ANALYSIS OF RAFT AND PILE CAPACITY DISTRIBUTION ON PILE RAFT FOUNDATION SYSTEM WITH PLAXIS 3D

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1 ANALYSIS OF RAFT AND PILE CAPACITY DISTRIBUTION ON PILE RAFT FOUNDATION SYSTEM WITH PLAXIS 3D Donny Chan Jurusan Teknik Sipil, Fakultas Teknik, Universitas Bina Nusantara, Jl. K.H. Syahdan No.9 Kemanggisan, Jakarta Barat 11480, Fax , Donny Chan, Ir. Gouw Tjie Liong, M.Eng., ChFC ABSTRACT In Jakarta design practice, design of foundation that used pile raft foundation system, does not take into account the capacity of the raft. Therefore, a numerical studies were done by using Plaxis 3D FEM program, to find whether the raft have a contribution to the overall carrying capacity of foundation. The approach is done by using 2 hypothetical soil condition one is a pile raft with floating pile condition and the second one is for end bearing pile. The case study from a project at Karet, Jakarta Pusat, was also carried out. On the hypothetical data, analysis were modeled with group piles formation starting from 5x5, 6x6, 7x7 and 8x8 with a center to center distance of each pile from 2,5D, 3D, 3,5D, 4D, 5D, 6D, 7D and 8D.Raft thickness is taken as 1 m. The result from the analysis shown that the raft had a contribution of the carrying capacity starting from 0% to greater than 50% against the total load. So the conclusion is that raft has a contribution to the pile raft foundation system. (DC) Kata Kunci : Raft, Pile Raft Foundation, Bearing Capacity GENERAL Due to the less land, so many buildings are designed to be higher than usual buildings, where the building is higher then the loads generated will also be greater and the foundation have to work harder to hold the load. One to solve the problem is to incorporate some piling into a single entity with a given raft foundation on the surface of the pile foundation. Raft foundation serves to bind the heads underpinnings to a given load can be distributed on other foundations. With the raft foundation shows that the load can be held by a foundation that will be much larger. But still many people who do not really know how much influence this foundation raft, then from that point with this paper are expected to know how much influence the raft foundation. Of the maximum load caused by the gravity load, the bearing capacity of pile groups via pile raft foundation must be factored into 2 carrying capacity of the raft and pile. Each pile of different groups will be different carrying capacity generated. Pile bearing capacity is different in each pile group spaced piles of different individuals. Then, thickness of raft foundation can also affect the carrying capacity generated. Thus, to know how to influence the distance between the pile and the thickness of the raft foundation to get the carrying capacity of the raft and pile foundation. By knowing the effect of the distance between the piles are tied by the head pile (raft) with a certain thickness and varying pile group formation, it can be calculated how much carrying capacity to be generated or received by its own pile and raft with maximum gravity load (vertical load) that results later expressed as a percentage. By doing that experiment using original soil data in the field, it can be seen that the use of pile raft foundation system off grade or on grade and will get the design of the pile raft foundation with more optimal and economical.

2 METHOD OF RESEARCH Figure 1Flowchart of This Research For this study will begin with the identification of the research problem. After identifying the problem, go to the next stage of the study of literature. Then enter into the stage of data collection will be taken from the 3 projects. After collecting the data, the analysis of the data has been obtained to support the required data for the study. If the data is ready, do the boundaries of the research will be based on existing data. After that do the calculations with the finite element method program, Plaxis 3D. First performed at the calibration program Plaxis 3D program to prove that the parameters entered will produce results that are correct that in this condition the calibration aims to determine how much of the reaction to be generated by the action of granting such that the value of action and reaction between the same or different is not much. In the analysis there are 2 pieces calculation parameters, namely the analysis of the differences in the calculation of pile group formation and analysis calculations with different distances between the pile foundation. Analysis will begin by experiment with 2 hypotheticalsoil data begins with group piles 5x5, 6x6, 7x7, and 8x8 with the distance between the pile starts from 2,5D, 3D, 3,5D, 4D, 5D, 6D 7D, and 8D and raft thickness used was 1m. Then the desired result is obtained from hypotheticalsoil data. Thus the pattern will be obtained on raft capacity in accordance with the existing soil type, then the result will be applied to the original soil data on the project to determine the capacity of the raft more including the patterns of what capacity. After this study was concluded and added suggestions.

