Fixed Earth Support Method
In fixed earth support method, the depth of penetration is adequate and soil below the dredge line provides considerable anchorage. The wall acts as a propped cantilever beam and cannot rotate freely at its lower end as shown in Fig.3 and the point of contra flexure lies close to the dredge line.
Prevention of free rotation at the bottom develops full passive resistance at the back of the wall above the lower end. This resistance is replaced by a concentrated force RD at 0.2 d above the lower end of the pile.
In the analysis, two beams, one above the point of contraflexure and another below the point of contraflexure, are considered. The position of the point of contraflexure, y is a function of angle of internal friction of the soil É¸. For sands, y is given by,
For approximate analysis ‘y’ may be assumed as zero and the point of contrafiexure lie at the dredge level.
By considering the upper beam, the unknown forces RC and T can be found out by âˆ‘M and âˆ‘H = 0. In the case of lower beam as shown in Fig.3 force RD and depth of penetration d are not known. By taking moment of all forces about the base of the pile the depth of penetration can be found out. The depth of penetration thus obtained by fixed earth support methodis increased by 20 to 40 %.