Abstract: Fixed point deformation observation, possessing a broad application prospect, plays an important role both in monitoring crustal deformation and capturing possible seismic precursors. However, a number of studies were conducted without taking the rock mass integrity in study areas into account, i.e., simply using general rock mechanical parameters rather than specific rock mass mechanical parameters, which therefore greatly affect the final interpretation and the elimination of disturbance, or even the identification of seismic precursory anomalies. In this study, Xiaoxinzhuang strain survey data, in Jixian County of Tianjin, were taken as an example to illuminate that the integrity or fragmentation of rock mass in each specific site should be considered when employing quantitative analysis, only thus can the influence of external load on deformation observation be evaluated more accurately. The results indicate that: (1) the exposed rocks are dominated by Middle Proterozoic dolomites and dolomites with minor limestone at Xiaoxinzhuang seismic station and its vicinity, and the corresponding volumetric joint counts of rock mass are more than 32, which means the bedrocks are medium fragmented; (2) the elastic modulus of rock mass in the study area is only 0.10-0.19 times (an averaged values of 0.14) of that of integral rock, which means that under the same stress the effect of external load will be magnified about 5-10 times; (3) during the impoundment period of Yuqiao reservoir from September to November in 2019, the theoretical compressive strain at Xiaoxinzhuang station in the north-south direction, produced by Yuqiao reservoir and calculated by an irregular load model, is about 93.76-200.91*10-8, accounting for about 10-21% of the actual observed strain; (4) therefore, it is concluded that the earlier claimed anomaly is not an earthquake precursory anomaly, but probably the effect of water level change of Yuqiao reservoir.

Key words: Deformation observation, rock mass integrity index, elastic modulus, joint statistics, volumetric joint counts

摘要： 定点形变观测是监测地壳形变和捕捉地震前兆的重要手段，具有广阔的应用前景。然而，不少研究没有考虑具体场地岩体的完整（破碎）程度，在定量分析中简单地采用了通用的“岩石力学参数”而非“岩体力学参数”，从而影响到最终结果的解释及异常或干扰的识别与排除。本文以天津蓟县小辛庄的洞体应变为例，阐明应当考虑具体场地岩体的完整性，才能更准确地评估外界载荷干扰的影响。结果表明：(1) 小辛庄周围岩体的体积节理数普遍超过了32条/m3，达到比较破碎的程度；(2) 研究区岩体的弹性模量仅为完整岩石弹性模量的0.10-0.19倍，即在相同的应力条件下，外界载荷的影响将被放大5-10倍左右；(3) 2019年9月至11月于桥水库蓄水期间，水库水位上升对小辛庄应变NS向所产生的压缩应变理论值为93.76-200.91*10-8，约占实际观测值的10-21%；(4) 2019年9月小辛庄洞体应变出现的破年变变化，并非是地震前兆异常，而有可能是受于桥水库的库容变化影响所致。

关键词: 形变观测, 岩体完整性指数, 弹性模量, 节理统计, 体积节理数