Groundwater Infiltration Research Articles

Influence of supported filtration on channel safety (based on the example of Swanley channel)

The article examines the problem of destruction and deformation of the banks of the Swanley Canal under the influence of backed-up groundwater filtration. An analysis of the current state of the canal and the dynamics of changes in groundwater levels along the canal bed was carried out. A hydraulic calculation of filtration flow was carried out and a method was proposed to reduce the negative impact of groundwater levels on the integrity of the canal.

Inflow and infiltration assessment of a prototype sanitary sewer network in a coastal city in China

Abstract A 16-month monitoring program was conducted on a prototype sanitary system in a coastal city in China. The groundwater infiltration (GWI) on dry weather days and the rain-derived inflow and infiltration (RDII) on wet weather days were quantified and analyzed. The proportion of monthly averaged GWI to total flow can be as high as 70% during the observation period mainly due to the high groundwater level. The results also show that the ratio of RDII volume to total rainfall volume (defined as R-value) reaches a limited value of approximately 10% for the studied system when the total rainfall depth increases. A reference indicator Rlim for the limited R-value was proposed for assessing the conditions of sewer systems in terms of RDII. The Rlim value depends on local sewer conditions and in general, a lower Rlim value represents a better performance on RDII and vice versa. This study enriches the case studies on the performance of a specific sanitary sewer system on inflow and infiltration in a typical coastal city with exceptionally high groundwater levels, excess rainfall events in the monitoring season and possible typhoon events, which addresses the unique locational and hydrological properties of a representative coastal city.

The telltale fluorescence fingerprints of sewer flows for interpreting the low influent concentration in wastewater treatment plant

Low degradability of wastewater treatment plant (WWTP) influents negatively affects its ability to effectively remove pollutants through wastewater treatment processes. Proactive assessment of urban sewer system performance is highly valued in the selection of targeted countermeasures for this occurrence. In this study, a fluorescence spectrum interpretation approach was developed to identify the causes of low biodegradability of WWTP influent by using parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) of excitation-emission matrix spectroscopy. Statistical analysis was also used to further interpret the PARAFAC- and FRI-derived data. The urban sewer catchment served by a WWTP in Wuhan City, China, was used as the test site to demonstrate the effectiveness of this approach. The results showed that electronics manufacturing industrial wastewater and groundwater input into the urban sewer would significantly decrease the biodegradability of the WWTP influents, and these sources were characterized by much lower fluorescence peak intensities, especially for protein-like substances, including tryptophan-like T and tyrosine-like B1 and B2. The potential conversion of high freshness T into low freshness B2 within the sewer may also contribute to this undesirable scenario. The ratio of peak T to peak B2 and the ratio of the FRI fraction of region I to that of region II can be used together to determine the predominance of industrial wastewater and groundwater. T/B2 < 1.3 indicates the entry of industrial wastewater or groundwater into urban sewers, and I/II > 0.5 further confirms the input of industrial wastewater. Accordingly, the low biodegradability of the WWTP influents in our study site is mostly due to the inflow of industrial wastewater rather than groundwater infiltration into the urban sewers. Therefore, actions should be focused on the surveillance of industrial wastewater rather than widespread sewer inspection and repairs. In this way, this methodology is cost-effective in aiding targeted countermeasures to improve the urban sewer system performance.

A smart sewer detection approach based on wavelet denoising of in-sewer temperature sensing measurement

