When domestic sewage and rainwater runoff are discharged into a single sewer pipe, it is called a “combined sewer system.” The sewage design standards in Korea specify the flow velocity based only on the volume of rainfall; therefore, sedimentation occurs on non-rainy days owing to the reduced flow rate and velocity. This sedimentation reduces the discharge capacity, causes unpleasant odors, and exacerbates the problem of combined sewer overflow concentration. To address this problem, the amount of sewage on non-rainy days, not just the volume of rainfall, should also be considered. There are various theories on sedimentation in sewer movement. This study introduces a self-cleansing velocity based on tractive force theory. By applying a self-cleansing velocity equivalent to the critical shear stress of a sand particle, sedimentation can be reduced on non-rainy days. The amount of sewage changes according to the water use pattern of citizens. The design hourly maximum wastewater flow was considered as a representative value, and the velocity of this flow should be more than the self-cleansing velocity. This design method requires a steeper gradient than existing design criteria. Therefore, the existing sewer pipelines need to be improved and repaired accordingly. In this study, five types of improvement and repair methods that can maximize the use of existing pipelines and minimize the depth of excavation are proposed. The key technologies utilized are trenchless sewer rehabilitation and complex cross-section pipes. Trenchless sewer rehabilitation is a popular sewage repair method. However, it is complex because the cross-section pipes do not have a universal design and require continuous research and development. In an old metropolis with a combined sewer system, it is difficult to carry out excavation work; hence, the methods presented in this study may be useful in the future.

If sewage flows for an extended time at low velocities, solids may be deposited in the sewer. Sufficient velocity or tractive force should be developed regularly to flush out any solids that may have been deposited during low flow periods. This study aims to evaluate the periods (T) during which sewage flow greater than the minimum tractive force maintains on a spot in sewer pipe system with lower tractive force or lower velocity than expected in the design step, when a storage tank installed in a place upsteam pours water into the sewer. The effect to T of design factors of storage tank and sewer pipes was evaluated assuming the uniform flow in sewers. When the area of orifice in the storage tank is 0.062 ㎡(or 0.28 m diameter), the maximum T of 31sec was maintained using the usually used preset range of values of several design factors. As the horizontal cross section of storage tank and water depth of storage tank and roughness in sewers increase, T linearly increases. Also, T linearly decreases as the diameter of a sewer pipe increases. Although T gradually decreases as the sewer pipe slope decreases to around 0.005, T decreases sharply when the slope is less than 0.003.

본 연구에서는 고속수로에서 변위센서를 이용하여 소류력 측정장치를 개발하였다. 최근 강우강도 및 홍수발생빈도의 증가로 제방, 고수부지, 저수로 등의 유실피해가 발생하고 있다. 이와 같은 문제점을 보완하기 위하여 호안블록 등의 다양한 보호공법이 적용되고 있다. 호안공법 및 호안공법 재료의 수리적 안정성 분석을 위해서 소류력에 대한 평가는 필수적이다. 대부분의 소류력 측정은 간접적인 방법으로 유속측정을 통하여 계산되어져 왔다. 하지만 하상유속을 정확히 측정하는 것은 매우 어려운 일이며 평균 소류력을 사용하여 수충부, 비수충부 등 구간별 소류력 분석 등에 대한 구체적인 연구가 미흡한 실정이다. 개발된 소류력 측정장치를 이용하여 공법 및 재료에 대한 정량적이고 객관적인 한계 소류력이 제시되면 하천 피해 절감과 과대 및 과소 설계를 방지 할 것으로 기대된다.

호안은 제방을 보호하기 위하여 제방법면에 설치되는 구조물로써, 국내·외 설계기준에 의하여 호안을 설계할 때, 하상과 호안법면에서의 최대 소류력을 산정하여 제방 사면에 평균적인 개념으로 적용하고 있다. 제방 사면의 허용소류력을 산정하는 경우에는 비점착성 토사를 기준으로 사면의 흘러내림을 고려하지만, 본 연구에서는 0 <Φ<90°의 경사를 갖는 점착성 제방 단면의 구간별 소류력 공식을 제안하였으며, 호안의 식생밀도와 공법 재료 변화에 따른 허용소류력을 산정하였다. 구간별 소류력을 산정하기 위하여 길이 20m, 폭 2m의 개수로를 설치하였고, 유량 조건을 변화하면서 수리모형실험을 수행하였다. 제방 사면의 구간별 허용소류력을 산정한 결과 호안 재료 변화에 따라서는 조도가 큰 공법의 허용소류력이 가장 크게 산정되었으며, 식생밀도에 의한 영향으로는 식생이 있는 경우 저항에 의하여 허용소류력이 증가되었지만, 밀도변화에 의하여는 큰 차이가 나타나지 않았다.

Revetment Mattress/Filter is the porous structure filled fillers in meshed structure so that it can use the fillers of various sizes and form various pores. The porous structure of the Mattress/Filter increases drainage so that it decreases the energy and velocity of flow therefore the tractive force is decreased and the erosion of revetment is mitigated. The filler of Mattress/Filter uses gravels, waste concretes and slags so that the surface is rough and the roughness coefficient increases and the increase of the roughness coefficient decreases flow velocity and tractive force. On the other hand Mattress/Filter and vegetation are combined so that the increase of roughness coefficient and flow velocity still more progress therefore the effect of decrease of tractive force is increased after a few months have passed since the Mattress/Filter is constructed so that the vegetation is developed and be stabilized. The vegetation channel of Mattress/Filter is set up and the inspection comes into operation by varing flowrate and vegetation spacing to examine these characters of the Mattress/Filter. The coefficent of flow velocity U/U*' is decreased exponentially as vegetation desity aH' or λ is increased and the coefficient of friction f is increased as vegetation desity aH' is increased but decreased as the coefficent of flow velocity U/U*' is increased. The effective tractive force F0 is decreased exponentially as the vegetation desity aH' is increased. From the inspection the results are obtained that the porous and vegetation structure of the revetment Mattress/Filter system increases the coefficient of friction of revetment so that flow velocity and effective are decreased therefore greatly contributes the stability of the revetment.