Haryati Awang

Evaluation of Stochastic Daily Rainfall Data Generation Models

In developing countries, data is usually a scarce resource as data collection is an expensive exercise. Therefore, analytical method is required to simulate the actual situations and provide synthetic data for forecasting purposes. This paper will compare several methods of synthetically generating rainfall data based on available data. Several models will be used, including lag-one Markov chain model, two-step model, and transition probability model to generate stochastic daily rainfall data of long-term duration, using data from a catchment in Australia. Three variations of lag-one Markov chain models were used: untransformed, logarithmic transformation, and square root transformation. Two-step model uses Markov chain to model rainfall occurrences and gamma distribution to model rainfall depths. Six variations of the Transition Probability Matrices were used, 3 using Shifted Exponential Distribution and 3 using Box–Cox Power Transformation was adopted to predict the high rainfall depths, and the parameters are determined using maximum-likelihood method on the available rainfall data. The models’ results were tested by comparing the statistics of the generated data against those of the available data. Direct comparisons of the means, standard deviations, and skews show satisfactory results. Further comparisons of monthly means, standard deviations, skews, maxima and minima, as well as the lengths of wet and dry spells had also shown satisfactory results. In conclusion, all the models have produced synthetic rainfall data, which are statistically similar to those of the available data. In comparison, the TPM model gave the most accurate results. Therefore, this model may be utilised for synthetic rainfall data generations, which can then be used for forecasting.

A Correlation Between P-Wave Velocities and Standard Penetration Test (Spt-N) Blows Count for Meta-Sedimentary Soils of Tropical Country

The conceptual foundation design acquires geotechnical parameters such as stiffness, elastic, strength, etc. As such, geophysical method such as seismic refraction may assist in providing parameters for geotechnical analysis and design. Using seismic methods, the information on the stiffness of the ground can be obtained. This study has been carried out to develop the correlation between P-waves velocity from seismic refraction method against Standard Penetration Test (SPT) N value from existing borehole data. The study area was located at Bandar Country Homes, Rawang, Selangor which was believed to be underlained by Terolak Formation, a geological formation consisting of meta-sedimentary rock. Three seismic lines were conducted across six numbers of existing boreholes with the aim of characterizing the subsurface of the study area. Interval of each geophone was set to 5 m with the total length of each seismic line 120 m. The seismic sources were used by 12 lbs sledge hammer and steel plate, then seismograph data received by geophones (24 Hz) and saved in ABEM Terralock MK6 as seismogram. The high quality data obtained was then processed using SeisOpt Picker and SeisOpt@2D software to produce a seismic tomography section for each survey line. The correlation was made between seismic velocities and SPT-N value at the same depth. The findings from this study, a linear regression was found to enhance the relationship between Vp and SPT-N value. Also, the subsurface information together with depth of each geomaterial at the study area could be determined. Thus, this study may assist engineers for estimating and predicting the properties of the subsurface geomaterials in meta-sedimentary soils especially in reducing the cost of site investigation and enhance the knowledge of understanding earth’s subsurface characterizations physical parameters.

Quantifying Cavity Through Volumetric Study by Resistivity Images

The complexity of karst system, referring to its geological and hydrological characteristics can be categorized among the most fragile and vulnerable environments in the world. Karst voids are commonly a major engineering risk associated with construction in areas underlain by carbonate rocks. Due to karst unique characteristics to exhibit sudden change in subsurface conditions, extensive geotechnical exploration is needed in order to achieve the best geotechnical results. A site investigation that can provide clearer picture of the overall underground condition should be carried out in order to overcome the problems related to karst void, such as cavity profiling. This study anticipated to determine the subsurface profile and investigate the underground cavities in limestone areas by electrical resistivity method and using the simulation of Voxler software. An electrical resistivity test was conducted at a proposed site at Jalan Sultan Ismail, Kuala Lumpur. The subsurface profile of the selected study area was successfully analyzed and determined from 2-D resistivity images, including identification of potential cavities and voids. The 2-D resistivity images and 2-D oblique images (sliced images from 3-D model) show similar subsurface profile indicating that the Voxler software is suitable and flexible to model the 2-D resistivity images to 3-D images. The potential cavity volume calculation was also successfully calculated.

Seismic Refraction Investigation on Limestone Area in Gopeng, Perak

Seismic refraction method is one of the most commonly used geophysical methods in civil engineering that is able to provide detailed information on the distribution and thickness of subsurface layer with characteristics seismic velocities. By necessity, it also could be a support to the interpretation of geological data. Two-dimensional (2D) seismic refraction tomography is one of the surface geophysical methods used in determining the continuous subsurface profile of ground damage with particular reference to geo materials based on P-wave (Primary velocity, v p ) results. This method was used in this study in purpose to determine the subsurface profile from the study area. ABEM Terraloc MK6 seismograph was used to record data from P-wave data acquired. Using OPTIM software package, the subsurface profile based on linear and delay time analysis would be investigated. Based on the study, it was found that overall strata along the study area were reasonable with the previous geological data by using the P-wave seismic velocity. Thus, this study helps in reducing the cost of site investigation significantly.

