Analysis of Different Flow Regime on Spillway Stepped Chute

The United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) estimates that nearly half of the small watershed dams constructed with their assistance will reach the end of their planned service life within the next 10 years. While many of these structures were originally built in rural environments, urban communities have encroached upon these structures over the years, making it difficult to address issues such as the maintenance of adequate spillway capacity to meet current dam safety standards. The urban infrastructure surrounding these structures limits the options available for dam rehabilitation. For instance, raising the dam or widening the existing auxiliary spillway to increase spillway capacity is often not a viable option due to land right constraints or changes in topography. Therefore, one of the more popular choices for increasing spillway capacity is the use of roller compacted concrete (RCC) stepped spillways. Two advantages of RCC stepped spillways are that they can be placed over the top of the dam and that they can provide considerable energy dissipation within the spillway chute. When placing an RCC spillway over an existing embankment dam, it is often desirable for the width of hydraulic control section to be greater than the width available to outlet the flow into the downstream channel. A generalized study utilizing a three-dimensional, 1:22 scale physical model was conducted to evaluate the influence converging training walls have on the flow characteristics on a stepped spillway. Vertical walls having convergence angles ranging from 0 degrees to 70 degrees were tested in conjunction with a spillway having a chute slope of 3(H):1(V) and a prototype step height of 0.3 m (1 ft). Water surface profiles in the central area of the chute and along the walls were collected and analyzed for each spillway configuration. Results of the study are presented in a format that will assist engineers in determining the required wall height for this type of a converging chute spillway.

Uncontrolled overtopping during flood events can endanger embankment dams. Erosion of the downstream slope and scouring of its base caused by the high velocity and energy of the overflow can indeed lead to breach formation until complete failure. In this context and faced with the important number of overtopped embankment dams to be rehabilitated, since the early eighties, researchers have investigated surface protection solutions for downstream slope. Overlays against erosion such as seeded goetextile or cable-tied cellular concrete blocks, are not sufficient. In fact, they can resist only short events with low discharge and velocity. Solution to overcome more severe overflow lies in overlays which dissipate flow energy along the downstream embankment slope. Conventional steps resulting from Roller Compacted Concrete (RCC) techniques fulfill efficiently this challenge. However, flows over steep stepped chutes are quite complex, characterizing by great aeration, high turbulence and confused wavy free surface. Then, most of hydraulic studies of such flows are performed on physical model. Yet, understanding and definition of flow behaviour and accurate approach to estimate energy dissipation are still lacking. General guidelines of hydraulics of aerated flows over stepped macro-roughness chutes and for optimal design of protection overlay remain confusing. To contribute to reduce these uncertainties, experimental study of flow over stepped chutes equipped with macro-roughness elements is performed in a laboratory gated flume for mild ( 1:7H : 1V ) and weak ( 3H : 1V ) chutes. Thus, they are representative of the range of embankment dams and spillways slopes. Three types of stepped macro-roughness overlays are assessed, namely rectangular conventional steps, steps equipped with endsills fixed on their nose over all the flume width and steps equipped with rectangular spaced blocks. Endsills overlays were characterized with different longitudinal distributions whereas blocks overlays consisted in different transverse patterns. Tests were conducted for the three nappe, transition and skimming flow regimes. Results can be extrapolated to 1/5 to 1/15 scaled prototypes using the Froude similarity with negligible scale effects. Flow depth, local air concentration and longitudinal velocities are measured with a double fiber-optical probe. Pressures at macro-roughness faces are taken with piezo-resistive sensors. Sequent depths of the hydraulic jump forced in the stilling basin at the flume base are measured with ultrasound sensors. Thus, this experimental phase of the thesis has allowed: to define flow parameters (regimes, depths, velocity and air concentration distributions, hydrodynamic forces) for tested overlays, to highlight that air-water flow depth is divided into: a rough boundary layer influenced by shear stress and by drag form (macro-turbulence) caused by macro-roughness, a homogeneous aerated layer which represents the main portion of flow involved in energy dissipation mechanism, a free surface layer which must be considered in the side walls design, to stress that energy dissipation is mainly a question of drag losses, to validate indirect method of hydraulic jump for energy dissipation estimation, to estimate relative energy loss for several stepped macro-roughness overlays. Tests finally show that an optimal alternative to dissipate the overflow energy during an overtopping event consists in spaced blocks, with transverse space larger than the width of block and fixed alternately on conventional steps. However, experimental results remain related and limited to their tested domains. Then, in order to provide more general governing equations of aerated flows over macro-roughness stepped chutes, a numerical modeling of two phase flows over conventional stepped flume was performed in collaboration with the Laboratory of Applied Hydrodynamics and Hydraulic Constructions at University of Liege. A quasi-2D numerical model based on the finite volume method was developed. It consists in applying the classical depth-averaged simplified Navier-Stokes equations (viscosity and Coriolis terms neglected) to a 1D incompressible air-water mixture flow over mild and steep slopes with a stepped topography. Self-aeration process is modeled by a transport equation of depth-averaged air concentration whereas turbulent structures are indirectly implemented through the Boussinesq coefficient. This first 1D-approach of semi-theoretical description of aerated flow over steps is tested for a 30o gated stepped flume and a 52° crested spillway laboratory model. This numerical model leads to realistic results regarding mixture depth, mean flow velocity, air concentration and wave amplitudes of the flow free surface. Finally, on the basis of existing protections of embankment dams and previous studies, the present experimental and numerical results contribute to extend the knowledge of high velocity aerated flows over macro-roughness and to provide elements of guidelines to optimize stepped macro-roughness overlays for embankment dams safety.

