Effects Of Groundwater Seepage Research Articles

Optimization of Embedded Retaining Walls Under the Effects of Groundwater Seepage Using a Reliability-Based and Partial Factor Design Approach

In this paper, a comparative analysis of the effects of groundwater, seepage and hydraulic heave on the optimal design of embedded retaining walls is carried out. The optimization model for an optimal retaining wall (ORW) minimizes the total length of the retaining wall considering design constraints. The model is extended to include the probability of failure as an additional constraint. This overcomes the limitations of the partial safety factor approach, which does not fully account for uncertainties in the soil. In contrast, the reliability-based design (RBD) approach integrates these uncertainties and enables an assessment of the impact of seepage and hydraulic heave on the reliability of the structure. A real-coded genetic algorithm was used to determine optimal designs for both optimization methods. The results of the case study show that the addition of seepage (groundwater flow) to the hydrostatic conditions has a modest effect on the embedment depth. The design based on partial safety factors, which takes seepage into account, leads to a slight increase in the embedment depth of 0.94% compared to a retaining wall design that only takes the hydrostatic conditions of the groundwater into account. When designing on the basis of probability failure, the percentage increase in embedment depth due to seepage is between 2.19% and 6.41%, depending on the target probability of failure. Furthermore, the hydraulic heave failure mechanism did not increase the required embedment depth of the retaining wall, which means that the failure mechanism of rotation near the base was decisive for the design.

Pockmarks and associated fresh submarine groundwater discharge in the seafloor of Puck Bay, southern Baltic Sea

This is the first well-documented report on the occurrence of pockmarks in Puck Bay. Pockmarks in the seafloor of Puck Bay were discovered during a hydroacoustic survey carried out in 2020. They are located at a depth of 25–27 m in the southwestern part of the bay. Significant depletion of chloride (Cl−) concentrations in sediment pore water was found within the depressions. Most likely, the formation of pockmarks was due to groundwater flow through the Miocene–Pleistocene system of aquifers, which extends from land to the bay area. One-dimensional modeling of vertical Cl− concentration profiles in pore water revealed the upward flow of freshened groundwater within the pockmarks. The magnitude of submarine groundwater discharge (SGD) was estimated to vary from 1.53·10−2 to 18·10−2 L·m−2·h−1. The effect of groundwater seepage was also observed at 3 cm above the seafloor within the pockmarks, which was identified as a decrease in salinity of approximately 0.12 PSU compared to reference sites.Furthermore, due to the effect of water advection, SGD can be detected even several meters above the seafloor as a decrease in salinity values within the thermocline layer.

Numerical modeling and thermal performance analysis of deep borehole heat exchangers considering groundwater seepage

Exploitation of deep geothermal energy based on a deep borehole heat exchanger (DBHE) system significantly promotes green and low-carbon development. The DBHE is the core apparatus of this system, and many mathematical models have been proposed to investigate its thermal performance. However, groundwater seepage which is one of the most important factors has not been considered in most previous numerical models. In addition, the temperature distribution of rock and soil with different seepage velocities during the thermal recovery period is still unclear. Therefore, to fill this research gap, there is a strong need to propose a novel numerical model for DBHEs that considers groundwater seepage and can be solved quickly. In this paper, a computationally efficient numerical model that considers groundwater seepage is proposed. Compared with the experimental data from a field test, the model’s root mean square error is 1.33 °C. Moreover, the time required for the simulation of DBHE operation for one year using this model is only 47.3 s. Then, the effects of groundwater seepage on the DBHE and rocky soil are investigated. The findings demonstrate that when the seepage velocity is high, the thermal performance of the DBHE will be underestimated if groundwater seepage is neglected. At the seepage velocities of 1 × 10-7, 3 × 10-7 and 5 × 10-7 m/s, the heat extraction rate of the DBHE increased by 4.92 %, 10.83 %, and 15.34 %, respectively, compared to the heat extraction rate of the DBHE calculated without taking the groundwater seepage into account. Furthermore, groundwater seepage can increase the temperature recovery capacity of rock and soil. The natural temperature recovery rate of rock and soil without seepage is 86.20 %, and the temperature recovery rate is 93.11 % if the seepage velocity reaches 1 × 10-7 m/s. This study provides essential theoretical guidance for DBHE system design in areas with high groundwater seepage velocities.