Engineering Characterisation of Kuala Lumpur Granite and Limestone

Rock properties are key elements that should be taken into account in designing substructures especially for underground structures such as tunnel and pile. For this reason, rock should be tested directly in the laboratory to measure the properties of the material particularly the physical and mechanical properties. This study is about investigating the quality of granite and limestone from Kuala Lumpur area for engineering purposes. As Kuala Lumpur is having a rapid development in urbanisation, construction in and on rock mass is an important element that cannot be avoided. Being part of tropical region, the quality of rock should be measured thoroughly because of deterioration and decaying of the material due to weathering. Referring to the problems encountered with rocks in tropical country, this study was carried out to characterise the engineering properties of granite and limestone found in the Kuala Lumpur area. Samples of granite and limestone were taken from a number of places where the borehole drilling for site investigation works is on progress. A finding of this study hopefully is useful in providing information of engineering properties of granite and limestone from Kuala Lumpur for technical communities.

Case Study on Geophysical and Geotechnical Assessment on Rock Subsurface: Road Construction

Most of the site investigation (SI) works for geotechnical design parameters are still using conventional methods such as borehole drilling, mackintosh probe, hand auger and others. For projects at hilly, marshy and jungle areas, site investigation work is harder to implement because of the difficulty in getting water resources, oil, food and others. Also, soil profile interpretation by borehole data sometimes cannot determine the location and size of boulders. Combination of two types of tests, borehole drilling and 2D electrical resistivity test, is able to get more accurate ground profile and the location of boulders and bedrock level can be determined. This will help engineers to design accurately and minimize other risks, avoiding under estimation project cost and thus, construction could be completed according to plan. This paper presents finding of a study that was carried out in rock subsurface material. The main objective is to compare subsurface profiles between resistivity and boreholes. The results showed that the resistivity image allows large areas to be covered in a short period of time whenever borehole results are limited to a single point. Besides that, borehole drilling cannot be implemented in all areas due to difficulty in mobilization of drilling machine as the study area is in hilly areas and high cliff. The resistivity image and boreholes profile give alike result. However, the result shows some irregularities due to several aspects, namely, level of ground water table where the water table is high and the resistivity is low. Resistivity image has to compliment with advancing boreholes for interpretation as the range of resistivity value to differentiate the material is very wide. Also, in order to identify relationships between resistivity and engineering properties a correlation between resistivity value and SPT N-value was developed.

Geophysical Characterisation of Road Subsurface

Road makes a very huge contribution for the development of economic and also to the social benefits. Poorly maintenance of the roads may reduce the efficiency of the business and trading. There are few non-destructive methods have been introduced and developed to measure the strength and deformation properties of layer that made up the pavement structure. The properties are either used to design new pavement structures or to diagnose the causes of existing problem so that appropriate rehabilitation strategies can be chosen. This study is about determining the ground profile of defect and non-defect pavement using electrical resistivity method. The purpose of this study is to investigate subsurface condition under the defect and non-defect of road pavement using electrical resistivity on actual field. Since the testing was conducted on pavement, the actual electrodes of one and half (1.5) foot steel were changed to 4 inches nails. The resistivity was measured by injecting current to the ground through electrodes and the resultant voltage difference was measured at two potential electrodes. In this study, 3 locations with different damages were selected and the resistivity value of defect and non-defect pavement were measured and profiled. Three types of defects which are crocodile cracking at the parking bay for busses, rutting and potholes at access road and transverse cracking located at car park area were investigated. The finding of this study shows that the value of electrical resistivity varies from one defect to another. This is because of influence of few factors during the early construction and the types of defect on the pavement. The advantage of using electrical resistivity method in determining the defect and non-defect pavement is its one of the non-destructive method that can be applied without making and leave major damage to the pavement surface.

Predicting Uniaxial Compression Strength (UCS) Using Bulk Density for Kuala Lumpur Granite and Limestone

In engineering practice particularly in measuring strength properties of rock, uniaxial compressive strength (UCS) is considered as one of the key in characterizing rock material. However, sometime it is quite difficult or impossible to full fill the test requirement especially when dealing with rock that consists of discontinuities or fractures. Samples that were sent to laboratory for UCS test sometime have not enough length due to breakage during coring process in drilling activities or during transportation. In order to overcome this problem, a study was carried out to use simple method of testing as an alternative to predict the strength. Bulk density test of rock sample is one of the simple measurements that can be used to predict the UCS. The values of UCS can be correlated with the corresponding bulk density of the rock. In this study a total of 73 samples consisted of 29 granite and 44 limestone were used for UCS and bulk density test. The significant of the bulk density as variable in the correlation was evaluated in the T-test responding by P-value. Both P-value and least squares regression (R2) showed the strong relation between UCS and bulk density of granite and limestone sample. The finding from experimental works and statistical analysis showed that, this study preceded a reliable method to predict the UCS of rock using bulk density.

Influence of velocity on local weathered granite properties

The non-destructive technique (NDT) such as for determined the velocity is an easy technique to apply and they are increasingly being used in geotechnical engineering. Most researchers studied the relations between rock properties and velocity and found that the velocity is closely related with rock properties. Wave velocity can be measured directly or indirectly in the laboratory. In this study, the wave velocity in rock was measured by detecting the arrival time or travel speed in rocks using a Free-free Resonant Column (FFRC). Various weathering grade of granite samples were used to determine velocity and other properties. The result shows that the velocity have a good correlation with other properties on various weathering grade of granite.