Thirapong Pipatpongsa

Performance of counterweight balance on stability of undercut slope evaluated by physical modeling

Abstract The frictional behavior of a block of moist silica sand No. 6 on a Teflon plate is studied thru a series of slip tests. A relation was found between the supports on the sides and toe and the stability of the sand block. The critical slope angles for the stability of the sand block on the Teflon plate were obtained for three cases of without supports, with only side supports and with both side and toe supports. Based on the results from slip tests, a series of undercut slope physical model tests were conducted where moist sand was uniformly layered inside a rigid acrylic frame fixed on a sloping Teflon plate. The model was instrumented by a set of miniature pressure cells buried inside the model and a row of potentiometers at the top of the slope model. A high speed camera with a capture speed of 500 frames per second was employed to record the crack initiation of the model. Moreover movement distributions of the slopes were recorded and analyzed using particle image velocimetry (PIV) and image processing software. The effect of counterweight balance on the stability of the slope model was studied thru model tests with different counterweight balances in size. It was confirmed that as the pillars of the model become stronger, the width of the span of the excavated area could be increased before the failure of the slope.

Statics of loose triangular embankment under Nadai’s sand hill analogy

Abstract In structural mechanics, Nadai’s sand hill analogy is the interpretation of an ultimate torque applied to a given structural member with a magnitude that is analogously twice the volume of stable sand heap which can be accommodated on a transverse cross-section basis. Nadai’s analogy is accompanied by his observation of a loose triangular embankment, based on the fact that gravitating loose earth is stable if inclined just under the angle of repose. However, Nadai’s analysis of stress distribution in a planar sand heap was found to be inaccurate because the total pressure obtained from Nadai’s solution is greater than the self-weight calculated from the heap geometry. This raises a question about the validity of his observation in relation to the analogy. To confirm his criterion, this article presents and corrects the error found in Nadai’s solution by analyzing a radially symmetric stress field for a wedge-shaped sand heap with the purpose of satisfying both force balance and Nadais closure. The fundamental equation was obtained by letting the friction state vary as a function of angular position and deduce it under the constraint that the principal stress orientation obeys Nadais closure. The theoretical solution sufficiently agreed with the past experimental measurements.

Theoretical and Experimental Studies of Stress Distribution in Wedge-Shaped Granular Heaps

The present work explains the statics of self-weight transmission restricted to a long prismatic heap inclined at an angle of repose and symmetrically formed on a rigid base. The closure of polarized principal axes with the mobilized state of stress along the slope surface is employed by imposing the orientation of principal stresses on the equilibrium equations. Comparisons were made with calculations based on the finite element method using an elastic model. Moreover, experiments on sand heaps deposited on a rectangular rigid base were conducted to validate the theoretical study. The measured pressure profile generally agreed well with theoretical results.

The relationships between electrical conductivity of soil and reflectance of canopy, grain, and leaf of rice in northeastern Thailand

Soil salinity is a global environmental problem and the most widespread land degradation problem that reduces crop yields and agricultural productivity. The characteristic of soil salinity is conventionally measured by the electric conductivity (EC) of soil while remote-sensing techniques have been extensively applied to detect the presence of salts indirectly through the vegetation using crop spectral reflectance. This study aims primarily to investigate whether salt stress the rice can be detected by field reflectance or not, and second, to search the significant bands of vegetation indices that can indicate the relationships between the EC of soil and field hyperspectral reflectance of canopy, grain, and leaf of rice, using the normalized difference spectral index (NDSI). Field investigations on various paddy fields in northeastern Thailand were carried out in late November 2010 during the ripening season just before harvest in an attempt to realize the applications of the field hyperspectral technique for monitoring the spread of saline soils and estimation of the effects of soil salinity on rice plants. Jasmine rice and glutinous rice were two different rice species selected for this study. Rice plant investigations were conducted by collecting data on crop length, panicle length, canopy openness, leaf area index, and digital photographs of plant conditions from each site. The statistical analysis revealed that the changes in soil EC were significantly sensitive to the ripening stages of both jasmine rice and glutinous rice planted on different levels of soil salinity. Among reflectance measurements, canopy reflectance was highly correlated with soil EC. However, the estimated accuracies of the relationship between soil EC and reflectance of glutinous rice were relatively lower than those of jasmine rice.

