II. FIELD TECHNIQUES 



1. Drill-Hole Study 



Seventeen wash-bore holes ranging in depth from 30 to 100 feet were 

 completed in this study Csee Figure 2) . This boring program employed an 

 Acker Model RGT wash -bore rig operated by a three-man crew. Figure 3 

 shows the barge-mounted drill rig at an estuarine drill site. The maxi- 

 mum drilling depth with this equipment is 100 feet. Except where till or 

 bedrock was encountered, the bore holes were drilled to that depth. Bore 

 holes were logged continuously by noting the nature of the washwater. 

 Holes were sampled at" 5- to 10-foot intervals, or at every change of sedi- 

 ment type. 



The wash-boring process consists of hammer driving a casing, washing 

 the inside of the casing clean, and then sampling beyond the end of the 

 casing. This project used an Acker NX flush-coupled casing, which has 

 an inside diameter of 3 3/16 inches. It is constructed of cold-drawn, 

 steel tubing and assembled in 5-foot lengths using couplings with square 

 threads. It is designed to withstand only limited driving, and is not 

 recommended for casing drill holes in sand beyond 100 feet. 



The casing was driven into the sediment using a 300-pound drive ham- 

 mer sliding on a pull piece attached to the casing, and was retrieved 

 by bumping the hammer against the top of the pull piece. Figure 4 shows 

 the drill-rig crew disconnecting the pull piece and a 5-foot section of 

 casing during casing removal. Casing should be driven into the sediment 

 vertically to eliminate sway in the hammer and prevent metal fatigue near 

 the connecting joints. 



The hammer was attached to a 1-inch manila line by a manila sling, 

 rather than by a chain or cable sling, to protect the threads on top of 

 the pull piece. The 1-inch manila line passed through a pulley on top 

 of the drilling mast and down to the cathead on the power unit. Figure 5 

 shows the manila line engaging around the cathead as the operator applies 

 tension to the slack end of the line. The manila line acts as a clutch, 

 engaging on the cathead when tension is applied and releasing when the 

 operator lets the line go slack. Casing is driven by alternately tighten- 

 ing and slackening the line to the cathead. Figure 6 shows the drill rig 

 and its operation. The number of blows per foot of penetration is record- 

 ed to obtain useful penetration data. The casing is cleaned of sand by 

 a chopping bit (Figure 7) before taking a sample. 



A high-pressure water jet is used; there is no rotary movement. A 

 working pressure of more than 100 pounds per square inch is developed by 

 a double-action piston pump opposite the cathead. Water is supplied to 

 the pump directly from a pond, estuary, or truck-mounted water tank. A 

 day's drilling, which usually averages 50 feet, requires about 1,000 gal- 

 lons of water. Saline, brackish or fresh water may be used if precautions 

 are taken to retard rust after use. 



