Pornkasem Jongpradist

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.

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.

Efficiency of Rice Husk Ash as Cementitious Material in High-Strength Cement-Admixed Clay

The potential and efficiency of using rice husk ash (RHA) to add up or partially replace Portland cement in deep cement mixing technique are examined. A series of unconfined compression tests on cement-RHA-stabilized clay are conducted to investigate the influence of RHA on the mixture properties. Special attention is paid to its efficiency for increasing the strength by partial cement replacement to obtain high-strength soil cement, and it is compared with fly ash. Test results indicate that up to 35% of RHA could be advantageously added up to enhance the strength if the cement content in the mixture is larger than 10%. The RHA enhances the strength of cement-admixed clay by larger than 100% at 28 days. For curing time of 14 and 28 days, the RHA exhibits higher efficiency on Portland cement replacement when the cement and overall cementitious contents are not less than 20 and 35%, respectively. The optimum condition for high-strength mixture is achieved when RHA is added to the 20% cement content mixture. When compared with fly ash of similar grain size, the efficiency of RHA is higher when the content to be added is greater than 15%. This indicates the suitability of RHA for use in high-strength soil-cement.

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.