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Microbially induced calcite precipitation (MICP) through the bio-stimulation approach is a promising ground improvement technique that can improve the engineering performance of calcareous sand. This study investigated the shear response of bio-cemented calcareous sand (with 16.2% and 54.6% initial relative density) treated by bio-stimulated MICP. The calcareous sand samples, prepared at two initial relative densities, were firstly subjected to the enrichment and cementation treatment to gain various cementation levels. Biochemical parameters including viable cell number, urea and ammonium concentration, and cementation content were measured during the two stages. The direct shear tests were then conducted at five different normal stresses, and the peak stress ratio, cohesion intercept, peak dilation angle, and stress-dilatancy relationship were obtained. The Mohr–Coulomb linear and bilinear failure envelopes were adopted to obtain the shear parameters. The results were further substantiated by microstructural observations. Finally, a conceptual framework was proposed to analyze the peak state shear behavior of bio-cemented calcareous sand. The interdependence between external influential factors (cementation level, initial relative density, and normal stress) and strength components (interparticle friction, interlocking (dilatancy), particle rearrangement, interparticle bonds and particle crushing) at the peak state were discussed in detail. [ABSTRACT FROM AUTHOR]

Achieving crack propagation and rapid deterioration of high-temperature rock masses by using cooling shocks is important for improving the efficiency of low-permeability oil and gas production, geothermal well pumping, and other engineering facilities. In this study, the temperatures of four groups of granite samples with holes were set as 150, 350, 550, and 750 °C. To study the crack propagation in high-temperature granite suffering from different cooling shocks, the cooling shock temperatures were set as −20, 0, 20, and 25 °C in experiments and an RFPA2D-Thermal numerical simulation. The results indicated that in the range of 350–550 °C, there is a critical temperature for the sudden change of the crack macroscopic shape. Numerous open cracks appeared on the rock surface, and the thermal damage caused by the cooling shocks was significantly enhanced within the temperature range. Additionally, under the action of the cooling shocks, cracks were initiated in the high-temperature granite at the boundary of the cooling shock hole and the sample and extended radially to the interior of the sample. Moreover, in the process of crack propagation, there was always an annular heat-balance zone inside the rock. Thus, the cracks generated at the boundary of the cube are not connected to the cracks formed at the center hole. A larger temperature gradient in the rock led to a higher crack propagation rate, larger penetration depth, and higher density of cooling-induced cracks. The results of this study can not only improve the permeability of reservoir rocks but also have important reference value for rock engineering in high-temperature environments. [ABSTRACT FROM AUTHOR]

Topography is a crucial characteristic reflecting the stability status of a landslide dam. The methods for measuring landslide dam topography in a laboratory-scale test study are currently operator dependent, time-consuming, or only applicable to the measurement of the two-dimensional section. In this paper, a laboratory-scale photogrammetric method based on the structure from motion (SfM) technique was proposed to measure the three-dimensional (3D) topography of a landslide dam. The SfM technique, which is a revolutionary, low-cost, user-friendly computer vision technique, was employed for reconstructing a landslide dam 3D computer model. A scientific method to determine the topography parameters of a landslide dam was put forward. Meanwhile, two materials with different particle sizes were used to simulate the formation process of the landslide dam in the laboratory-scale. Then, the measurement results of the two materials were compared. Five parameters of a landslide dam topography with 100 parallel measurement results for each parameter were obtained. The results show that the SfM technique could build a high-quality 3D point cloud in a laboratory scale. The proposed method of determining the topography parameters of a landslide dam was useful and has low measurement uncertainty. The material type affected the sparse density of the point cloud and then affected the measurement uncertainty of landslide dam topography parameters. The measurement uncertainty of the gravel-type landslide dam was significantly higher than that of the sand-type landslide dam. This research contributes to promoting the application of a photogrammetric method based on the SfM technique in geotechnical engineering laboratory-scale tests. [ABSTRACT FROM AUTHOR]

In order to evaluate and compare the accurate activation energy variations of two kinds of deposited clays (i.e. non-organic clay and organic clay), thermo-gravimetric analysis (TGA) was firstly conducted to study the reaction characteristics of the two clay samples. Two periods of weight losses were observed according to each TGA curve for both clay samples. The first period happened due to water evaporation, while the second period was mainly caused by the composition reactions of clay minerals, especially influenced by the de-hydroxylation of kaolinite. An obvious phenomenon is that the organic clay with a high soil organic matter (SOM) has a higher activity energy. Then, four common kinetics models [i.e. the Coats-Redfern method, the Doyle integral method, the maximum rate method, and the distributed activation energy model (DAEM)] were used to calculate and compare the activation energy values. And the Doyle integral method and the DAEM method are considered as two recommended models to analyze the activation energy performance during thermal treatment. Some interesting conclusions can be summarized as: (1) The multi-period reactions of deposited clays during the heating process are common, especially for organic clay. It would be beneficial knowing its biomass resource feasibility concerning the second weight loss; (2) The high SOM has a significant influence on the potential energy unitization of deposited clays, while the variations of activity energy for deposited clays are influenced by the mineral compositions and microstructure features; (3) It is possible to evaluate the accurate activity energy of deposited clays combined with TGA tests and two recommended models (i.e. the Doyle integral method and DAEM method). [ABSTRACT FROM AUTHOR]

Rainfall infiltration can be a major cause of slope failure. In the present paper, an indoor soil slope model was built; a distributed sensing fiber was designed based on Brillouin optical time-domain analysis (BOTDA). Two soil moisture probes were planted and a rainfall infiltration test was simulated to acquire the data of slope infiltration and deformation progress under rainfall infiltration. Time domain volumetric moisture content of the slope as well as the vertical and horizontal strain changes were monitored. The moisture content results showed the infiltration path and had obvious ascent at the sliding surface of the slope. The fiber results showed that there existed an apparent strain concentration near the shear section of the slope and strain conversion zone; the soil deformation law had a close spatial relationship with the infiltration path in the soil. In addition to the accurate determination of the sliding surface, a secondary shear surface was also detected by the BOTDA system. These results provide valuable information pertaining to the sliding mechanism and prediction of slope failure. [ABSTRACT FROM AUTHOR]