Advanced Materials Research Vols. 838-841

Abstract: The practical investigating and theoretic analysis Indicates that the rheologic action of the soft rock-soil could be accelerated by the dynamic loading, which induces more geotechnical engineering accidents and geologic disasters. The samples of marine deposit soft soil are collected in xiamen, and the dynamic stress-strain, the rheologic strain-time etc rheologic characteristics curves under the different breadth of dynamic loading of sinusoidal variation are tested using dynamic-triaxial device. The rheologic characteristics, rheologic rate and rheologic acceleration varietal process of four different breadths are analyzed. The research results indicate that all the samples are the same varietal process from decelerate rheology, relatively stable rheology to accelerate rheology stage. The dynamic strain slow growth and the rheologic process is relatively stable when the breadth of dynamic loading is low stress ranges of 10~20kPa.When the breadth of dynamic loading exceed 40kPa, the dynamic strain rapid growth and the rheologic is accelerate process till the samples destroy. The research results have academic and actual signification for us to open out the dynamic rheologic mechanics characteristic, explore the accelerating rheologic laws and the rheologic destabilizing dynamic condition of soft rock-soil under dynamic loading.

Abstract: Generalized Hoek-Brown criterion is indicated as a dimensionless quantity, on this basis, elastic-plastic analytical method of circular underground chamber is presented based on generalized Hoek-Brown criterion in uniform stress field. Take into account a number of factors such as deep rock mass quality, rock strength, etc, surrounding rock mass plastic zone of deep underground chamber is analyzed by the analytical method. The results show that taking measures to improve the quality of rock mass can effectively control surrounding rock mass plastic zone for soft rock underground chamber, however, taking measures to improve the quality of rock mass can not appreciably control surrounding rock mass plastic zone for hard rock underground chamber.

Abstract: Foundation pit engineering is a critical part during the development process of underground space. With the increasing demands of underground space, foundation pit engineering is exposed to new challenges. This article firstly reviews the main features of shallow foundation pits in Beijing as well as the relevant design concepts of support, and then elaborates the features and challenges of urban large-scale deep foundation pits; a case study was introduced with the exploring practice of design and construction of the large-scale deep foundation pit of Wangjing SOHO project, the innovations of support design for this foundation pit are summarized; new prospects for development of support techniques of foundation pits are proposed.

Abstract: Frost heaving and thawing settlement were the common diseases in seasonal frost area. In order to study the influenced factors of the subgrade thawing settlement, a series investigation were done on the subgrade of the Beijing-Baotou-Lanzhou railway line at the Chasuqi and Wulate qianqi sections from January to June. It was found that thawing settlement existed in embankment had great influence on the safety of subgrad running. This was less influenced by the even settlement, but was dangerous under the uneven state because of the track irregularity and its divorce from the ballast. The main factors affected the embankment thawing settlement included soil composition, water content and kind, environment temperature and the loading on soil. The larger thawing settlement would observed in the soil with large amount of silt particle, at the regions of low underground water level, with the kind of salt sensitive to frozen, at the atmosphere of the higher negative temperature sustaining a long time.

Abstract: In this paper, through the analysis of miscellaneous fill slope horizontal displacement of supporting structure and the vertical displacement monitoring results, the simulation results are compared and analyzed with FLAC^3D software, verify the support form the deformation in the controllable range, the actual monitoring data and simulation results in the difference between the standard allows range, fitting deformation curve can be used as a conventional deformation monitoring based on integral deformation analysis, advanced demonstration of engineering construction scheme optimization.

Abstract: In view of the deficiency of traditional saturated soil theory analyzing seepage and stability of slope under rainfall infiltration, based on the saturated-unsaturated flow theory, considering the mechanical behavior of slope which strongly coupled with flow behavior, the hydraulic-mechanical coupled finite element method on the case of rainfall induced instability in deposit body in Front of gushui Dam are used. The safety factor is calculated based on stress field obtained from the finite element method, with modified unsaturated Mohr-Coulomb failure criterion. The influences of rainfall duration and rainfall intensity to stability of deposit body are analyzed; the difference between calculated safety factor based on unsaturated flow theory and saturated flow theory is discussed.

Abstract: Based on geological conditions of working face 25110 in YiMa coal mine, the ground stress distribution around thrust fault is simulated by using FLAC^3D. In the fault profile, the intersection of fault footwall profile and the middle of coal seam tendency dip profile, ground stress distribution are analyzed. Distress is not continuous because of faults. Coal and rock show different stress states under high stress because of different physical and mechanical properties, and the maximum principal stress and the minimum principal stress distribute consistently with the z axis and the x axis. It provide basis on optimal design of outburst prevention of coal seam with impulsion pressure risk.

Abstract: The double-row piles supporting structure is a new type of supporting and protecting for deep foundation excavation. It is widely used to in design of deep foundation pit. Now how to simply and effectively design the structure of double-row piles is in a research and discuss stage. Using the Midas GTS finite element method, the displacement and stress distribution of double-row piles in the different stages of excavation are obtained, and the horizontal displacement and stress distribution of double-row piles in the different stages of excavation are calculated. The results of Midas GTS finite element analysis as follows: (1) after the excavation of foundation pit, the horizontal displacement of pile-top is maximum. The horizontal displacement decreases gradually with depth increases. And the displacement of front row piles is larger than that of back row piles; (2) the maximum shear stress is at the distance 5m to the foundation basement. The higher bending moment at the pile-top and the distance 10m to the foundation basement are consistent with the actual monitoring date. (3) the results of finite element analysis is close to the Richard software and actual monitoring data. It is show that using the finite element analysis to analyze the double-row piles supporting structure with is veritable and credible.

Abstract: This paper,according to the airport high fill measured data of Settlement, the filling height of not more than filling half the width of the settlement,is divided into central uniform settlement area and boundary affected zone; Central uniform settlement area can be regarded as one-dimensional compression state, layered summation method to calculate the theoretical final settlement value; then, according to the settlement data, using the hyperbolic method, exponential curve method to predict the final settlement, compared with the theoretical sedimentation value, thrust reversers experience in the specification formula coefficient, the ratio is the sedimentation coefficient of experience. The empirical coeffcient is 0.49~0.92.

Abstract: During the round gravel layer for water stop curtain construction,the failure of water curtain frequently occur.In this paper it points at the actual situation about the round gravel layer,based on the round gravel soil and similar river sand screening experiment,then according to the grading of soil conditions and other related data of the experimental results,it analyses the influence of round gravel soil distribution situation on underground engineering pile.