Part I

Primary Objectives
There are three primary objectives for the hammer drill-in casing evaluation. In priority order these are:

1.Determine the operational characteristics of the hammer drill. The hammer drill will be thoroughly tested on land before it is deployed at sea; however, it is difficult to simulate the shipboard deployment environment. We will deploy the hammer by itself for evaluation prior to using the entire hammer drill-in casing system.

2.Determine the viability of the hammer drill-in casing system. Once the shipboard operational characteristics of the hammer drill are established, we will deploy the complete hammer drill-in casing system for evaluation. Three boreholes in increasingly difficult environments are planned to completely test the equipment.

3.Determine the maximum allowable slope for hammer drill operations. If information on seafloor slope is available from a planned survey cruise that will occur before Leg 179, then we will drill multiple shallow (1-3 m) holes on progressively steeper slopes to determine maximum operational grade for the system.

Supplementary Objective
A supplementary objective for Leg 179 is to recover cores from a cased reentry hole established by the hammer drill-in casing system. We would like to recover at least two cores from each reentry site. Two cores (19 m penetration) will ensure that we penetrate through the cement bond pinning the casing to the formation. Recovering rock from below the casing string provides final proof of the viability of the system and allows us to identify with certainty the lithologies where the casing has been emplaced. Given the recent success on Leg 176, these cores will also help establish the lateral heterogeneity in lithologies exposed in the vicinity of Site 735.


The test site location is the same shallow-water platform on the east rim of the Atlantis II Transform on which Hole 735B is located (Figs. 2, 3). Five hundred meters of gabbroic rock was cored in this hole with >86% recovery during Leg 118. In 1997, Leg 176 deepened Hole 735B to more than 1.5 km below seafloor with similarly high recovery. This region provides a range of water depths from 700 m to over 6 km. This site also provides a variety of spudding surfaces ranging from relatively level massive outcroppings with clean surfaces to severely sloped talus covered surfaces. We will attempt the first set of holes directly adjacent to Hole 735B on the wave cut platform, whereas subsequent drilling will occur on the slopes adjacent to the platform.

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