Excavation assessment in wet tropically sedimentary rock

The selection of suitable methods to be employed for surface excavation works is particularly important in geotechnical engineering projects. Factors such as environmental constrains, rock properties and size of site may affect the selection of machine required for surface excavation. Wrong selection of equipment and technique can result in unrecoverable expenses and thus, should be avoided. Great challenges in excavation works are expected in sedimentary rock where the occurrence of discontinuity such as bedding thickness, foliation and the inhomogeneity of rock as well as effect of moisture can greatly affect its excavatability. This paper aims to identify and highlight the factors affecting the excavation works in wet tropically weathered sedimentary area as what have been experienced in Malaysia. Some of these factors, however, are not specified in the existing general excavatability assessments. Assessment by practical excavation was carried out at three sedimentary rock sites in Nusajaya, Malaysia, taking into account the related parameters. Statistical analysis by using SPSS was then being conducted in order to determine the correlation of each parameter with productivity of excavation and their significance in affecting the excavatability.Based on the results obtained, it was found that the parameters such as Is50, R, UCS, density, ITS, Js, JL, Jd, IP and moisture content play significant roles in affecting the excavatability of sedimentary rocks. Meanwhile, the existence of bedding, Id2 and Jn are deemed to be neglected. It is believed that this study can help to enhance the knowledge on factors that complicate the excavation works in sedimentary area

Estimating uniaxial compressive strength of tropically weathered sedimentary rock using indirect tests

Uniaxial compressive strength (UCS) of intact rock is particularly important in rock mechanic studies, especially for those involving civil and mining projects. However, the determination of UCS using direct test is generally expensive, time consuming and almost impossible in preparation of samples for highly weathered sedimentary rocks. In view of this, indirect tests are comparatively cheap, simpler, faster and more convenient to perform either in laboratory or at site. This paper aims to develop an estimation procedure in determining the UCS values of such weak weathered rocks. Among the indirect tests present herein are point load index, Schmidt Rebound hammer, Brazilian tensile test and slake durability test. Unfortunately, it was found that the accuracy of each single test varies with weathering states. Hence, a recommended procedure using combined indirect tests in determining UCS of weak sedimentary rocks is presented herei

Experimental tests on SSTT-confined HSC columns

The steel-strapping tensioning technique (SSTT) has been widely accepted as an effective method for enhancing the performance of high-strength concrete (HSC) columns. Previous experimental tests showed that SSTT can increase the ductility of HSC by up to twice that of unconfined HSC. However, most of the tests performed on SSTT-confined HSC columns have focused on concentrically loaded short specimens. In reality, however, columns with a length/diameter ratio greater than three and subjected to eccentric loading are very common. Against this background, experiments were carried out to investigate the slenderness effect of SSTT-confined HSC columns subjected to eccentric loads. It was found that SSTT increases both the strength and deformability of slender HSC columns, although the confining effects are reduced proportionally with an increase in slenderness ratio. The effects of the eccentricities and the eccentricity ratio are also presented in this paper

Circular HSC columns confined with pre-tensioned steel straps

Steel-straps tensioning technique (SSTT) has been proven to be an effective mean to confined High-strength concrete (HSC). The pre-tensioned force offers by this confining method can significantly restraint the small lateral dilation of HSC. However, most of the design guidelines only concerned with FRP-confined columns subjected to concentric compression. The direct application of these design guidelines on the SSTT-confined HSC column is being questioned due to different material and confining method adopted. Hence, a numerical study was carried out to compare the proposed model with the previous studies. The comparison between experiment results and previous studies has proven that external confinement using steel strap is comparable to others external confinement method. However, there is no definitive conclusion regarding the effectiveness of different confinement method as the geometry of the specimen is different

The design of short sstt-confined circular HSC columns

Steel-straps tensioning technique (SSTT) has been proven to be an effective mean to confined High-strength concrete (HSC). The pretensioned force offers by this confining method can significantly restraint the small lateral dilation of HSC. However, most of the design guidelines only concerned with FRP-confined columns subjected to concentric compression. The direct application of these design guidelines on the SSTT-confined HSC column is being questioned due to different material and confining method adopted. Hence, a numerical study was carried out in the view of developing a simple design equation for HSC column confined with SSTT. The parameters such as SSTT-confinement ratio, load eccentricities and slenderness ratio were tested. Based on the numerical results, design equations based on regression analysis were proposed to determine the ultimate load and bending moment of SSTT-confined HSC columns

