The corrosion drainage pipes with dense pipe bedding, void pipe bedding and polymer repaired pipe bedding were taken as the research object, and the field full-scale test was carried out for corrosion pipes with three different pipe bedding states under different vehicle axle loads. According to the field test, the refined three-dimensional finite element models of corroded drainage pipes with dense, void and polymer repaired pipe beddings were established, respectively, and the reliability of the test results was verified. The results showed that the measured data were in good agreement with the simulation results, and the maximum error was only 10.9%. When the vehicle axle load increased from 15 t to 20 t and 25 t, the strains on the inner wall of the bell and spigot crown of the void pipe were increased by 62%, 54%, 38% and 36%, 14% and 11%, respectively, compared with that of the dense pipe, which indicated that the void pipe bedding could significantly change the stress state of the pipe. The circumferential strains on the inner and outer walls of the bell and spigot of the dense pipe were very close to the repaired pipe, which indicated that the polymer grouting pretreatment technology had a significant effect on repairing the void pipe bedding.

Cement-treated marine clay has been widely used in ground improvement. Due to its significant spatial variability and complicated constitutive behaviour, the selection of characteristic strength of cemented soil is challenging. According to Eurocode 7, the characteristic value should represent the overall performance of the geotechnical system. And when a reliability-based design method is adopted, “the characteristic value should be derived such that the calculated probability of a worse value governing the occurrence of the limit state under consideration is not greater than 5%”. In this paper, the random finite element analysis was proposed to directly link the spatial variation in the point strength and the overall performance of geotechnical system, which was more directly related to system performance and allowed the probability of failure to be estimated or prescribed for cement-treated soil.

Due to the influence of urban characteristics, road traffic conditions, municipal pipelines and various buildings, the construction of metro station with shallow excavation method occupies an important proportion. Combined with the research results of the design of the metro station structure scheme in recent years, based on the risk control of subway station structure and surrounding environment,this paper introduced the research progress in calculation method of vertical soil pressure at the arch of metro station, control standard of surface subsidence, design of soil reinforcement, bearing capacity of initial support and key working conditions of structure etc.

Based on the system research data at home and abroad, the rock mass structure information collection and integration, dangerous rock stability reliability analysis, rock collapse disaster monitoring and prevention were summarized and researched, in order to analyze the current research status of the tunnel rock collapse disasters. Combined with the research work, the theory and technical defects of rock collapse disaster were summarized, and the relevant prevention and control measures against dangerous rock fall were also analyzed, so as to provide theory basics for dangerous rock collapse during tunnel construction.

Water and mud inrush disaster occurs frequently in weathered granite regions with abundant water, which does tremendous harm to the construction of tunnels and surrounding environment. Combining with the treatment practice of water and mud inrush disaster of Junchang tunnel in Guangxi Zhuang Autonomous Region, the treatment principle of water and mud inrush disaster was determined firstly based on the characteristic analysis of water and mud inrush disasters. The composite curtain grouting technique was established for sealing groundwater and reinforcing the surrounding rock, based on the laboratory and field tests. And the comprehensive evaluation method of grouting effect was proposed in order to evaluate the implementation results of curtain grouting work. The proposed treatment technology had successfully solved the water and mud inrush disaster in Junchang tunnel. And the research results could provide reference and guide for the prevention and treatment of water and mud inrush disaster in similar geological conditions.

Field tests were carried out to study the vibrations problem induced by moving train traffic under complex topography conditions on the viaduct section of Chongqing Light Rail Line 6 passing through typical slopes. Attenuation of train induced soil vibration under inclined topography conditions were analyzed. The results showed that the main frequencies of ground vibration caused by trains were distributed 30-95 Hz under the semi-concave field, and the ground vibration presented wave attenuation. Two vibration amplification zones appeared in the direction of 45, and 90 degrees from the track center line. Affected by the topography of the site, the vibration was mainly concentrated in the concave field, and the attenuation of vibration in the two directions was not obvious in the concave field, but the attenuations showed significantly different variations. The vibration with a low-frequency was obvious near the pier, and the train operation had obvious periodical loading phenomenon. The ground vibration was mainly concentrated in the high-frequency part, but the attenuation of the high-frequency part was not obvious, while the vibration of the low-frequency part attenuated to some extent. Whats more, the frequency vibration caused by the up train was greater than that of the down train.