Mechanistic and microstructural characteristics of roller-compacted concrete (RCC) produced from recycled asphalt pavement (RAP) and geopolymer cement binder (GPC) were evaluated and compared with mixtures produced from ordinary Portland cement (OPC). It was found that RCC using geopolymer binder exhibited higher unconfined compressive strength, modulus of elasticity, and flexural strength as compared to the mixture containing ordinary Portland cement. It was also discovered that the mechanical properties of the developed concrete depend on mixture constituents: sodium hydroxide molarity, the ratio of sodium silicate to sodium hydroxide, curing temperature, and gradation of RAP. The experimental results showed that RCC using geopolymer binder exhibited compressive strength, modulus of elasticity, and flexural strength in the range of 8.4–21.1 MPa, 18.3–35.0 GPa, and 2.9–4.1 MPa, respectively. On the other hand, RCC using 12% OPC presented similar mechanical strengths of 13.2 MPa, 32.8 GPa, and 3.32 MPa, respectively. Regression analysis was also performed to establish the relationship between mechanical characteristics and various mixture constituents. Morphological and microstructural analysis proved the formation of geo-polymeric compounds. Based on the mechanistic characteristics, the developed roller-compacted RAP-Geopolymer concrete could be used as a strong pavement base in composite pavement system or wearing course of low volume roads.

Approximately half of the over 11,000 small watershed dams designed and constructed under the supervision of the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) will reach the end of their planned service life within the next 10 years. Many of these dams have inadequate spillway capacity due to changes in hazard classification and revised dam safety laws. Urbanization of surrounding areas limits the rehabilitation options of these dams. Roller compacted concrete (RCC) stepped spillways provide an effective solution to this problem. Recent years have seen a growth in the research and application of RCC, but there are no readily available generalized guidelines. Research has been performed on converging spillway chutes with vertical training walls. Public safety, aesthetics, and construction efficiency suggest sloped training walls are often a more desirable option.

Roller Compacted Concrete (RCC) exhibits many characteristics of both asphalt and rigid pavements, but their use is restricted. Many reasons led to this decision, including the fact that RCC is a type of concrete mixture that requires a specific consistency. It should be firm enough to be compacted by a roller compactor but also have enough moisture to ensure even distribution. The lab-field performance difference of RCC is another reason for decreasing its use. The laboratory RCC mixes are prepared using the modified Proctor compaction method. Subsequently, specimens are fabricated utilizing a vibratory hammer (VH) to evaluate their strength properties. Nevertheless, in the construction industry, pavement is built utilizing static, pneumatic, and vibratory rollers. Consequently, quality control is carried out by acquiring pavement samples and comparing them to laboratory samples. Each of these procedures employs different processes and energies, resulting in variations in field and laboratory behavior. In this investigation, some studies will be discussed about the RCC behavior under field and lab conditions using various design methods, such as the vibrating table (VH), vibratory table (VT), gyratory compactor (GC), and modified proctor (MP). These studies showed a difference in RCC mechanical and macroscale properties between laboratory compaction methods. For instance, VH specimens led to a higher evaluation, while GY specimens produced a less favorable estimation of the hardened properties observed in the field. While the MP and VT compacted specimens had a comparable structural arrangement to the field, they exhibited notable differences in terms of porosity and strength. Other studies revealed the essence of the curing stage in terms of RCC mechanical properties and indicated that some curing processes, like compound curing, may improve RCC performance.

