ABSTRACT

Fractures investigation of outcrops with the area of 1km × 1km around borehole BS03 located at Jiujing section in Beishan area, Gansu province, has been conducted by using window statistic method. Fractures statistic characterization has been studied. It has been shown from the results of statistic that four sets of fractures are dominant in the studied area and orientation of each set is well fitted by Fisher distribution; Trace length of each set of fracture is fitted by log-normal distribution and distribution of fracture aperture is fitted by inverse exponent function. Fracture numbers in unit area, P21 has linear correlation with fracture length in unit area P20, P21=1.36P20. Modeling of 3D fracture network in the studied area has been carried out by using the software Fracman. The analysis of influence of fracture trace length and intensity of fractures on migration pathway of nuclide has been done.

1 INTRODUCTION

The environmental and safety assessment of high level radioactive waste disposal in an underground repository requires an understanding of radionuclide transport in the geosphere. In hard rock, groundwater flows primarily through fractures, fracture can accelerate radionuclide transport in rock mass and it also has an effect on rock strength and rock mass quality. Fracture investigation is an effective way to know fracture spatial distribution, Currently, Many mapping techniques method can be used in crystalline based outcrops, such as remote sense mapping and scan line fracture mapping (), detailed fracture mapping (Jan, H., Lars H., etc, 2004; Tomas, C., Ola F., et al, 2005), laser fracture mapping and photographing fracture mapping. Borehole acoustic televiewer, borehole radar are very effective and accurate methods for fracture survey in boreholes as well as general fracture logging method. Based on fracture investigation, a discrete fracture network was generated by applying software FracMan.

2 FRACTURE MAPPING
2.1 Outcrop Mapping

BS03 is the third borehole drilled in Beishan area, Gansu province for China's high level waste disposal. Fracture mapping in this study was performed by using window statistic method around BS03 with the area of 1km×1km. For each window, the location measured by GPS and outcrop's orientation such as trend (θ) and plunge (δ) were recorded. Fracture Parameters, such as location, trace length, Dip (α),Dip Direction (β), aperture and fracture fillings, in each window were measured. Figure 1 presents the distribution of sampling windows around BS03. 43 windows, 1796.06 m2 in total were measured, and 1376 fractures were sampled. Fracture characteristics in the study area were analysised including orientation, trace length, aperture and fracture intensity.

(Figure in full paper)

X shows distance to BS03, arrow directs east, Y indicates distance to BS03 along Y direction, Z shows elevation, unit: m, black dot shows location of sampling window

3 FRACTURE CHARACTERISTICS
3.1 Fracture orientation

Fracture orientation is a very important parameter which determines the flow direction. Fracture orientation can be expressed as the trend and plunge of the mean pole or expressed as the dip direction and dip of each fracture set, with variability quantified by one or more of the following models.

This content is only available via PDF.
You can access this article if you purchase or spend a download.