掘削方法と技術の概要
水質プローブ
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非固結帯水層における
非固結帯水層におけるCMT井戸の掘削技術
Drilling Method
Advantages
Preferred CMT Installation Technique
Comments
Sonic
Advancing casing during drilling minimizes redistribution of contaminants in borehole. Steel casing prevents borehole from collapsing as CMT well is being built. Vibrating casing during removal reduces likelihood of bridging annular materials.
Place CMT tubing into casing with anchor plate attached to bottom of tubing. Use tubing centralizers to center tubing inside of sonic casing. Add alternating lifts of sand and bentonite pellets* as casing is withdrawn, either by gravity placement, tremie methods.
Depths up to 300 feet. Use casing with an inside diameter (ID) of at least 4 inches. Addition of water to casing may be needed to prevent heaving as casing removed.
Drilling Method
Advantages
Preferred CMT Installation Technique
Comments
Hollow stem auger (HSA)
Rigs widely available. Augers provide temporary casing that can be withdrawn as CMT well is constructed.
Place CMT tubing with anchor plate into borehole inside of hollow stem augers. Add alternating lifts of bentonite pellets and sand pack from surface as augers are removed. CMT tubing centralizers may be needed to keep annular space open during well construction.
Generally limited to depths of approximately 100 feet. Water may need to be added to augers to counteract heaving sand conditions. Use augers with at least a 4-inch internal diameter (ID).
Drilling Method
Advantages
Preferred CMT Installation Technique
Comments
Direct-Push (DP)
Rigs are widely available.
Insert CMT tubing into DP casing, then withdraw casing.
Best for shallow installations where sand collapses around CMT tubing. May be difficult to tremie sand and bentonite due to small annular space between CMT tubing and DP casing.
Drilling Method
Advantages
Preferred CMT Installation Technique
Comments
Air rotary with casing advance
Casing prevents borehole from collapsing as CMT well is being built. Consistent-diameter borehole. Prevents redistribution of contaminants along borehole wall during drilling.
Place CMT tubing into casing with anchor plate. CMT tubing centralizers should be used to center tubing in borehole. Add alternating lifts of sand and bentonite pellets* as casing is withdrawn, either by gravity placement, tremie methods.
Select casing with at least a 4-inch ID. Addition of water commonly needed to prevent heaving as casing removed.
Drilling Method
Advantages
Preferred CMT Installation Technique
Comments
Mud rotary
Widely available.
Place CMT tubing directly into borehole with anchor plate attached to bottom of tubing. CMT tubing centralizers should be used to center CMT tubing in borehole. Place sand pack and bentonite with a tremie tube and grout pump.
Thin drilling fluid as much as possible prior to installing annular materials. Use a coarse-grained filter pack. Mud filter cake can be difficult to remove with development methods available for CMT wells.
* コーティングされたベントナイトペレットは水和が早くなく、より深いアプリケーションに有用ですが、コーティングされたペレットの中にはエタノールやアセトンを発生するものがあり、一部の対象化合物の検出下限を上昇させる可能性があります。通常、非コーティングペレットは水深100フィートまで適しています。