Urban sewer detection is important for the proper conveyance of sanitary water to wastewater treatment plant prior to environmental discharge. An effective approach to address this important process still needs to be developed. This study introduced a novel data-driven approach to sewer detection utilizing in-sewer distributed temperature sensing (DTS) measurement combined with wavelet-based denoising of DTS data. It underlines that the effective denoising of DTS data, and consequently the accurate determination of DTS noise threshold, is pivotal to reliable sewer detection. DTS background noise is chiefly influenced by the threshold rescaling. A reliable DTS background noise threshold was found to be ±0.25 °C in a field study, established with the threshold rescaling of a level-dependent estimation of level noise, and the associated threshold selection rule of heuristics threshold or minimum maximum variance. Deviation from this threshold could hamper the identification of true inflow or infiltration points. Applying the established threshold to the study site, our study identified two sewer problematic points including a groundwater infiltration point, and a clean water inflow point based on generated three-value image. Further interpretation of the three-value image revealed that both groundwater infiltration and clean water inflow into the sewer exhibited intermittent instead of constant behavior, which was due to time-variable water head difference associated with sewage discharge variation over the daily period and rainfall events. Thus, the methodology offers considerable potential for urban sewer detection, especially for its performance to capture intermittent sewer infiltrations and inflows without draining sewers.

Bedrock Fractures Control Groundwater‐Driven Mountain Slope Deformations

AbstractSeasonal deformation of mountain rock slopes can be driven by groundwater infiltration and depletion. Such processes could explain our field observation in the Aletsch Valley, Switzerland, where GNSS‐derived 3D annual displacement amplitudes reach 3.4 cm. However, the physical mechanisms behind such groundwater‐driven surface displacements are not well understood. Here, we develop a fully coupled hydromechanical model to simulate the relevant processes in a valley slope embedded with numerous fractures of variable sizes. The magnitude and orientation of transient annual slope surface displacement obtained from our model are in overall agreement with the field observations. The key geological factors controlling the type and magnitude of reversible mountain slope deformations are fracture network geometry, fracture aperture, and regional stress field. We show that the heterogeneity and anisotropy of bedrock hydromechanical responses, originating from depth‐dependent variations of fracture properties, play a critical role in groundwater recharge and valley slope deformation. During recharge events, pore pressure perturbations migrate downward from the groundwater table and toward the receiving stream and the deep subsurface. This process driven by pressure diffusion and poroelastic stressing develops in the subsurface with a great reach of up to a few kilometers, called critical hydromechanical response zone, and controls surface deformation patterns. During groundwater recession, this hydromechanical response zone expands downward and ground surface displacement vectors rotate upwards. Our results suggest that slope surface deformation can inform about subsurface permeability structures and pore pressure fluctuations, which have important implications for understanding groundwater flow in fractured bedrock slopes.

Partitioning blue and green water sources of evapotranspiration using the water evaluation and planning (WEAP) model

Abstract Understanding agricultural water use by sources such as rainwater (green water) or irrigation water (blue water) is vital to manage scarce freshwater resources. Tracing sources of evapotranspiration increases water management efficiency. This study proposes a two-bucket soil moisture water balance approach to trace sources of evapotranspiration over irrigated landscapes in the Awash Basin, Ethiopia, which is modeled in the water evaluation and planning model. Algorithms are devised to separate actual evapotranspiration into blue and green sources. The results showed annual basin renewable water of 15.78 BCM in the form of streamflow (4.65 BCM), stored water (3.54 BCM), and groundwater percolation (7.59 BCM). Annual actual evapotranspiration over irrigated landscapes was 805 MCM, which was separated as blue evapotranspiration (88.4%) and green evapotranspiration (11.6%). The findings also demonstrate that blue evapotranspiration predominantly occurs during dry months, indicating heavy reliance on stored water for irrigated landscapes. Subbasin-level analyses showed varying blue/green evapotranspiration patterns based on precipitation and irrigated agriculture. Irrigation accounted for less than 3% of the streamflow in upstream basins, while midstream and downstream basins utilized up to 30 and 70%, respectively. The complementary use of rainfall and irrigation in most parts of the basin is considered to be of interest to water managers.

