Hydrological Effects of Prefabricated Permeable Pavements on Parking Lots

Permeable pavements can infiltrate and reduce stormwater runoff in parking lots, but issues around long construction periods and proper maintenance still required proper research and further understanding. The application of precast concrete can help to solve this. In this study, precast concrete components were applied to the design of permeable pavements to form prefabricated permeable pavements. The laboratory study is one of the first to examine the hydrological effect of prefabricated pervious pavements in parking lots. Four kinds of permeable pavements were designed and manufactured. These had different materials (natural sand-gravel, medium sand) which comprised the leveling layer or different assembly forms of precast concrete at the base. Three scenarios of rainfall intensity (0.5, 1, and 2 mm/min) and three rainfall intervals (one, three, and seven days) were simulated using rainfall simulators. The initial runoff time, runoff coefficient, and runoff control rate of each permeable pavement were investigated during the process of simulating. Results showed that the initial runoff time was no earlier than 42 min, the maximum runoff coefficient was 0.52, and the minimum runoff control rate was 47.7% within the rainfall intensity of 2 mm/min. The initial runoff time of each permeable pavement was no earlier than 36 min when the rainfall interval was one day, whereas, the maximum runoff coefficient was 0.64, and the average runoff control rate was 41.5%. The leveling layer material had a greater impact on the hydrological effect of permeable pavements, while the assembly form of precast concrete had no significant effect. Compared with natural sand-gravel, when the leveling layer was medium sand, the runoff generation was advanced by 4.5–7.8 min under different rainfall intensities, and 7–10 min under different rainfall intervals. The maximum runoff coefficient increased with about 14.6% when the rainfall interval was one day. Among four kinds of permeable pavements, the type I permeable pavement had the best runoff regulation performance. The results revealed that all prefabricated permeable pavements used in this study had good runoff control performance, and this design idea proved to be an alternative for the future design of permeable pavements.

Nitrogen Migration and Transformation Mechanism in the Groundwater Level Fluctuation Zone of Typical Medium

Because of the nitrogen pollution problem in groundwater, the migration conversion mechanism of nitrogen in groundwater level fluctuations was analyzed. Technology and methods through indoor experiments and theoretical analysis were used to study coarse sand, medium sand, and fine sand groundwater level fluctuation in the aeration zone and saturated zone under the situation of nitrogen distribution characteristics, revealing groundwater level fluctuation with the nitrogen migration mechanism. The experimental results showed that the variation range of the nitrate-nitrogen (NO3−−N) concentration with the water level is medium sand > fine sand > coarse sand. The ammonium nitrogen (NH4+−N) concentration showed a downward trend after water level fluctuations, and there were more apparent fluctuations in coarse sand and medium sand. The nitrite nitrogen (NO2−−N) in coarse sand and medium sand first increased the water level and then gradually reached a balance. The sampling points below the water level in fine sand showed a downward trend with fluctuation of the water level, and then gradually reached equilibrium. The results provide a scientific basis for the remediation and treatment of soil and groundwater pollution.

Effects of Substrate Texture and Moisture Conditions on Ultra-High Performance Concrete and Silica Fume Concrete Overlay Bond Strengths

Direct tension tests were conducted to investigate the effects of substrate moisture conditions and texture on ultra-high performance concrete (UHPC) overlay bond strengths. Improper substrate surface preparation can result in inadequate bond strengths and, in severe cases, lack of bond. To demonstrate the importance of surface preparation, pull-off tests were performed on overlaid slabs that had two extreme substrate surface moisture conditions (saturated and dried) prior to overlay application. Saturated slabs had a tined, tined-light sand blasted, or tined-medium sand blasted substrate surface texture. Dried slabs had either a tined or an exposed aggregate surface texture. Saturated specimens with tined, tined-light sand blasted, and tined-medium sand blasted surface textures achieved average bond strengths of 0.924, 1.45, and 1.95 MPa, respectively. Dried substrate surfaced specimens had zero bond strength. Surface moisture conditions that ranged from saturated to dry were also investigated by allowing the substrate surfaces to dry for 15, 30, 45, and 60 minutes prior to application of an UHPC overlay. Tined-light sand blasted specimens with surfaces that dried for 15, 30, 45, and 60 minutes achieved average bond strengths of 2.86, 2.01, 1.59, and 0.165 MPa, respectively. Results showed tined-light sand blasted specimens with proper saturating achieved adequate bond strengths, and properly saturated, tined-medium sand blasted specimens produced excellent bond strengths. Results also exposed the drastic consequences of not maintaining a saturated substrate surface prior to overlay application and delaying overlay application up to 60 minutes can drastically reduce bond strength.

Evolution of a nourished sand beach under low wave energy in Thailand

Sand beaches are essential for coastal tourism in Thailand, but erosion narrowed some beaches significantly over the years. Pattaya is a famous resort near Bangkok in the upper Gulf of Thailand. The Pattaya beach is microtidal with the average tidal range of 1.5 m. The average significant wave height is 0.2 m and the wave energy is low. The beach was widened by placing 130 m3/m of medium sand along the shoreline length of 2.8 km between two terminal groins constructed in 2018. The bathymetry and topography were measured in 2015, 2019, and 2020. Approximately 14% of the placed sand in the water depth less than 2 m was lost after one year, as may be expected for nourished beaches. The bathymetry change in the water depth of 2-4 m varied alongshore. The sand volume change in this offshore zone beyond the surf zone was as large as that in the landward sand placement zone. The assumption of negligible profile changes seaward of a closure depth is not applicable to this beach during 2015-2020.

