300
BEHAVIOR OF PILES SUPPORTING OFFSHORE STRUCTURES
1. Construct the p-y curve in the same manner as for short-term static
loading, for values of p less than 0.72p .
2. Equate équations (11.7) and (11.8) and compute the depth z = zr where
the transition occurs. If the unit weight and shear strength are constant in the
upper zone, then
6cô
7'b + 0.5c
(U.ll)
3. If the depth to the p-y curves is greater than or equal to zr, then the
value of p is equal to 0.72p for ail values of y greater than 3p5o4. If the depth to the p-y curve is less than or equal to zr, then the value of p
decreases from 0.72pu at y = 3j/so to the value given by the following expression
at y = 15.V50p = 0.72pu (z/zr)
(H-12)
The value of p remains constant beyond y =15pso.
Examining the parameters used in the équations for the analysis of latéral
loading of piles reveals that the engineer can describe the pile with good accuracy, but describing the response of the soil dépends on the quality of the p-y
curves. Therefore, field experiments may be dictated in some instances.
S cour
At most of the places where offshore structures are installed, there is a
probability that a certain amount of scour or érosion of the surface soil will occur.
Much can be said about the use of available technology to predict the amount
of scour that will occur at a given site; however, the number of parameters
involved in making a prédiction and the variability of those parameters are such
that scour prédictions are usually inexact. Some characteristics of scour are
summarized as follows:
1. Scour is usually more severe close to the piles, but the mudline may be
lowered over the entire area occupied by an offshore, pile-supported structure.
2. Scour is usually minor at sites where the surface soils are clays; however,
some designers assume that the mudline may be lowered 3 to 5 ft (1 to 1.5 m)
at such sites.
3. If the surface soil consists of fine sands, the érosion of the mudline can be
severe. Some means of preventing such scour is usually adopted and installed
at the time when the platform is being erected.
4. Prédictions of the amount of scour are usually made on the basis of
observations at other structures in the vicinity. If no data are available, a
program for making periodic observations of the amount of scour is usually
established.
BEHAVIOR OF PILES SUPPORTING OFFSHORE STRUCTURES
1. Construct the p-y curve in the same manner as for short-term static
loading, for values of p less than 0.72p .
2. Equate équations (11.7) and (11.8) and compute the depth z = zr where
the transition occurs. If the unit weight and shear strength are constant in the
upper zone, then
6cô
7'b + 0.5c
(U.ll)
3. If the depth to the p-y curves is greater than or equal to zr, then the
value of p is equal to 0.72p for ail values of y greater than 3p5o4. If the depth to the p-y curve is less than or equal to zr, then the value of p
decreases from 0.72pu at y = 3j/so to the value given by the following expression
at y = 15.V50p = 0.72pu (z/zr)
(H-12)
The value of p remains constant beyond y =15pso.
Examining the parameters used in the équations for the analysis of latéral
loading of piles reveals that the engineer can describe the pile with good accuracy, but describing the response of the soil dépends on the quality of the p-y
curves. Therefore, field experiments may be dictated in some instances.
S cour
At most of the places where offshore structures are installed, there is a
probability that a certain amount of scour or érosion of the surface soil will occur.
Much can be said about the use of available technology to predict the amount
of scour that will occur at a given site; however, the number of parameters
involved in making a prédiction and the variability of those parameters are such
that scour prédictions are usually inexact. Some characteristics of scour are
summarized as follows:
1. Scour is usually more severe close to the piles, but the mudline may be
lowered over the entire area occupied by an offshore, pile-supported structure.
2. Scour is usually minor at sites where the surface soils are clays; however,
some designers assume that the mudline may be lowered 3 to 5 ft (1 to 1.5 m)
at such sites.
3. If the surface soil consists of fine sands, the érosion of the mudline can be
severe. Some means of preventing such scour is usually adopted and installed
at the time when the platform is being erected.
4. Prédictions of the amount of scour are usually made on the basis of
observations at other structures in the vicinity. If no data are available, a
program for making periodic observations of the amount of scour is usually
established.