Effects of eccentricity on SSTT confined HSC columns

Previous studies proved that the application of steel-strapping confining technique (SSTT) could significantly remove the undesireable properties of high-strength concrete (HSC) especially the brittleness. However, research studies so far have been concentrated on concentrically loading and neglected the effects of eccentricity on the effectiveness of SSTT-confined HSC columns. In this paper, 3 columns confined with SSTT were tested. These columns were subjected to eccentric loads of 25 mm and 50 mm which simulate moderate eccentricities and high eccentricties loadings, respectively. Results show that the efficiency of SSTT-confinement drops linearly with respect to the increment of eccentricities. An empirical equation was proposed to evaluate the efficiency of SSTT-confinement based on the test results

Design of short SSTT-confined HSC columns

steel straps,confinemnet, theoretical model, design equation, high-strength concrete, short column, flexural capacities Steel-straps tensioning technique (SSTT) has been proven to be an effective mean to confined High-strength concrete (HSC). The pre- tensioned force offers by this confining method can significantly restraint the small lateral dilation of HSC. However, most of the design guidelines only concerned with FRP-confined columns subjected to concentric compression. The direct application of these design guidelines on the SSTT-confined HSC column is being questioned due to different material and confining method adopted. Hence, a numerical study was carried out in the view of developing a simple design equation for HSC column confined with SSTT. The parameters such as SSTT-confinement ratio, load eccentricities and slenderness ratio were tested. Based on the numerical results, design equations based on regression analysis were proposed to determine the ultimate load and bending moment of SSTT-confined HSC columns

Rock strength assessment based on regression tree technique

Uniaxial compressive strength (UCS) is one of the most important parameters for investigation of rock behaviour in civil and mining engineering applications. The direct method to determine UCS is time consuming and expensive in the laboratory. Therefore, indirect estimation of UCS values using other rock index tests is of interest. In this study, extensive laboratory tests including density test, Schmidt hammer test, point load strength test and UCS test were conducted on 106 samples of sandstone which were taken from three sites in Malaysia. Based on the laboratory results, some new equations with acceptable reliability were developed to predict UCS using simple regression analysis. Additionally, results of simple regression analysis show that there is a need to propose UCS predictive models by multiple inputs. Therefore, considering the same laboratory results, multiple regression (MR) and regression tree (RT) models were also performed. To evaluate performance prediction of the developed models, several performance indices, i.e. coefficient of determination (R2), variance account for and root mean squared error were examined. The results indicated that the RT model can predict UCS with higher performance capacity compared to MR technique. R2 values of 0.857 and 0.801 for training and testing datasets, respectively, suggests the superiority of the RT model in predicting UCS, while these values are obtained as 0.754 and 0.770 for MR model, respectively

Flexural capacity enhancement of rectangular high-strength concrete columns confined with post-tensioned steel straps: experimental investigation and analytical modelling

The load-carrying capacity and deformability of concrete columns can be substantially enhanced by confining with post-tensioned steel straps. As interest in high-strength concrete (HSC) grows among structural engineers and researchers due to its superior performance, this confining technique is being extended to HSC columns with the hope that it can eliminate the undesired properties of HSC, especially its brittleness. However, experimental studies involving confined HSC columns subjected to eccentric loads are comparatively limited. It can be seen from past research that most studies of external confinement were conducted on small-scale normal-strength concrete (NSC) cylinders subjected to concentric loads. Since most columns are subjected to eccentric loads in reality, the scarcity of test data has prevented the potential of this confining technique from being fully exploited. In this paper, this confining technique is called the steel-strapping tensioning technique (SSTT) for brevity. Nine HSC columns were tested under eccentric loads. The specimens were grouped into three groups with each group having an unconfined HSC column as a control specimen, a two-layer SSTT-confined HSC column and a four-layer confined HSC column. The experimental results show that the flexural capacities of HSC columns can be enhanced with SSTT. The deformability of confined HSC columns is significantly improved with such confinement

Assessment on abrasiveness of rock material on the wear and tear of drilling tool

An assessment of rock material was carried out in this study to determine the wear resistances of drill bit due to physical properties of granite and old alluvium. This study intends to provide a current state-of-the-art comparison of petrographical analysis and interpretation of F-Schimazek's value in terms of its drillability rate and the wear and tear of the drilling tools. Rock samples representing the drilling locations were collected and tested for its physical and mechanical properties in the laboratory. The F-Schimazek's value is obtained from a number of easily measured parameters namely Brazilian Tensile Strength, mineralogical composition and grain size. In this study, samples of old alluvium were collected from drilling project prepared for blasting work from an interchange project at Gelang Patah, Johor, Malaysia. Besides that, samples of granite were collected from Maktab Rendah Sains Mara (MRSM) Project at Bandar Sri Alam, Masai, Johor for the same purpose. The results are then analyzed with the rate of penetration measured during the drilling work. The result shows a good relation between the parameters involved and the methods are simple and practical to be employed for the drilling assessment