Effect of sand particle size on interface shear behaviour between bio-cemented sand by MICP treatment and steel structure

Abstract

This study presents an experimental investigation of the effect of sand particle size on the shear behaviour of bio-cemented sand-steel structure interface, with sand treated by microbially induced calcite precipitation (MICP). Five sand groups were involved with different median particle sizes. The MICP treatment followed the surface percolation method featuring bacterial suspensions with a fixed optical density (linearly related to active cell concentration or urease activity). Scanning electron microscopy was used to identify the microstructure of the samples, while interface shear test was performed to observe the macro-scale mechanical behaviour. The testing results indicated that smaller sand particle size was associated with a relatively larger effective calcium carbonate bonding area, providing a more significant bonding effect. Thus, smaller sand particle sizes in the treated samples were associated with higher values for the interface cohesion and a more pronounced increase in the interface friction angle at the peak state (compared to the corresponding untreated samples). By contrast, because the bonding effect broke close to the interface during shearing, the bottom of the treated samples became planar and smooth. Hence, a lower interface friction angle at the ultimate state was identified for a treated sample, compared to the corresponding untreated one.

Investigation on the Shear Behavior and Mechanism of MICP-Treated Loess Soil

“…The pores between the particles began to bond from days 0 to 7 (Figure 7(b)). With a retention time of 14 d (Figure 7(c)), the loess samples considerably improved, indicating that the produced precipitation increased which cemented the loess particles and increased the compactness of natural loss, which is consistent with the existing literature [8]. The peak stress value increases by about 11%-22% when the retention time is 7 days, whereas the increasing rate is 7%-10% when the curing process lasts for the other 7 days.…”

“…After this period, the number of dead bacteria increased significantly, and the metabolic activity of the bacteria tended to stagnate. As instructed by Wang et al [8], the concentration of the bacterial suspension (cells/ml) at pH = 8 is approximately 1 2 × 10 8 cells/ml. Therefore, it is advisable to select bacteria cultured for 32-44 h for subsequent tests.…”

“…To explore a more efficient medium for bacteria, an inoculation ratio of 1 : 1 was used to cultivate the bacterial solution. Different types of culture media were compared based on the optical density of the bacteria at 600 nm (OD 600 ) using an ultraviolet-visible spectrophotometer [8]. Table 1 indicates five different sources of culture medium formulas, and a microplate reader was used to monitor the OD 600 value of the different culture media.…”

“…Thus, the feasibility of MICP for soil reinforcement has been verified in many experiments, particularly in sand [5][6][7]. Subsequently, influencing factors, such as temperature, pH, grain size and distribution, cementation concentration, and curing periods have been explored by many researchers [8][9][10]. Additionally, researchers conducted various experiments on the compressive strength and permeability of MICP-treated soils by conducting direct shear or triaxial tests.…”