이론적·수치해석적 접근을 통한 월류 시 제방도로 파괴원인 규명

Abstract

Rising sea level by global warming and rising water level by heavy rain and wind during typhoon or storm cause overflow on levee and sometimes lead to damage in the sea levee structures.

In particular, until now the results of the field surveys on levees failure show that the failure of the crown and scouring of the toe at the landward by overflow is the most representative example of levee failure patterns. And these destructions of levees are accompanied by the destruction of the built road on levees. Thus, many researches have already been done to understand the failure mechanism of levees with the laboratory model experiments and numerical model analyses. The numerical analyses were not included the levee structure and its surrounding ground and mainly focused on the hydraulics analysis.

In this study, with a view to complement the existing researches, the destruction mechanism of levee by overflow on a mound-type levee roads (such as the Saemangeum seadike road) is investigated with the theoretical approach and the numerical analysis, which have not been accessed yet.

Theoretical approach proposes a solution that can specifically compute the water pressure and velocity which are the causes of the destruction on the mound type levee road during overflow. Numerical analysis investigates the hydraulic characteristic of overflow and their effect on geotechnical characteristics on levee structure itself and its surrounding ground. The following approach is adopted.

First, theoretical solution developed by in condition of critical state flow and Bernoulli’s equation can determine the pressure and flow velocity at the vicinity of crown and toe of the levee. And then, this is confirmed through comparison with the existing hydraulic model experiment result and 2D-NIT numerical analysis result.

The results estimated by 2D-NIT are used as an input data in FLIP(Finite element analysis LIquefaction Program) model for investigation of time series dynamic responses in levee and ground such as excess pore water pressure, displacement, and effective stress path.

As a result, if the overflow depth increases, negative pressure increases at the vicinity of crown, meanwhile a significant amount of positive pressure increases at the toe and slope. Flow velocity also is changed by the overflow depth. The negative pressure induces a levee road failure at the vicinity of the crown and the positive pressure and flow velocity induce the liquefaction on the slope and ground near the toe of levee.

Therefore, in order to reduce the negative pressure at road crown, this study was proposed the increasing radius of the curve at the road shoulder. Also, in order to prevent road's ground liquefaction and slope's scouring by overflow, this study was proposed to assess the liquefaction of the levee material, build foundation block at the toe of the levee and cover the slope at the landward like covering layer at the seaward slope.