Interface identification of intricate weathered granite ground investigation in hong kong using drilling parameters

Abstract

The successful identification of interfaces of simple weathered granite ground in Hong Kong has encouraged its further use of instrumented drilling system as a ground investigation tool in intricate weathered granite strata. In this tested ground, the boreholes reveal that the weathered granite alternately changes between moderately and strongly. AR-20 rotary-hydraulic drill rig is instrumented at the appropriate locations with a digital drilling process monitoring (DPM) system and data acquisition can be automatically carried out during the drilling process. The qualitative and quantitative analyses of penetrating parameters indicate that effective thrust force, rotary speed, flushing pressure, penetrating rate and displacement of the bit fluctuate at ground interfaces. It shows that the parameters get well response with the change of rock strength at the interfaces, which can reveal the change of the intricate granite formation. Besides, a variable-slope method has been established for identification of dominative and subsidiary interfaces in the granite site. The result from t test shows that the confidence of the instrumented drilling system in identification of the geotechnical interfaces is 99%.

在采用儀器鉆進系統對復雜風化花崗巖地層界面進行成功識別的基礎上,在復雜風化花崗巖場址的勘探中進行進一步應用和檢驗。在該風化花崗巖地層中,強風化與中等風化花崗巖交錯,地層特征相當復雜。試驗采用R–20液壓回轉式鉆機,并安裝數字式鉆孔過程監測系統,在鉆孔過程中對穿孔參數進行自動采集。對穿孔參數的定性和定量分析表明,在此地層中,有效軸壓力、鉆具轉速、沖洗壓力、鉆頭位移及穿孔速率等監測參數在界面處亦具有明顯的漲落,說明這些參數與界面處巖石強度的變化具有很好的響應特征,能可靠地揭示復雜地層的變化。同時,采用變斜率法對地層中的主、次界面進行識別。t檢驗表明,儀器鉆進系統對巖土界面識別的置信度為99%。