ANALYSIS OF BEARING CAPACITY OF PILE FOUNDATIONS USING ANALYTICAL METHOD AND FINITE ELEMENT METHOD

The foundation is the lower part of a structure used as a load distributor for the loads generated by the upper structure, which are then transmitted into the hard soil layers. The selection of foundation types in building construction must consider the type and characteristics of the soil at the construction site to avoid construction failures. This analysis is conducted to determine the bearing capacity of pile foundations using analytical and finite element methods. The type of foundation used in this analysis is a pile foundation with a pile length of 8 meters and a pile diameter of 0.4 meters. For the analytical calculation, Standard Penetration Test (SPT) data obtained from PT. Adhi Karya (Persero) for the Infrastructure Green House Biodiversity LIPI Cibinong-Bogor project are used, employing the analytical method (Alpha Method) and the finite element method with the assistance of Plaxis 2D V.8 software. The results of the analysis show that the bearing capacity of the group pile foundation (Qg) for a pile diameter of 0.4 meters and a pile length of 8 meters on clayey soil, based on SPT data using the analytical method (Alpha Method), is 60.432 tons. Meanwhile, the bearing capacity of the horizontal pile foundation using the Broms method is 6.03 tons. The bearing capacity obtained using the Finite Element Method yields an ultimate load on the group pile (Qq) of 57.89 tons. The bearing capacity of the group pile foundation (Qg) from both sets of data, with a difference of 2.5%, meets the requirement, being greater than the axial load (P) of 42.6 tons that must be supported.


INTRODUCTION
The development of technology has become one of the supporting factors for the advancement of infrastructure, ranging from infrastructure in the fields of health, education, to personal housing.Infrastructure or construction is always associated with a strong foundation support, making foundation bearing capacity a crucial aspect in building construction.However, in reality, errors or mistakes in foundation work are still found in the field, which are typically caused by planning errors, thus posing a threat to construction safety.
Until now, the presence of high-rise building construction has been increasing in line with the need to fulfill public facilities supporting daily activities.Therefore, foundation bearing capacity planning must be carefully designed to withstand the construction loads above it up to the specified safety limits.
The foundation is the lower part of a structure used as a load distributor for the loads generated by the upper structure, which are then transmitted into the hard soil layers.The selection of foundation types in building construction must consider the type and characteristics of the soil at the construction site to avoid construction failures.
There are two types of foundations commonly applied in high-rise building construction, namely shallow foundations and deep foundations.Shallow foundations are used for buildings where the depth of hard soil is not far from the surface, while deep foundations are used for buildings where the depth of hard soil is considerable.
Pile foundations are a type of deep foundation that is driven or inserted to a certain depth to transmit the loads from the building's superstructure into the soil.Several factors influence the selection of the foundation type to suit the building, including the building's function, the magnitude of working loads, soil surface conditions, bearing capacity, settlement, and cost.
Analysis of foundation bearing capacity is conducted to withstand the construction loads above it.In the Green House biodiversity infrastructure development project, calculations of deep foundation bearing capacity, namely pile foundations, have been performed using conservative formulas (FK) and with the assistance of ETABS software.
The bearing capacity of pile foundations can be calculated using various methods such as the Alpha method, λ method, US Army Corps method, Tomlinson method, Paulos and Davis method, Coyle and Castello method, Kulhawy method, Broms method, and Brinch Hansen method.The choice of method depends on the soil type, as the soil type at the site is cohesive soil, and testing has provided the values of the internal friction angle (φ) and cohesion (c), thus the Alpha method and Broms method are used according to the parameters.
Therefore, there is a desire to reanalyze the bearing capacity of pile foundations using analytical methods (Alpha Method and Broms Method) and finite element methods with the assistance of Plaxis 2D V.8 software.This analysis aims to determine the bearing capacity value by comparing several different methods and using numerical methods to facilitate foundation bearing capacity planning.
Based on these considerations, there is an interest in conducting research on "Analysis of Bearing Capacity of Pile Foundation Using Analytical Methods and Finite Element Methods."The problem formulation to be discussed includes the results of the analysis and the differences in the results of foundation bearing capacity analysis with both methods.The research objective is to determine the results of foundation bearing capacity analysis using analytical and finite element methods, as well as their differences.The scope of the problem includes foundation types, calculation methods, and data used, with the exclusion of material strength calculations.The benefits of this research include increasing knowledge about foundation bearing capacity, providing references for the Green House Biodiversity LIPI Cibinong-Bogor project, and expanding understanding of different analysis methods and the application of different software in foundation bearing capacity research.