The freezing and thawing durability of Norway's first Roller Compacted Concrete (RCC) dam was studied using the Scandinavian slab test (European/CEN test method for freezing and thawing durability) and ASTM C671 freezing dilation test. RCC with W/(C+FA) = 0.53 and FA/(C+FA) = 0.67 had some scaling and severe internal cracking in the wet freezing and thawing exposure of the slab test. The period of freezing and thawing immunity of RCC in the separated absorption and sealed freezing procedure of the dilation test was shorter than that of the conventional facing concrete (FC). Air entraining improved the RCC's freezing and thawing resistance, although not to be as good as that of FC with W/(C+FA) = 0.50 and FA/(C+FA) = 0 and 0.40. The FC had low scaling and no sign of internal cracking in the slab test, and the RCC's period of freezing and thawing immunity was longer than the 120 days of absorption used in the dilation test. The air voids of the RCC were coarser and the protective share of voids (= voids that are not filled by capillary suction but filled by 10 MPa pressure head) was lower than in the FC. Critical degrees of saturation were determined for service life prediction by combining dilation- and degree of saturation measurements.

This research aims to produce roller compacted concrete (RCC) using recycled aggregates (RAs) from construction and demolition waste (CDW) with low cement content. Previous research has confirmed that RA performs favourably when applied to a road base layer as a granular material or as a cement-treated granular material. In addition, previous studies have made progress in analysing the feasibility of using RCC with different types of RA, such as recycled concrete aggregate (RCA) and recycled pavement aggregate (RPA). Under this framework, the technical feasibility of using RCC with a 100% coarse RA incorporation ratio and low cement content in the base layer of light-traffic roads was determined. For that purpose, two series of RCC mixtures were produced with different cement contents: 150 and 250 kg/m3. Each series consisted of RCC mixtures with one natural aggregate (NG) and three different types of RA, specifically, one RCA and two mixed recycled aggregates (MRA), as coarse fraction. The percentage of ceramic particles in the RA ranged from 2.5% to 23.4%. The mechanical properties (e.g. the compressive strength, splitting tensile strength and elastic modulus) and drying shrinkage were studied in the RCC specimens produced. Mechanical properties were diminished as percentage of ceramic increased. These reductions in mechanical properties were near 30% for the RCC with RA with the greatest ceramic elements, respect to RCC with NG. The results support the feasibility of using RCC with a 100% coarse RA incorporation ratio and low cement content to form light-traffic-road base layers, such as residential streets, sidewalks and bike lanes.

The evaluation of calcium carbonate added and basalt fiber reinforced roller compacted high performance concrete for pavement

The sedimentary architecture of hyperpycnites produced by transient turbulent flows in a shallow lacustrine environment

This paper provides a resource for the design of Roller Compacted Concrete (RCC) for port pavements. Field and laboratory testing results on the properties of RCC, from mix design through field placement, have been collected and compared to existing published correlations. Issues related to the design and construction of RCC pavements, with an emphasis on port pavements, are discussed. Starting with a one-acre test area in 2002, the Virginia Port Authority (VPA) embarked on a large-scale pavement replacement project at Norfolk International Terminals (NIT) that, when complete, will include approximately 56 ha (140 acres) of RCC pavement. To date (Summer 2006), over 18 ha (45 acres) have been placed. The first 6 ha (15 acres) of RCC (including the test area) has been in use for over 3 years. The performance of the installed RCC has been excellent.

Investigation into stress wave propagation across interlayers existing in roller compacted concrete (RCC) under impact loadings

The knowledge of the behavior of any roller compacted concrete (RCC) dam and its foundation is gained by studying the service action of the dam and its foundation using measurements of an external and internal nature. The information by which a continuing assurance of structural safety of the RCC dam can be gauged is of primary importance. Similarly, the fact that the information on structural and thermal behavior and the properties of concrete that may be used to give added criteria for use in the design of future RCC dams is of secondary importance. Wide spread attention is now being given to the installation of more expensive instrumentation for studying the behavior of concrete dams and reservoirs and forecasting of any adverse trends. In view of this, the paper traces installation and need of the comprehensive instrumentation scheme implemented to monitor the structural and thermal behavior of 102.4 m high RCC dam constructed near Mumbai in India. An attempt is made in the present paper to emphasize the need to undertake an instrumentation program and evaluate their performance during construction and post construction stage of RCC structures. Few typical results, regarding the thermal and structural behavior of the dam, obtained through instrumentation installed at the dam site are presented and compared with the design considerations. The fair agreement is seen in the response observed through instrumentation with that governing the design criteria.

