Search Results (5)

Cemented Sand, Gravel, and Rock (CSGR) dams have traditionally used either Conventional Vibrated Concrete (CVC) or Grout-Enriched Roller Compacted Concrete (GERCC) for protective and seepage control layers in low- to medium-height dams. However, these methods are complex, prone to interference, and uneconomical due to significant differences in the expansion coefficient, elastic modulus, and hydration heat parameters among CSGR, CVC, and GERCC. This complexity complicates quality control during construction, leading to the development of Grout-Enriched Vibrated Cemented Sand, Gravel, and Rock (GECSGR) as an alternative. Despite its potential, GECSGR has limited use due to concerns about freeze–thaw resistance. This project addresses these concerns by developing an air-entrained GECSGR grout formulation and construction technique. The study follows a five-phase approach: mix proportioning of C₁₈₀6 CSGR; optimization of the grout formulation; determination of grout addition rate; evaluation of small-scale lab samples of GECSGR; and field application. The results indicate that combining 8–12% of 223 kg/m³ cement grout with 2–2.23 kg/m³ of admixtures, mud content of 15%, a marsh time of 26–31 s. and a water/cement ratio of 0.5–0.6 with the C₁₈₀6 parent CSGR mixture achieved a post-vibration in situ air content of 4–6%, excellent freeze–thaw resistance (F300: mass loss <5% or initial dynamic modulus ≥60%), and permeability resistance (W12: permeability coefficient of 0.13 × 10⁻¹⁰ m/s). The development of a 2-in-1 slurry addition and vibration equipment eliminated performance risks and enhanced efficiency in field applications, such as the conversion of the C₁₈₀4 CSGR mixture into air-entrained GECSGR grade C9015W6F50 for the 2.76 km Qianwei protection dam. Economic analysis revealed that the unit cost of GECSGR production is 18.3% and 6.33% less than CVC and GERCC, respectively, marking a significant advancement in sustainable cement-based composite materials in the dam industry. Full article

A suitable range of paste and mortar margins (α and β) to enhance compressive strength in Rich-Mix cemented sand gravel and rock (CSGR) material for application in CSGRD construction is critical. SL 678-2014 recommends margins > 1, which are specifically designed to fill the voids within the fine and coarse aggregates with paste and mortar, respectively, while allowing some excess for workability. However, the optimum ranges of values after 1 are inadequately determined, often leading to high efforts and time-consuming trial mixes that are not economical. This study evaluates two datasets to identify the optimal ranges of α and β margins for compressive strength development in Rich-Mix CSGR, aiming to achieve the compressive strength class C₁₈₀20, intended for use as cushion, protective, and seepage control layers in CSGRD. Using Pearson correlations, t-statistics, and p-values, the first dataset (7, 28, 90, and 180 days) showed weak correlations between paste margins and compressive strengths (coefficients 0.172 to 0.418, p-values > 0.05) and negligible relationships for mortar margins (coefficients −0.269 to 0.204, p-values > 0.05), affirming the contribution of other factors in the compressive strength development in CSGR. The second dataset (14, 28, 90, and 180 days) revealed significant positive correlations between paste margins and strengths at 14, 90, and 180 days (coefficients up to 0.850, p-values < 0.05). Mortar margins, however, negatively impacted strength (coefficients −0.544 to −0.628, p-values < 0.05), revealing the need to control the sand ratio. The optimal range of values was 1.05 ≤ α ≤ 1.09 and 1.15 ≤ β ≤ 1.25, with a water–binder ratio of 0.7~1.3, vibrating–compacted value (VC) of 2~8 s, and sand ratio of 18~35%. These findings highlight the significance of precise paste and mortar margin ranges in the compressive strength development of Rich-Mix CSGR. Full article