Extraction, Mapping, and Analysis of Structural Lineaments using Geospatial Azimuth-Altitude Ratio Technique on a DEM of a Sub-Catchment of the Upper Benue River Basin, Nigeria

Lineaments have a wide range of implications and applications in geology, hydrogeology and geomorphology. The focus of this study was on structural or geological lineaments and their implication on hydrogeology and hydrogeomorphology. Hence, this study aimed at the extraction, mapping, and analysis of structural lineaments using a DEM in the Adamawa sub-catchment of the Upper Benue River basin. ArcGIS 10.8 was used for the geospatial technique of Azimuth-Altitude ratio (315:45, 200:50, 150:65, and 100:60) variation, manual digitization for the extraction, mapping and analysis of lineaments. The choice of manual or visual digitization was to apply expert experience to extract only structural and exclude geomorphological and pseudo lineaments. The Azimuth-Altitude ratio variation approach was to improve clarity and identification to aid the manual extraction. The lineament map generated after extraction was used to analyze for lineament density, total number, and total length. A further analysis applied the rose diagram to depict the directional orientation or trends of these lineaments. The result revealed that at various Azimuth and Altitude ratios, the features on the image become more distinguishable for extraction. At 315:45 Azimuth and Altitude ratio, the hill-shade produced revealed the major lineaments more clearly compared to other ratios but minor lineaments were undermined. Also, a total number of 343 lineaments were found in the Adamawa sub-catchment of the Upper Benue River Basin with a total length of 2897.81km. The lineament density was found to range between 1km/km2 and 5km/km2. The result of the lineament statistical analysis showed that the extracted lineaments have trends in the direction of N-S, NNE-SSW, NE-SW, E-W, SE-NW, and SSE-NNW. This therefore concluded that the Adamawa sub-catchment of the Upper Benue River Basin has high lineament density and lineament extraction from DEM at various Azimuth and Altitude ratios enhances lineament extraction. The implications of the findings from the results suggest that areas with a high density of lineaments might be affected by higher structural deformation, which signifies higher groundwater infiltration potential zones and initiation of first-order drainage networks. This information is vital for water resources management in the sub-catchment.

Soil water infiltration characteristics of reforested areas in the paleo-periglacial eastern Liaoning mountainous regions, China

Plantation forests (PF) and natural secondary forests (NSF) are the primary reforestation approaches. The establishment of PF can affect forest hydrological processes by changing soil structure. To date, few studies have focused on these changes and the effects on hydrological processes for the paleo-periglacial landform. To reveal reforestation approaches effects on water infiltration, including soil water infiltration capacity, retention capacity, and waterflow path pattern, we conducted field dye-tracer investigations with rainfall and laboratory infiltration experiments for the paleo-periglacial landform of eastern Liaoning mountains, China. The results showed that (1) Soil physical properties (including total porosity (TP), capillary porosity (CP), non-capillary porosity (NCP), initial soil water content (IWC), field water capacity (FWC)) and root abundance (RA) decreased with soil depth in both PF and NSF, while the soil bulk density (BD) and distribution of gravel content showed opposite changes. (2) Establishment of PF reduced the infiltration capacity and water retention capacity in the 0–20 cm layer, but enhanced the water retention capacity in 20–30 cm layer. Low IWC was conducive to increase soil water content (SWC) after infiltration. (3) Infiltration capacity parameters (including saturated hydraulic conductivity (Ks), SWC, difference between SWC and IWC (SWC–IWC), dye coverage ratio (DC)) were significantly correlated with BD, TP, CP, NCP, FWC, and fine roots RA (P < 0.05). Better connectivity gravels were more conducive to water infiltration. (4) Preferential flow was the main infiltration type, but with different waterflow paths pattern, with the 'funnel', 'finger' shape for PF, NSF, respectively. Increasing infiltration could increase flow path connectivity. Our findings show that soil physical properties, roots, and gravel occurrence affected soil infiltration, and different reforestation approaches had varying impacts on soil infiltration, water redistribution, transportation, and storage of surface and groundwater, improving the understanding of ecohydrological processes and effects of water resources management in forest ecosystems of paleo-periglacial landform.

