Disturbed Zone Research Articles

Research by Geophysical Methods of Hydraulic Structures of Water Management Purpose

Yield growth in the Southern Steppe is impossible without irrigation with the introduction of mineral and organic fertilizers, so the repair, restoration, and construction of new irrigation networks are one of the main tasks of regional and district water management. For the repair of water management networks, regulation of pools of irrigation systems it is necessary to use inexpensive effective methods of the establishment of their technical condition. Such methods are geophysical, which allow to identify the areas of filtration, flooding, violations of protective screens in the control pools of irrigation systems. The necessity of localization of areas of filtration water losses to concentrate repair and restoration works in the most disturbed zones is scientifically substantiated, which will significantly reduce the cost of time and money and increase the overall efficiency of the structure.

Experimental study on the physico-mechanical properties of Tamusu mudstone – A potential host rock for high-level radioactive waste in Inner Mongolia of China

Tamusu mudstone, located in Bayin Gobi Basin in Inner Mongolia of China, has been selected as a potential host rock for high-level radioactive waste (HLW) disposal in China. A series of tests has been carried out, including X-ray diffraction (XRD) tests, scanning electron microscopy (SEM) tests, disintegration tests, permeability tests and triaxial compression tests, to estimate the physico-mechanical properties of Tamusu mudstone in this work. The mineral composition of Tamusu mudstone was analyzed and it was considered as a stable rock due to its low disintegration rate, i.e. approximately 0.11% after several wet/dry cycles. Based on the results of permeability test, it was found that Tamusu mudstone has a low permeability, with the magnitude of about 10 –20 m 2 . The low permeability makes the mudstone well prevent nuclide migration and diffusion, and might be influenced by temperature. The triaxial tests show that Tamusu mudstone is a stiff mudstone with high compressive strength, which means that the excavation disturbed zone would be smaller compared to other types of mudstone due to construction and operation of HLW repositories. Finally, the properties of Tamusu mudstone were compared with those of Opalinus clay, Callovo-Oxfordian (COx) argillite, and Boom clay to further discuss the possibility of using Tamusu mudstone as a potential nuclear waste disposal medium.

Combined depth and heading control and experiment of ROV under the influence of residual buoyancy, current disturbance, and control dead zone

AbstractTo improve the underwater control effect of a Remotely Operated Vehicle (ROV) with residual buoyancy, current disturbance, and control dead zone, the depth and heading combined control of ROV is studied to improve the control accuracy of the control system. First, the heading control with fixed depth is divided into heading control and depth control. The tanh‐sigmoid‐surface control laws for designed degrees of freedom are designed by using tanh function. To suppress the influence of residual buoyancy and control law dead zone in depth control, and to offset the influence of control law dead zone of ROV thruster control, a reserved control quantity is introduced to map the depth deviation and control dead zone with residual buoyancy into a control deviation quantity. An adaptive amplification factor method is proposed for the amplification factors of depth control, speed control, and heading control. The proportional coefficient is adopted to make that the balance among rise time, convergence speed, and overshoot can be achieved by adjusting the proportional coefficient. Then the corresponding tanh‐sigmoid‐surface controller module is designed in MOOS‐IvP environment to track the desired heading and depth. The proposed controller refines fuzzy rules and reduces the complexity of parameter adjustment. Compared with the classical proportional, integral, and derivative control method, the experiment results show that the proposed method can resist the influence of residual buoyancy, current disturbance, and control dead zone and has a better control effect with less control error in depth and heading determination.

