本篇延續程(2002)之研究，進一步引用Twu et al. (2001)之理論，採用多段式透水結構物作為堤趾護基，在海堤前方設置多段式不同孔隙率之透水護基，進而試驗研究分析不同護基長度、高度以及不同段式，對於護基後方海堤溯升之影響。結果發現：安置單段式護基於海堤前，其溯升值會隨孔隙率增加而減少。如海堤坡度為1：2，平均每增加△b/h=1，溯升會較無護基時分別下降1.1%~2.9%( A型護基，孔隙率=0.41)、1.1%~3.0%( C型護基，孔隙率=0.45)、1.5%~3.6%( D型護基，孔隙率=0.77)、1.6%~4.0%( E型護基，孔隙率=0.9)。海堤坡度改變為1：3，溯升值較小，但不會改變此現象。

若是將單段式護基改為雙段式，則會進一步減少溯升，在坡度1：2之海堤前，將單段式D型護基改變為雙段式F型（孔隙率1=0.77、孔隙率2=0.41）或G型護基（孔隙率1=0.77、孔隙率2=0.45），平均每增加護基長度△b/h=1，溯升會進一步下降約0.8%~1.5%。若是將單段式E型護基改變為雙段式H型（孔隙率1=0.9、孔隙率2=0.41）或I型護基（孔隙率1=0.9、孔隙率2=0.45）或J型護基（孔隙率1=0.9、孔隙率2=0.77），平均每增加護基長度△b/h=1，溯升會進一步下降約1.3%~2.2%。海堤坡度改變為1：3，溯升值較小，但仍會進一步分別下降約0.2%~1.8%、1%~3.5%。

若是將雙段式護基改為三段式，則溯升值會進一步減少，在坡度1：2之海堤前，將雙段式J型護基（孔隙率1=0.9、孔隙率2=0.77）改變為三段式K型（孔隙率1=0.9、孔隙率2=0.77、孔隙率3=0.41）或L型護基（孔隙率1=0.9、孔隙率2=0.77、孔隙率3=0.45），平均每增加護基長度△b/h=1，溯升會進一步下降約0.3%~1%。海堤坡度改變為1：3，則約進一步減少0.2%~2.3%。

結果顯示：利用孔隙材料當作海堤前之護基，孔隙率愈大愈能降低溯升值，且分段式不同孔隙率之護基較單段式為佳，段數愈多愈有效。

This paper is aimed to continue the efforts of Chen (2002), trying to verify the theory developed by Twu et al. (2001). This work is performed by conducting experimental tests on wave run-up over a seawall with various aprons installed in front of the seawall. The aprons are made of porous material with different length, height and number of slices. It is shown that the wave run-up over the seawall decreases with increasing porosity if a single-sliced apron is used.

However if a double-sliced is adopted to replace a single-sliced apron, the wave run-up can be reduced further. For instance, if an apron of double-sliced F-type apron (porosity(1)=0.77, porosity(2)=0.41) or G-type (porosity(1)=0.77, porosity(2)=0.45) is used rather than a single-sliced D-type (porosity=0.77) in front of the seawall with slope of 1:2, the wave run-up can be reduced by 0.8%~1.5% for an increase of △b/h=1. Similarly, if a double-sliced H-type (porosity(1)=0.90, porosity(2)=0.41) or I-type (porosity(1)=0.90,porosity(2)=0.45) or J-type (porosity(1)=0.90, porosity(2)=0.77) is used instead of a single-sliced E-type (porosity=0.9), then the wave run-up would be reduced by 1.3%~2.2% for an increase of △b/h=1. For a seawall with slope 1:3, the reduction in wave run-up would be 0.2%~1.8%、1%~3.5%, respectively in the pervious two cases。

Moreover, the wave run-up over the seawall can be further reduced if a triple-sliced apron is employed. For instance, if an apron of triple-sliced K-type (porosity(1)=0.9、porosity(2)=0.77、porosity(3)=0.41) or L-type (porosity(1)=0.9、porosity(2)=0.77、porosity(3)=0.45) is installed in front of a seawall with slope of 1:2. The wave run-up could be reduced by 0.3%~1% for an increase of △b/h=1, as compared to a double-sliced one (J-type). For a seawall with slope 1:3, the reduction in wave run-up would be 0.2%~2.3%.

The results show that by using the porous material as an apron in front of seawall, wave run-up over the seawall can be reduced and the reduced level is increased with the increase of porosity and the number of vertically-stratified slices.

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