The double row pile retaining wall called the double-wall system is an unpopular old method. However, the analysis results from the two case histories in Taiwan showed that double-wall could significantly reduce the maximum wall deflection by around 63% to 72%. The main reason why double-wall is unpopular is that the lateral deflection mechanism of the double-wall remains unclear. In this thesis, the two case histories were analyzed using three-dimensional finite element analysis. The factors that influence the wall deflection, such as soil-structure interaction, penetration depth, spacing between the front and rear piles, capping beam, strut, and piles’ inclination, were examined to measure the effect. Moreover, the back-analysis and exact analysis of partial composite stiffness were conducted to explain each component's function in the double-wall. The partial composite stiffness adapted from structural engineering theory successfully explained the lateral deflection mechanism of double-wall.

The capping beam is one of the important components of the double-wall. The case histories showed that the lack of the capping beam quality induced excessive wall movement. Moreover, the analysis presented that the double-wall without the capping beam can lose the integrity reflected by drastically decreasing the average composite stiffness.

In order to optimize the double-wall, there are several options, such as increasing the front and rear piles spacing, using capping beam and strut, and using inclined front piles. The analysis of the two case histories resulted in the maximum wall deflection reduction of more than 45% from a standard double-wall design. Therefore, the double-wall design has a large space for improvement and could be the solution of the low-cost support system for excavation in rural areas.

The double row pile retaining wall called the double-wall system is an unpopular old method. However, the analysis results from the two case histories in Taiwan showed that double-wall could significantly reduce the maximum wall deflection by around 63% to 72%. The main reason why double-wall is unpopular is that the lateral deflection mechanism of the double-wall remains unclear. In this thesis, the two case histories were analyzed using three-dimensional finite element analysis. The factors that influence the wall deflection, such as soil-structure interaction, penetration depth, spacing between the front and rear piles, capping beam, strut, and piles’ inclination, were examined to measure the effect. Moreover, the back-analysis and exact analysis of partial composite stiffness were conducted to explain each component's function in the double-wall. The partial composite stiffness adapted from structural engineering theory successfully explained the lateral deflection mechanism of double-wall.

The capping beam is one of the important components of the double-wall. The case histories showed that the lack of the capping beam quality induced excessive wall movement. Moreover, the analysis presented that the double-wall without the capping beam can lose the integrity reflected by drastically decreasing the average composite stiffness.

In order to optimize the double-wall, there are several options, such as increasing the front and rear piles spacing, using capping beam and strut, and using inclined front piles. The analysis of the two case histories resulted in the maximum wall deflection reduction of more than 45% from a standard double-wall design. Therefore, the double-wall design has a large space for improvement and could be the solution of the low-cost support system for excavation in rural areas.

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