8 A TREATISE ON DREDGES AND DREDGING 



become very loose and are then easily removed by means of any 

 ordinary dredge. The ladder dredge, with its buckets that are 

 continuously scraping the loosened pebbles of the bank of gravel, 

 thus filling up the buckets to their full capacity, seems to be the 

 most efficient machine in this soil. The dipper and grapple dredges, 

 however, are found very efficient machines for dredging through 

 gravel. 



Hardpan. Hardpan is a soil composed of loam and boulders 

 and is considered very compact and resistent. Sometimes it is 

 encountered in such a hardened condition as to be considered almost 

 a conglomerate in which the cementing material is loam. Hard- 

 pans are met in numberless varieties, being christened by contractors 

 with the strangest names. In the reports of public works, when 

 the name of an unknown soil is mentioned, as a rule one may rest 

 assured that is a variety of hardpan. Only three types of dredges 

 can be used with advantage in this kind of soil, and they are the 

 dipper, the grapple and the ladder dredges, in which the buckets 

 are provided with strong steel teeth. The most efficient machine for 

 digging through hardpan at shallow depths is certainly the dipper 

 dredge. The large heavy bucket easily penetrates through the 

 soil and being of large dimensions may loosen and lift boulders 

 of any size. The grab dredge, provided with a clamshell bucket 

 in which the edges are furnished with strong tines may be found 

 very convenient, especially when dredging through hardpans located 

 at a certain depth from the surface of water. The ladder dredge 

 in which the buckets are armed with steel teeth for the double 

 purpose of breaking the loam and facilitating the picking up of 

 the boulders, can also be used for dredging through hardpan. In 

 this soil, however, the ladder dredge, in some cases, may not be 

 found so advantageous as the two other types of machines, owing 

 to the fact that the buckets, no matter how large, may be too small 

 for raising the boulders, especially when of large dimensions. Large 

 boulders may entangle the buckets and disarrange the machine. 



Clay and Loam. Clay and loam are as a rule considered among 

 the loose soils, and yet they are the worst kind of such materials 

 to remove. They stick to the buckets and cause a mvat deal of 

 trouble. All the different types of dredges can be used with more 

 or less advantage. The dipper and grapple dredges are considered 

 the most efficient. With these machines the impact of the buckets 

 in attacking the soil permits of easy penetration, thus filling the 



