Chee-Ming Chan

Influence of mix uniformity on the induced solidification of dredged marine clay

Ground improvement with soil solidification has been widely applied and has proven to be an effective pre-treatment of soft soil deposits. The solidification procedure usually involves addition and thorough mixing of hydraulic binders with in situ soils, consequently transforming the soft materials into a stronger and stiffer stratum for load bearing. Much has been done on the binder’s effectiveness and resulting enhanced properties of the soils, but not as much has been reported of the factors governing in situ mixing efficiency in producing uniform mixtures. While advancement in machinery and computerization of operations have significantly improved soil mixing, individual factors contributing to the process can be further examined to refine the effectiveness. This paper describes a series of laboratory tests, mainly unconfined compressive strength tests complemented with X-ray computer tomography, conducted on cement-stabilized dredged Kawasaki clay of different uniformities. A number of factors affecting uniformity were examined, namely the water/cement (WC) ratios, number of cement layers in the initial state as well as the number of mixing cycles adopted. Test specimens were prepared based on a systematic combination of these factors to enable a comprehensive cross-analysis of the results. It was found that the clay’s initial consistency was markedly altered by cement addition, which resulted in either enhanced or reduced workability of the mixture. While increased mixing vigor could apparently overcome poor distribution of binder in the mixture, the resulting strength remained very much affected by the WC ratio, suggesting dependency of the mixture’s overall uniformity on a combination of the factors.

SCREW-IN SOIL NAIL FOR SLOPE REINFORCEMENT AGAINST SLIP FAILURE: A LAB-BASED MODEL STUDY

Slope failures occur when the shear resistance along the slip plane is exceeded. This can be caused by excessive load imposed at the slope crest or compromised stability of the slope, e.g. disturbed dimensions of the slope. In order to prevent slope failure, stabilisation or reinforcement measures need to be taken. A common solution is to intercept the slope failure plane with reinforcement elements, such as soil nails and ground anchors. In soil nailing, reinforcement bars are installed on the slope to effectively resist the additional shear forces from the imposed loads, hence reducing the probability of failure in the long run. This paper describes the innovation of soil nail with screw-in installation mechanism instead of the conventional push-in approach. The screw-in installation ensures better soil-nail grip and less disturbance during the slope stabilisation procedure, especially in terms of noise and spoils. In addition, the novel nail has a hollow stem which improves shear resistance with greater soil-nail surface contact on the inner wall. The opening at the nail head also enables displaced air to escape as the nail is screwed into the slope and soil pushed into the inner hollow cavity. The prototype nails were tested in a slope model with different configurations, and were found to reduce the Angular Distortion Ratio by 37 % and the Volumetric Deformation Index as much as 33 % respectively. The novel screw-in soil nail could be potentially used to stabilize natural and man-made slopes, though full-scale simulations are recommended to formulate the installation procedure and to validate the effectiveness.

On the Bioremediation Potential of Inhabitant Microbes of Dredged Marine Soils: A Theoretical Framework

Biological degradation is one of the most beneficial and economical methods to clean up contaminated marine soils. Although biodegradation by microorganisms encourages the natural process of contaminant removal and serve as potentially cost-effective treatment, limited facts in microbes and contaminant interactions lead in treatment failure. The present study had identified the existence of potential microbes in marine soils dredged from the coasts of Peninsular Malaysia. These included the genera of Serratia, Vibrio, Enterobacter, and Pseudomonas. Among these, Vibrio and Serratia have potential to degrade oil and grease as well as Polycyclic Aromatic Hydrocarbons (PAHs). Irrespective of any additions of particular nutrients, the existence of these genera whereupon reduces the potential for bioaugmentation treatment. Major problem in bioaugmentation is rapid decline in number of introduce microbes due to abiotic or biotic stress. The first stage needed to develop treatment strategies are by understanding the environmental conditions and factors that limit the ability of microbes to degrade the contaminants. Considering these understanding, biodegradation treatments of contaminated dredged marine soils is ease to design. This theoretical framework therefore aims to assess on the bacteria capability to degrade correlated with the contaminant concentration.

