A Slip-Force Device for Maintaining Constant Lateral Pressure on Retaining Structures in Expansive Soils

Abstract

Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means have been studied to tackle problems associated with expansive soils. The majority of the methods are based on treatment of the soils. While the methods may be effective in some cases, their limitations are also obvious: The treatment normally involves complex processes and may not be eco-friendly in the long run. In many cases, the effectiveness of the treatment is uncertain. A retaining system that maintains a constant lateral pressure is proposed, which consists of three components: the retaining sheet, the slip-force device and the bracing column. The retaining sheet bears the pressure exerted by expansive backfills and is not embedded into the soils. Placed between the retaining sheet and bracing column, the slip-force device permits displacement of the retaining sheet but keeps the force on the sheet and the bracing column constant. The governing equation of the motion of the piston in the slip-force device is derived and a numerical simulation of a practical case is conducted based on the derived governing equation. Numerical results show that as the expansive soil swell, the spring force will increase and the piston will move accordingly. When the pressure of the oil in chamber reaches the open threshold of the unidirectional relief valve, the valve will open and the spring force and the oil pressure in the chamber will keep constant. The results also show that some parameters, such as damping ratio, have very slight influences on the device behavior, say 2 × 10-6 or even 4.8 × 10-9. Theoretical and numerical studies prove the effectiveness of the proposed retaining system.