Research Location
The Green House Biodiversity Infrastructure development project is a multistory Green House construction project consisting of 4 floors above ground level, located on clayey soil.This project is situated in the middle of the Cibinong LIPI Botanical Garden area, located on Jakarta-Bogor Highway, Km 46.Based on the points surveyed in zone 4 with 1 Standard Penetration Test (DB2) point, this building foundation uses a pile foundation type.

Data Availability
Data collection for this research was conducted secondarily, obtained from several sources as follows:  2021) is used for the calculation data of the upper structure loads, which will be used in modeling the foundation bearing capacity analysis with the assistance of Plaxis 2D software.

Ayu Nurjanah
Analysis Of Bearing Capacity Of Pile Foundations Using Analytical Method And Finite Element Method Flowchart 1. Data Collection Data is one of the most important factors in the analysis process, obtained from various data sources obtained by PT.Adhi Karya (Persero) in the Green House Biodiversity Infrastructure Development Project at LIPI-Cibinong.In this study, the data used includes SPT data, structural drawings, laboratory data, and structural analysis.
2. Literature Review Literature review is necessary as a reference for analysis after the subject is determined.This literature review is used as the theoretical basis for analysis referring to books, opinions, and theories related to the research.
3. Data Processing Data processing is carried out on the data obtained to calculate the bearing capacity of group pile foundations using analytical methods and finite element methods using Plaxis 2D application.

Foundation Design
In this section, foundation design is carried out, starting from the diameter and length of the foundation used.

Analysis with Analytical Methods
Analysis with analytical methods uses SPT data, and the foundation bearing capacity is calculated using the alpha (α) method.
6. Analysis with Finite Element Methods Analysis with finite element methods is carried out with Plaxis 2D V.8, inputting soil and pile parameters into this program modeling to determine the bearing capacity of pile foundations.
7. Analysis Control Analysis control is conducted to determine whether the calculated results using the available data meet the requirements by controlling using a safety factor for foundation bearing capacity.

Comparison Data Analysis
After obtaining the bearing capacity calculation results with analytical and finite element methods, both results are then compared to see the differences in the results obtained.

Results and Discussion
In this section, the results obtained from both analytical and finite element methods are elaborated step by step until obtaining the results.

Conclusion
This conclusion contains a brief and precise summary of the research results.

Analytical Method Planning Steps
1. Investigate the soil at the planned building location to determine the soil type at that location.2. Calculate the ultimate bearing capacity of the pile and check the safety factor.3. Calculate the magnitude of the horizontal load acting on the pile.4. Check whether the load acting on the pile transmitted by the upper structure is smaller than the calculated pile strength with the appropriate safety factor.

RESULT AND DISCUSSION
Technical Data of Pile Foundation In this study, pile foundation with the following specifications was used: Foundation Type: Pile Diameter: Ø 400 mm Concrete Quality: K-500

Calculating the Bearing Capacity of the Foundation
The axial bearing capacity of the pile foundation was calculated analytically based on field data collected by PT.Adhi Karya (persero).The calculation of the pile's bearing capacity used the alpha method.The analysis was limited to Standard Penetration Test (SPT) data at point BH-4 because this location was where borehole testing was conducted in the laboratory.
The bearing capacity analysis on this clayey soil was calculated using the alpha method to determine the pile frictional resistance in clayey soil with pile lengths of 8, 10, and 12 meters (trial and error) based on the adhesion factor values collected by McClelland (1974).
From the experiment results with pile lengths of 8, 10, and 12 meters, the following results were obtained as shown in the table.From the trial and error experiment, values for pile lengths of 8, 10, and 12 meters for control fs and fb were obtained.The pile length with the fs control closest to 15000 for fb and 107 for fs was chosen, which is 8 meters.

