128 



the construction is similar to that at Pier 50. Municipal Pier No. 2 at San Diego Is 1000 feet in length 

 and 500 feet in width and consists of a suction dredge fill with reinforced concrete wharves over the 

 slopes at the sides and outer end. Concrete jacketed wooden piles were used in the two inner rows 

 and reinforced concrete piles in the remainder of the work. 



"The fact that the jackets are capable of adjustment as to position over the piles was taken ad- 

 vantage of in the bulkhead walls which were built in conjunction with the piers and wharves referred 

 to and also in the wall which is now under construction in San Diego. In this wall which is 3000 feet 

 in length, the jackets are square on outside except for small chamfers on the corners. The piles are 

 driven on 10-foot centers and as the jackets are set they are turned so that the faces make an angle 

 of 45 degrees with the axis of the wall and so that they are vertical. Pre-cast reinforced concrete slabs 

 are used to close the intervening spaces and each jacketed pile is anchored into the fill on the inshore 

 side by means of a reinforced concrete tie and a timber anchor. This is typical of the work at the En- 

 cinal Terminals except that brace piles were used instead of inshore ties. In Municipal Pier No. 2 at 

 San Diego the jackets were set square with the axis of the wall and the slabs rest against the flat face. 

 The same detail is being used in Pier 50 in San Francisco. 



"It will be clear from the descriptions given above that the pre-cast concrete jackets as at present 

 used are in effect reinforced concrete piles with wooden cores. As the relative lengths of the jacket 

 and pile approach each other due to bottom conditions a point is reached at which it is more economical 

 to omit the wooden core and use a solid concrete pile. This was done at the outer end of I-'ier 50 and in 

 the outer rows in Pier No. 2 at San Diego. The adaptability to varying conditions, the rigidity and 

 durability of the resulting structures and the relative economy are the principal characteristics of this 

 type of construction." 



When the casings are made and placed with sufficient care, including adequate 

 bottom penetration of the concrete shell to insure that the wooden pile will not be 

 exposed by subsequent dredging or scour, good protection can be obtained. Their 

 durability is then affected by the factors which ordinariK' influence the life of good 

 concrete in sea water. There is some danger of de\eloping cracks during handling,^ 



Fig. 48. Concrete jacketed pile, pre-cast type, showing typical rusting crack above high tide level. 

 From bulkhead between Piers 28 and 30, San Francisco; driven 1909. 



which would admit sea water to the reinforcement and permit rust to form, but this 

 can be prevented by proper care in the handling. The cost is relatively high and a 

 long life is therefore necessar\' to justify it. 



