Grouted Pile-to-Sleeve Connection Tests

Abstract

ABSTRACT Eighteen grouted pile-sleeve connections were tested to examine the influence of combined loading (moment and axial load), relative shear key location between sleeve and pile, eccentric piles and sleeves, and grout strength. The specimens were divided into six series, each containing three replicates. The results showed that combined loading had no detrimental effect on the ultimate bond capacity of a grouted pile-to sleeve connection. The ultimate capacity was not affected by extremes in the shear-key arrangements or by variations in the thickness of the grout annulus. The capacity of the connections varied with the square root of the grout strength. INTRODUCTION In deep water the piles of a fixed steel offshore platform are normally installed through sleeves which are attached to the lower section of the structure. The annulus formed between the tubular steel sleeve and pile is usually filled with a cementations grout, which transfers the forces from the jacket into the pile. A typical grouted connection is shown in Fig. 1. The behavior of grouted pile-to-sleeve connections has been investigated by several researchers since the early 1970's [1,2,3,4]. The parameters reported to affect the strength of a grouted pile-to-sleeve connection were: tube and grout geometries; geometry and spacing of mechanical shear keys; grouted length to pile diameter ratio; grout compressive strength and elastic modulus; surface condition of steel tubes; and long-term shrinkage or expansion of grout. Based on their range of experimental research Tebbet and Belington [5] proposed the following equation which is a mean fit to the data (MATHEMATICAL EQUATION AVAILABLE IN FULL PAPER) where CL accounts for connection length, Cs is a surface roughness parameter, but is the ultimate bond stress, f c is the unconfined compressive strength of ground, K is the stiffness coefficient of the connection (MATHEMATICAL EQUATION AVAILABLE IN FULL PAPER) where E is the grout modulus of elasticity and L is the \routed length. The geometric parameters are defined in Fig. 1. (MATHEMATICAL EQUATION AVAILABLE IN FULL PAPER) Based on a study of data from 147 tests, Karsan and Krahl [6] recommended the following equation for the ultimate strength of the grouted connections which is the basis for the current API RP 2A [7]. (Equations 1 and 2 are in U.S. units.) A comparison of Eqs. 1 and 2 indicates that the API bond strength varies linearly with grout strength while Eq. 1 varies with the square root. In addition, tubular radial stiffness, K, and connection length coefficient, CL, are included in Eq. 1. Despite the large number of tests conducted on grouted connections, no systematic study has been conducted on the effect of moment loading, position of pile shear keys relative to the sleeve keys, and pile-sleeve eccentricity on axial capacity. Eighteen tests were conducted at The University of Texas to study these effects.