General deformation behavior of deep excavation support systems: A review

In geotechnical engineering, ground movement caused by excavations is a challenging issue. The excessive differential settlement generated by soil movement induced by wall deflection may cause damage to nearby structures. A detailed literature review on the general deformation behavior of deep excavation support systems is presented in this paper. Many factors, such as normalized horizontal deflection (δh-max/He%), vertical displacement (δv-max/He%), δvmax/δhmax ratio, settlement influence zone (Do), etc., can play significant roles in describing the deflection behavior of the excavation system. A descriptive analysis of the reviewed data was carried out. The concluded δh-max/He% values range between 0.17 to 1.5, with a mean value of 0.58 for soft clay, while in the case of sands and stiff clay soils δh-max/He% value ranges between 0.07 to 0.40, with a mean value of 0.20. δv-max/He% values range between 0.13 to 1.10, with a mean value of 0.49 for soft soil, while its value ranges between 0.02 to 1.10, with a mean value of 0.24 in the case of sands and stiff clay soils. The settlement influence zone (Do) reaches a mean distance of 2.3He, which falls within Do=1.5-3.5He in the case of soft clays, while Do reaches a mean distance of 2.0He and 3.0He in the case of sands and other stiff clay soils, respectively. The relationship between system stiffness and excavation-induced wall and ground movements was discussed. Unfortunately, the literature review offers limited data regarding system stiffness, the 3-D nature of excavation support systems, excavation processes, and time effects.

Influence of Spacing and Cross-Sectional Shaft of Screw Piles Group on Lateral Capacity

Although there are several high-capacity screw piles in use currently, there are few studies on their lateral performance. The aim of this study is to investigate the lateral behaviour of several models of screw pile group (1×2), (2×1), and (2×2) embedded in soft clay and extended to stiff clay under lateral static load. Three spacing between pile (1.5, 3, and 4.5) Dh (helix diameter) with a shaft diameter of 10 mm, single and double helix, and embedded length ratio L/d 40 were used. The results showed that increasing the number of the piles in the group had a larger effect, the lateral resistance of group (2×2) increase to about (2.5 and 3.2) times more than groups (2×1) and (1×2) respectively. While the increase of pile spacing in the groups from (1.5 Dh) to (3 and 4.5 Dh) increases the lateral resistance about 6-23% and 16-52% respectively. Also, the result showed that the screw pile with double helix gives an increase in lateral resistance about 3-8% from the single helix.

Experimental Study of the Bearing Capacity of Stiff Clay Overlying Sand with and without Geotextile Inclusion

The objective of this study is to investigate the potential benefits of using reinforcement inclusion to improve the bearing capacity of stiff clay over very loose to medium dense sand. Model load tests were performed on two layered systems, namely stiff clay over very loose, loose, medium dense sand with and without geotextile inclusion between the two layers and on stiff clay only. The load-settlement curves were plotted from the experimental test results, and the ultimate bearing capacity was obtained using Log – Log (L-L), Tangent (TIM), 0.1B and Hyperbolic (HYP) methods. Theoretical approaches were used to compute the ultimate bearing capacities of the tests without and with reinforcement. The test results have shown an increase in the ultimate bearing capacities due to increase in the relative densities of the bottom sand layer. The bearing capacity increased significantly with the inclusion of geotextile layer. The bearing capacity ratio (BCR) for the case of very loose sand as bottom layer was the highest compared to loose and medium dense cases. Load - settlement curve of the pure clay test plots above or is identical to the load - settlement curve of stiff clay overlying medium dense sand with geotextile layer. The maximum benefit for the geotextile inclusion was gained at large strain when the sand was very loose. The analytical methods were generally in good agreement with the experimental model test results obtained by the 0.1B method.