Role of Cyclic Thermal Shocks on the Physical and Mechanical Responses of White Marble

Marble is a common rock used in many buildings for structural or ornamental purposes and is widely distributed in underground engineering projects. The rocks are exposed to high temperatures when a tunnel fire occurs, and they will be rapidly cooled during the rescue process, which has a great impact on the rock performance and the underground engineering stability. Therefore, the role of cyclic thermal shocks on the physical and mechanical properties of marble specimens was systematically investigated. Different cyclic thermal shock treatments (T = 25, 200, 400, 600, 800 °C; N = 1, 3, 5, 7, 9) were applied to marble specimens and the changes in mass, volume, density and P-wave velocity were recorded in turn. Then, the thermal conductivity, optical microscopy and uniaxial compression tests were carried out. The results showed that both the cyclic thermal shock numbers (N) and the temperature level (T) weaken the rock properties. When the temperature of a thermal shock exceeds 600 °C, the mass loss coefficient and porosity of the marble will increase significantly. The most noticeable change in P-wave velocity occurs between 200 and 400 °C, with a 52.98% attenuation. After three thermal shocks, the cyclic thermal shock numbers have little influence on the uniaxial compressive strength and Young’s modulus of marble specimens. Shear failure is the principal failure mode in marble specimens that have experienced severe thermal damage (high N or T). The optical microscopic pictures are beneficial for illustrating the thermal cracking mechanism of marble specimens after cyclic thermal shocks.

Cyclic Liquefaction Resistance of an Alluvial Natural Sand: A Comparison between Fully and Partially Saturated Conditions

Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the strength and stiffness of soil. The liquefaction resistance of soils increases significantly as the degree of saturation decreases, making soil desaturation an effective measure for the mitigation of this phenomenon. This paper presents a comparative analysis of liquefaction resistance of an alluvial sand from Aveiro (Portugal) under fully and partially saturated conditions. For this purpose, an in situ characterisation based on CPTu and a laboratory series of cyclic triaxial tests were carried out. The cyclic triaxial tests were conducted under undrained conditions on remoulded specimens with different degrees of saturation, including the full saturation. On the other hand, the triaxial apparatus was instrumented with Hall-effect transducers to accurately measure the strains during all testing phases. In addition, it was equipped with piezoelectric transducers to measure seismic waves velocities, namely P-wave velocity, for evaluation of the saturation level of the specimen in parallel with the Skempton’s B parameter. Hence, relations between the B-value, and P-wave velocity and cyclic strength resistance are presented. The number of cycles to trigger liquefaction, considering the pore pressure build-up criterion, is presented for the different degrees of saturation. Results confirmed the increase in liquefaction resistance for lower degrees of saturation in this soil.

Application seismic refraction method to characterize the building site of Injibara University building site,injibara Ethiopia

Geophysical investigation using seismic refraction method was conducted for engineering characterization of the foundation conditions of Injibara University buildings construction site located in Injibara town of Amhara Regional State, northwestern Ethiopia. The principal objective of the research was studying the suitability of the foundation earth materials underlying the site, where Injibara University is established. The seven refraction seismic spreads, seismic velocity models interpretation have provided valuable geotechnical information incorporated with available geologic information in the study area. Interpretation of geophysical data revealed that the subsurface geology of the area is composed of three layers. The topsoil consisted of clay, silt and sand mixtures having a 1-4 m thickness and 255-510 m/s p-wave velocity ranges are mapped over the whole area. The second layer attributed to the highly weathered and fractured vesicular basalt is characterized by 948-1802 m/s P-wave velocity range and revealed somewhat undulating morphology. The depth extent of this layer varies from about 10m on the North West end and southeastern parts and to about 27m around the central part. The third layer occurred in the depth range of 10-27m is characterized by greater than 2550m/s average high p-wave velocity and it is due to moderately weathered and fractured basaltic bedrock, which is deeper near to the center of the profiles and gets shallower towards North West end and southeastern portions. Besides, analyses of collected data have suggested the possible locations of minor structural discontinuities (maybe local fractures).The geophysical results show that the bedrock is found at shallow depth in the northwestern end and southeastern part of the study area, whereas in the central part of the survey area the bedrock is found relatively at high depth. Therefore, setting the building foundation is more recommended in the southeastern part of the construction site.

Using Seismic Data to Predict Shale Pore Pressure and Overpressure Sweet Spots: A Case Study from the Lower Silurian Longmaxi Formation in Sichuan Basin, China

Practices of marine shale gas exploration and development in south China have proved that formation overpressure is the main controlling factor of shale gas enrichment and an indicator of good preservation condition. Accurate prediction of formation pressure before drilling is necessary for drilling safety and important for sweet spots predicting and horizontal wells deploying. However, the existing prediction methods of formation pore pressures all have defects, the prediction accuracy unsatisfactory for shale gas development. By means of rock mechanics analysis and related formulas, we derived a formula for calculating formation pore pressures. Through regional rock physical analysis, we determined and optimized the relevant parameters in the formula, and established a new formation pressure prediction model considering P-wave velocity, S-wave velocity and density. Based on regional exploration wells and 3D seismic data, we carried out pre-stack seismic inversion to obtain high-precision P-wave velocity, S-wave velocity and density data volumes. We utilized the new formation pressure prediction model to predict the pressure and the spatial distribution of overpressure sweet spots. Then, we applied the measured pressure data of three new wells to verify the predicted formation pressure by seismic data. The result shows that the new method has a higher accuracy. This method is qualified for safe drilling and prediction of overpressure sweet spots for shale gas development, so it is worthy of promotion.

New Regression Models For Evaluating The Tensile Strength of Some Natural Building Stones Using The Indirect Tensile Tests and P-Wave Velocity

The full text of this preprint has been withdrawn by the authors while they make corrections to the work. Therefore, the authors do not wish this work to be cited as a reference. Questions should be directed to the corresponding author.

Correlation of P-wave velocity with mechanical and physical properties of limestone with statistical analysis

This study aims to investigate the correlation between the P-wave velocity (Vp) and the mechanical and the physical properties of the limestone; Vp tests were conducted on over 320 limestone samples. Moreover, the effects of the mineralogical, textural, and chemical composition of limestone were also studied through thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF). The relationships between the Vp and the uniaxial compressive strength (UCS), point load index (PLI(Is(50)), 2nd cycle of slake durability index (Id2), natural unit weight (γn), specific gravity (Gs(c)), water absorption by weight (WA), and porosity (n) were estimated using representative empirical equations. The empirical equations were validated by Student’s t test that has indicated the existence of strong relationships between the mechanical and physical properties of the intact limestone with Vp; the calculated t-values were higher than the t-critical value. Furthermore, the results of previously available studies were compared with the results of this study in terms of the generated equations for Vp values and the slope of a 1:1 line, which was used to appraise the predicted and measured values. This study demonstrates that the UCS, PLI(Is(50)), Id2, γn, Gs(c), WA, and n values of an intact limestone can be predicted by using Vp, which is fast, easy, economical and nondestructive test.