Stability and Settlement Analysis of a Lightweight Embankment Filled with Waste Tyre Bales over Soft Ground

The waste tyre-derived products, including whole tyres, tyre bales, shreds, chips, and crumb rubber, have begun to be used in various geotechnical applications. In particular, the use of tyre bales in the construction of a lightweight embankment on the soft ground has the potential to satisfy the demand for low-cost materials exhibiting such beneficial properties. This paper presents the comparison between the common medium sand-filled embankment and two tyre-baled structures with various granular interlayers: medium sand and rubber aggregate. To assess the efficiency of tyre bale application in soft ground conditions, two subsoils were considered in the study: sandy clay and silty clay. The stability and settlement analysis of embankments, as well as subsoil bearing capacity checking, were performed for all structural cases. Bishop’s limit equilibrium slicing method and the finite element method were used in the embankment and subsoil analysis. The comprehensive testing of tyre bales and filling materials was also carried out to obtain the set of parameters used in both analyses. The comparison allowed qualitatively assessing the effectiveness of using waste tyre bales as a filling of road embankment when founded on soft ground. The analysis revealed that the application of tyre bales generally enhanced the embankment stability, effectively reduced the embankment settlement, and reduced the normal stress in the subsoil. In the tyre-baled embankments, the slip surface is located mostly within the embankment slope, showing good rotational stability, independent of subsoil conditions.

Mapping of Sediment on the Waters Around Panjang Island, Banten Bay, Indonesia

This study was conducted to map the surface sediment conditions in the waters around Panjang Island, Banten Bay. The survey method was conducted in February 2015 by taking sediment samples using a grab sampler at 15 stations. Sediment analysis was conducted to determine the grain size using the granulometry method which was then processed using the KUMMOD-SEL software to obtain the composition and texture of the sediment. The results of processing sediment samples at each station obtained that the grain size of sediments in the waters around Panjang Island ranged from -0.7 to 2.6 in the phi (φ) scale. Sediment composition consists of sand and gravel, with sand dominance of 89.1 %. Sediment textural classification consists of only 4 categories i.e. very coarse sand, coarse sand, medium sand, and fine sand. In general, the pattern of sediment distribution follows the pattern of water depth, where fine sand occupies deeper areas. Meanwhile, medium sand dominates surface sediment distribution in the study area.

Seabed disturbance and sediment mobility due to tidal current and waves on the continental shelves of Canada

Waves and tidal currents can interact to produce strong seabed shear stress and mobilization of sediments on continental shelves. Modelled wave and tidal current data for a 3-year period were used in a combined-flow sediment transport model to simulate the seabed shear stresses and the mobilization of uniform medium sand on the continental shelves of Canada. The modelling results are presented to establish the first national framework of seabed disturbance and sediment mobility on the continental shelves of Canada. Strong waves and tidal currents on the Canadian continental shelves produce mean bed shear velocity >5 cm·s⁻¹. Medium sand can be mobilized >50% of the time over many areas on the shelves. The mobilization by tidal currents occurs over 36% and by waves over 50% of the shelf area, demonstrating that mobilization of sediments is dominated by waves on the Canadian continental shelves. Combined shear stresses due to wave and tidal current interaction further increase sediment mobilization to over 68% of the shelf area. The spatial variation of the relative importance of wave and tidal disturbances allows classification of the continental shelves into six disturbance types. Innovative Seabed Disturbance (SDI) and Sediment Mobility (SMI) indices are proposed to quantify the seabed exposure to oceanographic processes and sediment mobilization, incorporating both the magnitude and frequency of these processes. The proposed SDI and SMI, together with the disturbance type classification, can be used as standard parameters to best quantify seabed disturbance and sediment mobility on other shelves of the world.

Laboratory Plate Loading Test on Calcareous Sands from a Hydraulic fill Reef Island

The landforms and vertical strata distribution characteristics of Yongxing Island show that the reclaimed reef island is characterized by soft upper strata (calcareous sand) and hard lower strata (reef limestone). In this study, a series of plate loading tests was conducted to examine the influences of particle gradation, compactness, and moisture condition on the bearing mechanism and deformation properties of the calcareous sand foundation. When the foundation is shallowly buried, the relative density range corresponding to a calcareous sand foundation exhibiting local shear failure is narrower than that of a terrigenous sand foundation. For the same compactness, dry calcareous medium sand has a much larger bearing capacity and deformation modulus than dry calcareous fine sand. The effect of water on the bearing capacity of the calcareous medium sand is greater than the effect on calcareous fine sand. Its weak cementation and low permeability make the initial deformation of saturated calcareous fine sand slightly smaller than that under dry conditions. The stress dispersion angle of the calcareous medium sand foundation is 52°, which is larger than that of terrigenous sand. A larger stress dispersion angle leads to a higher bearing capacity and deformation modulus than those of terrigenous sand.

Ecomorphology of Ostrea edulis (Linnaeus, 1758) in Kuala Gigieng Waters, Aceh Besar District

Ostrea edulis is one of the most common types of meat oysters and is commonly consumed by people in Kuala Gigieng, but until now there is not much scientific information about this species. The purpose of this study was to describe the ecomorphology of Ostrea edulis in Kuala Gigieng waters. This research was conducted from August to September 2013 in Kuala Gigieng Waters, Aceh Besar District. The method used in this research is purposive sampling. Identification of samples based on shell morphological characteristics including the exterior and interior of the shell using a magnifier lamp. The results showed that Ostrea edulis found in Kuala Gigieng waters had round, rough, hard, thick and uneven shells. The two valves are also not the same size, where the left valve is more concave than the right valve which tends to be flat. This is a form of the adaptation pattern of Ostrea edulis in Kuala Gigieng which tends to have a medium sand and clay sand substrate with a fairly high predation from both natural and human predation.