On the numerical implementation of hyperplasticity non-linear kinematic hardening modified cam clay model

A continuous hyperplasticity model named kinematic hardening modified cam clay (KHMCC) is a constitutive soil model based on thermodynamic principles. This model has addressed some shortcomings of the modified cam clay (MCC), specifically on small strain stiffness. Because of employing multiple surfaces plasticity, it can simulate a smooth transition from elastic to plastic behaviour as well as the effect of immediate past stress. This article aims to present some important issues on the numerical implementation of the continuous hyperplasticity non-linear KHMCC model. The incremental stress–strain response is calculated based on a rate-dependent algorithm. A significant advantage of the rate-dependent calculation is that it is not necessary to attach with the consistency condition during calculation of plastic strains. Effect of time step and number of yield surfaces in rate-dependent algorithm will be also presented. A discussion on using of numerical integration rules of hardening functions is addressed. Furthermore, model verification is performed against analytical solution of ideal undrained response which has been obtained from theoretical integration of the MCC function over the imposed stress or strain path. Finally, some numerical demonstrations are also carried out to illustrate several key features of the model.

In-Flight Excavation of Slopes with Potential Failure Planes

AbstractThe stability of an in-flight undercut slope with a potential failure plane was investigated under a centrifugal acceleration of 50g. The experimental results confirmed the formation of passive arch action in the undercut slope and were found to be in good agreement with the results of 1g physical model tests showing that the arching-type failure in undercut slopes is a scale-independent phenomenon. The maximum stable undercut span is compared with that in the theory developed by the authors, and the results are discussed.

Stress–Strain Relationship for the Singular Point on the Yield Surface of the Elasto-Plastic Constitutive Model and Quantification of Metastability

In this chapter, the stress–strain relationship on the singular point of the yield surface of the original Cam clay model and the Sekiguchi-Ohta’s model is derived in order to compute the volume change correctly. Metastable space, the range of increment of strain in which effective stress does not get away from the singular point of yield surface, was theoretically derived. In metastable space, the increment of volumetric strain is larger than the increment of deviatoric strain.

Experimental studies of floor slip tests on soil blocks reinforced by brittle shear pins

Abstract Massive slope failures in open pit mines are essential issues for mining projects because they can cause the loss of lives, damage to machineries and the delay of works. To understand the effect of shear pins on slope stabilisation, the aim of this paper is to employ experimental models to investigate the stability and failure mechanisms of the floor slip resistance of soil blocks that are reinforced by brittle shear pins and rest on a low-interface friction plane. The soil blocks were made of humid silica sand No. 6 and placed on a Teflon sheet. Pencil leads, 2 mm in diameter, were used as the brittle shear pins and installed perpendicularly to the bedding plane. A series of tests were carried out for the floor slip resistance of the soil blocks with shear pins by gradually tilting the models until failure was observed. Parametric studies were performed by varying the number of shear pins, the shear pin installation, and the soil block thickness. The experimental studies revealed that these parameters have a significant influence on the stability and the failure mechanisms. Three different failure mechanisms were observed in this study, namely, slip failure, punching failure and detachment failure.

Threshold of Friction Stabilizes Self-Weight Transmission in Gravitating Loose Sand Heaps

Self-weight transmission under friction inequality in gravitating loose earth can be analyzed under the framework of continuum theory. This chapter concentrates on load transmission of prismatic sand heaps in loose conditions. Nadai’s idealization of a gravitating loose earth was adopted to solve for the closed-form stress field solution. The solution shows good agreement with the experimental data. This chapter reviews this ongoing research and presents graphic illustrations and interpretations. A sand heap is found to be stable on a threshold of resistance, indicating that the load-bearing structure of a sand heap can be promptly destabilized by a marginal disturbance.

Particular Stress Distributions in Granular Wedges under Coulomb Friction Inequality

Constitutive relation governs the performance of stress distribution prediction in granular heaps. However, there is no unique closure of stress relation which can generally characterize the pattern of weight transmission. Under the rigorous theory of continuum mechanics, this study proposes the generalized formulation of admissible stress field solutions satisfying Coulomb friction inequality. The governing equation of stress distributions involving the trajectories of principal axes can be essentially formulated to non‐homogeneous second‐order linear differential equation. Derivations of particular stress distribution regularized by the closures of fixed principal axes, polarized principal axes and its extension are presented. It is found the trajectories of major compressive stress could be considered as arching criterion.