determined using the monogram by drawing a straight line from the CBR value to the SBC value.Table8shows the results of the original soil bearing capacity (SBC), which were analyzed from the results of the laboratory CBR.Correlation of CBR values of clay soil with stabilizer againts SBC

Table 9 .
Correlation of curing CBR value with stabilizer againts SBC