ABSTRACT
Exploring the flow mechanism of fluid in rock mass is important in solving the water inrush problems during tunnel excavation. However, it is difficult to obtain an undisturbed rock mass from the actual site conditions and study the flow mechanism of fluid through a fracture network composed of multiple single fractures. Therefore, a solution to simulate rock seepage using rock-like samples with single microfracture was presented in this paper. Water flow through microfracture was tested and the deformation of microfracture was recorded by quasi-distributed fiber Bragg grating (FBG) technology. Experimental data showed that Forchheimer's law and Izbash's law could well describe the nonlinear relationship between flow velocity and hydraulic gradient. The coefficient b in Forchheimer's equation decreased with the increase of microfracture aperture. A critical value of E = 0.8 was proposed to classify the nonlinear flow regime: weak turbulence (E < 0.8) and fully developed turbulence (E > 0.8).
ABSTRACT
The grouting technique is an important method in underground engineering that prevents water seepage and reinforces fractured rock mass. In this research, ultrafine cement-based grouting material, including ultrafine cement (UC), ultrafine fly ash (UFA), polycarboxylate superplasticizer (SP), colloidal nanosilica (CNS), sodium sulfate solution (SS) and water, was developed. The flow time, viscosity, bleeding, setting time and uniaxial compressive strength of the UC-based slurry were measured by orthogonal experiments, and the optimal mix proportion of the UC-based slurry was obtained based on the Taguchi-Grey relational analysis method. Microstructure analysis of the UC-based slurry was conducted using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The results showed that the Bingham model could provide a satisfactory description of the rheological properties of the UC-based slurry. The addition of CNS and SS could promote the hydration of the UC-based slurry and improve the microstructure of the hardened slurry, thereby increasing the strength of the hardened slurry. The optimum ratio for the UC-based slurry was water/solid (W/S) ratio of 1.0, and the contents of UFA, SP, CNS and SS by mass of UC were 40%, 0.2%, 4% and 4%, respectively.
ABSTRACT
BACKGROUND: Probucol, a lipid-lowering drug with potent antioxidant properties, may reduce the risk of cystatin C (CyC)-based contrast-induced acute kidney injury (CIAKI). The aim of this study was to observe the incidence of CyC-based CIAKI and assess the efficacy of probucol on prevention of CIAKI following primary or urgent coronary angioplasty. METHODS: A total of 204 patients with acute coronary syndrome (ACS) were prospectively randomized to a control group (108 patients, 74 male, 65.4 ± 12.5 years) or probucol group (96 patients, 67 male, 65.1 ± 10.5 years) 1000 mg orally before primary or urgent angioplasty and 500 mg twice daily for 3 days following intervention. Serum CyC and serum creatinine (Scr) concentrations were measured before, and on day 1, day 2 and day 3 after coronary intervention. RESULTS: The clinical characteristics of the patients from the two groups were similar. Scr-based CIAKI was developed in 23 patients of the control group (21.3%) and in 4 patients of the probucol group (4.2%) (P<0.001). Furthermore, CyC-based CIAKI occurred in 56 patients of the control group (51.9%) and 28 patients of the probucol group (29.2%) (P<0.001). The CyC increase ≥ 10% after exposure to contrast medium was the best increment cutoff value for the early identification of patients at risk of CIAKI. CONCLUSIONS: Our study suggests that CyC is a reliable marker for early identification and ruling out the patients at the risk of CIAKI. Among the patients with ACS who are undergoing primary or urgent angioplasty, prophylactic treatment with probucol reduces the risk of both Scr and CyC-based CIAKI.
