Finite Element Analysis of the Non-Uniform Behavior of Structured Clay under Shear

Jirayut Suebsuk,Suksun Horpibulsuk,Martin D. Liu 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.4

Conventional triaxial tests are widely used to interpret the stress-strain behavior of soils. The non-uniformity of their stress-strain relationship and the localization of deformation normally occur during shear test and affect the observed test results. This article investigates the non-uniform behavior of artificially structured (i.e., cemented) specimens experiencing shear due to an end restraint under various testing conditions. The conditions investigated include the stress state, the drainage conditions, and the strength improvement associated with the cementation effect. A finite element analysis has been performed using the Modified Structured Cam Clay (MSCC) model, which was developed as a generalized constitutive model for destructured, naturally structured, and artificially structured clays. The shear behavior of artificially structured cylindrical specimens was simulated under both drained and undrained shearing by a coupled hydro-mechanical finite element analysis. The stress-strain distributions and the local stress-strain relations of the artificially structured specimens are compared with those of the destructured specimens. It is evident that the end restraint significantly influences the shear response in drained conditions, particularly for the tests with a high yield stress ratio (YSRiso, which is the ratio of the yield stress to the current stress) and a highly cemented structure. The non-uniform stress-strain behavior is attributed to the non-uniform lateral deformation, which results in a variation in stress paths for different points within the specimen. The different effective stress paths for different points within the specimen affect the overall performance of the specimen, including the yield stresses, the yield strengths and the destructuring processes for a structured specimen. The specimens experiencing shear with high confinement in a Normally Consolidated (NC) state deform relatively uniformly, while those with low confinement in an Over-Consolidated (OC) state display a non-uniform lateral deformation. Hence, the destructured and structured NC specimens exhibit more uniform stress-strain behavior than the OC specimens. The highly structured specimens show more nonuniform stress-strain behavior than the destructured specimens. In conclusion, the end restraint plays significant role in the specimen deformation for both destructured and structured specimens. Special care should be taken for destructured specimens in an overconsolidated state, and for structured specimens in both normally and over-consolidated states.

Numerical And Sensitivity Analysis of Bearing Reinforcement Earth (BRE) Wall

Cherdsak Suksiripattanapong,Suksun Horpibulsuk,Avirut Chinkulkijniwat,Jin Chun Chai,Shui-Long Shen,Arul Arulrajah,Apichat Suddeepong 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.1

Numerical and sensitivity analysis of the Bearing Reinforcement Earth (BRE) wall were carried out using PLAXIS 2D. The numerical and sensitivity analysis was performed by varying the foundation conditions (thickness, T and modulus of elasticity, E of the weathered crust) and the BRE wall properties (number of transverse members, n, reinforcement length, L, wall height, H, reinforcement vertical spacing, Sv and axial stiffness of reinforcement, EA). The studied L/H ratio is between 0.7 and 1.0 and the geotextiles elements were used to model the reinforcement. The settlement of the BRE wall is governed by E, T, and H, irrespective of the BRE wall properties. The bearing stress distribution is essentially the same even with different E, T, n, Sv, EA. The magnitude of bearing stress is mainly controlled by H. The lateral movement pattern is primarily dependent upon Sv for a particular H. The inward movement exists for small Sv value while the outward movement exists for large Sv value. The magnitude of lateral movement is controlled by E, T, L and n. For a particular foundation condition (E and T), an increase in n is more advantageous than an increase in L because the lateral movement is insignificantly reduced when L/H > 0.8. The maximum tension and AASHTO recommended failure plane were found not to coincide in the serviceability state. In the serviceability state, the tie points must be stronger than the reinforcements for the wall height > H/2 while the reinforcement must be stronger than the tie point for the wall height < H/2. The simplified K versus H relationship is a practical tool to examine the factor of safety based on the conventional method.

Nonlinear Frame Element with Shear– Flexure Interaction for Seismic Analysis of Non-Ductile Reinforced Concrete Columns

Worathep Sae-Long,Suchart Limkatanyu,Woraphot Prachasaree,Suksun Horpibulsuk,Pattamad Panedpojaman 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.5

This paper presents and emphasizes the essence of inclusion of shear response and shear–flexural interaction in the investigation of reinforced concrete (RC) columns characterized by light and inadequately (substandard) detailed transverse reinforcement. This column type commonly exists in old-constructed RC frame buildings before the regulation of modern seismic codes. A stiffness-based RC frame element with shear–flexure interaction is formulated within the framework of Timoshenko beam kinematics assumption. Linked displacement interpolation functions are employed to remedy the problematic shear-locking phenomenon. The axial and flexural actions are interacted via the fiber-section model while shear-strength deterioration with inelastic flexural deformations is accounted for within the framework of the UCSD shear-strength model. The numerical procedure for shear–flexure interaction is modified from the Mergos–Kappos procedure. The proposed element is simple, computationally efficient and able to describe several salient features of RC columns with substandard detailed transverse reinforcement, including gradual spread inelasticity, shear–flexure coupling effects, and shear-strength deterioration with increasing curvature ductility. Three correlation studies are conducted to examine the model accuracy and its capability to predict the rather complex responses of non-ductile RC columns. Comparison with conventional flexural frame element is also presented to emphasize the essence of inclusion of shear response and shear–flexure interaction.

Reuse of dredged sediments as pavement materials by cement kiln dust and lime treatment

Yoobanpot, Naphol,Jamsawang, Pitthaya,Krairan, Krissakorn,Jongpradist, Pornkasem,Horpibulsuk, Suksun Techno-Press 2018 Geomechanics & engineering Vol.15 No.4

This paper presents an investigation on the properties of two types of cement kiln dust (CKD)-stabilized dredged sediments, silt and clay with a comparison to hydrated lime stabilization. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted to examine the optimal stabilizer content and classify the type of highway material. A strength development model of treated dredged sediments was performed. The influences of various stabilizer types and sediment types on UCS were interpreted with the aid of microstructural observations, including X-ray diffraction and scanning electron microscopy analysis. The results of the tests revealed that 6% of lime by dry weight can be suggested as optimal content for the improvement of clay and silt as selected materials. For CKD-stabilized sediment as soil cement subbase material, the use of 8% CKD was suggested as optimal content for clay, whereas 6% CKD was recommended for silt; the overall CBR value agreed with the UCS test. The reaction products calcium silicate hydrate and ettringite are the controlling mechanisms for the mechanical performance of CKD-stabilized sediments, whereas calcium aluminate hydrate is the control for lime-stabilized sediments. These results will contribute to the use of CKD as a sustainable and novel stabilizer for lime in highway material applications.

Enhancement of Soft Soil Behaviour by using Floating Bottom Ash Columns

Razieh Moradi,Aminaton Marto,Ahmad Safuan A Rashid,Mohammad Moeen Moradi,Abideen Adekunle Ganiyu,Mohamad Hafeezi Abdullah,Suksun Horpibulsuk 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.6

The current disposition worldwide is for sustainable construction, and the application of by-products is one of the ways to achieve it. In this research, bottom ash was used as a substitute material in a granular column to decrease settlement and enhance the bearing capacity of soft soil. Bottom ash is a derivate of the coal burning process, it has similar engineering properties to sand and fine gravel. A set of reduced scale physical modelling tests were performed on floating bottom ash columns to assess the improvement in the bearing capacity of the composite ground. The results clearly showed that the bearing capacity of the model soil was greatly improved with the installation of bottom ash column sand. There was an obvious enhancement of the load capacity of the granular columns when they were encased. The usage of bottom ash instead of aggregate or sand for granular columns will reduce the project cost and it aligns with the goal of sustainable construction development.