Membrane Filtration of Surface water and Groundwater and the Application of Nanotechnology - A Far-reaching Review and a Visionary Future

The world of membrane separation processes and nanotechnology are in the avenues of new scientific regeneration and divinity. There are serious environmental engineering concerns in the global scenario. Excessive industrialization and rampant economic growth are threatening the global scientific and social fabric. Thus the need of conventional and non-conventional environmental engineering tools. In this treatise we discuss the rapid advances in the field of membrane separation processes and nanotechnology in the field of treatment of surface water and groundwater. The other areas of research endeavor are the application of membrane filtration and nanotechnology in arsenic and heavy metal groundwater remediation. This is a burning and vexing problem in many developing and developed nations around the globe. Thus the need of a deep scientific introspection and vast scientific and engineering vision in drinking water and industrial wastewater treatment.

The Development of a Coupled Soil Water Assessment Tool-MODFLOW Model for Studying the Impact of Irrigation on a Regional Water Cycle

In regions with arid and semi-arid climates, water consumption for agricultural irrigation is much higher than that used for urban and industrial purposes. Intensive irrigation plays a vital role in influencing the interaction between groundwater and surface water. Understanding the impact of irrigation on the local hydrological cycle is of great significance for maintaining regional food production and -security. In order to study the impact of irrigation on the regional hydrological cycle, the present study employed the SWAT-MODFLOW coupled model to analyze the Weigan River Basin from 2002 to 2016. In the modeling process, detailed agricultural management measures were considered, including the zoning of crop types, amount of irrigation water for different crops, irrigation methods, and different sources of irrigation water. Before coupling, each model was set, calibrated, and validated separately. After coupling, the irrigation pumps and drainage units were mapped with the SWAT automatic irrigation and subbasins. Calibration and validation studies showed that the SWAT-MODFLOW coupled model could simulate the river flow and groundwater levels in the Weigan River Basin well. The model simulation results showed that the sources of water in the soil included groundwater irrigation (1147.5 mm) and surface water irrigation (68.4 mm), as well as precipitation and snowmelt recharge (97.62 mm). The groundwater balance was influenced by the river leakage (75.6 mm), lateral inflow from surrounding areas (3.6 mm), unsaturated zone infiltration (197.7 mm), and irrigation pumping (1275 mm). When compared with the scenario without irrigation, the surface runoff, groundwater infiltration, soil moisture content, and evapotranspiration increased by 7.9%, 3.2%, 4.1%, and 2.3%, respectively. Irrigation activities increased the soil moisture content and permeability, resulting in more groundwater recharge and evaporation, as well as a higher surface runoff. This model provides guidance for evaluating drought irrigation systems in future sustainable water resource management.

Hydrogeology and Hydrogeochemistry of Saline Groundwater Seepage Zones in Wadi Bani Malik Basin, Jeddah, Saudi Arabia: Impacts on Soil and Water Resources

The water seepage zone affects dryland salinity, soil sodicity, land degradation, waterlogging, and rainfall pollution. The priority in terms of the remediation measures was determining the cause of the seepages. Nine water and six soil samples were collected from the Al Tayseer area of the Wadi Bani Malik, Jeddah, Saudi Arabia (SA). The water samples were analyzed for major and toxic metals. For the soil samples, granulometric analysis and infiltration rate analysis were performed. The total dissolved solids (TDS) in water seepages ranged from 1880 to 54,499, whereas boron (B) and iron (Fe) values ranged from 1.9 to 38 mg/L and 0.02 and 0.47 mg/L, respectively. These concentrations were the same for the aquifer in Lake Al Misk, confirming that groundwater infiltration from the lake area was the main reason for the water seepage. The concentrations of silica (Si), aluminum (Al), cobalt (Co), nickel (Ni), zinc (Zn), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb) were low, indicating that there was no contamination. The nitrate (NO32−) value ranged from 2.2 to 35 mg/L, indicating agricultural wastewater contribution. According to the granulometric examination, most sediment was sand, followed by gravel, with few fine-grain particles. The infiltration rate ranged from 85 to 864 cm/d, indicating significant leakage. The percentage of ferrugination, ferromagnesian, OH-bearing, and carbonate (CO₃2−) minerals is determined by the 4/2, 5/6, and 6/7 band ratios.

