BLACKPOOL COAST DEFENCE WORKS 97 



the Corporation favourably considered a scheme of amalgamation with the 

 Urban District of Bispham with Norbreck, and, in 1917, promoted and 

 obtained a Bill in Parliament to extend the borough in a northerly direction, 

 with powers to construct a sea-wall to protect that length of cliff suffering so 

 severely from erosion by the sea. 



Owing to the prohibitive cost of stone suitable for work of this description, 

 coupled with the difficulty of getting delivery of same, it was decided, when the 

 work was started, in August, 1917, to build a self-faced wall, built in situ, 

 using a facing mixture of 4 to 1 P.C. concrete, 9 inches thick, with a backing of 

 8 to 1 P.C. concrete, with a reasonable number of displacers for the bulk of 

 the wall. The almost uniform level of the boulder clay along the line of the 

 wall is 1 1 .50 above Ordnance Datum, and has an inclination seawards of 1 in 20, 

 with an average covering of 12 inches of gravel, where it meets the sandy 

 foreshore at a mean level of 4 feet above O.D. : the foreshore then falls seaward 

 at an almost uniform gradient of 1 in 100 to low water. The excavation for 

 the wall in boulder clay was taken down 7 feet below the surface level of the 

 boulder, at the front of the wall, and then benched up. On account of the 

 rock-like toughness of the boulder clay, gelignite was used to facilitate and 

 cheapen the cost of getting out the trench : small charges were put in some 

 3 feet away from the seaward side of the trench, so as not to break up the 

 ground on the west side of the wall, and somewhat heavier charges were used 

 for the centre and back. 



In the running sand foundation permanent king piles were driven at 1 2 feet 

 centres and 18 feet below toe level : on account of the high cost and difficulty 

 in obtaining balk timber suitable for the purpose, the author suggested using 

 old tramway rails, 7 inch section, and weighing 98 lbs. and upwards per yard. 

 Holes were drilled in the piles before driving, through which the permanent 

 walings were bolted, and close sheeting piles, 10 feet long, were spiked to the 

 wahngs. 



There was an ample supply of splendid gravel and grit suitable for concrete 

 lying close to the line of the wall. Screening was unnecessary with the 

 exception of the facing material, when all stones over | inch were eliminated. 

 The concrete was mixed on light portable stages fixed over or alongside the 

 trench, and easily removed at high water. 



Fig. No. 9 shows the method the author designed to form the wall. 



Four-inch diameter cast-iron pipes were built through the wall 40 yards 

 apart to act as ream water outlets : a substantial dry lining backing was built 

 on the landward side of the wall at each outlet. 



Nine-inch diameter cast-iron pipes spaced 60 yards apart were also laid 

 through the wall well above high water level to provide for the surface water 

 draining of any future lay-out. 



Fig. No. 10 shows a section of the last 270 yards of the work, a reinforced 

 P.C. concrete stepped apron having an 8 inch rise and a 1 5 inch tread, with a 

 bull-nosed top, a light wall 3 feet in width built to form a " seal " on the 

 landward side of the apron, and to carry the bull-nosed top, being the main 

 features. A similar section was adopted in forming the apron to the first slade 

 for vehicular traffic, and was completed in June of 1919. The work is standing 



