SETTLEMENT OF GEOSYNTHETIC ENCASED STONE COLUMNS LIQUEFACTION CONDITION IN BOX CULVERT

. When the box culvert system is placed on a sandy soil layer with a relatively low bearing capacity and is disposed to potential liquefaction, the soil layer must be repaired to avoid damages to the box culvert structure. The proposed method is Geosynthetic Encased Stone Columns (GESC) to increase the bearing capacity and anticipated the liquefaction potential. however, to meet the criteria for a stable and safe GESC soil improvement in liquefaction conditions, the value of the settlement must meet the requirements for the settlement permit limit. This research was conducted to determine the potential for liquefaction at the study location, to calculate the value of single and group settlements in liquefaction conditions and to analyze the stability of single and group settlements including safe or unsafe in liquefaction conditions. Analysis of liquefaction potential was analyzed based on SPT data using the Valera and Donovan method, and settlement analysis applied the Almeida and Alexiew method. The analysis shows that potential liquefaction due to an earthquake with a magnitude of 9.0 SR will be at a depth of 4 to 8 m. Single and group settlements (144 sets) with an installation distance of 1.2 m with a diameter of 0.4 m and at a depth of 10 m are 246.23 and 214.92 mm, respectively. The entire GESC system is considered to be in an unstable and unsafe condition against potential liquefaction and box culvert loading.

. ,89,& Then in reviewing the dangers and analysis of the potential for liquefaction, the method used by Valera and Donovan aims to find the critical value of SPT or Ncrit as a determination of liquefaction or nonliquefaction conditions with the following Eq. (4) [15]- [17].
Where +2:; is the critical value of N-SPT, & is the depth of the sand layer being reviewed, then < is the depth of the groundwater level from the ground surface then the value is a function of the vibration intensity due to tectonic earthquakes. The MMI scale is determined based on the damage to buildings and things felt by humans due to the earthquake.
When liquefaction, the frictional strength of the clay layer only receives 30 percent of the total overburden stress, meaning that the frictional resistance is corrected up to 30 percent [18], [19]. In this study, it is determined that the resistance of friction is corrected by 30-50% of phenomena due to liquefaction that can affect the value settlement of Geosynthetic Encased Stone Columns in single or group settlement.
The purpose of this study was to see the potential for liquefaction in the sewer box review area using the Valera and Donovan method based on standard penetration test (SPT) data. then to calculate the settlement of single and group Geosynthetic Encased Stone Columns in liquefaction conditions based on the results of potential analysis liquefaction method of Valera and Donovan. and for analysis stability the settlement of Geosynthetic Encased Stone Columns in single and group against box culvert loading. .

METHODS
In this study, the box culvert planning located at STA 127 + 100 Trans Sumatra Toll Road Kisaran-Tebing Tinggi section Indrapura-Kisaran with a sandy soil layer that has a relatively low bearing capacity and is in an area with a high potential for earthquakes and the potential for liquefaction shown in Figure 1. In this case, the Geosynthetic Encased Stone Columns was provided as soil improvement at the STA 127 + 100 box culvert location.

Design Data
The data used in this study are secondary data from the results of field investigations standard penetration test (SPT) point BH-01 STA 127 +100 and laboratory testing by PT. Cipta Indah Citra and PT. PP also USU soil mechanics laboratory are shown in Table 1 and Figure 2. and other data in the form of box culvert dimensions, road cross-sections shown in figure 3.  As an preliminary design planning for the box culvert design, dimensions of 1.5 x 1.5 are used with a length of 86 m according to the cross section of the road STA 127+100 shown in figure 3. Then in the initial design Geosynthetic Encased Stone Columns using a diameter of 0.4 m and 3D distance or 1.2 m with a length of 10 m using Ringtrac 6500 PM geosynthetic tubular protective material with a diameter of 0.4 m shown in figure 4.and then stone material with specifications γs is 2.2 t/m², ϕ is 34˚, C or cohesion is 0 t / m² [7], [20].  Research in this study includes several stages, including preliminary design, calculation of loading, soil cohesion analysis and correction of N on N-SPT, etc. there are several stages in this research that must be carried out in data analysis. 1. Calculating the load on the box culvert using references to SNI 1725: 2016 and SNI 1726: 2019 [21], [22].
Calculated based on the dimension data of the box culvert and the cross section of the road. 2. Perform axial, transverse and moment force analysis on the calculation results of the box culvert loading using SAP 2000 software. 3. Calculate soil cohesion along the soil layer depth and make corrections to the N value using standard penetration test (SPT) data 4. Performing critical Ncrit or N calculations along the depth of the soil layer based on standard penetration test data and determining the soil condition for potential liquefaction or non-liquefaction based on the Valera and Donovan liquefaction potential analysis method. 5. Calculating and determining the geosynthetic encased stone column design parameters in liquefied soil conditions, namely the corrected soil cohesion in the soil layer that occurs liquefaction based on the results of the analysis of the potential liquefaction of the Valera and Donovan method and several other parameters such as void ratio, soil weight, active soil pressure coefficient and passive, lateral rest pressure coefficient based on Broker and Ireland also Jaky, Poisson ratio, modulus of soil elasticity based on Webb [23]. 6. Planning a geometric pattern of the distance and diameter of the geosynthetic encased stone column based on the Raithel and Kempfert models. 7. Calculating column and soil stress, vertical stress on the column and, also calculate horizontal stress on the column and the surrounding soil based on the Raithel and Kempfert method. 8. Calculating the geotextile requirement using the Ringtrac 6500 PM to produce the horizontal geotextile stress and the total horizontal soil stress based on the Raithel and Kempfert methods 9. Perform geosynthetic settlement calculations for single and group encased stone columns using the Almeida and Alexiew method [14]. 10. Analyze settlement stability of single and group Geosynthetic Encased Stone Columns. 11. Conducting final conclusions on single and group settlement of Geosynthetic Encased Stone Columns under liquefaction conditions based on the analysis of liquefaction potential using the Valera and Donovan method .

