This paper describes a new method called electro-biogrouting for the improvement of soft soil with low hydraulic conductivity. In this method, bacteria, urea and calcium ion are injected by an applied electric field. Initially, the calcium ions are moved across the specimen by electromigration from the anode to the cathode. Then, the urea, which is non-ionic and solvable, is transported by electro-osmotic flow from the anode to the cathode. Finally, the bacteria with negative surface charge are induced as particles by electrophoresis mobility from the anode to the cathode. Polarity reversal is applied to ensure homogeneous distribution of agents. As the bacteria expose the urea, the urease enzyme is released, and carbonate ions are produced, which results in CaCO3 precipitation in the porous media of the soil. This increases the shear strength of the soil up to 1080%. The CaCO3 was detected using the acid washing technique.

This study addresses the use of alkali-activated binder to evaluate the feasibility of using this promising technique to stabilise soils. One of the well-known agro-wastes, palm oil fuel ash (POFA), was used as a source binder. Also, sodium hydroxide (NaOH) and potassium hydroxide (KOH) were used as alkaline activators. The influence of four factors including the kind of alkaline activator, the use of source binder, the curing condition and the water content of the soil on the strengthening performance of soil was evaluated according to the improvement of the unconfined compression strength (UCS). At the same alkaline concentration, both sodium hydroxide and potassium hydroxide were able to enhance the strength development rate of specimens. However, potassium hydroxide-POFA-stabilised soil yielded the highest UCS value following a long curing time (90 and 180 d of curing). The size and charge density of the alkaline activator play significant roles in controlling the rate and extent of the activation process for the strength performance. With regard to soil strength improvement, when the POFA content in the activation process increased from 0% to 15%, the UCS value increased substantially, irrespective of the alkaline activator type. This achievement implies a tremendous effect of this agro-waste on the strength behaviour of treated soil.

Factors that influence microbially induced carbonate precipitation (MICP) include bacterial species, bacterial cell concentration and urea and calcium ion (Ca2+) concentrations for determining the most effective laboratory conditions for calcium carbonate (CaCO3) precipitation by Sporosarcina pasteurii and Sporosarcina aquimarina bacteria. In this study, the most effective laboratory conditions for MICP by S. aquimarina were 12·8 × 109 bacterial cells/ml, 0·25 M urea and 2 M calcium chloride (CaCl2). On the other hand, the most effective conditions for S. pasteurii were 9 × 109 bacterial cells/ml, 1 M urea and 2 M calcium chloride.

This paper presents the results of experiments designed to investigate the effect of acid rain on the compressibility behaviour of residual soils. Sedimentary residual soil (SRS) and igneous residual soil (IRS) with different mineral compositions were collected from two locations in Malaysia. The specimens were infiltrated by artificial acid rain (AAR) at varying pH values of 2, 3, 4, 5 and 5·6 and at different fluxes of 1, 5 and 20 years. At the end of each AAR flux interval, compressibility, zeta potential, atomic adsorption spectroscopy, X-ray diffraction and scanning electron microscope analyses were performed to study the behaviour of the soil in an acidic environment. It was found that AAR has a strong effect on soil structure; consequently, the compressibility of both SRS and IRS increased as the pH value decreased and/or as the flux of AAR increased. Microstructural analyses confirmed that this process destroyed the bonds between clay particles/aggregates and induced significant changes in mineral structure due to the dissolution of alumina and silica from SRS and IRS, resulting in the formation of ‘loose’ structures with larger voids.

Construction on peat deposits represents a major challenge for the geotechnical community. Waterlogged peat deposits have great potential for buoyancy generation. The premise of the present investigation is that this can be beneficially incorporated in foundation design practice, thereby reducing the net bearing pressure and hence resulting settlements. A novel foundation system, comprising a bamboo frame (BF) structure incorporating recycled plastic block (RPB) inclusions, is presented for supporting lightweight structures bearing on peaty ground. The buoyancy effect is produced by the lower bulk density of the foundation construction materials combined with the waterlogged condition of the peat deposit. A programme of reduced-scale 1 g physical modelling was conducted to investigate the performance of BF- and BF–RPB-type footing bearing on remoulded peat with different water content and fibre content (FC) values. The mobilised undrained bearing capacity (q f) increased for lower-water-content and higher-FC peat materials. Deeper BF footings and the inclusion of the RPBs within their cavities significantly improved the mobilised q f value. Advantages of the presented foundation system over conventional solutions for peaty ground include its simple technology, reduced earthworks in construction, reduced settlement due to the buoyancy contribution and being more sustainable and economically viable.