Thermal performance of medium-deep U-type borehole heat exchanger based on a novel numerical model considering groundwater seepage

The medium and deep U-type borehole heat exchanger (MDUBHE) system is a novel technology to extract deep geothermal energy for building heating. The thermal performance of MDUBHE is influenced by multiple factors, where groundwater seepage is one of the most significant factors. To our best knowledge, the effects of groundwater seepage on MDUBHE are still unclear. In this paper, a novel numerical heat transfer model for MDUBHE considering groundwater seepage is proposed, and validated by CFD simulation and experimental data, with root mean square errors of 0.5 °C and 1.8 °C, respectively. Based on the novel numerical model, the effects of groundwater seepage on thermal performance of MDUBHE and thermal recovery characteristics of rock-soil are investigated. The results show that the computational efficiency of the novel numerical model is improved by two orders of magnitude compared with CFD software in the same case. The heat extraction rate of MDUBHE gradually increases with increase of seepage velocity. The heat extraction rate is improved by 13.63 % when the seepage velocity is 5.0 × 10−7 m/s. Furthermore, groundwater seepage can improve the thermal recovery rate of rock-soil. Compared with no groundwater seepage, the thermal recovery rate is improved by 7.60 % when the seepage velocity is 1.0 × 10−7 m/s. This study is significant for revealing the effect of groundwater seepage on the MDUBHE system.

Interactive effects of raindrop impact and groundwater seepage on soil erosion

Raindrop impact (RI) and groundwater seepage (GWS) play important roles in slope erosion processes. However, reliable quantification of their interactive effects on erosion is still lacking. Therefore, a laboratory study was conducted to reveal the effects of RI and GWS on hillslope erosion. A soil box (5.0 m long, 0.5 m wide, and 0.5 m deep) was subjected to rainfall simulation experiments under free drainage (FD) and GWS conditions. The effect of RI was studied by dissipating raindrop energy, i.e. without raindrop impact (WRI). The results indicated that compared with WRI, RI increased the runoff rate, soil loss and sediment concentration by about 3–14%, 74–696%, and 64–560%, respectively. With a higher runoff rate of 27–54%, GWS increased soil loss and sediment concentration about 70–588% and 27–411% compared with FD, respectively. A power function relation were found between soil losses and runoff rate. The increasing rate of soil loss increased with runoff followed the order: GWS + RI > FD + RI > GWS + WRI > FD + WRI. The erosion and sediment yield seemed to be detachment-limited. As a result of crust formation, RI, compared with WRI, marginally enhanced the average flow velocity and shear stress, and reduced the resistance coefficient. The effects of GWS on flow parameters were more pronounced than RI. The mean weight diameter of aggregates was reduced by about 13–69% because of breakdown by raindrop impact or slaking. The loss of <0.25 mm aggregate accounted for 77–98% of the total aggregate loss in all treatments.

Effect of Groundwater Seepage on Uplift Resistance of Buried Pipelines

The uplift resistance of pipelines buried in sands, in the presence of inclined groundwater flow, considering both upward and downward flow directions, has been determined by using the lower bound finite elements limit analysis in conjunction with nonlinear optimization. A correction factor (f (gamma) ), which needs to be multiplied with the uplift factor (F (gamma) ), has been computed to account for groundwater seepage. The variation of f (gamma) has been obtained as a function of i(gamma (w) /gamma (sub) ) for different horizontal inclinations (theta) of groundwater flow; where i = absolute magnitude of hydraulic gradient along the direction of flow, gamma (w) is the unit weight of water and gamma (sub) is the submerged unit weight of soil mass. For a given magnitude of i, there exists a certain critical value of theta for which the magnitude of f (gamma) becomes the minimum. An example has also been presented to illustrate the application of the results obtained for designing pipelines in presence of groundwater seepage.

