The bedding planes of unconventional oil and gas reservoirs are relatively well developed. Bedding planes directly interfere with hydraulic fracture expansion. Determining how bedding planes influence hydraulic fractures is key for understanding the formation and evolution of hydraulic fracturing networks. After conducting X-ray diffraction analysis of shale, we used Python programming to establish a numerical model of mineral heterogeneity with a 0-thickness cohesive element and a bedding plane that was globally embedded. The influence of the bedding-plane angle on hydraulic fracture propagation was studied. Acoustic emission (AE) data were simulated using MATLAB programming to study fracture propagation in detail. The numerical simulation and AE data showed that the propagation paths of hydraulic fractures were determined by the maximum principal stress and bedding plane. Clearer bedding effects were observed with smaller angles between the bedding surface and the maximum principal stress. However, the bedding effect led to continuous bedding slip fractures, which is not conducive to forming a complex fracture network. At moderate bedding plane angles, cross-layer and bedding fractures alternately appeared, characteristic of intermittent dislocation fracture and a complex fracture network. During hydraulic fracturing, tensile fractures represented the dominant fracture type and manifested in cross-layer fractures. We observed large fracture widths, which are conducive to proppant migration and filling. However, the shear fractures mostly manifested as bedding slip fractures with small fracture widths. Combining the fracture-network, AE, and fractal dimension data showed that a complex fracture network was most readily generated when the angle between the bedding plane and the maximum principal stress was 30°. The numerical simulation results provide important technical information for fracturing construction, which should support the efficient extraction of unconventional tight oil and gas.

<!-- *** Custom HTML *** --> Hou, F.-J.; Han, X.-M.; Li, S.-C., and Li, W.-J., 2019. Optimization research of construction methods and parameters of large-span city coastal tunnel in horizontal layered rockmass. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 232–236. Coconut Creek (Florida), ISSN 0749-0208. A city coastal tunnel was a four-lane road tunnel. Maximum excavation width of tunnel reached to 19.51 m in Class IV surrounding rock. The surrounding rock of tunnel was medium-thick horizontal layered limestone. To obtain the mechanical parameters of transverse isotropic material, some tests, including rock mechanics test, on-site structural characteristics survey of rockmass, bearing plate test and numerical back analysis, field test of shear strength, were conducted. Then numerical simulation were adopted to study the reasonable excavation method and parameters of tunnel in Class IV surrounding rock. To verify effectiveness of the conclusion, stress of shotcrete and steel frame of primary support of tunnel were monitored on site. Research showed that normal elasticity modulus of rockmass was obviously less than transverse elasticity modulus, and it have remarkable transverse isotropy. Settlement of vault was the main deformation in horizontal layered surrounding rock. The failure characteristic of layered rockmass were rock-falling in spandrel and delaminating collapse of vault. Bench method could be employed in Class IV surrounding rock to speed up the construction progress. Stress test results of shotcrete and steel frame of support structure indicated the tunnel was safe under the optimized excavation method and parameters.

The problem that existing pipe-jacking tunnel was disturbed by adjacent foundation pit excavation had arose relative researcher’s attention, especially in soft clay stratum. Firstly, by means of numerical simulation, the deformation of diaphragm wall and settlement law of soil outside the pit during foundation pit construction were analyzed. Then deformation and stress characteristics of existing pipe-jacking tunnels were studied influenced by different spacing between foundation pit and pipe-jacking, different excavation depth of foundation pit and different buried depth of pipe-jacking. The main conclusions were as follows. (1) The maximum horizontal displacement of the diaphragm wall was located at 3/4 of the excavation depth of pit. (2) Due to the blocking or isolation effect of existing rigid pipe-jacking on the deformation of surrounding soil, the surface settlement became smaller.(3) Deformation, structural stress of pipe-jacking would gradually decreased under the conditions of increase of the spacing between foundation pit and pipe-jacking, decrease of excavation depth of pit and buried depth of pipe-jacking, (4) Due to the influence of pit excavation, deformation and stress of pipe-jacking near the end wall and middle of the foundation pit were relatively large. (5) When the buried depth of pipe-jacking was located at near 3/4 of excavation depth of pit and the spacing was less than 10m, excavation of the pit has a great impact on the existing pipe-jacking tunnel.

Jiangshuiquan tunnel was a highway tunnel with four lanes. Its maximum excavation cross section was 170.1 m2 in Class III surrounding rock. The host rock was horizontal layered limestone, and it have obvious transverse isotropy. Based on laboratory experiments and site survey of rockmass structure, mechnical parameters of rockmass were determined. Numerical simulation and field test were used to study the deformation and failure characteristics of tunnel, pressure of surrounding rock, stress of shotcrete and lattice girder. It was concluded that lateral elasticity modulus of rockmass was obviously bigger than vertical elasticity modulus. Settlement of vault was the main deformation form of surrounding rock. Rock-falling in spandrel and delaminating collapse of roof were the common failure phenomenon. Setting rock bolt in vault was necessary in horizontal layered rockmass. Compared wtith other postions, pressure of surrounding rock, stress of shotcrete and steel frame of the vault were relatively small.

In order to meet the requirements of China’s economic development for traffic construction, the four-lane highway tunnels have appeared in recent years. Compared with the three-lane highway tunnel, it has the advantages of increasing vehicle speed, shortening mileage, saving fuel and saving time. But the four-lane highway tunnel has the characteristics of large span, large section and stress concentration. It is still in the initial stage in China, and there are many problems need to be studied urgently. The Ji’nan bypass highway was a separate tunnel of four-lane super large section highway. When the entry entrance was weak surrounding rock and the surrounding rock stability was poor, the stress and deformation rules of surrounding rock and supporting structure are analyzed by used CD method.