Assessment of Micropiled Rafts Performance under Pure Lateral Loading

A micropile is a small diameter “cast-in-situ” pile which was initially used to repair historic buildings. In this paper, a numerical analysis was conducted on the performance of micropiled rafts under pure lateral loading using the finite element modelling. The FEM was calibrated against full scale lateral and axial field tests. Numerous cases were analyzed to investigate the lateral performance of micropiled raft on soft clay soil underlain by a layer of dense sand. The factors that may affect its performance were considered such as: the micropiles spacing, the undrained shear strength and thickness of upper clayey soil layer. The lateral load response of the micropiled raft was assessed. Moreover, the variation of lateral load capacity of single free head micropile with the clay cohesion was evaluated. Then, the effect of the micropiles spacing on the group efficiency was studied. The group effect was found to be insignificant for spacing to diameter ratio larger than 2.31

The Effect of Jet Grouting on Enhancing the Lateral Behavior of Piled Raft Foundation in Soft Clay (Numerical Investigation)

Soft clay soils cannot usually support large lateral loads, so clay soils must be improved to increase lateral resistance. The jet grouting method is one of the methods used to improve weak soils. In this paper, a series of 3D finite element studies were conducted using Plaxis 3D software to investigate the lateral behavior of piled rafts in improved soft clay utilizing the jet grouting method. Parametric models were analyzed to explore the influence of the width, depth, and location of the grouted clay on the lateral resistance. Additionally, the effect of vertical loads on the lateral behavior of piled rafts in grouted clay was also investigated. The numerical results indicate that the lateral resistance increases by increasing the dimensions of the jet grouting beneath and around the piled raft. Typical increases in lateral resistance are 11.2%, 65%, 177%, and 35% for applying jet grouting beside the raft, below the raft, below and around the raft, and grouted strips parallel to lateral loads, respectively. It was also found that increasing the depth of grouted clay enhances lateral resistance up to a certain depth, about 6 to 10 times the pile diameter (6 to 10D). In contrast, the improvement ratio is limited beyond 10D. Furthermore, the results demonstrate that the presence of vertical loads has a significant impact on sideward resistance

Global sensitivity analysis in hydrological modeling: Review of concepts, methods, theoretical framework, and applications

Sensitivity analysis (SA) aims to identify the key parameters that affect model performance and it plays important roles in model parameterization, calibration, optimization, and uncertainty quantification. However, the increasing complexity of hydrological models means that a large number of parameters need to be estimated. To better understand how these complex models work, efficient SA methods should be applied before the application of hydrological modeling. This study provides a comprehensive review of global SA methods in the field of hydrological modeling. The common definitions of SA and the typical categories of SA methods are described. A wide variety of global SA methods have been introduced to provide a more efficient evaluation framework for hydrological modeling. We review, analyze, and categorize research into global SA methods and their applications, with an emphasis on the research accomplished in the hydrological modeling field. The advantages and disadvantages are also discussed and summarized. An application framework and the typical practical steps involved in SA for hydrological modeling are outlined. Further discussions cover several important and often overlooked topics, including the relationship between parameter identification, uncertainty analysis, and optimization in hydrological modeling, how to deal with correlated parameters, and time-varying SA. Finally, some conclusions and guidance recommendations on SA in hydrological modeling are provided, as well as a list of important future research directions that may facilitate more robust analyses when assessing hydrological modeling performance

Influence of Evaporation, Groundwater and Their Associated Model and Data Uncertainties on the Hydrologic Budget of Lake Nasser, Egypt (Invloed van verdamping, grondwater en geassocieerde model- en data-onzekerheden op de waterbalans van het Nassermeer in Egypte)

