Advanced Materials Research Vols. 261-263

Abstract: Based on uniaxial compression test, the mechanical properties and acoustic emission characteristics of rock had been obtained, including the relationship between AE and time, AE and stress level, and so on, in the whole process of rock failure. Research shows AE rate of rock has the subparagraph features obviously. There are three obvious AE sections for the higher strength elastic-brittle rock: First section is compaction stage, corresponding stress is 10% of compressive strength of rock; Second section is crack-development stage, corresponding stress is 80% of compressive strength; Third section is rupture stage, corresponding stress is the compressive strength. Furthermore, AE signals for the rupture stage is strongest. The law is still correct in cycle loading conditions. However, the subparagraph phenomenon isn’t clear for elastic-plastic rock, and the AE peak is lagging behind the ultimate strength of rock, the AE signal in the decline stage of strength is the most intensive and strong. The lagging phenomenon is due to X-shear rupture model of soft rock. The significant stress concentration in cone tip between the two relative extrusion cones leads to local rock broken seriously. Then, many acoustic signals have been observed.

Abstract: Through analyzing excess pore pressure dissipation datum measured by CPTU probe and pore pressure mini- transducers on CPTU model test, the permeability coefficient of soil of CPTU model test has been computed. According to Strain Path method based on Terzaghi consolidation theory, computation formula of soil horizontal permeability coefficient on CPTU model test has been acquired; on CPTU model test dissipating time of 50% degree of consolidation which has been used as calculation standard to compute horizontal permeability coefficient has been acquired by normalized excess pore pressure dissipation curves based on excess pore pressure dissipation datum; through a series of indoor variable head permeability tests, the permeability coefficient of remolded soil of CPTU model groove sampling by horizontal and vertical direction has been acquired, and the results show that horizontal permeability coefficient is about 1.62 times greater than vertical permeability coefficient on indoor variable head permeability test, and large difference between horizontal and vertical permeability property of remolded clay soil on CPTU model test has been existed; compared with the value of two test methods, the value of horizontal permeability coefficient acquired by CPTU model test is roughly an order of magnitude greater than the value of horizontal permeability coefficient acquired by indoor variable head permeability test. The achieved result can provide a foundation for further study for CPTU mechanism.

Abstract: Due to the effect of deterioration and corrosion, large amounts of oil and gas pipeline segments need to be replaced in offshore platforms every year. By using traditional reconstruct method, it needs to stop production in offshore platform firstly, then follows insulation, backout, baiting, jointing, installation, pressure test for tightness, etc. This process will take a long time and much work, and it will greatly influence the regular manufacture of oil and gas. In this work, a new method is introduced that oil and gas pipeline segments are replaced without stopping production. The technology includes precisely measuring geometry dimension of the oil and gas pipeline segments to be replaced, making prefabricate replacement segments exactly offline, and replacing the pipeline segments on site in a speedy and safety way. Last, an engineering applications case is given to show the whole detail process. It proves that the technology not only makes great progress in pipeline reconstruction, but also results in good social and economic benefits.

Abstract: Direct shear tests were performed to study the shear rate effects of reticulate red clay around Dongting Lake. In the direct shear tests, four sets of undisturbed specimen of reticulate red clay were sheared under the different vertical pressure of 50kPa, 100kPa, 200kPa and 300kPa. Specimens were sheared with six different shear rates of 0.04mm/s, 0.02mm/s, 0.01mm/s, 0.007mm/s, 0.004mm/s and 0.003mm/s under each vertical pressure. Test results show that: (1) shear strength of reticulate red clay increases along with the vertical pressure; (2) shear rate effects of reticulate red clay are affected by vertical pressure significantly; (3) due to its reticulate structure of reticulate red clay, it shows some differences in shear rate effects comparing with other clay.

Abstract: Triaxial compression creep tests were performed on the undisturbed specimens of reticulate red clay from Dongting Lake area (China) under different confined stress. By analyzing the laboratory test results, following conclusions were drawn: (1) creep deformation occurred in all compression tests; (2) creep deformation increases as the increasing of the creep stress (compress stress) slightly; (3) the creep deformation occurred in the triaxial compression creep tests can be well simulated with Singh-Mitchell model.

Abstract: The underground caverns were divided into underground spherical cavity and underground tunnel. From bean-slab theory and energy principle, the catastrophe models of underground spherical cavity and tunnel were built and the necessary and sufficient condition of roof failure was derived. Taken the cavern roof of Wenfu phosphate mine for example, the minimum thickness of roof was derived. The analysis of spherical cavity shows that the roof fails more easily when the roof thickness is smaller, the elastic modulus is smaller, the Poisson's ratio is smaller and the roof span and loads are bigger. The analysis of tunnel roof shows that the stability of tunnel roof is closely related to the vertical load and the horizontal load. In order to guarantee the roof stability, the observation of load acted on roof should be reinforced and some control measures should be taken according to the necessary and sufficient condition of roof failure.

Abstract: The settlement observation usually adopts precision geometric leveling method, to improve the accuracy, generally requiring the value of central cross-hair to be in the range of 0.5m to 2.8m. However, it may easily exceed the range in the regions that have big value of slope. After analyzing, the conclusion is as follow: when the value of slope is certain, we can adjust the height of instrument, sighting distance and distance of slope, so as to make the value of central cross-hair in the range of our requirement. Thus make a compromise of the measurement efficiency and accuracy of measurement. When the values of slope are in the range of 10 degree to 20 degree, the critical values of sighting distance and distance of slope vary greatly. In the process of actual field measurement, combining with the slope acquisition method, taking the critical values of sighting distance and distance of slope as experience values, and it achieves a good effect.

Abstract: This paper first introduces the inter-city railway settlement observation implementation scheme, and then makes a statistics analysis on the monitoring data of Wuhan to Xianning inter-city railway. The conclusion is as follow: the main factors that influence the precision of settlement observation are the misclosures of direct and reversed observations, if they are both at a certain range, all monitoring points’ mean square errors of height would reach 0.1mm. Finally summarizes some methods that can improve the precision of settlement observation, in the actual work they make very good effect.

Abstract: Based on the principle of elastic stability, this paper deduces the calculating formulas for dynamic stability critical length of foundation piles when lateral syntony occurs under the axial dynamic loads, and analyzes the effects on dynamic stability critical length of foundation piles from the aspects of parameters such as section dimensions of piles, horizontal resistance forces of foundation soil and excitation frequency etc. Study shows that different soil stratum has the bigger effects on the critical length of piles, while damping coefficient smaller. It also puts forward some related measures for reducing vibration of foundation piles, and can provide reference values to the practical engineering.

Abstract: Considering the characteristic that rock mass can transform from brittleness to plasticity and the dynamic change of post-peak strength parameters of the rock mass, the invariability of elastic modulus and poisson's ratio, constitutive model of rock mass could be described with the characteristic that strength parameters obey different Mohr-Coulomb failure criterions under different plastic strains. This model may reflect the post-peak subsequent characteristics of rock mass and the fact that rock mass can transform from brittleness to plasticity with the increase of confining pressure. Numerical calculation is applied to simulate the triaxial compression test under different confining pressures and underground engineering example, which proves that this model has the characteristic of reflecting the damage extent of surrounding rock.