Horizontal Piling Bearing Capacity
Calculation of the horizontal (lateral) carrying capacity of piles, using the broms method (1964).This horizontal carrying capacity is calculated using the broms method with the type of soil, namely cohesive soil.

Checking the carrying capacity against external loads
The load that acts on the foundation is generally the load obtained from the upper structure and the soil pressure from the side of the pile foundation, this load is usually known as vertical load and horizontal load.This load is carried by several poles that are held together by pole bearing plates or pilecap which serves to spread the load from the upper structure to the pole which is then channeled to the soil layer.

Calculating the carrying capacity with finite elements
The carrying capacity capacity by finite element method is a calculation of the axial bearing capacity of pile foundations, in this method using the Mohr -Coulomb model which is a general model in soil investigation.Mode; This requires parameters such as Young's modulus, stiffness modulus, Poisson's ratio, shear angle in the field, cohesion factor, angle of discharge and weight of the soil content.
These parameters are obtained from the results of laboratory tests, due to limited data, some parameters are assumed based on soil mechanics theory using the all pile program.

B. Dimensions
This dimension is intended for display in the space used for the depiction of soil layers and foundations to be analyzed as well as units used in the process of inputting materials and loads.The length and width are adjusted to the depth of the soil to be analyzed, for units used units m for length and satan kN for load.C. Soil Model After filling in the dimensions of the drawing space, then the process of drawing the soil layer according to the depth of the soil is carried out based on the data.In this analysis there are 2 soil layers to be analyzed with soil depth 1 is 1-6 m and soil to 2 6-12 m.  (sumber: Plaxis 2D V.8, 2010) Then new to enter the soil parameters according to the layer, after that a display will appear that must be filled in according to the soil data of each layer.(source: Plaxis 2D V.8, 2010) Next, an interface is done on the outer side of each pile, this is done to facilitate the analysis process of each pile or soil element.

H. General Mesh
After all inputs are carried out, then a general mesh or element division process is carried out to facilitate the analysis process of each element.Then a new

Ayu Nurjanah
Analysis Of Bearing Capacity Of Pile Foundations Using Analytical Method And Finite Element Method window will appear that displays the results of the previously inputted structure in the form of a structure with a net of elements, then updated then the initial condition to proceed to the next step.This step aims to analyze the structural safety, previously a calculation structure step was arranged starting from piles, pile caps, loads to safety factors.For piles, pile caps, and load types, the calculation type is chosen as plastic or loading, while for safety factors, the phi/c reduction or safety factor type is chosen. When all input structures in the calculation turn into green check marks, it means the calculation process was successful, if one of the input structures has a red check mark, then there was an error in the input process.

K. Output Results
The output of this result is in the form of a large decrease that occurs in the foundation due to working loads, the magnitude of the decrease occurs by 103.26 x 10 -3 m or 0.001 m less than the allowable decrease of 1 inch or 0.0254 m.

Ayu Nurjanah
Analysis Of Bearing Capacity Of Pile Foundations Using Analytical Method And Finite Element Method Analysis of the carrying capacity of the group pile foundation with a diameter of 0.4 and a pile length of 8 m The Green House Biodiversity Building of LIPI Cibinong-Bogor analytically using the Alpha (α) method obtained the ultimate carrying capacity of the pile group (Qg) of 60,432 tons and using the broms method obtained a lateral carrying capacity of 6.03 tons while with 2D V.8 plaxis using the Frame Element method(FE) obtained the ultimate carrying capacity of the pole group (Qg) of 57.89 tons with a difference in ratio of 2.5%.

CONCLUSION
Based on the analysis of carrying capacity using the Alpha method and finite elements on PC 2 group poles with a diameter of 0.4 m and a length of 8 m, the results show that the bearing capacity of the pile foundation (Qg) is 60.432 tons based on the Alpha method, 6.03 tons using the Broms method, and 58.60 tons with the Finite Element method.The comparison between analytical methods and finite elements shows a difference of 2.5%.The suggestion for more accurate calculations is to have complete technical and laboratory data, as well as to conduct detailed field and laboratory tests to avoid inaccuracies in results and ensure compliance with established standards.

