Engineering geological zonation using interaction matrix of geological factors: An example from one section of Sichuan-Tibet Highway

Yanjun Shang,Hyeong-Dong Park,Zhifa Yang 한국지질과학협의회 2005 Geosciences Journal Vol.9 No.4

From in situ stress and discontinuities to the strength of granites: comparison and case study

Yanjun Shang,박형동,Guangxiang Yuan,Yuanchun Sun,Qian Gao 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.4

The distinctive weathering profile and discontinuity of granites, dipping slightly at shallow depths and steeply in larger depths, are regarded as being due to their physical and geo-mechanical properties. This paper compares vertical stress (Sv) and overlain weight (h) drawn from different kinds of in situ stress measurements, as well as coefficients of lateral stress. Stress trends are connected with discontinuities (joints and dykes), which reveal their relationships in space and dip angles of joints and dykes are compared in space, together with shear plane plunges and the strength of rocks from laboratory tests. As a result, it was found that the relict structural geo-stress contributes to maximum horizontal stress, especially at shallow depths. The most common feature is the high coefficient of lateral stress, which is mostly attributed to unloading in shallow depths and stress concentration at a certain depth after the erosion of overlain beds and the exposure of granites at the ground surface. Therefore, the weathering profiles and weathered capsule of granites could be interpreted from this viewpoint. One of the two main features of this paper is the connection of the extraordinary values of the lateral coefficient of in situ stress with unloading and the typical weathering profile at shallow depths. Another is the comparison of the shear stress and strength from in situ and laboratory tests, with a series of data from the same location and depth. The distinctive weathering profile and discontinuity of granites, dipping slightly at shallow depths and steeply in larger depths, are regarded as being due to their physical and geo-mechanical properties. This paper compares vertical stress (Sv) and overlain weight (h) drawn from different kinds of in situ stress measurements, as well as coefficients of lateral stress. Stress trends are connected with discontinuities (joints and dykes), which reveal their relationships in space and dip angles of joints and dykes are compared in space, together with shear plane plunges and the strength of rocks from laboratory tests. As a result, it was found that the relict structural geo-stress contributes to maximum horizontal stress, especially at shallow depths. The most common feature is the high coefficient of lateral stress, which is mostly attributed to unloading in shallow depths and stress concentration at a certain depth after the erosion of overlain beds and the exposure of granites at the ground surface. Therefore, the weathering profiles and weathered capsule of granites could be interpreted from this viewpoint. One of the two main features of this paper is the connection of the extraordinary values of the lateral coefficient of in situ stress with unloading and the typical weathering profile at shallow depths. Another is the comparison of the shear stress and strength from in situ and laboratory tests, with a series of data from the same location and depth.

Some large values of in-situ stress and related engineering geological problems in China

Yanjun Shang,박형동,Yongyue Shi,Guangxiang Yuan,Yuanchun Sun 한국지질과학협의회 2010 Geosciences Journal Vol.14 No.2

In recent years, different methods have been applied to in-situ stress estimation for stability analysis of increasing large-scale tunnels in China. It was found that some extraordinary stress values are mostly associated with, although not a necessity of, engineering geological problems such as collapse, rock burst and squeezing. This paper focuses on finding the relationship among abnormal in-situ stress component values. The exposure in ground surface with unloading and erosion contributes a lot to relatively higher horizontal stress and lateral coefficient values of igneous and metamorphic rocks, while this situation is not the case for sedimentary rocks. Comparing stress data and connecting some abnormal values with typical case examples for better understanding and estimating stress is the main feature of this paper.

Brittle fracture and plastic creep of the completely decomposed granite presented in CT

Yanjun Shang,Zhongqi Yue,박형동,현창욱 한국자원공학회 2015 Geosystem engineering Vol.18 No.6

Completely decomposed granite (CDG) with different structures shows different patterns in deformation and failure as brittle fracture or as plastic creep in triaxial test. It is necessary to monitor and to compare the fabric changes due to stress in real time during test. By means of the computerized tomography (CT) technique for monitoring deformation and failure of soils in real time without suspending the mechanical test and disturbing samples, a newly designed triaxial test machine was used to test CDG from Hong Kong in a procedure of saturation, consolidation and undrained condition. It was found that CT data (images and values) depicts the failure patterns as brittle fracture or as plastic creep at 3-D in real time. The results were concordant with stress–strain curves and observation of the appearance of samples before and after tests.

