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Stone columns are the most common and effective technique used for enhancing the overall strength and performance of soft soils. They are more effective for moderately lightweight structures. This investigation presents a parametric study of stone columns embedded in ground to strengthen the soft clayey soil under stiff raft foundation. This research is based on a computational analysis by creating a foundation finite element model consisting of a group of stone columns that are mounted under rafting using PLAXIS 3D. A certain range of parameters (for example spacing, diameter and angle of friction of stone columns) is considered and it is concluded that the increase in diameter and angle of friction of stone columns can improve the ultimate load bearing capacity of the foundation system. Furthermore, the failure mechanism of this foundation scheme is analysed and a semi-empirical model for the determination of the bearing capacity ratio (BCR) is developed from the results of the parametric analysis.

A growing interest of sugarcane bagasse fibre composite has been observed in recent years due to its attractiveness properties such as low specific weight, renewable source and producible with low investment at low cost. However, these materials have a low interfacial adhesion between fibre and matrix which lead to reduction in certain mechanical properties of the composite. To overcome this problem, studies show that certain chemical treatments on the surface of the fibres are some alternatives that significantly increase the adhesion reinforcement/matrix, in some cases improving its mechanical properties. The objective of this study was to evaluate the effect of different type of chemical treatment which are alkali and acid treatment on sugarcane bagasse fibre surface morphology. Seeking to improve the adhesion fibre matrix, the fibre has been treated with 5% of NaOH and 5% of HCL solution with added of bagasse fibre used in the range of 0% to 3% of cement weight respectively. Through SEM investigation, it is confirmed that chemical treatment helps to remove hemicelluloses from raw bagasse fiber as well as improved fibre matrix adhesion.

Cement as an essential element for cement-based products contributed to negative environmental issues due to its high energy consumption and carbon dioxide emission during its production. These issues create the need to find alternative materials as partial cement replacement where studies on the potential of utilizing silica based materials as partial cement replacement come into picture. This review highlights the effectiveness of microstructural characterization techniques that have been used in the studies that focus on characterization of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H) formation during hydration process of cement-based product incorporating nano reactive silica based materials as partial cement replacement. Understanding the effect of these materials as cement replacement in cement based product focusing on the microstructural development will lead to a higher confidence in the use of industrial waste as a new non-conventional material in construction industry that can catalyse rapid and innovative advances in green technology.

The ASTM standard provides guidelines for the drained direct shear test (DST) and requires the samples to be sheared at rates estimated from time to failure, t f ≥ 50 t 50 (where t 50 is the time required to achieve 50% consolidation). This paper investigates the potential of estimating the undrained strength of peat in the DST owing to its ease of accessibility and simplicity over other laboratory tests. In this experimental study, peat samples were sheared at various displacement rates at t f / t 50 values of 0.065–70. The samples tested at the ASTM specified rate of t f ≥ 50 t 50 exhibit continuous increase and decrease in shear stress and volume respectively with increasing shear strain. Hence, determining the drained strength properties of peat in the DST apparatus is complicated. However, it is concluded that the shear stress ratio, τ / σ ′ v of the DST test samples sheared at rates corresponding to t f ≤ 0.2 t 50 , reasonably corresponds to that measured in undrained direct simple shear (DSS) tests on peat, found in the literature. Therefore, DST conducted at high displacement rates will be adequate for preliminary evaluation of the shear strength of peat at close to undrained conditions, when constant volume DSS apparatus is not available.

Natural peat is considered incapable of supporting built structure due to its poor engineering properties. Chemical stabilization is one of the peat soil improvement methods which has been studied by many researchers. This study describes an investigation of water additive (W/A) ratio application on cement-stabilized peat strength. Peat soil at different moisture contents, which are 1210%, 803%, and 380%, were stabilized with cement by W/A ratio of 2.0, 2.5, 3.0, 3.5, and 4.0. Unconfined compressive strength (UCS) test was conducted after the specimens were being air-cured for 28 and 56 days. The result shows that there is an increase of UCS value as the decrease of W/A ratio (the increase of cement dosage) and the increase of curing time and peat moisture content. The higher strength found in the specimen with higher moisture content, compared to the lower one at the same W/A ratio, shows that the mix design of cement-stabilized peat using W/A ratio should have differed under different peat natural moisture contents. From the result, it is also found that cement hydrolysis reaction occurred despite the presence of humic acid in the peat soil, which by many studies is assumed will hinder the cement-soil reaction.

The general objective of this research was to measure the peat soil shear strength using Wenner four-point probes and vane shear strength methods. Specifically, the objective of this study was two-fold, namely, (a) investigating the relationship between laboratory soil resistivity and undrained shear strength and (b) determineing the relationship between in-situ soil resistivity and undrained shear strength. Data were randomly collected over six locations in Meranek, Sarawak, for in-situ test and three repetitions for each data were set based on three parameters. The selected parameters were soil density, moisture content, and salinity for both laboratory and in-situ test using Wenner four-point probes and vane shear method. The soil resistivity and vane shear strength readings for laboratory test were correlated with soil salinity, moisture content, and density. The R2 values showed a good correlation for soil salinity (R2 =0.8468) and density (R2 =0.9475), respectively. However, a weak correlation of R2 =0.1205 was observed for soil moisture. The R2 value for in-situ correlation between soil resistivity and three parameters (soil salinity, moisture content, and density) was R2 =0.8916. It can be concluded that the peat soil shear strengths of the study area using Wenner four-point probes from in-situ were (4.38 ohm.m) and laboratory was (2.47 ohm.m) and when using the vane shear strength method, in-situ was (23 kPA) and laboratory was (5 kPA). This study implies that the peat soil of the study area can be categorized as texture (soft loamy soil) and it is suitable for agriculture instead of construction. The relationship established between Wenner four-point probes and vane shear method can be beneficial for ground engineering design to enhance investigation on site suitability. Future work on DUALEM-421 technique should be emphasised for better subsurface exploration accuracy and resolve peat depth for an in-situ test.