RESULTS AND DISCUSSION 3.1 Calculation of box culvert loading
Calculation of box culvert loading using SNI 1725: 2016 and 1726: 2019 and loading analysis using SAP 2000 [21], [22]. The following are the results shown in Table 2.

Soil Cohesion Analysis
Secondary data obtained were processed by data processing in the form of soil cohesion analysis and N correction on the N-SPT data. The results are shown in Table 3.

Analysis of the Liquefaction Potential of the Valera and Donovan method
In the analysis of the liquefaction potential of the Valera and Donovan method, the largest earthquake data in the last 100 years was used, namely the Aceh earthquake in 2004, the magnitude of the earthquake was 9.0 SR including the maximum intensity on the MMI level IX scale [24]. The value of with MMI level IX was obtained values of 16 blows/feet [15]- [17]. !"#$ at a depth of 0-24 m at the test point BH-01 STA 127 +100.
If > , which means that there is no liquefaction in the existing depth with a 9.0 SR earthquake, then if the results are < , which means the soil is in the existing depth of liquefaction with a 9.0 SR earthquake, the results of the analysis and calculation of the potential liquefaction of the Valera and Donovan method can be seen in Table 4.  Table 4 shows the results at a depth of 4-8 m, there will be liquefaction, so that the area is safe at a depth of more than 8 m.

Settlement Geosynthetic Encased Stone Column Design Parameters
The GESC design parameters are determined in liquefaction conditions at a depth of 4-8 m based on the analysis of the liquefaction potential of the Valera and Donovan method, namely the value of FS or in this case the corrected cohesion of 30% at a depth of 0 to 8 m. and corrected 50% at a depth of 9 to 24 m is shown in Table 5.

Geometric Plan Geosynthetic Encased Stone Columns
Diameter GESC is 0.4 m with a distance of 1.2 m with a rectangular pattern. then calculate several parameters including calculated area of the column (Ac) see in Eq. (5).

Calculation of vertical and horizontal stress Column and Soil Vertical Stress
Calculation of the stress received by the stone column and surrounding soil is calculated by multiplying the stress due to the box culvert load by the stress ratio. For vertical stress on column refer to Eq. (12).
And vertical stress on soil refer to Eq. (13).
After that, the calculation of the vertical stress on the soil and stone column per soil layer is shown in Table 6. due to loading on the box culvert structure produces horizontal pressure. And The summary of the horizontal stresses from the column (σhc) and the horizontal stresses from the surrounding soil (σhs) is shown in Table 7 and 8. Horizontal stress calculation after encased is installed From Table 7 and 8, it can be seen that the soil is not able to withstand the horizontal stress from the column because ( ℎ + > ℎ & ) it requires a geotextile. calculation of ℎ D8, with the Ringtrac 6500 PM high modular low creep geotextile encased material refer to Eq. (14)- (15).
After obtaining the horizontal stress that the geotextile is able to withstand, it can be added with the horizontal stress of the soil in an effort to withstand the horizontal stress of the column. A summary of these conditions can be seen in Table 8.

Single Settlement of Geosynthetic Encased Stone Columns
In the results of the design parameters, the calculation of vertical and horizontal stresses can be calculated settlement consisting of Layer 1 with a length of 2 m at a depth of 0-2 m and Layer 2 with a length of 8 m at a depth of 3-10 m. with the modulus of constrain, it is determined by an average value of 8D above and 4 D down of 3757.9 t / m². The following is the calculation of a single settlement Geosynthetic Encased Stone Columns using the Almeida and Alexiew method at the length of the Geosynthetic Encased Stone Columns 0-2 m depth refer to Eq. From the calculation results, the results can be formulated in Table 9.
Calculation of the Settlement of the 144 Geosynthetic Encased Stone Columns group using the Almeida and Alexiew method. The calculation results are then recapitulated in Table 10.

Stability Analysis on Single Settlement of Geosynthetic Encased Stone Columns
From the calculation results shown in Table 9 for a single settlement Geosynthetic encased stone columns, it was found that 246.23 mm exceeded the permit requirements of 25.4 mm. thus the single settlement of the