Performances of SDCM and DCM walls under deep excavation in soft clay: Field tests and 3D simulations

This study presents the results of full-scale tests and three-dimensional finite element analyses of deep cement mixing (DCM) and stiffened deep cement mixing (SDCM) columns under lateral loads and DCM and SDCM walls under deep excavation in soft clay. The DCM walls used in this study comprised one, two and three rows of DCM columns, whereas the SDCM walls consisted of only one row of DCM columns with steel H-beams inserted in either all DCM columns or in alternating DCM columns. The measured and simulated results are presented in terms of profiles of lateral displacement, settlement and bending moment.     

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing (TDM) pile-supported embankments over soft soils. The uncertainties of the mechanical properties of the in-situ soil, pile, and embankment, and the effect of the pile shape are considered simultaneously. The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging (using adaptive sampling algorithm). Individual and system failure probabilities, in terms of the differential and maximum settlements (serviceability limit state (SLS) requirements), are considered. The reliability results for the embankments supported by TDM piles, with various shapes, are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes. The influences of the inherent variabilities in the material properties (mean and coefficient of variation values) on the reliability of the piled embankments, are also investigated. This study shows that large TDM piles, particularly those with a shape factor of greater than 3, can enhance the reliability of the embankment in terms of SLS requirements, and even avoid unacceptable reliability levels caused by variability in the material properties.     

Parametric study and optimization of a food can corrugation design using a response surface method

This paper presents the parametric design and functional optimization of a thin-walled food container with a corrugated surface. The configuration of the can corrugation should be designed to minimize the use of raw material subject to the constraints of the targeted structural performance. In the present study, the failure behaviors and the buckling strengths of a commercial food can under paneling pressure and axial loading are investigated with a series of experiments and finite element analyses. Full factorial design is implemented to study the effects of the geometric parameters of the corrugation (e.g., depth, radius, spacing and number of beadings) on its strength. Parameter optimization using a rotatable central composite design is employed to identify an optimal corrugation design by approximating the response surfaces of the can strength in terms of the significant design variables. The obtained surfaces are derived through the analysis of variance, and the suitability of the response is justified. A light- weight can body is then achieved by reduction of the can body thickness according to the required strength characteristics. Finite element analysis of the optimal model is also performed to confirm the predicted results. By using the proposed procedure, the can-body weight can be reduced by up to 12% compared with the original design.     

Bearing capacity and failure behaviors of floating stiffened deep cement mixing columns under axial load

This research aims to clarify and gain an insight into the impact of the length of the stiffened core and the strength of the deep cement mixing (DCM) socket on the behaviors of floating stiffened deep cement mixing (SDCM) columns. The observed behaviors include the axial ultimate bearing capacity, settlement and failure mode. The study begins by conducting a series of physical model tests as a preliminary investigation. The results reveal that the strength of the DCM socket can be reduced to a certain value by inserting a sufficiently long reinforced core to achieve the highest possible load-carrying capacity, indicating an optimum length of the stiffened core for a specific DCM socket strength. For a parametric study on the actual scale condition, full-scale load tests on a floating DCM and an SDCM column with eucalyptus wood as a core in the thick soft clay layer area were carried out to provide a reference case. The extended numerical analysis results suggest that the modes of failure depend on the length of the stiffened core and the strength of the DCM socket. The results from the numerical parametric study were used to establish a guideline chart for suggesting the appropriate length of the core in accordance with the strength of the DCM socket of the floating SDCM columns. The field pile load test results also confirm that core materials with a lower strength and stiffness, such as eucalyptus wood, could potentially be used as a reinforced core.     

Effective Void Ratio for Assessing the Mechanical Properties of Cement-Clay Admixtures at High Water Content

Portland cement is widely used for the improvement of soft clay in many applications and construction methods. Because of the high initial water content of in situ soft clay, the additional water in the cement slurry to be mixed, and the added air in some applications, the mixtures have a high water content and void ratio in either almost-saturated or unsaturated conditions. The mechanical properties of cement-clay admixtures—including cement-treated clay and air-cement-treated clay—are affected by several parameters, e.g., mixing proportions, curing time, and the initial state of the mixture. To facilitate engineering decisions regarding mixing design and the development of a constitutive model, a single parameter that can characterize the mechanical properties of such mixed materials is advantageous. This paper recommends a parameter defined as the effective void ratio that could appropriately quantify the dependency of the mechanical properties of cement-clay admixtures on the influencing parameters on the basis of the results of unconfined compression, oedometer, and triaxial tests. The proposed parameter tends to capture the mechanical characteristics of cement-clay admixtures under different test conditions.     

Comparative flexural performance of compacted cement-fiber-sand

This research investigates the influence of seven different fiber types on the flexural performance of compacted cement-fiber-sand (CCFS) with four fiber fractions (0.5, 1, 1.5 and 2% by volume). The seven types of fibers are 12?mm polypropylene, 19?mm polypropylene, 40?mm polypropylene, 55?mm polypropylene, 33?mm steel, 50?mm steel and 58?mm polyolefin fibers. The overall CCFS performance was divided into seven sub design performance indicators: (1) peak strength; (2) peak strength ratio; (3) residual strength ratio; (4) ductility index; (5) toughness; (6) equivalent flexural strength ratio; and (7) maximum crack width. The interaction mechanism of the fiber/cement-sand interface was investigated by scanning electron microscopy. Finally, the effectiveness of each fiber type was compared and rated in terms of the overall performance. The results show that the 50?mm steel fiber provided the best overall sub performance, resulting in an excellent overall flexural performance; in comparison, the 12?mm polypropylene fiber exhibited very poor performance. However, the 19?mm polypropylene and 33?mm steel fiber specimens provided very good and good overall performances, respectively. The nature of the fiber surface and the fiber length affects the overall performance of CCFS. The surface of the steel fibers, compared to the other synthetic fiber types, is more hydrophilic and is more compacted in a cemented-sand matrix without separation of the interfacial zone, providing the best overall flexural performance.     

Influence of Curing Stress on One-Dimensional Yielding of Cement-Admixed Bangkok Clay at High Water Content

The influence of curing stress on the one-dimensional compression characteristics of cement-admixed clay at high water content is investigated by oedometer tests, with special attention paid to the primary vertical yield stress. From the test results, the stress acting during the formation of cementation plays an important role in the one-dimensional compression characteristics of cement admixed clay. The stress compresses the treated clay and results in an increase in the vertical yield stress. For the cement-admixed clay studied, the effect of the curing stress inherently reflects on the after-curing void ratio. Therefore, the primary vertical yield stress in one-dimensional compression is a function of the after-curing void ratio and the ratio of the clay water content to the cement content ratio.