Schlieren depiction on flow characteristics and dynamic evolution of RBCC inlet under the combined impact of rocket jet and back pressure

Stable and reliable operation of an RBCC inlet in the extremely wide flight speed range determines the normal operation of the whole RBCC engine. And in different modes, the interior flow characteristics and operational stability of the inlet are impacted comprehensively by both the embedded rocket jet and the back pressure. The flow characteristics and dynamic evolution of a RBCC inlet under the impacts of rocket jet and back pressure are studied by cold flow tests combined with schlieren photography. The experimental results show that: 1) The interior flowfield along the flow passage is differentiated into four distinct zones by the impact of the back pressure, named “easily disturbed zone”, “hardly disturbed zone”, “transition zone”, and “isolated zone”. As the back pressure functions independently, the pressure distribution demonstrates significant stepping characteristic propagating upstream from the “easily disturbed zone” to the “hardly disturbed zone” through the “transition zone”. 2) Low pressure rocket jet relieves the flow separation on the ramp wall, but 150% rise of the back pressure will yield an 80% pressure increase at the isolator exit. The stepping characteristics are weakened during the back pressure develops from the “easily disturbed zone” to the “hardly disturbed zone”. 3) High pressure rocket jet improves the comprehensive back pressure resistance of the RBCC inlet effectively. The pressure at the rocket exit is reduced by 33.45% and the pressure at the isolator exit is decreased by 38.04% when the rocket pressure of Procket/P∞ is increased from 0.95 to 1.91. 4) The stability of the inlet flowfield is synchronously affected by the rocket jet and the back pressure. The independent function of low back pressure at Pb/P∞=0.16 causes obviously low-frequency and wide-range oscillations of the flowfield. As the back pressure is increased by 137.5%, the axial oscillation range is significantly suppressed by 83.1%. The independent function of rocket jet causes no significant oscillation, but as the back pressure of Pb/P∞=0.38 functions collectively, the low pressure rocket jet at Procket/P∞=0.95 drives the interior flowfield return to the oscillation mode of low-frequency and wide-range. Nevertheless, the 105.3% increase of rocket pressure can decrease the axial oscillation range by 7.7%.

New Perspectives on Excavation Disturbance Zones: Main Driving Forces

The support theory of the excavation disturbance zone (EDZ) cannot provide an accurate physical explanation or theoretical description of the time-dependent properties required for the development of an EDZ. Therefore, the primary factors that cause the formation of an EDZ should be determined to further improve the support theory of the EDZ and grasp the principle underlying the control of the long-term stability of rock masses. Considering the headrace tunnel and nuclear waste repository as the research background, this study aimed to understand the deformation damage evolution process of the surrounding rock after tunnel excavation under different working conditions using the self-developed realistic failure process analysis (RFPA2D) code. The simulation revealed the following. First, an EDZ is formed, although the deformation damage to the surrounding rock is relatively small under the action of environmental factors. Second, under the action of stress in the abovementioned case, the deformation speed, damage degree, and scope of the surrounding rock significantly increase, accelerating the formation and development of the EDZ. Therefore, the boundary of the EDZ expands significantly. Third, when environmental factors are blocked, the range of the EDZ is small due to the small deformation damage to the surrounding rock. Thus, the main factors responsible for the formation of the EDZ are environmental factors, whereas stress is only an auxiliary factor. A numerical simulation method that considers environmental factors can more accurately reproduce the formation of an EDZ. Therefore, a study of the internal mechanism of the EDZ phenomenon can provide a more in-depth understanding of the essential characteristics of an EDZ at the macro level. Furthermore, it can provide a scientific basis and method for the construction and support designs of underground excavation projects and widen the possibilities for further improving the support theory of the EDZ.

Mechanisms underlying the succession of plant rhizosphere microbial community structure and function in an alpine open-pit coal mining disturbance zone