Distribution of Escherichia coli in Dredged Marine Soils Collected from Waters Around Peninsular Malaysia: A Relation with Geotechnical Properties

Dredging is a necessary procedure for marine infrastructure development and maintenance, such as ensuring sufficient depth and breadth of shipping channels in port facilities. Dredged marine soils (DMS) are a geowaste inadvertently produced from the dredging activities. The soils are either being disposed offshore or in confined disposal facilities on land. The fact that characterization study of DMS shows the material to be largely similar to other soils, albeit saturated with water hence soft and weak; DMS can be potentially reused as a sound geomaterial in backfills, especially in strategically located reclamation sites along the shoreline. Nonetheless the close proximity to anthropological activities upstream of feeder rivers means high probability of bio-contamination. Therefore for the reuse potential to be explored, environmental and health risks associated with DMS must first be considered. This paper describes an examination of the relationship between geotechnical properties of DMS and distribution of indicator bacteria, E. coli in the soil. 4 samples of DMS were retrieved from maintenance dredge site in waters surrounding Peninsular Malaysia, covering the eastern, western and southern coasts. The geotechnical properties included soil particle size distribution, fines content, pH, water content (wc) and Liquid Limit (LL). In general it was found that the presence of E. coli is closely associated with the fines content and pH of the DMS, where greater quantity of fine particles seemed to accommodate more microbes in an alkaline condition. The highest count of E. coli was isolated from the DMS sample with the lowest water content, but this is postulated to be influenced by the location of sampling as affected by potentially contributing sources of the microbe. The results are essentially useful for making environmental and health risks assessment of DMS prior to reuse to avoid mishaps among users of the reclaimed land.

An alternative soil nailing system for slope stabilization: Akarpiles

This research proposes an innovative solution for slope stabilization with less environmental footprint: AKARPILES. In Malaysia, landslide has become common civil and environmental problems that cause impacts to the economy, safety and environment. Therefore, effective slope stabilization method helps to improve the safety of public and protect the environment. This study focused on stabilizing surfacial slope failure. The idea of AKARPILES was generated from the tree roots system in slope stabilization. After the piles are installed in the slope and intercepting the slip plane, grout was pumped in and discharged through holes on the piles. The grout then filled the pores in the soil with random flow within the slip zone. SKW mixture was used to simulate the soil slope. There were two designs being proposed in this study and the prototypes were produced by a 3D printer. Trial mix of the grout was carried out to obtain the optimum mixing ratio of bentonite: cement: water. A series of tests were conducted on the single-pile-reinforced slope under vertical slope crest loading condition considering different slope gradients and nail designs. Parameters such as ultimate load, failure time and failure strain were recorded and compared. As comparison with the unreinforced slope, both designs of AKARPILES showed better but different performances in the model tests.This research proposes an innovative solution for slope stabilization with less environmental footprint: AKARPILES. In Malaysia, landslide has become common civil and environmental problems that cause impacts to the economy, safety and environment. Therefore, effective slope stabilization method helps to improve the safety of public and protect the environment. This study focused on stabilizing surfacial slope failure. The idea of AKARPILES was generated from the tree roots system in slope stabilization. After the piles are installed in the slope and intercepting the slip plane, grout was pumped in and discharged through holes on the piles. The grout then filled the pores in the soil with random flow within the slip zone. SKW mixture was used to simulate the soil slope. There were two designs being proposed in this study and the prototypes were produced by a 3D printer. Trial mix of the grout was carried out to obtain the optimum mixing ratio of bentonite: cement: water. A series of tests were conducted o...

Strength characteristics of lightly solidified dredged marine clay admixed with bentonite

Strength characteristic is a significant parameter in measuring the effect of soil improvement and effective composition of solidification. In this study, the dredged marine sediment (DMS) collected from Kuala Perlis (Malaysia) was examined to determine its strength characteristics under light cement solidification with bentonite. Dredged marine clay generally has the low shear strength and high void ratio, and consists mainly of soil particles of the fine-grained type. As a discarded geo-waste, it can be potentially treated to for reuse as a backfill material instead of being disposed of, hence reducing the negative impact on the environment. Physico-chemical parameters of the dredged sample were first determined, then solidification was carried out to improve the engineering properties by admixing ordinary Portland cement (OPC) as the binder and bentonite as a volume enhancer to the soil. The DMS was treated with the addition of 3 % and 6 % cement and bentonite within the range of 0-30 %. The specimens were cured at room temperature for 3, 7 and 14 days. The strength gain was measured by unconfined compression test and vane shear test. The laboratory test results were analyzed to establish the relationship between strength properties and solidification specifications. In summary, the strength of specimens increased with the increase of the quantity of bentonite and cement to get the effective composition of the specimen.

