孔內測傾管數值模擬與異常量測肇因探討

Abstract

為監測地層滑動面與位移變化以了解邊坡穩定性，目前國內外最常用方式是採用測傾管(Inclinometer)的監測。然而在測傾管正常量測判讀程序的情況下，仍然可能出現多種異常結果，這些異常結果的肇因可能為儀器不穩定、感應器量測位置不正確、測傾管段面變形、孔深未達不動點、套管周圍回填不實或者地下水位隨雨/旱季升降等，確切的肇因未必易於確知。本研究使用地工分析軟體FLAC3D進行測傾管異常結果肇因情境之模擬。為分析與歸納異常之量測位移曲線，首先廣泛收集國內歷年來以測傾管監測邊坡滑動之案例中的測傾管量測曲線圖共計370筆，以進行歸納與分析。透過大量資料之歸納與分析，整理良好位移曲線與異常位移曲線特徵，並將異常曲線歸納為自管底開始有位移、S型曲線、位移往負向移動，以及同時包含上述兩種以上之複合型異常曲線。經肇因歸納探討後，接著考慮ABS套管埋設未達不動點、填充層或地層有空洞、以及灌漿配比等因素，以探討各因素對位移曲線之影響進行小尺度範圍之數值模擬分析。最後並針對現地以測傾管監測案例，針對地下水位升降進行二維邊坡模擬分析與比對。研究顯示: 1. 管身若未能埋設於於不動點以下或埋設深度不足，在受薄層位移作用下，會於位移反側產生反曲位移，模擬結果符合貼近現地監測數據，可能於滑動面以下出現往負向之位移而與整體位移趨勢相反之案例。 2. 當填充物有空隙，當填充七厘石，以及灌漿不實等均可令位移曲線正負擺盪之情形。 3. 若未使用與地層材料性質相近之灌漿配比，會造成ABS套管回傳之位移與實際位移數值有落差，尤其在位移較小時，其落差更為明顯。

Inclinometer is often adoped to monitor the stability of a potentially unstable slope. However, even with the normal measuring procedures, it is still possible to retrieve anomalous data. The possible causes of the abnormal messages could be from the instability of instrument, the incorrect measuring position of the sensor, the deformation of inclinometer casing, the insufficient buried depth of inclinometer casing, the cavities around the backfill, and the change in ground water table. Very often, the exact reasons cannot be determined. This study made use of the software FLAC3D to model the anomalous situations of the inclinometer setup conditions and measurements. First, this work collects 370 records of monitoring measurements in order to analyze and to classify various anomalous displacement profiles. The anomalous profiles may include: (1) displacement from the bottom of the casings, (2) S shape curves, (3) displacement towards the negative directions, and (4) combined cases with more than one of the above anomalous causes. This thesis then conducted a series of numerical simulations of inclinometer-setup anomalies (including buried depth, cavities between the stratum, backfill and casing). Finally, this thesis carried out a case study with an anomalous profile of displacement (which was determined from inclinometer readings) through numerical simulation of an unstable slope deformation. The case study compares the simulated and measured results to explain the reason of anomaly in the displacement profile. The major findings from this thesis are the following. (1) A reverse displacement profile may appear if the casing bottom does not reach the fixed point, or does not pass the fixed point deep enough. (2) A S-shaped displacement profile may appear if there are some cavities inside the boring hole or the grouting material. (3) The mechanical properties of grouting material affect the accuracy of measured displacement, especially when the displacement is small. The mechanical properties of grouting material should be as close to those of the in-situ geomaterial as possible.