# Identification for Abutment Stress by Drilling Cuttings
## 1 Introduction  
With the continuous mining of the coal seam, the stress distribution in the coal seam will move forward and change. The vertical stress is called the abutment pressure. The concentration of abutment pressure in the coal seam generally causes serious damage to roadways, even more induces rock burst. Therefore, how to determine abutment pressure distribution has become a hot topic. Generally, analytical and numerical simulations are the commonly used methods in rationale analysis [1]. Vibration wave detection and online stress monitoring are utilized in situ [2; 3]. However, because of the complexity of different scale fissures or cracks in the coal seam structure and the influence of roof movement, the detection accuracy of abutment pressure and its changes by using vibration wave detection and online stress monitoring should be improved.  
As one of the methods for monitoring the danger of rock burst, the drilling cuttings method has been utilized. Its principle is to drill small-diameter holes into coal; the amount of cuttings discharged through a hole per unit length is used to understand the stress concentration. This method was used first in the early 1960s in Germany [4] and then spread to the Soviet Union, Poland and the United Kingdom [5]. In China, drilling cuttings began to be trialed for rock burst early warning in coal mines in 1985 [6; 7]. In recent years, many investigations such as early warning threshold determination of drilling cutting amount [8; 9; 10], methods of obtaining the evaluation index of drillingcuttings [11; 12], analyses of influencing factors [13; 14] and tests of pressure relief effect [15] were done. One successful example is the prediction of rock burst risk in Kaiping Mines, Hebei Province, China, in the early 1980s. The index of drilling powder rate was used to determine the danger level of rock burst. After that, Longfeng Coal Mine in Fushun, China, put forward a method combining drilling cuttings, laboratory experiments and theoretical calculations to determine the grade of shock hazard. Many coal mines in China, such as Mentougou Coal Mine in Beijing, Quantai Coal Mine and Sanhejian Coal Mine in Jiangsu Province, Zaozhuang Mining Bureau and Xinwen Coal Mine in Shandong Provence, and Qianqiu Coal Mine in Henan Province have also carried out on-site drilling cuttings monitoring for the prevention of rock burst. As an indicator of stress level, drilling cutting was also used to evaluate gaseous properties of coal and gas stress [16; 17]. Much more, the relationship between acoustic emission (AE) signals and diamond drill bit wear was obtained in order to gather and interpret data to allow overall improvement of drilling performance, and through understanding the characteristics of AE signals in terms of the operational parameters of the drilling apparatus, drilling performance was improved [18; 19].  
Because distribution of abutment pressure or stress concentration is closely related to roof movement, investigating the roof weighting influence on abutment stress changes by drilling cuttings is worth doing. This paper intends to analyze the relationship between drilling cuttings amount and the stress firstly, then to investigate the relationship between drilling cuttings and abutment pressure distribution in different stages of roof movement as the coalface advances.