Figure 4 .
Figure 4.11 Type Material Set Soil(sumber: Plaxis 2D V.8, 2010) Then new to enter the soil parameters according to the layer, after that a display will appear that must be filled in according to the soil data of each layer.

Figure 4 .
Figure 4.12 Ground Parameter Input(sumber: Plaxis 2D V.8, 2010) Furthermore, when all parameters have been completed, the parameters of each layer are then inputted into the image of the soil layer that has been drawn by means of the input results click then held and dragged to the soil layer according to the parameter data.

Figure 4 .
Figure 4.13 The process of entering the input parameter results according to the soil layer.(source: Plaxis 2D V.8, 2010)

Figure 4 .
Figure 4.14 Pile and Pilecap Model (source: Plaxis 2D V.8, 2010) F. Pile and Pile Cap Parameter InputAfter the pole and pile cap models are made, it is continued by inputting the parameters of the pole and pile cap in the material set, plates are selected for the pole material .

Figure 4 .
Figure 4.15 Material Type Pile Set and Pile cap(source: Plaxis 2D V.8, 2010) Then new to enter the parameters of the pole and pile cap, after that a display will appear that must be filled according to the pole and pile cap data.

Figure 4 .
Figure 4.17 Process of Inputting Parameter Results to Pile and Pile Cap.(source: Plaxis 2D V.8, 2010) Next, an interface is done on the outer side of each pile, this is done to facilitate the analysis process of each pile or soil element.

Figure 4 .
Figure 4.18 Interface on Pile (source: Plaxis 2D V.8, 2010) After the interface is done, standard fixities are applied to input standard boundary conditions.

Figure 4 .
Figure 4.19 Standard Fixities (source: Plaxis 2D V.8, 2010) G. Load InputAfter soil, pile, and pile cap have been input according to their parameters, the next step is to input loads.Loads are drawn with a centralized load image, then at the load end, double-click until a table appears to input horizontal and vertical load values, then the horizontal load value of 60.33 kN and the vertical load value of 426 kN are entered.

Figure 4 .
Figure 4.21 Mesh Element Model (source: Plaxis 2D V.8, 2010) I. Groundwater LevelThe next step is to draw the groundwater level according to the depth where the groundwater level is located.

Figure 4 .
Figure 4.23 Active Pore Pressure (source: Plaxis 2D V.8, 2010) Next, general initial stresses are applied to know the main effective stress obtained at -105.22 kN/m2 then click calculate to proceed to the calculation step.

Figure
Figure 4.24 Main Effective Stress (source: Plaxis 2D V.8, 2010) J. CalculationThis step aims to analyze the structural safety, previously a calculation structure step was arranged starting from piles, pile caps, loads to safety factors.For piles, pile caps, and load types, the calculation type is chosen as plastic or loading, while for safety factors, the phi/c reduction or safety factor type is chosen.

Figure 4 .
Figure 4.25 Pile Foundation Input in the Calculation Process (source: Plaxis 2D V.8, 2010) Continued with the parameter menu option then devine, then a new window appears containing the initial geometry image.If the input is pile foundation, then only the pile foundation is selected on the image until it turns blue.

Figure 4 .
Figure 4.26 Selection of Pile Structure for Analysis(source: Plaxis 2D V.8, 2010) The same steps are repeated for pile cap, load, and safety factor types.After all are selected according to their respective structures, the next step is to proceed with the calculation step.

Figure 4 .
Figure 4.27 Calculation Process (source: Plaxis 2D V.8, 2010) The result of the calculation process is the value of ∑ When all input structures in the calculation turn into green check marks, it means the calculation process was successful, if one of the input structures has a red check mark, then there was an error in the input process.

Table 4
A. Model SelectionIn this modeling, a plane strain model is used for pile foundation with 15-Node elements.Figure 4.8 Model Selection for Plaxis Analysis (source: Plaxis 2D V.8, 2010) Ayu Nurjanah Analysis Of Bearing Capacity Of Pile Foundations Using Analytical Method And Finite Element Method