Levee failure due to nappe flow and subsequent erosion presents a significant challenge to flood protection infrastructure. This study evaluates the effectiveness of horizontal drainage layers, a common seepage control method, in mitigating these risks. While many traditional solutions to mitigate overtopping are costly and complex, horizontal drainage layers offer a promising and cost-effective alternative. These layers not only address seepage control but also manage nappe flow-induced erosion, potentially reducing construction and maintenance costs. Despite extensive research on their role in seepage control, a gap remains in understanding their effectiveness against overtopping-induced erosion, particularly in managing reverse flow. Existing studies often address seepage control or nappe flow erosion separately, overlooking the integrated impact of these layers. This study aims to address this gap by evaluating the performance of horizontal drainage layers under simulated overtopping conditions. The research involves two series of experiments, Series I: Focuses on newly built levees equipped with full (HD15L50 and HD25L50, where the thicknesses are 15 and 25 cm, respectively, with a horizontal drainage layer length of 50 cm and a crest length of 40 cm), partial length (HD15L40 and HD25L40), and short/reduced length (HD15L30 and HD25L30). The results showed that full-length layers reduce erosion inside the levee body and foundation by almost 100% and enhance levee stability due to their superior ability to dissipate hydraulic energy. Series II: Investigates practical solutions for retrofitting existing levees using shorter drainage layers with extended crests and gauzed sheets (HD15L15L30C60GH and HD25L30C60GH, where the thicknesses are 15 and 25 cm, the drainage length is 30 cm, and the crest is extended to 60 cm with gauzed sheets). Although shorter layers were less effective than full-length ones, extending the levee crest significantly improved their performance, achieving protection levels comparable to full-length layers, providing a valuable solution for upgrading existing levees. Overall, this study offers valuable insights by systematically evaluating and optimizing seepage control techniques. These findings can be directly applied to guide levee design, maintenance, and risk reduction strategies. This research contributes significantly to improving the resilience of levee systems against water pressure and ensuring their long-term stability. Full article

Effective seepage control is crucial for maintaining the structural integrity of Cemented Sand, Gravel and Rock (CSGR) dams. Traditional methods using conventional concrete (CVC) or grout-enriched roller-compacted concrete (GERCC) are costly and disruptive. This paper presents a novel technique for constructing the protection and seepage control layer in Cemented Sand, Gravel and Rock (CSGR) dams. The method involves grouting and vibrating the loosened Cemented Sand, Gravel and Rock (CSGR) material to create vibrated grout-enriched Cemented Sand, Gravel and Rock, which performs similarly to concrete. A new surface water stop structure has also been developed for the structural joints. Laboratory tests revealed that Cemented Sand, Gravel and Rock (CSGR) with a vibrating–compacted (VC) value of 2–6 s and a compressive strength of 4 MPa meets design requirements for medium and low dams when the slurry addition rate is 8–12%. The T-shaped surface water stop demonstrated a bonding strength of over 1.8 MPa, withstanding a water pressure of 1.6 MPa. This method, integrated with dam body construction, reduces material costs by about 50% and eliminates construction interference. Specialized equipment for this technique has been developed, with a capacity of 12 m²/h. Implemented in the Minjiang Navigation and Hydropower Qianwei Project and Shaping I Hydropower Station, it has shown significant economic, environmental and safety benefits, promoting sustainable dam construction. Full article

This paper presents test results of comprehensive laboratory and field-testing program efforts for the development of bioengineering solutions such as growing vegetation for protection of slopes from erosion and landslides in a tropical environmental setting. Saturated shear strength of soil was determined using direct shear tests and unsaturated soil properties, such as soil water retention curve (SWRC), were obtained using a computer-controlled hydraulic property analyzer (HYROP) system as well as a WP4C instrument. Climate data were obtained via field instrumentation and appropriate vegetation data were assumed to perform a finite element method-based transient seepage analysis and coupled slope stability analysis to test the potential of tropical hillslope to fail with and without vegetation over a period of one month. Results show that the factor of safety (FOS) for test slope considering case (a) the rainfall and bare ground, case (b) no rainfall with vegetation, and case (c) rainfall with vegetation were found to be 1.630, 1.763, and 1.650, respectively. Although FOS is marginally improved during storm events due to consideration of vegetation as compared to bare slope, this improvement in FOS is much pronounced during antecedent rainfall (i.e., long duration and small intensity) up to the first 26 days of analysis before the storm event (i.e., high intensity and short duration rainfall), which occurs on 27th day and can be instrumental in preventing slope failures. Similarly, the negative pore water pressure (i.e., matric suction) in the top layer is reduced for case (a) from −260 kPa to −40 kPa, increased for case (b) from −260 kPa to −320 kPa, and decreased for case (c) from −260 kPa to −60 kPa. The practical application of these findings is more applicable to the engineered slopes with vegetation during the dry season when the slope is more stable due to high FOS which, however, will need careful watering just to keep them healthy but prevent complete loss of developed matric suction resulting from root water uptake (RWU). In addition, the small improvement in FOS due to matric suction induced from RWU could play a key role in keeping the slope just stable during extreme storm events especially, when FOS of the bare slope is close to 1. To the best knowledge of the authors this is the first documented geotechnical study, using the tropical soil of Guam, which considers the hydro-mechanical effect of RWU-induced matric suction in slope stability analysis in a tropical setting. Full article