CHAPTER XV. 



FOUNDATIONS. 



Founding upon rock Difficulties attending execution of work near low water- 

 Benching rock Steeply inclined strata Advantages of staging as compared 

 with over-end machines in preparing foundations Under-water mass-concrete 

 foundations Levelling foundations with small broken stone Grouting 

 Founding upon sand Curved profiles Mud Pile work foundation Founding 

 upon gravel Founding upon clay Founding upon rubble mounds. 



VERTICAL breakwaters, with which we may for the present 

 associate the upright superstructures of breakwaters of com- 

 posite types, are, more than any others, dependent for their 

 stability upon the excellence of their foundations. These should, 

 therefore, be prepared with exceptional care, and without stint 

 of time, labour, or material, so far as the same may be requisite 

 for rendering them as perfect as possible. 



Rock Foundations. Rock is generally held to be the beau 

 ideal of a foundation; but rock foundations are often very 

 treacherous, and they are, moreover, beset with difficulties, some 

 of which we will notice shortly. 



In preparing a rock foundation within the tidal range, where 

 the surface is too irregular or too hard to admit of being easily 

 dressed to the required level, one or other of the systems illus- 

 trated below may be adopted. For convenience of reference, 

 we will call these System A and System B respectively. 



CONCRETE FOUNDATION. 

 System A. 



In this system the rock is roughly dressed and levelled to 

 receive a course of face stones. These should be squared and 

 well bedded in cement mortar. 



In situations where the tide will quickly reach the new 



S 