Estimation of hydraulic parameters in a hard rock aquifer using integrated surface geoelectrical method and pumping test data in southeast Guangdong, China

Muhammad Hasan,Yanjun Shang,Weijun Jin,Gulraiz Akhter 한국지질과학협의회 2021 Geosciences Journal Vol.25 No.2

Estimation of hydraulic parameters is important for the prediction of the future availability of groundwater reserves. Conventionally, pumping tests are conducted on boreholes to measure these parameters. However, such tests are costly and time consuming, and can only provide limited spatial information. An integrated approach of geophysical method and pumping tests is cost-effective and efficient alternative for the estimation of aquifer parameters. A geophysical method of vertical electrical sounding (VES) was carried out in Huizhou ADS site of China for the delineation of aquifer potential zones to assess the groundwater resources contained within the weathered rock. Initially, the pumping test data were used to determine the hydraulic parameters namely hydraulic conductivity (Kw) and transmissivity (Tw) for available production wells. Afterwards, one empirical relation between pumped hydraulic conductivity (Kw) and aquifer resistivity (ρa), and another between pumped transmissivity (Tw) and transverse resistance (Tr) were obtained to estimate hydraulic conductivity (K) and transmissivity (T) for all VES stations where pumping tests were not conducted. In this way, the entire study area was investigated to delineate the aquifer potential zones i.e., high potential aquifer zone with ρa < 100 Ωm, T > 150 m2/day and K > 4 m/day, medium potential aquifer zone with ρa ranging from 100 to 150 Ωm, T from 100 to 150 m2/day and K from 3 to 4 m/day, poor potential aquifer zone with ρa from 150 to 300 Ωm, T from 50 to 100 m2/day and K from 2 to 3 m/day, and negligible potential aquifer zone with ρa > 300 Ωm, T < 50 m2/day and K < 2 m/day. This investigation also deciphers functional analogous relation of ρa with K and Tr with T in Huizhou, China. Therefore, similar integrated approach can be used in any geological similar area where the aquifer propertiesare required for the management of groundwater reserves.

Numerical Simulation of Hydraulic Fracture Propagation within Fractured Shale Gas Reservoir Based on a Three-dimensional Fracture Network Model

( Yanyan Li ),( Yanjun Shang ),( Lihui Li ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

This research presents coupled hydro-mechanical modeling of hydraulic fracturing processes within fractured reservoir based on a three-dimensional fracture network model. Field investigation was conducted to collect joint data from shale outcrops of the Yanchang Formation using the window sampling method. A three-dimensional joint network model was built using the Monte Carlo simulation method. Lamina data were collected from conventional logging, borehole TV and cores. The Monte Carlo method was also used to model artificial laminas. The fracture network model was built by adding the artificial laminas to the joint network model. The interactions between hydraulic fractures and natural fractures are analyzed, providing a better insight into the performance of hydraulic fracturing jobs in naturally fractured reservoir. Numerical results show that the hydraulic fracture may arrest, cross, or divert into natural fractures depending on the rock mechanical properties, direction of rock principal stresses, and fracture intersection angle. The propagation direction of hydraulic fractures is controlled the maximum horizontal stress. Laminas change the propagation direction of hydraulic fractures, suggesting that the heterogeneity of shale influences the propagation of hydraulic fractures. The influence of the injection rate of fracturing fluid on the propagation of hydraulic fractures was studied. The results show that there is only one major hydraulic fracture when the injection rate is 0.1 ㎥ per minute. With the increase of the injection rate, several major hydraulic fractures perpendicular to laminas were produced, improving the fracture complexity and expanding the reservoir drainage area.