Through on-site CPTU testing, software which interprets CPTU data was used to interpret the test data, and CPTU method was used to classify the site and stratify the soil layer. The physical and mechanical parameters of the soil in the engineering area were calculated, and the applicability of CPTU technology in deep marine soft soil area was proved by comparing the indoor test results. The CPTU method was used to predict the vertical bearing capacity of pile foundation theoretically. The numerical model of rigid pile composite foundation was established, and the field static load test was simulated. The results of single pile vertical ultimate bearing capacity of composite foundation obtained by theoretical formula calculation, numerical simulation and field static load test were compared and analyzed, and the failure forms of composite foundation are discussed. On this basis, the determination of bearing capacity characteristic value of single pile in composite foundation was deeply studied and the interaction mechanism between pile and soil in composite foundation and the working behavior under design load were studied.

The elastic sliding isolation bearings were fixed at the top of the middle columns, a two-dimensional finite element model for the static-dynamic coupling interaction of soil-underground structure was established, and the seismic response of underground subway station, such as the lateral deformation, stress responses and the seismic damage were analyzed. It showed that the elastic sliding bearings fixed on the top of columns could effectively mitigate the seismic damage of the middle columns and the middle plate and keep middle columns completely under compress condition during the earthquake. As a result, it could improve the overall seismic performance of the underground station structure due to the important role of middle columns in the seismic resistance of underground subway station. However, the elastic sliding bearings fixed on the top of columns could also weaken the anti-lateral rigidity of the underground station structure and the plane buckling rigidity of the plates, which significantly amplified the lateral deformation response of the underground station structure. Meanwhile, middle columns changed the dynamic deformation mode of the underground station structure, which obviously aggravated the seismic damages of the top and bottom plates close to the side wall of the underground station structure.

With the development of railway, water conservancy, mining and other projects, increasing caverns need to be excuvated in the deep. Dynaimic loads includying blasting excavation and fault-ship burst seriavsly affect the stability of surrounding rockmass of undergroud cavern. The finite difference software FLAC3D was used to simulate the surrounding rockmass stability of underground cavern under blasting and fault-slip burst conditions. The peak ground velocity(PGV)was used, and the mathematical relationship of the surrounding rock PGV under different focal mechanisms was obtained by fitting the Sadovs formula and the McGarrs formula. It was concluded that under the blasting load condition, the distance between the underground cavern and the source had a significant influence on the stability of the cavern. The Sadovs deformation formula could well characterize the PGV of the surrounding rockmass response, but the McGarrs deformation formula was not applicable. Under the condition of fault-slip, the Sadovs deformation formula and the McGarrs deformation formula did not have high goodness of fit, the slip angle had a greater influence on the stability of the cavern. Based on the above analysis, it was recommended that deep underground cavern support should consider the influence of the source, such as PGV. For the source of fault-slip, the influence of the slip angle on PGV should be considered. The above conclusions provide data support and technical basis for the excavation and support of geotechnical engineering underground cavern.

An understanding of the characteristics and areas of the excavation damage zone plays an important role in stability assessment and support design. In this study, we presented the definitions and criteria for the three excavation damage zones in terms of failure, open and shear zones, as well as the discrete element method for simulating the excavation damage zone in fractured rocks based on the Barton-Bandis fracture constitutive model. We built a discrete fracture network model for the 4# diversion tunnel excavated in columnar jointed rocks at the Baihetan Hydropower Station, and the agreement of the depth of the excavation damage zone between numerical modeling and the field monitoring demonstrates that the proposed discrete element method for simulating the excavation damage zone in fractured rocks was an accurate and robust modeling tool. Considering the random distribution of JRC(Joint Roughness Coefficient)in fractured rock mass, the area of the excavation damage zone decreases with the increasing JRC average, and the depth of the excavation damage zone high probabilities increased with the increasing standard deviation of JRC distribution.