3 RESULT AND DISCUSSION Result of Raft Capacity Calculation for Hypothetical Data 1 Tanah Lempung Kohesif γ t = 18 kn/m 3 Ep = 3.e 7 kn/m 2 γ d = 17 kn/m 3 Es = kn/m 2 c u = 50 kn/m 2 ν = 0,3 ϕ = 0 o ψ = 0 o Figure 2Modelling of Hypothetical Data 1 Figure 3Floating Pile 5x5

4 Figure 4Floating Pile 6x6 Figure 5Floating Pile 7x7 Figure 6Floating Pile 8x8

5 Result of Raft Capacity Calculation for Hypothetical Data 2 Tanah Lempung Kohesif γ t = 18 kn/m 3 Ep = 3.e 7 kn/m 2 γ d = 17 kn/m 3 Es = kn/m 2 c u = 50 kn/m 2 ν = 0,3 ϕ = 0 o ψ = 0 o Pasir γ t = 20 kn/m 3 Es = kn/m 2 γ d = 20 kn/m 3 ϕ' = 42 o ψ = 12 o c' = 1 kn/m 2 ν = 0,2 Figure 7Modelling of Hypothetical Data 2 Figure 8Hard Soil Layer 5x5 Figure 9Hard Soil Layer 6x6

6 Figure 10Hard Soil Layer 7x7 Figure 11Hard Soil Layer 8x8 Result of Raft Capacity Calculation for Project Data Figure 12 Denah Pile Raft Foundation pada Proyek

7 Figure 13 Modelling of Project Soil Data Table 1 Soil Parameter on Project Parameter Value Soil Type Sand Clay 1 Clay 2 Clay 3 Clay 4 Material Modelling Mohr Coulomb Mohr Coulomb Mohr Coulomb Mohr Coulomb Mohr Coulomb Drainage Type Drained Undrained Undrained Undrained Undrained γ sat (kn/m 3 ) 16,2 16,2 16,6 16,6 17,5 γ unsat (kn/m 3 ) 15,5 15, E' (kn/m 2 ) 14375, c u (kn/m 2 ) ν 0,35 0,33 0,33 0,33 0,33 ϕ ( o ) ψ ( o ) c inc ,152 1,152 Figure 14Project Modelling Using Plaxis 3D

8 Result Analysis Of some modeling has been done in the above it can be seen that the raft had apparently contribution in carrying capacity of pile raft foundation where large contribution varies depending on the distance between the pile and the pile group formation. For modeling the data first can be seen that the cohesive soil, it turns raft has a contribution that varies in pile raft foundation, which can be seen from the graph the raft contribution increases with the distance between the piles. With FEM modeling analysis proves that the raft has a significant contribution so that the system can be said to be a raft foundation on grade. For data modeling refers to the modeling of both the raft off grade for the system it was found that the distance 2.5D - 3D does not contribute to the bearing capacity of pile raft foundation and the greater distance of the 3D shows that the greater the contribution of raft with the pile distance large. This is because of subgrade soil at the end of the pile is a pile hard so that the burden on the resulting shortening that occurs on the distance between the pile with the pile over a relatively large 3D which shows that the pile becomes less rigid so that the raft go down and hit the ground, thus participating in fulfilling the raft load. Because of these conditions, the results obtained for the raft carrying capacity is large enough. Sample taken on 5x5 models with the formation and spacing between piles 3.5, the decrease in the pile around m or 3.5 cm. For images attached as below. Figure 15Shorterner that Happened on 5x5 Formation with Distance = 3D And for the last modeling project that uses the data field located in Karet, Central Jakarta piling diameter of 1 m and a distance of 2.5D pile with pile number as many as 232 pile turns out to prove that the pile raft foundation raft used can contribute to the power support of 5.9% of the total applied load at the pile raft foundation. in this experiment proved that the foundation raft system uses ongrade. With some of the results of this experiment it can be concluded that in fact the pile raft foundation raft can contribute carrying capacity that had been on the regulations in the Jakarta area, the carrying capacity for the raft always ignored or considered absent. CONCLUSION AND SUGGESTION Conclusion The conclusion that can be drawn from some of the analysis that has been performed using Plaxis 3D program is on the pile raft foundation raft is: Raft has contributed to hold the load carrying capacity that is on top. Where such analysis in the previous chapter with the raft thickness is 1 m and the formation of the group who started from pile 5x5-8x8, with the distance between the pile starts from 2,5D, 3D, 3,5D, 4D, 5D, 6D, 7D, and 8D as well as certain vertical load, raft can hold between 0% to> 50% of the total vertical load that was on it. In the analysis using the data field project, the raft turns contributing carrying capacity which amounted to kn, or about 5.9% of the total loading that occurs.