Elucidating the responses and potential functions of soil microbial communities during succession is important for understanding biogeochemical processes and the sustainable development of plant communities after environmental disturbances. However, studies of such dynamics during post-mining ecological restoration in alpine areas remain poorly understood. Microbial diversity, nitrogen, and phosphorus cycle functional gene potential in the Heishan mining area of Northwest China was studied, including primitive succession, secondary succession, and artificial succession disturbed by mining. The results revealed that: (1) The dominant bacteria in both categories (non-remediated and ecologically restored) of mining area rhizosphere soil were Proteobacteria, adopting the r strategy, whereas in naturally occurring soil outside the mining area, the dominant bacteria were actinomycetes and Acidobacteria, adopting the k strategy. Notably, mining perturbation significantly reduced the relative abundance of archaea. (2) After restoration, more bacterial network node connections were observed in mining areas than were originally present, whereas the archaeal network showed the opposite trend. (3) The networks of microbial genes related to nitrogen and phosphorus cycle potential differed significantly, depending on the succession type. Namely, prior to restoration, there were more phosphorus related functional gene network connections; these were also more strongly correlated, and the network was more aggregated. (4) Soil factors such as pH and NO3–N affected both the mining area remediation soil and the soil outside the mining area, but did not affect the soil of the original vegetation in the mining area. The changes in the structure and function of plant rhizosphere microorganisms after mining disturbance can provide a theoretical basis for the natural restoration of mining areas.

Discrete Element Simulation of Fracture Evolution around a Borehole for Gas Extraction in Coal Seams.

The stability analysis of underground caverns, tunnels, and boreholes is of great significance to underground engineering. In order to study the stress change of the coal around a hole and the evolution law of fractures during the coal seam drilling process, the discrete element simulation of the coal seam drilling process was carried out by using the particle flow code (PFC2D). The results show that during the drilling process, under the influence of confining pressure and drilling disturbance, the coal stress field around the hole and the development of fractures around the hole have the characteristics of zoning and dynamic evolution. In the axial direction of the borehole, it is divided into front and rear areas, and in the vertical axial direction, it is divided into the drilling disturbance zone and the confining pressure main control zone. During the drilling process, the direction of the maximum principal stress in the front zone gradually changes from the vertical hole axis to the direction parallel to the hole axis, and tension fractures are mainly developed along the drilling direction. In the rear zone, the principal stress direction tends to be stable and the principal stress value undergoes dynamic changes, and a large number of vertical hole axis tension fractures are developed. The drilling disturbance zone appears near the hole wall and has an important influence on the stability of the hole wall, while the confining pressure main control zone determines the antireflection effect around the hole and the influence radius of the hole. This work helps the understanding of the damage range and failure characteristics of the surrounding rock during the drilling process and has great significance for the guidance of drilling design.

Analysis of the top coal stability of the large section open-off cut under the gob in thick seams slicing mining

The reserved thickness of top coal has an important influence on the stability of a large section open-off cut under gob in the thick seams slicing mining. The destabilization extremum conditions of the open-off cut top coal were derived from by elastic–plastic theory, and the optical fibre sensing technology was utilized to monitor the top coal deformation law with different thicknesses (3, 3.5, and 4 m) in the physical similar simulation experiment in the paper. The results show that the top coal thickness is greater than 3.4 m without tension cracks. In the vertical direction, the top coal of the large open-off cut is divided into mining and excavation disturbance zones under the influence of the upper slice coal mining and the excavation disturbance. In the direction of the span of the top coal can be divided into the roof fall risk zone and the warning zone. The deformation changes from exponential to linear to logarithmic in the roof fall risk zone, and it changes from linear to logarithmic in the roof fall warning zone as the number of excavations increases. The sinking amount in the two zones is smaller as the thickness of the top coal becomes larger. It is comprehensively determined that the thickness of the top coal of open-off cut is set as 3.5 m, the stability is moderate, and the field application shows that the integrity of the top coal is good after support, and the maximum off-layer value is 6 mm, which can satisfy the production requirements.

Analysis of Regional and Residual Gravity Disturbance of Major Fault Belts in the Tarim Basin, Western China

