COMPARISON BETWEEN THE RESULTS OF THE PILE BEARING CAPACITY ANALYSIS BASED ON EMPIRICAL METHOD AND FINITE ELEMENT METHOD USING THE RESULTS OF DYNAMIC ANALYSIS ON THE FIELD

There are many methods for calculating the bearing capacity of a pile foundation. The problem is finding the most representative method for analysis dynamic load testing (PDA) results in the field. This study only covers the areas of West Surabaya and North Surabaya. The method used to analyse the bearing capacity of the pile foundation in this study is the empirical method, namely the Schmertmann, Meyerhof, and L. Decourt method and the finite element method (FEM.). This research only for calculating the bearing capacity of precast pile foundations. The initial stage of the research was to collect soil survey data in the form of N-SPT boring logs and PDA test results in the area. Then the calculation analysis is carried out using the empirical method and FEM, which will be compared with the PDA results. FEM analysis uses dynamic load with pile-driving modelling, which is similar to PDA testing. After comparison, the researchers find some ratios for each calculation method and results of PDAs in the field of study. This study indicates that the most representative method for PDA results in West Surabaya is the Meyerhof method. For the North Surabaya area, these methods have not shown expected results of PDA results in the field


INTRODUCTION
There are many ways to calculate the bearing capacity of the pile foundation. Each method has its characteristics and suitability depending on the constraints and parameters used. However, most of the methods used to result from application or research in other countries whose soil patterns may not be the same as those in Indonesia [1]. In general, to get the actual pile bearing capacity in the field, a full-scale load test is carried out (Static Load Test, SLT) or using dynamic load testing (Dynamic Load Test, DLT). Most geotechnical experts use the empirical method and the Finite Element Method (FEM) to estimating the bearing capacity of the pile. Each of these methods will produce different results, and the results, compared with the test results with Pile Dynamic Analysis (PDA), are not always consistent.

RESEARCH SIGNIFICANCE
This paper analyses which method is the most representative of the PDA test results by comparing the empirical method calculation results with the PDA test results on the field. The comparison results will produce ratios as a representative indicator of the method to the PDA results. If the balance is between the Analytical method and the PDA result is 0.75 to 1.25, conclusively, the analytical method is representative of PDA. So far, there has been no research aimed at finding out which method of the estimated bearing capacity of piles is more suitable for the city of Surabaya based on variations in soil conditions in it, which can be compared with the PDA results. For more details, the locations reviewed in this study can be seen in Figure 1.

METHODOLOGY
In the early stages of the research, Researchers collected all required data collection in the form of soil investigation data, laboratory test results to determine mechanicalphysical properties, and data from PDA and SLT testing in West Surabaya and North Surabaya areas. The calculation of the bearing capacity of precast pile foundations using empirical methods consisting of L. Decourt, Schmertmann, and Meyerhof [2].It was also using FEM to calculate the bearing capacity using soil parameters from soil investigations in the field and the laboratory test results in West Surabaya and North Surabaya.

A. DATA COLLECTION OF SOIL INVESTIGATION
Soil investigation data were taken from each field study and its surroundings as many as 30 points. From all the data collected from the soil survey, a statistical analysis was carried out, and the results were shown in Table 1 Table 3 and Table 4.

ANALYSIS AND DISCUSSIONS
As explained in the previous chapter regarding the comparison of the empirical method and the finite element method with the SLT test results, an analysis of the bearing capacity calculation was carried out for a spun pile foundation with a cross-sectional size of 45 cm at a depth of 31 m in the West Surabaya area. SLT testing has been carried out on these pile conditions and produces a bearing capacity of 392 tonnes using the Davisson method by reading the Load vs Settlement curve. The researcher then analyzed calculations using the method of L. Decourt, Schmertmann, and Meyerhof. [2] and the Finite Element Method.

A. COMPARISON RESULT of Empirical Methods and FEM with SLT Test Results IN WEST SURABAYA
Comparison result of these methods with the SLT test is in Table 2. From these results, the researcher concluded the most suitable is Meyerhof. The other method is still reliable for the SLT results with an average ratio of 1.25, which can be continued to the following analysis stage.  [3] research, which also examines the condition of the pile foundation in areas with clay-dominant soil, it gives a ratio of 0.98 for the L. Decourt, Meyerhof, and Schmertmann methods which are in the very high category. In this study, the L. Decourt method provides a ratio of 0.51, the Schmertmann method of 0.53, and the Meyerhof method of 0.81 for the West Surabaya area, predominantly clay. This conclusion can occur due to variations in the crosssectional size, length of the pile, and the number of pile foundations being analyzed.

C. COMPARISON RESULTS OF EMPIRICAL METHODS WITH PDA TEST RESULTS IN NORTH SURABAYA
After analyzing using the empirical method and FEM using Dynamic load, the results of the analysis are compared with the PDA test results in Table 6. From these results, the researcher concluded that there was no sufficiently representative method for PDA results in North Surabaya. However, the method with the closest Qp ratio number to 1 is the Meyerhof method. Whereas for the method with the Qs ratio number most relative to 1 is the method is L. Decourt.

CONCLUSIONS
From the data and analysis in the previous chapter, it can be concluded that the comparison between the empirical method and the FEM on the PDA results shows that not all methods are reliable with the PDA results.
The most representative empirical method for analyzing the bearing capacity of friction pile foundations with medium to stiff clay prevailing soil conditions such as in the West part of Surabaya and its surroundings to PDA results is the Meyerhof method with the average ratio Qp and Qs is 0.91 and 0.71. The ratio of the Meyerhof method is the closest ratio to 1 compared to the L. Decourt and Schmertmann method with its Qp ratio of 0.39 and 0.23.
There is no empirical method that is most representative for analyzing the bearing capacity in the area, such as in the North part of Surabaya and its surroundings on the PDA results. This can be seen from the Qp ratio of L. Decourt, Schmertmann, and Meyerhof are 2.10, 1.66, and 1.33. It happens because, for soil conditions such as in North Surabaya, the value of Qp from PDA does not necessarily = Qp-ultimate analyzed using empirical methods. It is thought to occur because the energy from the hammer at the time of testing was not large enough to ultimately mobilize the end-bearing pile foundation in soil conditions such as North Surabaya.
The FEM method with Dynamic Load on pile foundations with PDA results gives the most representative results with a ratio of 1.1 in West Surabaya soil conditions and a ratio of 1.3 in soil conditions in North Surabaya on the comparison of RMX results.