Groundwater recharge assessment using GIS approach in Chiang Mai basin

The geographic information system (GIS) techniques were used to groundwater recharge estimation and groundwater recharge potential map in Chiang Mai Basin. The groundwater recharge estimation use slope, rainfall and infiltration factor for calculation. Amount of groundwater recharge are 597.20 – 896.19 m3/year. The study used lithology, land use, lineaments, drainage and slope gradient as influence factors to the groundwater recharge potential. The groundwater potentiality was integrated from thematic maps and derived from the sum of the weighted factor using weight overlay method in the GIS system. Almost of the study area is classified as the high groundwater recharge potential zone. The moderate groundwater recharge potential zone is located in the western part of study area and along with the Ping River.

Microplastic pollution in the groundwater under a bedrock island in the South China sea

Groundwater is the only freshwater resource on islands. Research on microplastic pollution in groundwater on islands is scarce. This study is the first to explore microplastic pollution in the groundwater under a bedrock island (Dawanshan Island) located in the South China Sea. The influence of hydrogeological factors on the distribution, source, and ageing features of microplastics in the groundwater were investigated. Despite the small scale of industrial and agricultural activities on the island, the amount of microplastics in the groundwater ranged from 34 to 64 particles/L, with over 80% of the microplastics being polyester fibres with diameters smaller than 2 mm, which is comparable to those in coastal cities. These microplastics were originated from inland plastic usage, rather than from the surrounding sea, which was confirmed by the lack of seawater intrusion on the island. Owing to the low permeability of granite, microplastics were mainly distributed in the water of the loose layer of porous sediment, and their quantity decreased with depth. In addition, the abundance of microplastics in pore groundwater increased with an increase in the velocity of groundwater flow. The severity of microplastic pollution in the groundwater increased with an increase and decrease in the content of total dissolved solids and dissolved oxygen, respectively. The microplastics originated from plastic waste disposed of on the island, rather than from seawater intrusion. Also, through groundwater infiltration into exposed soil at recharge areas, artificial wells at residential areas, and water exchange with surface water at valley areas. Microplastics buried in the groundwater aged faster along the migration path of the groundwater. These microplastics threaten the safety of people and plants on the island through exposure resulting from the extraction of groundwater for irrigation, while they endanger marine life through submarine groundwater discharge.

Evaluation of Groundwater Infiltration in Sewer Networks Using Fluorescence Spectroscopy

Diagnosing water infiltration is imperative to assess the integrity and operation performance of sewer networks, which is challenging and costly due to the complex nature of these networks. This study proposes a simple approach to evaluate the extent of groundwater infiltration via a fluorescence spectroscopy method, i.e., the identification and quantification of the fluorescent signature components of the dissolved organic matter sewage. A newly built sewer network in Shantou, Southern China, was selected for the case study, and a mass balance method based on water quality characteristic factors (total phosphorus and NH4+-N) was applied in parallel for comparison. The results showed that the mass balance method was substantially influenced by fluctuations in sewage and external water concentrations, rendering it unreliable due to the extensive data and calculations required. Conversely, three-dimensional excitation–emission matrix–parallel factor analysis enabled the identification of terrestrial humus compounds as the signatures of underground water sources. The estimation indicates that the groundwater proportion across the four surveyed inspection wells along the pipeline network ranged from 10.8 ± 2.5% to 9.6 ± 3.5%, conforming to the allowable groundwater infiltration limits set for municipal sewage pipelines (10–15%). This study presents a simple method for the in-depth analysis of groundwater infiltration in urban sewage networks, providing valuable insights into maintaining water quality and network integrity.