A lab-based study of subground passive cooling system for indoor temperature control

Passive cooling is an alternative cooling technique which helps to reduce high energy consumption. Respectively, dredged marine soil (DMS) is either being dumped or disposed as waste materials. Dredging works had resulted high labor cost, therefore reuse DMS as to fill it along the coastal area. In this study, DMS chosen to examine the effectiveness of passive cooling system by model tests. Soil characterization were carried out according to BS1377: Part 2: 1990. Model were made into scale of 3 cm to 1 m. Heat exchange unit consists of three pipe designs namely, parallel, ramp and spiral. Preliminary tests including flow rate test and soil sample selection were done to select the best heat exchange unit to carry out the model test. Model test is classified into 2 conditions, day and night, each condition consists of 4 configurations which the temperature results are determined. The result shows that window left open and fan switched on (WO/FO) recorded the most effective cooling effects, from 29 °C to 27 °C with drop of 6.9 %.

Admixing dredged marine clay with cement-bentonite for reduction of compressibility

Cement-based solidification/stabilization is a method that is widely used for the treatment of dredged marine clay. The key objective for solidification/stabilization is to improve the engineering properties of the originally soft, weak material. Dredged materials are normally low in shear strength and bearing capacity while high incompressibility. In order to improve the material’s properties for possible reuse, a study on the one-dimensional compressibility of lightly solidified dredged marine clay admixed with bentonite was conducted. On the other hand, due to the viscous nature, particularly the swelling property, bentonite is a popular volumising agent for backfills. In the present study, standard oedometer test was carried out to examine the compressibility of the treated sample. Complementary strength measurements were also conducted with laboratory vane shear setup on both the untreated and treated dredged marine clay. The results showed that at the same binder content, the addition of bentonite contributed significantly to the reduction of compressibility and rise in undrained shear strength. These improved properties made the otherwise discarded dredged marine soils potentially reusable for reclamation works, for instance.

FOOTING WITH INVERTED PYRAMIDAL PROTRUSIONS FOR SETTLEMENT CONTROL IN SANDY DEPOSITS

This paper examines the feasibility of using an innovative footing with a corrugated base to enhance the load-bearing capacity of shallow foundation, and to reduce the substructure’s subsidence as a whole or differentially. The corrugated base consists of inverted pyramidal protrusions which give a 3-fold advantages: (1) the pointed tips help smoothen the process of installation on site, (2) the protrusions provide additional contact surface between the foundation and the soil for better load-bearing, (3) the corrugated base entraps soil between the individual protrusions, improving the foundation’s stability against settlement and sliding. Scaled models of the 8 cm x 8 cm footing were produced using 3D printing: CONTROLsmooth base, Design A corrugated base with16 inverted pyramidal protrusions of 2 cm x 2 cm x 2 cm each, and Design Bcorrugated base with 64 inverted pyramidal protrusions of 1 cm x 1 cm x 1 cm each. Both designs had the same contact surface area with the soil, though the penetration depth of the pyramids and the space between the protrusions varied. Maintained load tests were carried out in simulated soil beds to determine the improved performance of the foundation. It was shown that the corrugated slabs reduced settlement up to over 85 % compared with the conventional smooth-base footing, with Design B giving slightly better results. It was also observed that the larger pyramidal protrusions (Design A) tended to entrap air between them, forming air cushions which resisted further penetration of the corrugated base into the soil, i.e. inhibiting mobilization of the maximum load-bearing capacity.

IMPROVED SOIL-PILE INTERACTION OF FLOATING PILE IN SAND WITH SHAFT TREATMENT

The present study explored the efficacy of pile shaft surface treatment on the improvement of soil-pile frictional resistance for floating or friction piles. 4 surface conditions of model piles measuring 200 mm long and 20 mm in diameter were examined, namely smooth (control), roughened, fishbone and checked shafts. A pile cap made of plywood was fixed to the top of the pile with 10 mm embedment depth, leaving 190 mm clearance for installation in the sand bed. The test chamber was a see-through glass tank with a footprint of 100 mm x 200 mm and 300 mm height. Coarse sand of D50 = 1.5 mm were loosely placed in the chamber by layers up to 200 mm height before the piles were installed either in single or triple group formations. The incremental load test of conducted via application of dead load ranging between 0.01-0.08 kPa on the pile cap, and the corresponding settlement was recorded. The test results revealed settlement to be reduced by the piles in the order of roughened > fishbone > checked > smooth for the single pile configuration, with maximum reduction of 40 % recorded by the roughened pile. As for the pile group, settlement reduction of the piles with surface treatment clearly outperformed the control pile by almost 50 %, though differences between the former were marginal with seemingly overlapping stress-strain plots. All in all the surface treatment of pile shaft enhanced the shaft friction for the piles installed in sand, but field implementation would require further examination of the pile-driving efficiency as the improved piles could cause additional resistance during installation.