Sompote Youwai

The interaction mechanism and behavior of hexagonal wire mesh reinforced embankment with silty sand backfill on soft clay

Abstract The pullout/direct shear mechanisms as well as the behavior of hexagonal wire mesh reinforced embankment with silty sand backfill had been investigated by numerical method. Finite element method under plane strain condition using SAGE CRISP software has been utilized in the numerical simulations. For the numerical simulation of full-scale reinforced wall, the reinforcement stiffness, backfill soil properties, soil/reinforcement interaction, properties of soft clay foundation, and consolidation period were significantly considered in the analysis. The equivalent interaction coefficients of the interface element were used in the simulations for the pullout and direct shear modes. The results have been favorably compared with the previous simulation using PLAXIS FEM software. The numerical technique has reasonably captured the actual behavior of the reinforced embankment on soft foundation. Most of the interaction mode obtained from the simulation is governed by the direct shear mechanism.

Interaction of nonwoven needle-punched geotextiles under axisymmetric loading conditions

Abstract Geotextiles have been successfully used for reinforcement of unpaved roads on soft subgrade to improve the performance of a reinforced fill layer placed on soft ground. The tension–strain behavior of a nonwoven needle-punched geotextile under axisymmetric loading condition as well as the mechanism and effects of the different grades of geotextile on the increase in bearing capacity of reinforced unpaved roads over weak subgrade under traffic load were considered. The strain energy capacity concept is proposed to describe the tension–strain of geotextile under an axisymmetric loading condition. Modified CBR tests on soft and weathered clay overlain by compacted sand as well as on soft and weathered clay overlain by compacted sand reinforced with fix- or free-end nonwoven needle punched geotextile were carried out. Finite element method (FEM) using the PLAXIS software was utilized to back-analyze the results of the modified CBR tests. No significant difference between in-air and in-soil stiffness has been found for geotextile reinforcement of unpaved road. The calculated results indicate an additional load capacity due to the presence of the geotextile using an axisymmetric stiffness which demonstrated a significant contribution of membrane action by the different types of geotextile on the increase in bearing capacity of soil–geotextile system. The effects of the different types of geotextile obtained in this study can be used to preliminary select the appropriate grades of nonwoven needle-punched geotextile corresponding to the allowable rut depth in the design of the reinforced unpaved roads under traffic load.

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.

INTERACTION BETWEEN HEXAGONAL WIRE REINFORCEMENT AND RUBBER TIRE CHIPS WITH AND WITHOUT SAND MIXTURE

The interaction between tire chips with and without sand mixtures and the hexagonal wire reinforcement, as well as the strength characteristics of mix, were investigated by in-soil pullout tests and large-scale direct shear tests. Rubber tire chips with and without sand mixtures have lower shear strengths than pure sand. Compared with the tests in sand, the hexagonal wire reinforcement in the rubber tire chips with and without sand mixtures had lower pullout resistances. However, with increasing sand content in the mixtures, the pullout resistances of hexagonal wire in mixtures increased. The proposed empirical equations successfully predicted the pullout resistances of hexagonal wire with different mixing ratios. Based on limit equilibrium method, the results of the parametric studies of a reinforced wall for the required spacing and embedment length of hexagonal wire reinforcement have been presented. For a reinforced wall, the total amount of the required hexagonal wire reinforcement in rubber tire chip fill is less than in sand and tire chip-sand fills. Furthermore, the required embedment length of the hexagonal wire reinforcement in sand and tire chip-sand fills is approximately identical, but lower than those in tire chip fill.

Simple Dynamic Hammer for Evaluation of Physical Conditions of Pavement Structures

Even though low-volume roads usually serve as secondary roads on the entire road network, they are of great importance for the distribution of goods to a number of rural areas in Thailand. However, the budgets for evaluation of the physical condition of the pavement structure of roads in this category and for their subsequent maintenance are surprisingly limited. In addition, the number of specialists required to perform visual inspections is small, and simple static tests on road surfaces are time-consuming and thus expensive. Consequently, it is difficult, if not impossible, to evaluate the physical conditions of pavement structures at a sufficient number of locations. To mitigate this, it becomes necessary to develop a simple test device and a simple means of test analysis to evaluate the physical condition of the pavement structure. This paper introduces a dynamic hammer and discusses a procedure for analysis of the test data. Experiments were performed on both asphalt-paved and unpaved surfaces, which are usually used for low-volume roads. In addition, plate load tests were performed in parallel to compare the test results and validate the analytical framework. It was found that the test device and the framework for analysis of the test data presented in this paper are relevant for use, in particular because of the simplicity of device production, the ease of device use, the time-effectiveness of test performance, and the procedures used for data analysis. Therefore, maintenance can be performed at sufficient numbers of locations of low-volume roads to keep them in good physical condition for serving the entire road network.