Evaporation losses and groundwater interaction of Lake Nasser were studied to determine the influence of both processes on the hydrologic budget of the lake. Lake Nasser, southern Egypt, is located in a hyper-arid region. Since evaporation is by far the most important factor in explaining the water losses from the lake, accurate estimation of the evaporation losses is essential to be able of better managing the lake resources. This research presents an update of previous evaporation estimates, making use of local meteorological and hydrological data collected from instrumented platforms (floating weather stations) at three locations on the lake: at Raft, Allaqi and Abusembel (respectively at 2, 75 and 280 km upstream of the Aswan High Dam). Results from seven conventional evaporation methods were compared with the values obtained by the Bowen Ratio Energy Budget method (BREB). The results of the BREB method showed that there is no significant difference between the evaporation rates at Allaqi and Abusembel. At Raft, higher evaporation rates were obtained, which were assumed to be overestimated due to the high uncertainty of the Bowen Ratio (BR) parameter. The average BR value at Allaqi and Abusembel was used to eliminate the overestimated evaporation. Several of the seven conventional methods showed substantial bias when compared with the BREB method. These were modified to eliminate the bias. For the daily time scale the Penman method yielded the best agreement with the estimates of the BREB method, while for the monthly time scale the best match with the BREB method was obtained with the Priestley-Taylor and the deBruin-Keijman methods. Differences in mean evaporation estimates of these methods with respect to the BREB method were found to be in the range 0.14 and 0.36 mm/d. All estimates were based on calculations at the daily time scale covering a 10 years period (1995-2004). As pointed out by various researches, variations in lake evaporation can have a significant impact on the energy and water budgets of lakes. For accurate water management under current and climate change conditions it is important to fully understand these variations. To this end a comprehensive 10-year analisis was conducted of the seasonal, intraseasonal, and interannual variations of the lake evaporation analyzing the meteorological data at Raft station to provide bi-weekly energy budget estimates of the lake evaporation rate. The mean evaporation rate for Lake Nasser over the study period is 5.88 mm/d, with a coefficient of variation of 63%. Considerable variability in evaporation rates is found on a wide range of timescales, with seasonal changes having the highest coefficient of variation (32%), followed by the intraseasonal (28%) and interannual timescales (11.6%; for summer means). Intraseasonal changes in evaporation are primarily associated with synoptic weather variations, with high evaporation events tending to occur during incursions of cold, dry air (due, in part, to the thermal lag between air and lake temperatures). At the other hand seasonal variations in evaporation are largely driven by temperature and net energy advection, but are out-of-phase with changes in wind speed. On interannual timescales, changes in summer evaporation rates are strongly associated with changes in net energy advection and show only moderate connections to variations in temperature or humidity. A qualitative identification and evaluation of sensitivity and uncertainty analysis in the context of the evaporation estimates from Lake Nasser was made using data collected at the floating station Raft and 12 evaporation models. Based on their approach the evaporation models were ranked in 5 classes, respectively the BREB approach, 3 energy-aerodynamic based methods, a mass transfer method, 2 temperature and 5 solar radiation-temperature approaches. State dependent parameter models were used to estimate the sensitivity indices of the different evaporation estimation methods at daily and monthly frequencies. A drastic reduction in the cost of the sensitivity analysis was obtained when coupled with efficient sampling methods, producing quasi Monte Carlo sequences (Latin Hypercube samples). Analysis of the sensitivity indices (Si) revealed that the energy and advective parameters (Qx and Qv) in the BREB method most strongly affect evaporation estimates. The most sensitive parameters for the energy-aerodynamic methods (Penman, Priestley-Taylor and the deBruin-Keijman methods) are the change in heat storage (Qx) and solar radiation. For the other methods the most sensitive parameters are solar radiation, air temperature and vapor pressure, but with lower sensitivities. After investigation of the first and second order sensitivity indices, it was found that the first-order sensitivity indices capture more than 90% of the total variance of the evaporation estimates. Interactions between input parameters were found limited with a maximum contribution to variance of less than 3.3% for daily frequency and less than 8.5% for the monthly frequency. Results indicated that many parameters in the 12 evaporation models could be fixed without appreciably affecting the output of these models. This helped to reduce the computational load of these models. The uncertainty results show that the Dalton group is subject to the highest error. The overall uncertainty ranged from 9% (BREB method) to 15% (mass transfer method) of the mean evaporation rate.The groundwater recharge from/or groundwater discharge to Lake Nasser is another significant factor to be considered in the analysis of the lake water budget. A cross sectionmodeling using the analytical solutions of Edelman (1947) was applied at 7 transects distributed over 4 geological cross sections to estimate groundwater heads and recharge from/or groundwater discharge to Lake Nasser. The cross section model, constrained by regional-scale groundwater flow and groundwater head data in the vicinity of the lake, was successfully calibrated to timeseries of piezometeric heads collected at the cross sections in the period 1965-2004. Inverse modeling using Edelman s analytical solution(s) (1947) yielded high values for the horizontal hydraulic conductivity in the range 6.0 to 31.0 m/day and storage coefficient in the range 0.01 to 0.40. The results showed the existence of a strong vertical anisotropy of the aquifer; the calibrated horizontal permeability is systematically higher than the vertical permeability (≈1000:1). The calibrated model was used to assess the temporal and spatial variations in the recharge from/or groundwater discharge to Lake Nasser. The analysis for the last 20-year period, 1985-2004, revealed that recharge from Lake Nasser reduced by 37% compared to the estimates for the first 20-year period, 1965-1984. In the period 1965-2004, seepage of Lake Nasser to the surrounding was estimated as 1.15 billion cubic meter per year. This led to a significant increase of the groundwater table. Variance-based sensitivity and uncertainty analysis on the Edelman results were conducted applying the quasi-Monte Carlo sequences (Latin Hypercube sampling). The maximum standard deviation of the total uncertainty on the groundwater table was 0.88 m at Toshka (west of the lake). The distance from the lake, followed by the storage coefficient and hydraulic conductivity, were identified as the most sensitive parameters.In this study, MATLAB® environment was selected for modeling the hydrologic budget of Lake Nasser. MATLAB® is a high-performance language for technical computing. The hydrologic budget of Lake Nasser is modeled using a lumped model approach. Similar flow items considered by preceding studies were also taken into consideration. These flow items include inflow, evaporation, groundwater lake interaction terms of through-flow and bank storage, and release. The developed model possesses several distinctive features such as a GUI, and forward and inverse modeling capabilities. An ordinary differential equation governs the water budget of Lake Nasser, which is a delay differential equation and is solved numerically using the Euler and the Runge Kutta methods. The forward model is linked internally to an optimization algorithm, the trust-region method, to optimize a least-square objective function to estimate optimum parameter values. Sensitivity coefficients required by the optimization algorithm are obtained using the variance based method. The results showed that the evaporation parameter and bank storage parameters are among the most sensitive parameters that greatly affect the model results. Data from 1968 to 1997 are used to obtain unknown model parameters. One of such obtained optimal values is the mean annual evaporation equal to 2.1 m/yr. The hydrologic budget of Lake Nasser is analyzed for the10-years study period. Evaporation is found to be the most significant component controlling the water budget. Changes in the evaporation rates indeed can substantially alter the lake stage. Groundwater fluxes (bankstorage and leakage) are also significant, but less important than the evaporation, which is found to be the major outflowcomponent of the lake water budget.status: publishe