Large fault belts often influence the paleo-geomorphic changes in basins and control hydrocarbon accumulation and distribution in basins. Based on the gravity field model European Improved Gravity model of the Earth via New techniques (EIGEN)-6C4, this study calculated the residual Bouguer gravity disturbance of the Tarim Basin by using the minimum curvature method and analyzed gravitational characteristics of major fault belts of the Tarim Basin. The residual Bouguer disturbance exhibits linear residual Bouguer disturbance zones in the Tianshan Mountains, West Kunlun, and the Altyn region, which is consistent with the spatial distribution of their related fault belts. The regional Bouguer disturbance is related to crust–mantle boundary depth, which can be used to roughly estimate crust thickness. Thus, we suggest that the crust–mantle boundary depth order of major faults from deep to shallow is the Altyn region, West Kunlun, and Tianshan Mountains. There is a discontinuity in the residual Bouguer disturbance of West Kunlun, which compares well with the fault belt of West Kunlun. Furthermore, the residual Bouguer disturbance of the Tarim Basin has a series of elliptical areas with a central positive disturbance located within the Bachu uplift and other uplift structures. The residual Bouguer disturbance also reflects the position and distribution of the major fault belts and the boundary of the Tarim Basin, which can provide guidance for dynamic evolution analysis of large basins.

Электро-механическая модель тактильного полимерного оптоволоконного пьезоэлектролюминесцентного покрытия

An electro-mechanical model has been developed for the functioning of a tactile polymer coating with a built-in fiber optic piezoelectroluminescent (PEL) sensor and many villi (vibrisses) on the surface of the coating along the sensor. Local deformation of the coating and the built-in sensor is carried out in the disturbance zones, witch are local areas of the coating (sensor) near the points of cantilever fastening of the tufts at their contacts with the analyzed object. Mechanoluminescent effect occurs on deformed sections of sensor when electric field of section of its piezoelectric layer affects adjacent section of electroluminescent layer. Modeling and analysis of substantially inhomogeneous deformation and electric fields occurring in piezoelectric and electroluminescent layers of the sensor were carried out and characteristic forms of generated informative light signals for different cases of deformation of bending villi in different planes and torsion as a result of contact of villi ends with the surface of the analyzed object were revealed.

Modelling of the LTDE-SD radionuclide diffusion experiment in crystalline rock at the Äspö Hard Rock Laboratory (Sweden)

This study shows a comparison and analysis of results from a modelling exercise concerning a field experiment involving the transport and retention of different radionuclide tracers in crystalline rock. This exercise was performed within the Swedish Nuclear Fuel and Waste Management Company (SKB) Task Force on Modelling of Groundwater Flow and Transport of Solutes (Task Force GWFTS).Task 9B of the Task Force GWFTS was the second subtask within Task 9 and focused on the modelling of experimental results from the Long Term Sorption Diffusion Experiment in situ tracer test. The test had been performed at a depth of about 410m in the Äspö Hard Rock Laboratory. Synthetic groundwater containing a cocktail of radionuclide tracers was circulated for 198 days on the natural surface of a fracture and in a narrow slim hole drilled in unaltered rock matrix. Overcoring of the rock after the end of the test allowed for the measurement of tracer distribution profiles in the rock from the fracture surface (A cores) and also from the slim hole (D cores). The measured tracer activities in the rock samples showed long profiles (several cm) for non- or weakly-sorbing tracers (Cl-36, Na-22), but also for many of the more strongly-sorbing radionuclides. The understanding of this unexpected feature was one of the main motivations for this modelling exercise. However, re-evaluation and revision of the data during the course of Task 9B provided evidence that the anomalous long tails at low activities for strongly sorbing tracers were artefacts due to cross-contamination during rock sample preparation. A few data points remained for Cs-137, Ba-133, Ni-63 and Cd-109, but most measurements at long distances from the tracer source (>10mm) were now below the reported detection limits.Ten different modelling teams provided results for this exercise, using different concepts and codes. The tracers that were finally considered were Na-22, Cl-36, Co-57, Ni-63, Ba-133, Cs-137, Cd-109, Ra-226 and Np-237. Three main types of models were used: i) analytical solutions to the transport-retention equations, ii) continuum-porous-medium numerical models, and iii) microstructure-based models accounting for small-scale heterogeneity (i.e. mineral grains, porosities and/or microfracture distributions) and potential centimetre-scale fractures. The modelling by the different teams led to some important conclusions, concerning for instance the presence of a disturbed zone (a few mm in thickness) next to the fracture surface and to the wall of the slim hole and the role of micro-fractures and cm-scale fractures in the transport of weakly sorbing tracers. These conclusions could be reached after the re-evaluation and revision of the experimental data (tracer profiles in the rock) and the analysis of the different sets of model results provided by the different teams.