Evaluation of Guy Anchorage Strength in Clay for Transmission Tower

Due to the growth of the economy in Thailand, the electricity transmission system must be regularly maintained so that electricity is effectively and safely distributed for uses in daily life and industries. Natural disasters often cause damage to transmission towers. In addition, some damage has occurred due to vandalisms and soil excavations near transmission towers. Foundation scouring and tilting typically occur at transmission towers. In practice, repair of damage to a transmission tower typically begins with transferring the foundation pressure of the damaged tower to other firm foundation soil using a guy fixed to a guy anchor. The transmission tower is then restored to its original condition. In this study, a series of field anchorage strength tests were performed in the Bangkok metropolitan region which is well-known for its very soft to soft clay deposits. Additionally, Kunzelstab penetration tests were performed to evaluate the undrained shear strengths of the clay with depth at the test locations. The measured ultimate anchorage strengths were then compared with values estimated theoretically on the basis of measured undrained shear strengths. The measured values were found to be approximately 70 % of the theoretical values. This was probably due to the clay disturbance caused by anchor installation. Based on this fact, the ultimate anchorage strengths were then estimated for other clay conditions.

Hypoplastic Model for Simulation of Deformation Characteristics of Bangkok Soft Clay with Different Stress Paths

This paper presents the development of hypoplastic model for simulating deformation characteristics of Bangkok Soft Clay. The results from drained triaxial tests of Bangkok Soft Clay were simulated by the new hypoplastic model with applied stress path of 0–180 degrees in p–q stress space. The proposed hypoplastic model has satisfy performance to predict the deformation characteristics of Soft Bangkok Clay. The stiffness of proposed model varied according to load and unloading condition and different applied stress path.

Correlations Between Strains in a Thin Asphalt Pavement Structure and Deflection Basins: Investigation by Linear Elastic Analysis and Experiments

In rural areas, thin asphalt surface pavement structures have been constructed for low-volume road networks. For this type of road, a light weight deflectometer (LWD) may be useful for evaluating the responses of a pavement structure. Of the responses, the mobilized horizontal tensile strain at the bottom of asphalt pavement indicates the fatigue cracking potential, while the mobilized vertical compressive strain at the top of the base layer indicates the rutting potential. A series of linear elastic analyses was performed on a thin asphalt surface pavement structure. Correlations between the two mobilized strains and deflection basin parameters were found. A model thin asphalt surface pavement structure was constructed in the field. Many sensors were installed for measuring the mobilized stresses and strains during an LWD test. The test results generally were in agreement with the linear elastic analyses. The mobilized strains in the thin asphalt surface pavement structure could be predicted with the correlations with deflection basin parameters obtained from the LWD test.

Deep Excavation Induced Pile Movement in Bangkok Subsoil-A Numerical Investigation

Semi-empirical equations for predicting lateral pile movement due to adjacent braced excavation in Bangkok subsoil are developed in this paper. The equations are derived from multiple-linear regression analysis of the artificial data, which are the relation between lateral pile deflection and influenced parameters. These data are generated from a large number of finite element (FE) analyzes of pile adjacent to deep excavation using the reasonable soil models and parameters of Bangkok subsoil condition. The soil model in the analyses is specially paid attention to soil stiffness at small strain range. The results of prediction of maximum pile deflection by developed equations are in good agreement with FE analysis data. However, this study deals with only one soil profile, more data with varying soil properties are necessary in further study for more general equations.

Deformation Characteristics of Asphaltic Concrete in Uniaxial Compression

Assistant Professor, ditto ABSTRACT: A series of unconventional unconfined uniaxial compression tests were performed on cylindrical specimens of compacted hot-mix asphaltic concrete. Not only continuous monotonic loading tests at different constant strain or load rates but also sustained loading tests and minute cycles of unload/reload during otherwise monotonic loading were performed. Axial and radial strains were measured locally respectively by a pair of local deformation transducers (LDTs) and a set of three clip gauges. Therefore, it becomes possible to precisely evaluate: 1) initial Youngs moduli (Eo) and Poissons ratios (ν o); 2) equivalent elastic Youngs moduli (Eeq) and Poissons ratios (ν eq) for different axial stress values; and 3) tangential stiffness values (Etan) and Poissons ratios (ν tan) which vary with an increase in the axial stress. Then, it becomes possible to predict the deformation of HMA from a given loading history based on the elastic theory when all parameters above can be determined.