Title

Compressive behavior of grouted helical foundations

Date of Award

12-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Samuel P. Clemence

Keywords

Grouted, Foundations, Compression

Subject Categories

Civil Engineering

Abstract

The grouted helical foundation is a newly developed foundation system installed by constructing a grout shaft around the helical screw anchor. In this study, the load capacities of nine grouted helical foundations were interpreted from field load displacement curves by modified Davisson's method, Chin's method, Brinch Hansen's method and De Beer's method, respectively. Various analytical methods originally developed for pile foundations and helical screw anchors were also used to predict the load capacities of the nine grouted helical foundations. The predicted load capacities were compared with the interpreted values to evaluate the accuracy of each analytical method.

The exhumation of grouted helical foundations embedded in cohesionless and/or cohesive soils revealed a corrugated shape of the grout shaft. A series of laboratory direct shear tests were conducted to evaluate the interfacial shear strength between the corrugated grout shaft and sand. The shape effects of the grout shaft on the load capacity were examined.

An axisymmetric finite element model was developed to predict the compressive behavior of grouted helical foundations. The grouted helical foundation was assumed to act elastically, while the surrounding soils were simulated with the Mohr-Coulomb model. The soil-foundation interaction was modeled using "contact pair" and "tie constraint" incorporated in the finite element program ABAQUS. The feasibility of using the finite element method to predict the compressive behavior of grouted helical foundations was demonstrated by comparisons made between the finite element results and field full-scale load test data.

A design method was proposed to predict the load capacity of grouted helical foundations, taking into consideration the shape effects of the grouted shaft. The total load capacity of grouted helical foundations is assumed to be the sum of the skin friction capacity mobilized along the grout shaft and the end bearing capacity generated below helical bearing plates and the tip of the grout shaft. The accuracy of the proposed method was evaluated by comparisons made between the predicted results and field load test results.

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