Papers by Keyword: Red Sandstone

Abstract: Developing a true 3D experimental stress analysis technique has been the holy grail of solid mechanics researchers since the genesis of the field. Combined the high-resolution x-ray computer tomography (Micro CT) with the 2D speckle photography technique developed by one of us (Chiang), we recently proposed a new 3D strain analysis technique called Digital Volumetric Speckle Photography (DVSP). The elements of DVSP technique are as follows. A reference volumetric image of the specimen is recorded by a Micro-CT scan and stored as a reference. Under load the deformed CT image of the specimen is also recorded. Both volume images are divided into subimages of certain voxel arrays. Each corresponding pair of the subimages are ‘compared’ via a two-step 3D Fourier Transform analysis. The result is a 3D map of displacement vectors representing the collective displacement experienced by all the speckles within the subset of voxels. Strain distribution of the entire specimen can then be calculated using appropriate displacement strain relations. Application of this technique to strain mapping of red sandstone and composite are presented.

Abstract: Direct shear tests by laboratory to study the red sandstone aggregate mixture under the action of water intensity decay law, got red sandstone aggregate mixture, fill high subgrade compaction experimental study, tests showed that dynamic compaction compacted earth and rock mix fill embankment feasible, Rayleigh Wave test results show that the effect of dynamic compaction compaction good.

Abstract: Due to the internal structure of red sandstone is loose, the influence factors of acoustic velocity are variety, it is necessary to make a quantitatively research on the influence factors. With the aid of the ultrasonic testing for the rock, p-wave velocity of red sandstone decreased with the increase of porosity under the condition of no coupling medium, when the porosity exceeded a certain value, its internal pores and fractures had a great influence on wave velocity. When the density of red sandstone was greater than 1.82 g/cm³, wave velocity changed little, while the density was less than 1.82 g/cm³, wave velocity decreased rapidly. Under water-solid coupling condition, the change of wave velocity and porosity had no obvious regularity, part of the specimens’ wave velocity decreased a bit, while some specimens’ wave velocity were slightly higher, but the amplitude were small; Under oil-solid coupling condition, longitudinal wave velocity changed significantly, the biggest percentage of increase was 46.3%, the average was 33%.

Abstract: Red sandstone with a strong water softening can cause difficulties of construction projects, especially for slope excavation and support engineering. Therefore, the study on the engineering properties of saturated red sandstone has a important meaning. The mechanical parameters of saturated red sandstone are obtained by the triaxial compression tests. The test results indicate that the ralations between peak strength, elasticity modulus and confining pressure for the saturated specimens are similar with the natural specimens, that is, with the increasing of confining pressure, the peak strength and the elasticity modulus will increase, but the growth rate becomes slowly. Under the same confining pressure, the peak strength and the elasticity modulus of saturated specimen are more smaller than the natural one. The mechanical damage caused by water recedes when the confining pressure increases, so for the geotechnical engineering with larger influence of water, the increasement of confining pressure by the supporting structures is conducive to the stability of rock mass. The research results will provide a theoretical basis for the red sandstone engineering.

Abstract: The particles of red sandstone will be softened under the dry-wet-cycle condition which leads to the decrease of red sandstone strength. In addition, the roadbed of red sandstone shows larger post construction settlement and differential settlement under mixing effects of the external load and the soil weight. For this reason, the research on the change of characteristics of settlement of red sandstone dynamic compaction embankment was conducted, adopting unequal interval grey model and equal-dimensional new information prediction model to predictively analyze the result of settlement variation. The results show that the results of equal-dimensional new information prediction model is much closer to the measurement, which means this prediction model is more applicable for the settlement prediction of dynamic compaction embankment. Consequently, practical reference could be provided for analogous project.

Abstract: The cyclic fluctuation of reservoir water level makes soft rock in bank slope under cyclic seepage pressure and will bring certain effects on permeability characteristics of the soft rock. In order to obtain the relationship between the seepage pressure and seepage time, permeability tests were conducted on red sandstone specimens (from Three Gorges Reservoir Area, China) under cyclic seepage pressures by the self-developed equipment with the function to simulate cyclic fluctuation of reservoir water level. Experimental results show that the water infiltration of the sample was not stable in first three cycles, and it changed from 0.444 mL to 0.086mL. After three cycles, the water infiltration fluctuated between 0.060mL and 0.069mL. It can be drawn that the seepage velocity increase with the raise of pressure and it fit a four times polynomial in each cycle. The study indicates that increasing the seepage pressure appropriately can improve the seepage velocity, and greatly shorten the seepage time.

Abstract: Aimed at the feature of expressway subgrade drainage facilities in typical red sandstone areas in Jiangxi province and based on the importance of the structure, damage conditions, service requirements and the current specification requirements related to various types of ditches, the designed repetition period of rainfall and proposed safety depth values for drainage facilities were put forward by considering reasonably the key design parameters to regional drainage facilities. The relationship between prerequisite of discharging sediment in ditches or conduits and minimum longitudinal gradient was discussed. Combined with the characteristics of red sandstone subgrade drainage with high requirements, the design elements of red sandstone area expressway subgrade drainage system were obtained, which can provide beneficial references for the subgrade drainage design in red sandstone areas.

Abstract: The research object presented in this paper is coupling effect of porous red sandstone which is more frequently encountered. And this paper use the test system of Split Hopkinson Pressure Bar (SHPB) to survey the impact test action of different porosity red sandstone in different coupling medium in order to obtained the dynamic waveform of fluid-solid coupling red sandstone under impact loading using theoretical analysis and laboratory data. The paper analyzes the impact of porosity, coupling medium on the dynamics characteristics of red sandstone. Based on the experiment study of different coupling medium red sandstone under cyclic impact loading, this paper discussed the dynamic characteristics law of porous sandstone under cyclic impact loading and analyzed theoretically the mechanism of coupling medium under cyclic loading. Porosity has a great influence on dynamic performance of red sandstone. Coupling medium has certain influence on the dynamic characteristics of red sandstone. All those conclusions laid a theoretical foundation for practical application.

Abstract: The portable falling weight deflectometer (PFWD) test, bearing plate test, beckman beam test, and compaction test were carried out in this study. The relation of dynamic modulus and static modulus, dynamic modulus and deflection, dynamic modulus and compaction ratio, dynamic modulus and water content (consistency) was built. It turns out that there are good power function regression relationship between dynamic modulus and static modulus, dynamic modulus and deflection, dynamic modulus and compaction ratio, dynamic modulus and water content and consistency. Key words: red sandstone; dynamic modulus; resilient modulus; deflection; compaction ratio; water content

Abstract: In order to treat the collapse problem of red sandstone slope on Hunan Liu-Li Highway, laboratory experiments of its lithology were conducted, and the main parameters of red sandstone were acquired, including its basic physical properties, its disintegration characteristics, and its mineral compositions. By collecting research information of red sandstone slope, the main features and reasons of the slopes collapse were concluded. In comparison to the original and other treatments, the conclusion that the flexible protective technology is suitable for red sandstone slopes was reached.