This paper presents the findings from the field observation and site exploration for construction on peat in Sri Aman, Sarawak, Malaysia. A visit to Balai Bomba and Pejabat Metrologi in Sri Aman has been done in August 2019. From the observation and measurement conducted on the two locations of the constructed area on peat shows the settlement, δ recorded ranges from 100 mm to 150 mm. A field sampling for the determination of geotechnical properties of peat has been done in Balai Bomba Sri Aman. The depth of the peat in the area is about 2.88 m and the results show that the peat has high natural moisture content ranges from 900 % to 1400 %. The organic content (OC) for the site is in the range of 70 %-90 % for a depth of 0.5 m to 2.88 m, and categorized as H3, fibrous peat except for the first 0.5 m is 63 % which fall under H5, hemic peat group according to Von Post classification.

This study focuses on identifying and evaluating critical parameters of various drainage configurations, arrangement, and filter which affect the efficiency of water draining system in slopes. There are a total of seven experiments with different types of homogeneous soil, drainage envelope, filter material, and quantity of pipes performed utilizing a model box with a dimension of 0.8 m × 0.8 m × 0.6 m. The pipes were orientated at 5 degrees from the horizontal. Rainfall event was introduced via a rainfall simulator with rainfall intensity of 434.1 mm/h. From the experiments performed, the expected outcomes when utilizing double pipes and geotextile as envelope filter were verified in this study. The results obtained from these experiments were reviewed and compared with Chapter 14 “Subsurface Drainage Systems” of DID’s Irrigation and Agricultural Drainage Manual of Malaysia and the European standard. It is recommended that the pipe installed in the slope could be wrapped with geotextile and in tandem with application of granular filter to minimize clogging without affecting the water discharge rate. Terzaghi’s filter criteria could be followed closely when deciding on new materials to act as aggregate filter. A caging system could be introduced as it could maintain the integrity of the drainage system and could ease installation.

Rainfall is inevitably one of the main factors that trigger landslides. However, not much study has been conducted on the impact of groundwater rise on slope stability. Thus, this study is intended to focus on the rise of the groundwater level from the bottom of the slope which would lead to landslides due to pore pressure development by eliminating other landslide-triggering factors (i.e., infiltration and surface runoff). Saturated sand was used for slope modeling, and sand densities of 1523 kg/m3, 1562 kg/m3, and 1592 kg/m3 were tested with a constant slope angle of 45°. Another set of experiments was also performed on slopes having angles of 25°, 45°, and 60° and with a maintained density of sand at 1562 kg/m3. Through observation, failure was initiated first at the toe of the slope before minor and major slips or total collapse occurs. Dimensions of slip surfaces were measured and included in SLOPE/W for the computation of the safety factor. In conclusion, safety factors are found to be higher in denser soil and in the lowest slope angle. However, faster occurrence of collapse in denser soil was identified and could be contributed by the faster pore water pressure development.

Soil nailing is a method to stabilise existing slopes and new cuts that has been used for over 3 decades. The method is easy and flexible, mainly due to ease of construction and is adaptable to heterogeneous soil. Soil nailed structures built on clayey soil can bring complications especially if the structures are exposed to adverse environment. Studies on clay slopes behaviour and failure mechanisms reinforced with soil nails were performed here to expand our understanding on them. A large number of centrifuge tests on soil nailing were performed on sand. This investigation is to explore the nature of soil nailed clay slopes when tested in the centrifuge. Six centrifuge tests on soil nailed clay slopes and on an unreinforced clay slope for comparison were performed in this investigation. The design of the slopes was performed based on HA 68 of Department of Transport (1994) and BS 8006 (1995). Since the centrifuge models were brought to failure by gravity turn on method, the slip surface would be deep which caused the nails, intentionally designed to have insufficient embedment length. The slope configuration was maintained the same throughout the tests but the nails length, size and material were varied. Apart from that, different excavation methods were simulated in these tests to explore each method suitability and ease of application in the centrifuge. The settlement and the strain on the nail were also measured throughout the tests. In addition, a digital camera was also installed in the centrifuge and used to observe the deformation on the model slopes. The safety factor values of the models at failure were checked and the stability number of the models against failure was obtained. In general, the results show that all the models enhanced stability due to inclusion of reinforcement and failed due to pullout failure and soil slippage against reinforcement. Measurement from strain gauges on nail proved that in clay slopes, axial force was also mobilised as early as during the excavation method and the bending moment was mobilised at a later stage when approaching failure. Axial force and bending moment were also mobilised at the nails facing plate. In addition, results from digital images were processed and analysed via a method called PIV (Particle Image Velocimetry) as introduced by White (2002) for use in geotechnical engineering analysis. A program called MatPIV (Sveen, 2004) was used and results in terms of vector representation of the movement on the slopes were obtained. This is an investigation of soil nailed models built in clay and tested in the centrifuge, which has not been extensively performed. The results obtained will add to the current theoretical understanding of the mechanism of soil nailed structures in clay.