The in-situ deep mixing technique has been established as a means to effect columnar inclusions into soft ground to enhance the bearing capacity and reduce settlement. Since the inception of this method, developments in the plant and machinery, as well as associated field techniques, have surpassed the basic understanding of strength developments in high water-content clays admixed with cementing agents.In this paper an attempt is made to identify the critical factors governing the engineering behavior of cement-stabilized clay, which helps not only to control the input of cementing agent to attain strength development with curing time and clay water content, but also to understand the subsequent engineering behavior. It is revealed that the clay-water/cement ratio, $wc/ c$ is the prime parameter for the above purposes .

Engineering Behavior of Cement Stabilized Clay at High Water Content (IS-YOKOHAMA 2000「沿岸域の地盤工学における理論と実際」特集号〔英文〕)

Red mud is highly alkaline slurry produced during alumina extraction from bauxite. Its disposal generates serious environmental pollution. The best way to solve red mud disposal issues is to develop economic utilization technologies that consume significant amounts of red mud. This paper reviews the possibility of utilizing red mud as a road base material, weak subgrade soil stabilizer as well as a subgrade material. Results showed that red mud can be used for those purposes. It was also found that the stabilizing content needed to meet a certain standard differs due to differences in requirements from one country to another. Therefore, there is a need to design proportions with UCS, CBR, leaching characteristics required by the country in which red mud is intended for use. The effect of various stabilizers on performance of red mud is discussed and it transpired that lime showed the best performance followed by dolime fine, ground granulated blast furnace slag, cement kiln dust and fly ash. Findings indicated that red mud shows better performance as a subgrade material than natural soil. Also the synergistic use of red mud and other wastes also improves the mechanical and durability properties of the material compared with using red mud alone. Based on mechanical, economic and environmental benefits, it is recommended to use red mud in road base structure rather than in subgrade despite higher red mud consumption in subgrade than in road base. The scope for future research in this area is also suggested.

Utilization of red mud in road base and subgrade materials: A review

Soil stabilization is a technique to improve the engineering and geotechnical properties of soils such as mechanical strength, permeability, compressibility, durability and plasticity. Much has been learned about soil stabilization techniques and additives over the past century. The state of the practice in stabilization techniques and challenges is presented with a discussion. Moreover, available studies regarding the effects of various types of stabilizing agents on the engineering and geotechnical properties of stabilized soils are reviewed here. These stabilizing agents include both calcium-based and non-calcium-based additives. Eco-friendly additives as alternative materials to conventional stabilizing agents are also discussed in this paper. In addition, the problems associated with the presence of disruptive salts and sulfate as well as the techniques to overcome these problems in soil stabilization projects are reviewed.

Soil and clay stabilization with calcium- and non-calcium-based additives: A state-of-the-art review of challenges, approaches and techniques

Clay stabilization using coal waste and lime — Technical and environmental impacts

Effect of freeze–thaw cycling on the mechanical properties of lime-stabilized expansive clays

Effect of freeze–thaw cycles on durability and strength of very soft clay soil stabilised with recycled Bassanite

Effect of freeze–thaw cycles on the strength and physical properties of cement-stabilised soil containing recycled bassanite and coal ash

The use of recycled bassanite and coal ash to enhance the strength of very soft clay in dry and wet environmental conditions

安価で耐火性，断熱性等に優れる石膏ボードは，建築資材として広く普及しているが，その生産量を反映して，建築物や住宅の解体によって発生する廃石膏ボードの量は近年益々増加している。このような現状から，処分場の容量不足に関する問題が指摘され始めており，廃石膏ボードのリサイクル技術の開発が急務であるといわれている。そこで本研究では，まず廃石膏ボードを再生するために，予め廃石膏ボードを紙と石膏とに分別粉砕した二水石膏に対して加熱処理を施し，水硬性の半水石膏に転化させる半水石膏生産システムを開発したので，その概要を報告する。さらに本システムから得られた半水石膏の地盤改良材としての有効性を明らかにするため，その半水石膏のセメント安定処理土への適用性を検討した。その結果，半水石膏の混入率と一軸圧縮強さ，乾燥密度および含水比との間に高い相関関係があることを明らかにし，廃石膏ボードから再生した半水石膏の地盤改良材としての有効性を実証している。

Toshihide Shibi

Papers

Effect of freeze–thaw cycles on durability and strength of very soft clay soil stabilised with recycled Bassanite

Effect of freeze–thaw cycles on the strength and physical properties of cement-stabilised soil containing recycled bassanite and coal ash

The use of recycled bassanite and coal ash to enhance the strength of very soft clay in dry and wet environmental conditions

Development of bassanite production system and its geotechnical engineering significance - Recycling of waste plasterboard -

Influence of applying overburden stress during curing on the unconfined compressive strength of cement-stabilized clay