Microbial Induced Carbonate Precipitation (MICP) via urea hydrolysis is an emerging sustainable technology that provides solutions for numerous environmental and engineering problems in a vast range of disciplines. Attention has now been given to the implementation of this technique to reinforce loose sand bodies in-situ in nearshore areas and improve their resistance against erosion from wave action without interfering with its hydraulics. A current study has focused on isolating a local ureolytic bacterium and assessed its feasibility for MICP as a preliminary step towards stabilizing loose beach sand in Sri Lanka. The results indicated that a strain belonging to Sporosarcina sp. isolated from inland soil demonstrated a satisfactory level of enzymatic activity at 25 °C and moderately alkaline conditions, making it a suitable candidate for target application. Elementary scale sand solidification test results showed that treated sand achieved an approximate strength of 15 MPa as determined by needle penetration device after a period of 14 days under optimum conditions. Further, Scanning Electron Microscopy (SEM) imagery revealed that variables such as grain size distribution, bacteria population, reactant concentrations and presence of other cations like Mg²⁺ has serious implications on the size and morphology of precipitated crystals and thus the homogeneity of the strength improvement.

This paper is devoted to the experimental investigation of effective stress coefficient for peak and residual strengths of saturated Kimachi sandstone. Authors have described the Modified Failure Envelope Method (MFEM), which can be used to obtain the effective stress coefficients for peak and residual strengths (α-Peak and α-Residual). The effective stress coefficients for intact and fractured Kimachi sandstone (α-Biot׳s and α-Fractured) were also evaluated using conventional methods, and the data were compared with the coefficient values obtained by MFEM for the peak and residual strengths. The effective stress coefficient for intact rock, α-Biot׳s decreased with increasing confining pressure, and was in the range 1>α-Biot׳s>0.8. The effective stress coefficient for fractured rock, α-Fractured, was larger than that for intact rock and was close to unity. The effective stress coefficient calculated for peak strengths, α-Peak, using both the single and multistage MFEMs decreased with increasing effective confining pressure and was in the range 0.8>α-Peak>0.4. For residual strength states, effective stress coefficient, α-Residual, was between the peak strength value and that for intact rock. Based on the results, multistage MFEM is suitable for obtaining an effective stress coefficient for the peak strength, α-Peak. An equation to obtain the effective stress coefficient from total confining pressure and pore pressure, and a method to choose the coefficients for elastic stress analyses and failure evaluations for intact rock structures or structures in rock mass were proposed

To develop affordable countermeasures against the roof falls, the accident records of Mchenga Mine were investigated as the first step. Based on the accident records, it was found that roof falls occurred most in April and May. Humidity measurements were taken both in the underground mine and at surface, and humidity peak appeared in April. The accident occurrence and the underground humidity had a positive correlation in which no roof falls could be expected under a humidity of less than a certain value. Effect of humidity on the indirect tensile strength of the rock samples collected from the mine was investigated, and it showed that the indirect tensile strength decreased with humidity. The diffusion coefficient was measured for the rock samples collected from Mchenga Mine as well as from Kaziwiziwi Mine, and the migration of water vapor into rock mass in the roof was calculated for Mchenga case. It was clarified that the weakening of tensile strength was transmitted upward at several centimeters per day from the immediate roof. This could explain the slight difference of the accident peak in April and May from the humidity peak in April. Introducing fresh and dry outside air, if possible, will not only improve the working environment but also contribute to a decrease in roof falls.

A persistent increase in the permeability of rock mass caused by transient stress disturbances, if present, could explain the variation in the groundwater level in far fields, increase in petroleum production caused by earthquakes or artificial vibrations in enhanced oil recovery, and induction of earthquakes by seismic waves in intermediate and far fields. However, it has not been verified whether the transient stress disturbances induce an increase or decrease in the rock permeability. In this study, the permeability values of intact and triaxially fractured Kushiro Cretaceous sandstone and Shikotsu welded tuff were measured before and after transient axial stress or pore pressure disturbances to clarify the effects of transient stress disturbances on rock permeability. According to the experimental results, the stress disturbances showed either decreasing or increasing effects on the permeability depending on the rock type and experimental conditions. However, when focusing on the fractured rocks rather than the intact ones, which would be more important in field applications, the argillaceous Kushiro Cretaceous sandstone mainly exhibited decreasing effects and the glassy Shikotsu welded tuff mainly exhibited increasing effects.

Catastrophic volcanic eruptions, large earthquakes beneath big cities, or giant earthquakes at subduction zones are apparently the biggest problems facing the sustainability of human society. However, imminent prediction methods for these events have never been established, except that volcanic eruptions can only be predicted by exceptional efforts by dedicated researchers. Even if a prediction method has been established, the method cannot significantly reduce infrastructure damage, although it could slightly reduce the number of fatalities. On the other hand, prevention of eruptions or earthquakes could significantly reduce, not only the number of fatalities, but also infrastructure damage. Therefore, the authors propose (1) gradual energy release by supercritical power generation to prevent catastrophic eruptions; (2) gradual seismic energy release by injecting water into seismic sources to prevent large earthquakes beneath big cities; and (3) exploding existing nuclear warheads underground to prevent giant earthquakes at subduction zones. Necessary technical developments, costs, risks, and problems will also be explained.

Face squeezing, floor heave, and buckling of invert were found after a 10-day holiday in 2014 around the serpentinite face of a tunnel in Hokkaido, Japan. The damage continued for over 2 months, extending 400 m toward the entrance causing a massive roof fall. The tunnel was excavated again with a circular section and extra-thick shotcrete, and the face had crossed the damaged part 6 years after the damage occurred. Uniaxial and triaxial compression tests were carried out to obtain the mechanical properties of the serpentinite to clarify the severe damage mechanism at the tunnel. The main experimental findings are as follows. The uniaxial compressive strength of the serpentinite samples was very low, and the ratio of the strength to the estimated overburden pressure was extremely low. The parameter n indicated that the time-dependent deformation of the serpentinite was not large but the same as ordinary rocks. All specimens showed strain-hardening in the triaxial compression test, and the friction angle was very low by the brucite content. Only primary creep was observed in the multistage triaxial creep test. The pressure on the shotcrete from rock mass for the damaged tunnel was enough to cause creep deformation and failure of shotcrete. From the above findings, designing the concrete lining that can support the earth and water pressure is recommended for tunnel excavation in such a weak serpentinite rock mass, particularly with a very low friction angle by brucite. Highlights: Face squeezing, floor heave, and buckling of invert were found after a 10-day holiday around the serpentinite face in Hokkaido, Japan. The time-dependent deformation of the serpentinite was not large but the same as ordinary rocks. All specimens showed strain-hardening in the triaxial compression test, and the friction angle was very low by the brucite content. Only primary creep was observed in the multistage triaxial creep test. The severe damage to the tunnel was not a brittle creep failure of the serpentinite rock mass itself but the shotcrete lining.