Analysis of the climate variability on Lake Nasser evaporation based on the Bowen ratio energy budget method

Variations in lake evaporation have a significant impact on the energy and water budgets of lakes. Understanding these variations and the role of climate is important for water resources management as well as predicting future changes in lake hydrology as a result of climate change. This study presents a comprehensive, 10-year analysis of seasonal, intraseasonal, and interannual variations in lake evaporation for Lake Nasser in South Egypt. Meteorological and lake temperature measurements were collected from an instrumented platform (Raft floating weather station) at 2 km upstream of the Aswan High Dam. In addition to that, radiation measurements at three locations on the lake: Allaqi, Abusembel and Arqeen (respectively at 75, 280 and 350 km upstream of the Aswan High Dam) are used. The data were analyzed over 14-day periods from 1995 to 2004 to provide bi-weekly energy budget estimates of evaporation rate. The mean evaporation rate for lake Nasser over the study period was 5.88 mm day-1, with a coefficient of variation of 63%. Considerable variability in evaporation rates was found on a wide range of timescales, with seasonal changes having the highest coefficient of variation (32%), followed by the intraseasonal (28%) and interannual timescales (11.6%; for summer means). Intraseasonal changes in evaporation were primarily associated with synoptic weather variations, with high evaporation events tending to occur during incursions of cold, dry air (due, in part, to the thermal lag between air and lake temperatures). Seasonal variations in evaporation were largely driven by temperature and net energy advection, but are out-of-phase with changes in wind speed. On interannual timescales, changes in summer evaporation rates were strongly associated with changes in net energy advection and showed only moderate connections to variations in temperature or humidity.status: publishe

High-order, sensitivity analysis of the Bowen-ratio energy budget technique to enhance the effectiveness of evaporation estimates from Nasser Lake, Egypt

The Bowen ratio energy budget method (BREB) was evaluated and examined for determining evaporation from Nasser Lake. Parameters sensitivities were obtained based on an extension of the State Dependent Parameter modelling using a smoothing spline Anova recursive method. The relative importance of the input parameters in the BREB method was quantified by means of variance based sensitivity indices. The sensitivity results showed that the change in stored energy parameter is the most influential parameter followed by the Bowen ratio parameter. The first and second-order indices proved that there must be interactions among the input errors in the BREB method.status: publishe