Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

El Naggar, M. Hesham

Abstract

The pressure grouted helical pile (PGHP) is an innovative pile foundation system that allows a significant increase in the helical pile capacity with some additional cost. The pile is constructed by applying pressurized grout during the installation of a closed ended helical pile through two grout nozzles welded to the hollow pile shaft. Torquing PGHP into the ground allows the grout nozzles to create a cavity around the pile shaft. The cavity then expands under the effect of pressurized grout and helix rotation. This thesis presents a comprehensive laboratory study and three-dimensional finite element analysis to investigate the effects of the different testing conditions, including grout nozzle configurations, soil properties, and grouting pressure on the shape and performance of PGHPs under monotonic axial and lateral loading.

The experimental program includes the installation of five un-grouted helical piles and seventeen PGHPs in loose, medium, and dense sand with two different grouting pressures; 480 kPa and 690 kPa. The piles were then tested under monotonic uplift, compression, and lateral loading. The results reveal a significant increase in the PGHP’s shaft resistance over the un-grouted helical pile due to the formation of a large diameter grout column, enhanced friction angle at the pile-soil interface, and increased lateral earth pressure around the pile shaft as a result of the cavity expansion (Δr) that occurred during installation. The shape and diameter of the created grout column depend on the nozzle configuration, the relative density of the surrounding sand (R.D), and the grouting pressure used during construction (Pg). An increase in the unit end-bearing resistance is also observed due to the densification of the supporting soil and the permeation of some grout into its voids during the pile construction. Moreover, PGHPs offer a significant increase in the lateral pile capacity due to the larger shaft diameter and the existence of a disturbed soil zone around the un-grouted pile shaft.

A three-dimensional (3D) finite element model was developed using ABAQUS software. The model was calibrated and verified using the experimental data set. A strong relationship was observed between Δr, Pg, and R.D. Finally, two equations are proposed to calculate the placement method coefficient (kmo) for the design of PGHPs in order to account for the influence of the novel installation technique (i.e. cavity expansion) on the surrounding soil.

Summary for Lay Audience

Pressure grouted helical pile (PGHP) is a new deep foundation system that involves grout injection under high pressure during the installation of a closed-ended helical pile with a hollow pipe shaft. The grout is injected into the surrounding soil through two grout nozzles welded to the pile shaft. Although PGHP is expected to be successful in many engineering applications with different soil conditions, it is not used in practice due to the lack of knowledge regarding the shape of the created grout column around the pile and its performance under different loading conditions.

A comprehensive investigation program was designed and implemented that included laboratory experiments and three-dimensional finite element (FE) modelling. The laboratory experiments comprised the installation of 5 small helical piles and 17 model PGHPs into cylindrical sand beds with different relative densities to represent loose, medium, and dense soil conditions. The PGHPs were installed with two different grouting pressures; 70 psi (480 kPa) and 100 psi (690 kPa). The piles were subjected to monotonic uplift, compression, and lateral load tests, then the PGHPs were extracted from the sand bed to provide a visual description of the created grout mass along their shafts. The pile load testing results revealed significant improvement in the axial and lateral resistances of PGHP over the conventional helical pile.

The commercial software ABAQUS (SIMULIA, 2013) was then used to simulate the laboratory experiments to further understand the load transfer mechanism and quantify the effects of the novel installation technique on the pile behavior. Following the calibration and validation of the created FE models with the experimental data, the models were used to analyze the PGHP performance under different testing (i.e. relative density and grouting pressure) and loading (uplift, compression, and lateral) conditions. The FE models were extended to simulate the response of full-scale PGHPs and full-scale conventional helical piles under monotonic compression loading considering different shaft and helix diameters. Finally, an approach was developed to allow practitioner engineers from estimating the PGHP capacity analytically.

Available for download on Wednesday, September 08, 2021

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