Data-driven analysis and integrated modeling of climate change impacts on coastal groundwater and sanitary sewer infrastructure

The variation of the coastal groundwater table and the vulnerability of sanitary sewer infrastructure under a changing climate is considered for Imperial Beach (CA, USA) by incorporating the compound impacts of Sea-Level Rise (SLR), groundwater shoaling, and precipitation intensification. For 2 m of SLR, marine inundation is expected to impact only 2% of the urbanized area; however, SLR-driven groundwater shoaling is projected to impact 36% of the subterranean sewer system. Due to GroundWater Infiltration (GWI) and Rainfall-Derived Inflow and Infiltration (RDII), the sanitary sewage flow increases by 21% and 49% during dry- (i.e., consecutive days without precipitation) and wet-weather conditions (i.e., 24-hour rainfall with a 25-year return period), respectively. At SLR = 2 m, defect flows (GWI + RDII) can be elevated by 84% and 120% in dry- and wet-weather conditions, respectively. Such elevated hydraulic loads may place $0.5−$2.7 M additional cost on the collection system and treatment facilities every year. Moreover, pressurized junctions due to the above-mentioned hydraulic loading are likely to expose the community and the environment to raw sewage pollution. By involving structural, hydrological, and hydraulic criteria, a holistic approach is presented and implemented for prioritizing sewer system rehabilitation.

ASYMPTOTIC SOLUTION OF FOKKER-PLANCK EQUATION BASED ON DARCY-BUCKINGHAM APPROACH IN UNSATURATED SOIL

The present study discusses one dimensional groundwater infiltration phenomenon in unsaturated soil. The mathematical formulation is developed using Dracy’s law, equation of continuity, and standard relations between diffusivity coefficient and hydraulic conductivity. We solved the obtained system using double power series method in the form of asymptotic expansion which represents moisture content in soil.

Features of the numerical modeling of the hydrogeological conditions of the soil massive during the excavation of the pit in the Plaxis software complex

The construction of multi-storey civilian buildings, especially in the central districts of cities, is often accompanied by a developed underground part, which requires deep pits. The construction of such pits often leads to a change in the hydrogeological condition at and near the construction site.&#x0D; This paper presents a comparison of the stress-strain state of the " base - pit enclosure" system, depending on the method of modeling hydrogeological conditions.&#x0D; The study is divided into two stages: determination of the main features of the Plaxis software complex toolkit for modeling and determining pore water pressures; creating of numerical models and performing calculations. . The first part of the study describes the basic principle of determining stresses in saturated soils, pore pressure calculation types, hydraulic boundary conditions, and types of soil drainage.&#x0D; In the second part of the study, the numerical models were developed in Plaxis 2D, based on the real object and hydrogeological conditions at the construction site. The two most popular methods for modeling hydrogeological conditions during dry excavation in the pit are described. A step-by-step calculation is performed taking into account the stages of excavation in the pit and dewatering and the construction of retaining structures according to the scheme provided by the design solutions.&#x0D; The results of the calculations demonstrate the difference in the obtained values of forces and horizontal displacements of the retaining wall for models created using different methods of setting the hydrogeological conditions of the base.&#x0D; In order to improve the accuracy of calculations and determine the impact of soil permeability, the impact of the stratigraphy of the base was excluded by solving theoretical problems with a homogeneous soil massif composed of clay or sandy soil with groundwater filtration rates in a wide range (kx=ky=0.001...6m/day). Based on the results obtained, it was found that both methods correlate with each other in the case of the presence of poorly filtering soils with a filtration coefficient of k=0.001...0.05 m/day, the calculations demonstrated similarity in the displacements and forces of the retaining wall in such schemes up to 97.9-99.9%. Instead, in the case of soils with high water permeability (k=0.4...6 m/day), the difference in results is up to 56.5%.