In order to study the safety performance of the subway assembled external channel in the fire scenario, the ABAQUS finite element software was used to establish the numerical model of tunnel segments, longitudinal connection bolts and external channel. The temperature and stress distribution of the new structure under the HC heating curve were obtained. The study showed that the existence of external channel could significantly improve the temperature value of longitudinal connection bolts. Compared with the results without external channel, the temperature distribution on the contact surface of the hand hole which close to the hanging ear was significantly different, the temperature value was about 100 ℃ higher. The external channel had little influence on the temperature of the concrete which at the side of the hand hole and away from the hand hole, but it could accelerate the heating of the longitudinal connection bolts which at the exposed end as the same as the contact surface. Additional thermal stress was generated as the external channel further increased the temperature inhomogeneity between the longitudinal connection bolts and the surrounding concrete, but the final result was still within the safe range.

In order to further analyze the complicated propagation path of hydraulic fracture in combined rock masses, the coal-rock combined models were established from the aspects of hard roof-floor management, permeability enhancement of coal seam, and fracturing coal-shale unconventional reservoirs. The propagation of hydraulic fractures in different cases was investigated, and breakdown pressures were compared correspondingly. Complex and tortuous fractures were induced when fracturing coal seam, which were suitable for coal seam permeability enhancement while not for hard surrounding rock management. Straightforward fractures were obtained when hydraulic fracturing was performed in hard surrounding rocks, which was beneficial to roof management instead of coal permeability enhancement, since limitation 2019年 - 第1卷第3期于永军,等:北山隧道式大跨度地下四季滑雪场围岩稳定性研究 \=-was detected as fracture penetrated into coal seam. Setting pairing wellbores could increase the fracture penetrating into coal seam, whereas mutual interference among wellbores and fractures was also emerged. Wellbores should be configured rationally based on softening surrounding rocks and permeability enhancement for coal seam, aimed at an optimized fracturing effectiveness and reducing engineering costs. Both the leak-off of injected fluid and pore pressure distribution were influenced by configuration of natural fractures embedded abundantly in shale. The propagation of hydraulic fractures was affected by both natural fracture distributions and in-situ stress regimes. Comparisons were made between numerical and analytical solutions of breakdown pressure in different cases. Divergent data of breakdown pressure were obtained by analytical equations while numerical results were in the range of analytical solutions. Furthermore, more reservoir geological and fracturing engineering factors can be incorporated during simulations. The research may provide insights regarding of hard surrounding rock management, coal permeability enhancement and shale reservoir stimulation.

Aiming at the problems of complex engineering geology, long service life and stability of large-span chamber(exposure area up to 2 000 m² or more)of Beishan cross-country ski resort rebuilt by Jilin Beishan Civil Air Defense Project, refinement investigation of rock mass structure was carried out. The indoor rock mechanics experiment and wave velocity test in borehole were conducted. Structural surfaces investigation based on photogrammetry method combined with the method based on in borehole radar and television was adopted to study the surface joints, fractured zones and spatial distribution of loosening zone of surrounding rock mass. The quality of surrounding rock was classified and zoned, the mechanical parameters were determined, and the stability of surrounding rock was studied. Through numerical simulation analysis and calculation of large-span tunnel, the tension stress zone of roof was delineated, the reinforcement scheme was proposed. This study has reference significance for similar tunnel expansion and reconstruction projects. 2019年 - 第1卷第3期高源,等:北山隧道式大跨度地下四季滑雪场围岩稳定性研究 \=-

The interaction between the hob and the rock mass is the core of TBM technology, and numerical simulation plays an important role in studying this process. In this paper, a hob and a soft-strong inter-bedded rock model was built based on further development of discrete element software MatDEM, which contained 502 thousand particles. By simulating the process of the rock breaking by a hob, as well as recording and analyzing, including boundary and hob force, particle connection, energy conversion, heat distribution and so on. The simulation results showed that, when strong rock breaked, the force of boundary and hob changing obviously, and the particles had greater force in the direction perpendicular to the hob and layer, but when weak rock layer was breaking, the inner boundary and the hob bore less stress, and the force of the hob was uniform; There were a few of broken joints in strong rock layer, and breaking volume of rock mass was small; During this process a lot of frictional heat was produced, and the accumulate of energy in strong rock was larger. MatDEM could simulate rock breaking process by hob effectively. By modifying the shape of hob and parameter of rock, this method could be further used for simulation of large-scale rock breaking by hob in other engineering conditions. It also provided a new way for numerical simulation of large-scale hob breaking rock.