Numerical investigations of pile load distribution in pile group foundation subjected to vertical load and large moment

Ukritchon, Boonchai,Faustino, Janine Correa,Keawsawasvong, Suraparb Techno-Press 2016 Geomechanics & engineering Vol.10 No.5

This paper presents a numerical study of pile force distribution in a pile group foundation subjected to vertical load and large moment. The physical modeling of a pile foundation for a wind turbine is analyzed using 3D finite element software, PLAXIS 3D. The soil profile consists of several clay layers, which are modeled as Mohr-Coulomb material in an undrained condition. The piles in the pile group foundation are modeled as special elements called embedded pile elements. To model the problem of a pile group foundation, a small gap is created between the pile cap and underlying soil. The pile cap is modeled as a rigid plate element connected to each pile by a hinge. As a result, applied vertical load and large moment are transferred only to piles without any load sharing to underlying soil. Results of the study focus on pile load distribution for the square shape of a pile group foundation. Mathematical expression is proposed to describe pile force distribution for the cases of vertical load and large moment and purely vertical load.

Optimal Design of Reinforced Concrete Cantilever Retaining Walls Considering the Requirement of Slope Stability

Boonchai Ukritchon,Sophea Chea,Suraparb Keawsawasvong 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.7

A Reinforced Concrete Cantilever Retaining Wall (RCCRW) is one commonly used soil retaining structure in engineering practice. Various optimization techniques to obtain the optimal design of cantilever walls have been proposed, where the three basic geotechnical constraints of overturning, sliding and bearing failures have generally been taken into consideration. However, none of these approaches have considered the geotechnical requirement of slope stability. In this paper, a novel formulation for the optimal design of RCCRWs that considers the more complete requirements of geotechnical stability of overturning, sliding, bearing and slope failures, is described. The objective function of the minimum cost of materials, geotechnical constraints of wall failures (overturning, sliding and bearing) and the structural requirements for steel reinforcements in the wall sections all followed the conventional approaches used in previous works. Using the Ordinary Method of Slices (OMS) with a circular arc failure surface (CAFS), the factor of safety against slope failure (FSOMS) for a RCCRW was implicitly derived. Constraints for ensuring that the minimum FSOMS was higher than the required factor were enforced in the formulation. Design variables were the dimensions of the wall sections, corresponding steel reinforcements and the x-y coordinate of center of the CAFS, where the latter are the additional unknowns in this novel formulation. Computational performance of the proposed optimization method is demonstrated and verified through its application to the optimal design of two examples of RCCRWs.

Investigation of Stability and Failure Mechanism of Undercut Slopes by Three-Dimensional Finite Element Analysis

Boonchai Ukritchon,Rithy Ouch,Thirapong Pipatpongsa,Mohammad Hossein Khosravi 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.5

Slope failures along a bedding plane were critical issues and mostly happened in an open pit mining project such as the Mae MohMine, Thailand. The prediction of maximum width to maintain stable slope after an excavation process is required. This paperpresents an investigation of 3D finite element analysis for the stability and failure mechanism of undercut slopes resting on a lowinterface friction plane. In numerical models, the soil slope was modeled as volume elements with the hardening soil material. Interface elements were used at the bottom plane to simulate the low interface friction plane and at the side support to simulate fullyrough surface for the models with side supports. Stage analyses in numerical models were performed following excavation processesin physical models until failure. The effects of the side support and the slope length to increase the stability of undercut slopes wereconsidered. Failure widths, failure mechanisms, and stress distributions associated with slope angles and boundary conditions of sidesupport were discussed and compared.

Undrained lateral capacity of rectangular piles under a general loading direction and full flow mechanism

Boonchai Ukritchon,Suraparb Keawsawasvong 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.7

New upper and lower bound solutions of undrained lateral capacity of rectangular piles under a general loading direction and fullflow mechanism were investigated by using finite element limit analysis with plane strain condition. The true collapse loads of thisproblem were generally bracketed by computed upper and lower bound solutions to within 3%. Results were summarized in the formof three dimensionless variables, including soil–pile adhesion factor, pile aspect ratio, and lateral loading direction. Predicted failuremechanisms of laterally loaded rectangular piles associated with these parameters were examined and discussed. Approximateequations of failure envelopes for rectangular piles under a general loading direction were proposed for a convenient and accurateprediction of their undrained lateral capacity in practice.

Finite element analyses of the stability of a soil block reinforced by shear pins

Ouch, Rithy,Ukritchon, Boonchai,Pipatpongsa, Thirapong,Khosravi, Mohammad Hossein Techno-Press 2017 Geomechanics & engineering Vol.12 No.6

The assessment of slope stability is an essential task in geotechnical engineering. In this paper, a three-dimensional (3D) finite element analysis (FEA) was employed to investigate the performance of different shear pin arrangements to increase the stability of a soil block resting on an inclined plane with a low-interface friction plane. In the numerical models, the soil block was modeled by volume elements with linear elastic perfectly plastic material in a drained condition, while the shear pins were modeled by volume elements with linear elastic material. Interface elements were used along the bedding plane (bedding interface element) and around the shear pins (shear pin interface element) to simulate the soil-structure interaction. Bedding interface elements were used to capture the shear sliding of the soil on the low-interface friction plane while shear pin interface elements were used to model the shear bonding of the soil around the pins. A failure analysis was performed by means of the gravity loading method. The results of the 3D FEA with the numerical models were compared to those with the physical models for all cases. The effects of the number of shear pins, the shear pin locations, the different shear pin arrangements, the thickness and the width of the soil block and the associated failure mechanisms were discussed.

Ultimate lateral capacity of two dimensional plane strain rectangular pile in clay

Keawsawasvong, Suraparb,Ukritchon, Boonchai Techno-Press 2016 Geomechanics & engineering Vol.11 No.2

This paper presents a new numerical solution of the ultimate lateral capacity of rectangular piles in clay. The two-dimensional plane strain finite element was employed to determine the limit load of this problem. A rectangular pile is subjected to purely lateral loading along either its major or minor axes. Complete parametric studies were performed for two dimensionless variables including: (1) the aspect ratios of rectangular piles were studied in the full range from plates to square piles loaded along either their major or minor axes; and (2) the adhesion factors between the soil-pile interface were studied in the complete range from smooth surfaces to rough surfaces. It was found that the dimensionless load factor of rectangular piles showed a highly non-linear function with the aspect ratio of piles and a slightly non-linear function with the adhesion factor at the soil-pile interface. In addition, the dimensionless load factor of rectangular piles loaded along the major axis was significantly higher than that loaded along the minor axis until it converged to the same value at square piles. The solutions of finite element analyses were verified with the finite element limit analysis for selected cases. The empirical equation of the dimensionless load factor of rectangular piles was also proposed based on the data of finite element analysis. Because of the plane strain condition of the top view section, results can be only applied to the full-flow failure mechanism around the pile for the prediction of limiting pressure at the deeper length of a very long pile with full tension interface that does not allow any separation at soil-pile interfaces.