A new approach to circularity assessment for a sustainable water sector: Accounting for environmental functional flows and losses

Resource recovery solutions can reduce the water sector's resource use intensity. With many such solutions being proposed, an assessment method for effective decision-making is needed. The water sector predominantly deals with biogeochemical resources (e.g., nitrogen) that are different from technical resources (e.g., industrial coagulants) in three ways: (1) they move through the environment in natural cycles; (2) they fulfil different human and environmental functions; and (3) they are subject to substantial environmental losses. Whilst several circularity assessment methods exist for technical resources, biogeochemical resources have received less attention. To address this, a well-established material circularity indicator (MCI) method is modified. This is done by redefining the terms: restoration, regeneration, and linear flows to create a new circularity assessment approach. The new approach is demonstrated in a real-life case study involving treated wastewater (TW) fertigation. The new approach reveals that using the original MCI method underestimates the circularity of resource recovery solutions involving biogeochemical resources. This is because, in the original MCI method, only the flows that are reused/recycled for human functions can be considered circular, whereas, in the new approach, one also considers flows such as N2 emission and groundwater infiltration as circular flows. Even though these may not be reuse/recycle type flows, they still contribute towards future resource availability and, thus, towards sustainability. The modified assessment method shows that TW fertigation can significantly improve nitrogen and water circularity. However, careful planning of the fertigation schedule is essential since increasing fertigation frequency leads to lower water but higher nitrogen circularity. Additionally, collecting drainage water for reuse can improve nitrogen circularity. In conclusion, using the modified MCI approach, circularity can be assessed in a manner that is better aligned with sustainability.

Monitoring Analysis of a Deep Foundation Pit with Water Supported by Cast-in-Place Pile and Internal Bracing in a Soft Soil Area of Fuzhou

In addition to selecting an effective support structure to control deformation, precipitation and water stopping should also be considered when designing a support scheme for water-bearing foundation pits in soft soil areas. This paper presents a detailed description of the foundation pit support scheme, the precipitation and water-stopping scheme, and the monitoring scheme of the foundation pit project of Taijiang Square in Fuzhou. During the construction of the foundation pit, the monitoring data of 12 items such as the deep horizontal displacement of the enclosure pile, the horizontal displacement at the top of the foundation pit, the settlement at the top of the foundation pit, the axial force of the internal bracing, and the axial force of the enclosure pile were obtained through 12 months of monitoring. The analysis of the monitoring data for each item led to the following two main findings. The first finding is that, during the construction of the pit, the monitoring values of the 12 monitoring items did not exceed the alarm values, which proves that the support scheme of the cast-in-place pile enclosure structure and internal bracing can meet the design requirements of deep foundation pits in soft soil areas. The second finding is that tube-well dewatering is an effective way to lower the groundwater level in water-containing deep foundation pits in soft soil areas, and double-wheel deep-mixing water-stopping curtain walls can effectively control the infiltration of groundwater outside the water-containing deep foundation pits in soft soil areas. This foundation pit project is representative, and it provides a good reference case for the design of water-bearing deep foundation pit projects in soft soil areas.

Hydrogeological controls on formation of Patearoa saline site in Central Otago, New Zealand and definition of geoecological salt lines

ABSTRACT The Patearoa saline site in Maniototo basin has developed on variably clay-altered Otago Schist. Decomposition and sedimentary redistribution of schist outcrop components has led to formation of bare soil-free substrates (upper metre scale) with contrasting permeability to rain and shallow groundwater percolation. Relatively impermeable clay-rich substrates, with a surface crust (cm scale) of detrital clay and muscovite, are saline with electrical conductivity (EC) of 1–35 mS/cm and locally hyperalkaline (pH > 10), with evaporative mineral accumulations. These saline substrates are downslope of more permeable substrates consisting of coarse schist debris and fractured outcrops, which have lower salinity (EC < 1 mS/cm) and lower pH (<7). A salt line can be mapped at metre scale between these substrate types on hillsides. The geochemical contrasts across the salt line have strong effects on plant communities that are colonising bare ground. Initial colonisation of bare saline substrates by some plants changes the geochemical signatures of the surficial few centimetres to form proto-soil with lower EC and pH. Proto-soil development facilitates further colonisation by pasture grasses, but the underlying substrates remain saline and highly alkaline. Salt lines similar to the one at Patearoa are mappable elsewhere in the Otago area and constitute fundamental geoecological boundaries.