Monitoring of Radon-222 Concentration in Surface Waters of the Ban Phai Subwatershed Northeast Thailand Using a Method to Concentrate Radon by Air-circulation

Radon-222 ( 222 Rn) concentration in surface water is a useful indicator for groundwater seepage. However, the natural concentration of 222 Rn in surface water is too low to measure. It is therefore necessary to concentrate 222 Rn content in water samples before analysis. This is a difficult operation requiring specialized equipment. We developed a method of measurement of 222 Rn concentration in surface water (a method to concentrate radon by air-circulation) and applied it to detect groundwater seepage in the Ban Phai subwatershed, northeast Thailand. We also measured electric conductivity to determine whether dissolved ions in water were brought by groundwater. In areas of high-elevation (>180 m above sea level), 222 Rn concentration in surface water was low, indicating that the velocity of subsurface water flow was slow even in the rainy season. This result supported a flow velocity previously calculated from the permeability of surface soil and the hydraulic gradient. Our measurements of 222 Rn concentrations revealed that groundwater can be obtained by digging to a depth of about 1 m in the river bed in some areas. In areas of low-elevation (<160 m above sea level), electric conductivity increased markedly in the dry season. This was attributed to evaporation, rather than the effect of groundwater seepage, because the 222 Rn concentration was low, suggesting little influence of groundwater.

The Effect of Groundwater Seepage on Nutrient Delivery and Seagrass Distribution in the Northeastern Gulf of Mexico

A hypothesis was tested to determine if a relationship exists between rates of submarine groundwater discharge and the distribution of seagrass beds in the coastal, nearshore northeastern Gulf of Mexico. As determined by nonparametric statistics, four of seven seagrass beds in the northeastern Gulf of Mexico had significantly greater submarine groundwater discharge compared with adjacent sandy areas, but the remainder exhibited the opposite relationship. We were thus unable to verify if a relationship exists between submarine groundwater discharge and the distribution of seagrass beds in the nearshore sites selected. A second objective of this study was to determine the amount of nitrogen and phosphorus delivered to nearshore areas by submarine groundwater discharge. We considered new nutrient inputs to be delivered to surface waters by the upward flux of fresh water. This upward flux of water encounters saline porewaters in the surficial sediments and these porewaters contain recycled nutrients; actual nutrient flux from the sediment to overlying waters includes both new and recycled nutrients. New inputs of nitrogen to overlying surface waters for one 10-km section of coastline, calculated by multiplying groundwater nutrient concentrations from freshwater wells by measured seepage rates, were on the order of 1,100±190 mol N d−1. New and recycled nitrogen fluxes, calculated by multiplying surficial porewater concentrations by measured seepage rates, yielded fluxes of 3,600 ±1,000 mol N d−1. Soluble reactive phosphate values were 150±40 mol P d−1 using freshwater well concentrations and 130±3.0 mol P d−1 using porewater concentrations. These values are comparable to the average nutrient delivery of a small, local river.

The effect of groundwater flow on the strength and stability of silicate grouted soils

ABSTRACT A considerable volume of data on the strength of silicate grouted soils has been published in recent years. In particular there has been considerable discussion of the confined and unconfined strengths of grouted sands and the effect of creep on those strengths. Little has been said on the effect of groundwater seepage on the strength and residual permeability of the sand/silicate system. Following observations on site into the effectiveness of silicate grouting, a small laboratory programme was set up to examine the effect of seepage on strength and residual permeability. The findings of the programme are summarised.

Effects of Ground-Water Seepage on Fluvial Processes

Field observations of a small stream have indicated that seepage of water into or out of a stream may greatly alter stream competence. Theoretically, water seeping through the stream bed exerts a drag on quartz grains that changes stream competence by the factor 1.65/(1.65 − i ) where i is the seepage gradient. Experiments in laboratory flumes, however, indicate that seepage through a stream bed, despite its effect on effective grain density, causes no change in competence in gaining streams nor in losing streams that lack a mud seal. Possibly the expected change in competence is partially counteracted by the accompanying changes in form drag and surface drag on the grains. Flume experiments also show that upward seepage reduces the steepness of bed forms and decreases bed roughness, whereas downward seepage steepens the bed forms and increases bed roughness, but these changes appear to be insufficient to cause any measurable change in the slope of the water surface. Downward seepage in the presence of sufficient suspended sediment, however, can lead to the formation of a mud seal on the surface of a stream bed; this results in a great increase of the effective density of the bed sediment and may result in the total elimination of sediment entrainment from the bed.