الفهرس 
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Abstract
Skirted foundations is common foundation system for offshore structures, this system provides offshore structure with sufficient stability even though this structure rested on undesirable soil properties or subjected to harsh environmental loads and its also have economic advantage compared with other foundations systems.
This study concerned with investigation of the performance of skirted foundations in cohesive soil along life service. The performance of skirted foundation shall be monitored along life service, so numerical study analysis using FEM have been conducted to investigate the performance of skirted foundations in short term and long-term loading conditions. Two cases studies adopted for short term and long-term analysis.
The first case study dealt with a small scale field tests performed on bucket foundations carried out at at the Aalborg University clay test site, Denmark. The field case study was back analyzed by 2D axisymmetric model applying three constitutive models. The hardening soil model proved more accuracy in presenting real soil performance.
The second case study involves 1-D consolidation test conducted on soft clay soil samples. By using FEM “PLAXIS 2D”, axisymmetric model has been developed to simulate oedometer test. Two different constitutive models are applied to simulate the stress-strain relationship of the soft clayey soil .The results from Soft soil model are more converge to laboratory test results. This model have been adopted for investigation consolidation analysis of skirted foundations.
The parametric study was performed to investigate the bearing capacity and consolidation response of circular and strip skirted foundations subjected to uniform and non uniform loads. Many parameters were investigated in the performance of skirted foundations such as: embedment depth ratio, skirt roughness and skirt inclination.
6.2 Conclusion
Based on the results of conducted analyses for different dimensions, loading conditions as well as under short and long term for both smooth and rough skirted footings, following conclusions and recommendations can be summarized:
1- The Hardening soil model give better results in simulating the Overconsolidated clay and the Soft soil model give good results in representing the normally consolidated clay.
2- The Hansen 80% criterion method was found to be an appropriate method to detect the failure load from the calculated load settlement curve applying finite element method to model the performance of skirted footing.
3- The loading transfer mechanism in skirted foundations are similar to loading mechanism in pile foundations in which the bearing capacity of foundations depends on end bearing below base plate and at skirt tip level and depends also on skin friction generated around skirts.
4- Increasing embedment depth improves the bearing capacity of skirted foundations under both centric and eccentric inclined loads and it also reduces the settlement of foundations.
5- The settlement performance as well as the bearing capacity of skirted foundation depends mainly on the load share taken by the skin friction. Therefore, the conventional methods to determine either the time consolidation and/or the bearing capacity of skirted foundation overestimate the time of consolidation and underestimate the bearing capacity of the skirted footings.
6- The bearing capacity of rough skirted foundation under both centric and eccentric inclined loads are greater than those in smooth skirted foundations, especially with increasing embedment depth.
7- There are a converge between bearing capacity of skirted foundations and buried foundation at same embedment depth.
8- Increasing skirt inclination angle provides the foundation system with some resistance to the foundation system against rotation and sliding under eccentric inclined loads.
9- The buildup excess pore pressure is largest at the bottom of the clay plug (skirt tip level).
10- The expected pore pressure generated blow base plate of rough skirted foundations are much lower than those in smooth skirted foundations , especially with increasing embedment depth due to skirts roughness resistance due to skin resistance.
11- The non-uniform distribution of excess pore pressure which generated below base of strip skirted foundations subjected to eccentric inclined load are reduced and transformed to uniform pore pressure with increasing the embedment depth and skirt roughness.
12- The immediate settlement of rough skirted foundations are more reduced with increasing the embedment depth compared with smooth skirted foundations.
13- The consolidation degree of rough skirted foundation are more faster compared with smooth skirted foundations especially with increasing the embedment depth.
14- The consolidation settlement of rough skirted foundations are significantly less with increasing embedment depth compared to smooth skirted foundations.
15- The consolidation settlement rate is much faster in rough skirted foundation compared with smooth skirted foundation especially increasing the embedment depth.