9 If the pile lies on the ground hard with the distance between the pile<3.5d, the system falls into the category of pile raft slab on grade, which means raft contributes to the overall carrying capacity. Then if the distance between the pile>3.5d then said slab-off grade, which means it does not contribute raft carrying capacity. While the end of the pile foundation that does not reach the ground hard, it can be said to share the burden raft. Underpinnings are not reaching the ground hard, also known as Floating Pile and can be designed as a slab on grade. According to the results obtained from the analysis using 2 soil data hypothetical and 1 soil data of the project, proving that the raft on pile raft foundation can contribute to the load carrying capacity in the hold. In practice the distance between the piles usually range between 25D - 3,5D. Suggestion By doing the analysis of the carrying capacity of the raft foundation raft pile sistme be advised that: When designing the bearing capacity of the foundation raft can be taken into account in the design so that the load bearing foundation piles do not become a conservative, which according to the rules of Jakarta since the first that considers all of the burden borne only by piling themselves without taking into account the contribution of the raft. If the distance between the piles ranged between 2,5D - 3,5D and a pile of floating raft, the contribution can be calculated as a slab on grade. While the foundation piles that reach the ground hard with the distance between the pile<3.5 D, it can be designed as a slab on grade. If the distance between the piles> 3,5D it is designed as a slab-off grade. REFERENCE Das, Braja M. (1941). Principles of Foundation Engineering. (4 th edition). Unites States of America : Brooks/Cole Publishing Company, Pacific Grove, California Fleming, K., A. Weltman., M. Randolph., K. Elson. (2009). Piling Engineering. (3 rd edition). Abingdon, Oxon OXI4 4RN : Taylor & Francis. Hadiwibawa, C. (2013). Analisa Pengaruh Ketebalan Pile Cap dan Jarak Antar Tiang Terhadap Kapasitas Kelompok Pondasi dengan Menggunakan Plaxis 3D. Skripsi S1. Binus University, Jakarta. Lebeau, Jean S. (2008). FE-Analysis of Piles and Piled Raft Foundations Liong, Gouw T. (2013). Pondasi Dalam. Jakarta. GTL Office. Liong, Gouw T. (2014). Sample o Derivation of Derivation of Soil Parameters from a Soil Investigation Report. Jakarta. GTL Office PLAXIS b. v. (2012). PLAXIS 3D Manual DELFT University, Netherlands. Ryltenius, A. (2011). FEM Modelling Piled Raft Foundation in Two and Three Dimensions. 69. Sture, S. (2004). Determination of Soil Stiffness Parameters. Boulder, Colorado. CURICULLUM VITAE Personal Data NIM : Nama : Donny Chan donn.chan93@gmail.com Address : Current Jl. KH Syahdan No. 4C, Kemanggisan, Jakarta Barat Permanent Jl. Setia Budi No.8, Ketapang, Kalimantan Barat Phone Numbers : Gender : Male Birth Place / Date : Pontianak / 1 Januari 1993 Nationally : Indonesian Marital Status : Sigle

10 Religion : Katoloik Formal Education TK Persid, Ketapang, Kal-Bar SD Pangudi Luhur Santo Yosef, Ketapang, Kal-Bar SMP Pangudi Luhur Santo Albertus, Ketapang, Kal-Bar SMA Pangudi Luhur Santo Yohanes, Ketapang, KaL-Bar 2010 Present Jurusan Teknik Sipil, Universitas Bina Nusantara, Jakarta Non-Formal Education 2013 Present ILP Organization Experience HIMTES (Himpunan Teknik Sipil Binus University), as Staff of Events Section As a Mentor SAC in Binus University