Technical Report on Proposed Land Reclamation Utilizing Mud and or Clay

Report on Proposed Land Reclamation Utilizing Mud and orClay (Cohesive) Soils Preamble Many methods are currently available when it comes to land reclamation, in recent times though the focus has shifted more to a sustainable design that would be beneficial on all fronts. The utilization of mud or clay (cohesive) soils has generally been looked into with many design effort focusing on the use of dredged in-situ soils from the bed on the water body. This provides dual advantages in both the soil utilization and the lowering of the water level due to increased depth. On the economic side, it is found that in most cases where a suitable filling material is readily not available within the locality, the option of modifying the characteristics of the in-situ soil has been found much cheaper and sustainable. Introduction Land reclamation is the process of claiming back submerged land from water bodies like oceans, sea, bays and rivers. This activity has played a significant role in the urban development of coastal areas in many parts of the world, such as Hong Kong, Japan, Singapore, South Korea and the Netherlands. The Netherlands is noted for reclaiming land from the ocean. It has wrested almost half of its working and living area from the sea over seven hundred years. In Japan, reclamation of its coastal regions has been vigorously pursued for hundreds of years. For example, it has used the technique to create the industrial hub beside Tokyo harbour and Osaka's Kansai Airport. Hong Kong also has a long history of creating urban land by reclamation. Reclaimed lands account for 5.47% of its total land area in 1997. Need for Geotechnical Information Geotechnical Site Investigations for Reclamation projects typically involve taking of soil borings to obtain samples for material classification and testing. Classification and testing can be done both in- situ during the boring process and in the laboratory on samples obtained from the borings. It is expected that before any bid package is tendered for the construction works it must include logs from the borings indicating the soil stratigraphy and classification, the results of in-situ testing of the material and results from subsequent laboratory testing of soil samples from the borings. Contractors interpret and use this geotechnical information to select equipment and methodologies, to quantify the location, quantities and physical properties of the soils to be used, to estimate project costs, to assess risks and to plan the performance of the project. The geotechnical information is a primary driver of the ultimate project performance. Reclamation Methods using Soft Soil 1. Band Drain and Surcharge: Typically used in soft ground to accelerate consolidation of the compressible soils for the drained reclamation. In reclamation areas with thick soft marine clay/silt, long term consolidation under reclamation loads can continue for many years. With band drains and surcharge load, the soft compressible soils can be pre-consolidated prior to development in a matter of weeks or months. 2. Stone Column: Typically used in soft soil applications in order to accelerate consolidation of the compressible soils for the drained reclamation increase the shear strength of the soil dealing achieved by the use of vibro-displacement or vibro-replacement method involve the installation of gravel compacted piles commonly referred to as “stone columns”. 3. Use of Sand Compaction Pile: In this method large diameter compacted sand piles are installed in soft clay/ mud. Diameter of sand piles is about 1.2m to 2.0m. Used to improve bearing capacity, slope stability and consolidation settlement by replacing the soft clay/ mud by the compacted sand piles. Widely adopted in Japan and Korea. 4. Deep Cement Mixing: In this method the soil soil/Clay is mixed with specially prepared cement mix using blades driven into the clay/ soft soil stratum. Challenges with the use of this method include; Heaving, Possible seepage during soft soil and cement slurry, Possible cement slurry leakage from mixing shaft during extracting the blades from the mud