INTRODUCTION 



This report describes the development of a dynamic penetrometer for 

 testing seafloor sediments at water depths to 20,000 feet. The work was 

 funded by the Naval Facilities Engineering Command. The purpose in 

 developing this tool was to provide an expedient means to determine seafloor 

 characteristics and properties relevant to site selection for and design 

 of direct embedment anchors. This tool has several intended and potential 

 applications. 



For noncritical embedment anchor installations the penetrometer can 

 probably be used by itself to select the fluke size to be used (most 

 embedment anchors have several fluke sizes or types to accommodate a 

 variety of seafloors). This can be done based on the penetration depth 

 of the penetrometer. Experience will be required, but in general shallow 

 penetration would indicate using a small fluke and deep penetration would 

 indicate using a large fluke. Fine grained soils that are approximately 

 normally consolidated in the upper 50 feet of sediment (defined as having 

 a surface shear strength less than one pound per square inch) cover about 

 30 percent of the seafloor. In these soils it is anticipated that the 

 penetrometer can provide sufficiently accurate soil strength data to 

 determine the short-term holding capacity of an embedment anchorage. Be- 

 cause the short-term capacity will govern in these soils (Beard and Lee, 

 1975, and Yen, 1975) this capacity is the design capacity. For other soils 

 where the long-term capacity will govern this is not possible because the 

 penetrometer cannot measure the soil density and friction angle required 

 to estimate the long-term capacity. 



One use of the penetrometer will be to supplement coring and geophysical 

 measurements. Penetrometer data gathered intermittently between cores 

 will allow interpolation between cores of strength measurements made on 

 the cored soil. This information could otherwise be acquired only with 

 additional coring, which is several times more time-consuming and costly 

 than performing penetrometer tests. 



For final site selection it is necessary to determine the homogeneity 

 of the proposed anchor location. Anomalous conditions, such as small 

 submarine lava flows and ice-rafted detritus at selected sites, are of 

 concern because they can prevent proper embedment anchor performance. 

 Multiple penetrometer tests will help determine the probability of 

 occurrence of anomalous conditions and therefore help to estimate the site's 

 homogeneity. 



The penetrometer would also be valuable in helping to determine the 

 fluke angle to use on a conventional drag anchor with adjustable flukes. 

 The fluke angle is changed to maximize anchor holding capacity in soft and 

 firm seafloors. The penetrometer should easily detect whether the seafloor 

 is soft or firm. 



