Scour Protection of Submarine Pipelines Using Ionic Soil Stabilizer Solidified Soil

A novel scour protection approach for pipeline using the Ionic Soil Stabilizer (ISS) solidified soil was proposed in this study. The ISS-solidified slurry can be poured adjacent to the pipeline immediately after it was placed, or in the growing scour holes. In the present study, the first type was utilized as the scour protection layer around the pipeline. A series of laboratory flume tests were conducted to validate the protective capacity of ISS-solidified slurry for the pipeline in waves and combined waves and current. Then, the scanning electron microscope (SEM) tests and pore size tests were carried out, respectively, to investigate the mechanism of ISS-solidified slurry for scour protection around the pipeline. Finally, the effects of the ISS-solidified layer for liquefaction stability of non-cohesive subsoil were evaluated. The results indicated that the ISS-solidified slurry is a reliable, economic approach for scour protection around pipelines in the ocean environment. It is noteworthy that if a non-cohesive soil layer underlies the ISS-solidified slurry, it is vulnerable to suffer accumulated liquefaction due to the dense crust structure of the ISS-solidified layer, so the adverse effects for accumulated liquefaction should be considered carefully due to the set of the ISS-solidified layer.

Breaking-wave induced pressure and acceleration on a clifftop boulder

The movements of some massive ( ${O}(100)\ \textrm {t}$ ) clifftop boulders, once thought to have been caused by tsunami, have been reattributed to storm waves in several recent papers. However, the precise wave-impact modes and transport mechanisms are unknown. We present preliminary linear acceleration, pressure and displacement data recorded by a $1\,{:}\,30$ scale clifftop boulder impacted by a focused breaking wave in a laboratory flume. The 8 kg boulder was placed atop a 0.25 m high platform and struck with a breaking wave of 0.34 m amplitude. Wave focus position was varied from 0.8 m fore of the platform to 0.27 m aft of the platform to alter the breaking crest shape and wave impact type while maintaining total wave spectral energy. Pressure and acceleration time series measurements from within the boulder show distinct impact types across focus positions. All impacts produced boulder displacement, ranging from 5 mm to 42 mm (0.15 m to 1.3 m at full scale, assuming Froude scaling). The largest boulder pressures were recorded when the wave crest and trough struck the boulder at the same position (flip-through). The largest boulder displacements were measured when high pressures and long impact durations occurred simultaneously and wave focusing was close to flip-through.

Protection and Guidance of Downstream Moving Fish with Electrified Horizontal Bar Rack Bypass Systems

Horizontal bar rack bypass systems (HBR-BS) are characterized by a horizontal bar rack (HBR) with narrow clear bar spacing of 10–20 mm and an adjacent bypass (BS) to efficiently protect and guide downstream moving fish at water intakes. The small bar spacing may lead to operational challenges, such as clogging and high head losses. This study investigated whether combining an HBR with a low-voltage electric field (e-HBR) allows one to increase the clear bar spacing while maintaining a high standard of fish protection and guidance efficiency. To this end, an HBR-BS with 20 mm bar spacing and an e-HBR-BS with 20 and 51 mm bar spacing were tested with spirlin (Alburnoides bipunctatus) and European eel (Anguilla anguilla) in a laboratory flume. The racks were electrified with 38 V pulsed direct current. The protection efficiency of the e-HBR with 51 mm was 96% for spirlin and 86% for eels, which are similar results to those of the HBR with 20 mm. Some eels passed through the e-HBR, but only when they were parallel to the rack. Fish injuries of variable severeness due to the electrification were observed. The results highlight the potential of hybrid barriers for the protection of downstream moving fish. However, fish injuries due to electricity may occur; and reporting applied voltage, electrode geometry, resulting electric field strength and the pulse pattern of the electrified rack setup is necessary to ensure comparability among studies and to avoid injuries.

An ensonified bubble curtain blocks 4 species of invasive carp in a laboratory flume but also deters other fish, while sound alone is less effective overall and does not target carp

Four species of invasive carp from Asia are advancing up the Mississippi River through its locks and dams and threatening to damage to its ecosystems. It has been hypothesized that sensory stimuli could be projected into locks to block the movement of these carp. Sound has garnered attention because carp are hearing specialists, so they might be targetable. A recent study demonstrated that when a broadband cyclic sound was projected into an air curtain to create an ensonified bubble curtain (EBC), it was especially effective at blocking bighead and common carp and less effective at blocking a native species that lacked hearing specializations, while sound alone was generally less effective. However, whether an EBC might be similarly and uniquely effective at blocking all species of carp, and what its effects might be on other fishes in general, has not yet been addressed. To answer these questions, this study examined the responses of 10 species of fishes including 4 carps, 2 native hearing specialists, and 4 native non-specialists in a darkened laboratory flume while either a cyclic sound was played on its own or projected into an air curtain. The EBC blocked all 4 carps 9297% of the time without habituation, but 5 native fish were also partially blocked. In contrast, sound alone only blocked 2 carps and affected the other fishes in ways not related to their hearing abilities. An EBC appears well suited to blocking carp invasions, especially if native fish movement is a secondary concern.

Turbulent Flow through Random Vegetation on a Rough Bed

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

Laboratory Investigation of Geobag Revetment Performance in Rivers

Geobag (sand-filled geotextile bags) revetments have recently emerged as long-term riverbank protection measures in developing countries; however, their performance is still not well understood. The hydraulic stability of geobag revetments used for riverbank protection has been studied within an extensive laboratory programme to improve our understanding of the complete failure processes of geobag revetments. A 1:10 scale distorted physical model was tested in a laboratory flume, comparing a range of different construction methods and revetment side slopes, subjected to different flow loading. The results indicate that whilst failure mechanisms are highly dependent on water depth and revetment slope, the construction method had no noticeable impact. It was thus concluded that the dominating factor is the friction between individual geobags, which itself is dependent on bag longitudinal overlap rather than a specific construction method.

Impact of the Weir Slit Location, the Flow Intensity and the Bed Sand on the Scouring Area and Depth at the Dam Upstream

A total of 48 experiments were conducted to investigate the impact of slit weir dimensions and locations on the maximum scour depth and scour area created upstream. The slit weir model was a 110 mm slit opening, and it was installed at the end of the working section in a laboratory flume. The flume was 10.0 m long, 30 cm wide, 30 cm deep, and almost middle. It includes a 2 m working section with a mobile bed with 110 mm in thickness. In the mobile bed, two types of nonuniform sand (with a geometric standard deviation of 1.58 and 1.6) were tested separately. The weir dimensions and location were changed with flow rates. Then dimensions of the slit weir were changed from 60 x 110 mm to 60 x 70 mm (width x height), while the location of the slit weir was changed from the center of the flume to its side. Finally, the flow rates were changed from 2.6 to 8 l/s. The maximum value of scour depth and scour area was recorded 72 mm and 32357 mm2 when the slit height, the flow rate, D50 of the movable bed were 110 mm, 8 l/s, 0.3 mm, respectively.