Roller-compacted concrete (RCC) is roller-compacted concrete that is quite stiff with zero slump. RCC pavement has several advantages because it is strong, dense, durable, and economical. The mixed materials used were water, coarse aggregate, fine aggregate, Portland Composite Cement (PCC), and superplasticizer (SPC). There were 12 cylindrical test specimens of diameter 15 cm and height 30 cm, with two variations of curing, namely plain water and sodium sulfate solution (Na2So4), and two variations of curing time, 14 and 28 days. The average compressive strength test value at 14 days of immersion in plain water and sodium sulfate solution is 37.35 MPa and 37.43 MPa. At 28 days of curing, the average compressive strength obtained soaked with plain water and sodium sulfate solution is 43.45 MPa and 54.02 MPa. Based on these results, the compressive strength of concrete cylinders immersed in sodium sulfate has increased compared to ordinary water immersion. The results of the overall compressive strength of the test specimens exceeded the plan compressive strength of 25 MPa, so the composition of the RCC mixture using PCC and SPC has the potential to be used as pavement material. Keywords: Roller Compacted Concete, Water, Compressive Strength, Sodium Sulfate Abstrak Roller- Competed Concrete (RCC) adalah beton yang dipadatkan dengan roller dan memiliki sifat yang cukup kaku dengan slump nol. Penggunanaan perkerasan RCC memiliki beberapa keunggulan karena kuat, padat, dan tahan lama serta ekonomis. Bahan campuran yang digunakan adalah air, kerikil, pasir, semen Portland Composite Cement (PCC) dan superplasticizer (SPC). Benda uji silinder diameter15 cm, tinggi 30 cm sebanyak 12 benda uji, dengan dua variasi perendaman yaitu air biasa dan larutan sodium sulfat (Na2So4) dan dua variasi lama perendaman yaitu 14 dan 28 hari. Nilai uji kuat tekan rata-rata pada perendaman 14 hari air biasa dan larutan sodium sulfat sebesar 37,35 MPa dan 37,43 MPa. Sedangkan pada perendaman 28 hari diperoleh kuat tekan rata-rata yang direndam dengan air biasa dan larutan sodium sulfat sebesar 43,45 MPa dan 54,02 MPa. Berdasar hasil tersebut, kuat tekan silinder beton yang direndam sodium sulfat mengalami kenaikan dibandingkan perendaman air biasa. Hasil kuat tekan keseluruhan benda uji melebihi kuat tekan rencana 25 MPa, sehingga komposisi campuran RCC yang menggunakan PCC dan SPC memiliki potensi untuk digunakan sebagai bahan pavement. Kata kunci: Beton RCC, Air Biasa, Kuat Tekan, Sodium Sulfat.

Carbon dioxide (CO2) injection in low permeability shale reservoirs has recently gained much attention due to the claims that it has a large recovery factor and can also be used in CO2 storage operations. This research investigates the different flow regimes that the CO2 will exhibit during its propagation through the fractures, micropores, and the nanopores in unconventional shale reservoirs to accurately evaluate the mechanism by which CO2 recovers oil from these reservoirs. One of the most widely used tools to distinguish between different flow regimes is the Knudsen Number. Initially, a mathematical analysis of the different flow regimes that can be observed in pore sizes ranging between 0.2 nanometer and more than 2 micrometers was undergone at different pressure and temperature conditions to distinguish between the different flow regimes that the CO2 will exhibit in the different pore sizes. Based on the results, several flow regime maps were conducted for different pore sizes. The pore sizes were grouped together in separate maps based on the flow regimes exhibited at different thermodynamic conditions. Based on the results, it was found that Knudsen diffusion dominated the flow regime in nanopores ranging between 0.2 nanometers, up to 1 nanometer. Pore sizes between 2 and 10 nanometers were dominated by both a transition flow, and slip flow. At 25 nanometer, and up to 100 nanometers, three flow regimes can be observed, including gas slippage flow, transition flow, and viscous flow. When the pore size reached 150 nanometers, Knudsen diffusion and transition flow disappeared, and the slippage and viscous flow regimes were dominant. At pore sizes above one micrometer, the flow was viscous for all thermodynamic conditions. This indicated that in the larger pore sizes the flow will be mainly viscous flow, which is usually modeled using Darcy's law, while in the extremely small pore sizes the dominating flow regime is Knudsen diffusion, which can be modeled using Knudsen's Diffusion law or in cases where surface diffusion is dominant, Fick's law of diffusion can be applied. The mechanism by which the CO2 improves recovery in unconventional shale reservoirs is not fully understood to this date, which is the main reason why this process has proven successful in some shale plays, and failed in others. This research studies the flow behavior of the CO2 in the different features that could be present in the shale reservoir to illustrate the mechanism by which oil recovery can be increased.

The flow over stepped chutes can be classified into skimming flow regime, transition flow regime, and nappe flow regime. The aeration efficiencies of the three flow regimes differ significantly due to the different air entrainment mechanisms in the nappe, transition, and skimming flow regimes. It is well known that aeration efficiency increases in the stepped chutes due to earlier self-aeration and slower flow velocities compared to the smooth chutes. This paper investigates the aeration efficiency of stepped chutes, particularly the effect of mean air concentration. The results showed that mean air concentration had a significant effect on aeration efficiency. They also showed that the aeration efficiency increased as the mean air concentration increased. A design equation was also developed to predict the aeration efficiency in the stepped chutes as a function of mean air concentration and roughness Froude number.