Prediction of the stress-strain state and stability of the front of tunnel face at the intersection of disturbed zones of the soil mass

The article presents a numerical solution of the spatial elastic-plastic problem of determining the stability of the tunnel face soils at the intersection of disturbed zones of the soil mass. The relevance of the study is related to the need to take into account the zones of disturbed soils when assessing the face stability to calculate the parameters of the support. Based on the finite element method implemented in the PLAXIS 3D software package, the construction of a finite element system "soil mass-disturbance-face support" and modeling of the intersection of the disturbed zones of the soil mass were performed. To assess the condition of soils, deformation and strength criteria are taken. The deformation criterion is expressed by the value of the calculated displacement of the tunnel contour in the face, and the strength criterion - by the safety coefficient until the maximum values of the stress state are reached according to the Coulomb–Mohr criterion. The results of the study are presented in the form of histograms of the safety coefficient dependences on the distance to the disturbance at different bending stiffness of the face support structure, as well as the isofields of deformation development. The parameters of rockfall formation in the face zone at the intersection of zones of disturbed soils were determined. The local decrease in strength and deformation properties in the rock mass along the tunnel track should be taken into account when assessing the stability of the tunnel face and calculating the parameters of the support. Within the framework of the constructed closed system, a qualitative agreement of the simulation results with the case of a collapse in the face during the construction of the Vladimirskaya-2 station of the St. Petersburg Metro was obtained.

Dynamic failure mechanism of tunnel under rapid unloading in jointed rockmass: A case study

Field observations demonstrate that rapid unloading can induce intensive dynamic failure of a tunnel in a jointed rockmass. In this study, we demonstrate the characteristics of the dynamic failure and establish a series of validated discrete element models to investigate the mechanism of the dynamic failure. Our results indicate that the excessive release of strain energy and the complex nonlinear behavior of joints together resulted in the dynamic failure. Primarily, joints can enlarge the unloading disturbance zone (UDZ) and lead to the excessive release of strain energy, especially for a model with smaller joint spacing and higher unloading rate. Secondly, joints can significantly decrease the dependence of the dynamic effect on the unloading rate and expand the unloading time threshold that can induce the dynamic effect, more importantly, the nonlinear variation of joint stiffness not only induces vibration localization but also increases vibration amplitude and reduces vibration frequency.

Characterization of Typical Complex Hydrogeological Condition of Structurally Disturbed Shear Zone Areas of Palakkad District in Western Ghats Region, Central Kerala

Aquifer characteristics and hydrogeological condition of structurally disturbed shear zone areas of Palakkad district in Western Ghats Region of Palakkad district have been studied. The study of sub-surface hydrogeological framework of aquifers up to 200 meters below ground level (m bgl) was carried out to quantify groundwater resources, water quality, hydraulic properties with an aim to evolve a sustainable aquifer management plan in consideration with the water level monitoring and exploratory drilling. The hard rock terrains have been structurally controlled by shear a zone, which facilitate to develop numerous fractures and becomes potential repositories of groundwater. The thickness of lateritization changes between 1.02 and 24.1 m. The premonsoon depth to water level varies from 1.58 to 14.20mbgl, but that of PSM in between 0.60 and 21.50 m mbgl with a fluctuation about 6m. The quantification of groundwater potential in the aquifers of consolidated formation within the shear zones and establishment of a futuristic model of aquifer management plan for the area are the highlights of the work. Keywords: Laterite, Aquifer, Potential, Management, GIS, SWOT

Double-O-Tube Shield Tunneling-Induced Soil Displacement Considering Burial Depth and Convergence Mode: Transparent Soil Experiment and DEM Simulation

Double-O-tube shield tunneling technology has gained extensive attention due to saving space and the high cost-effectiveness of the underground construction method. Estimating and predicting DOT shield tunneling-induced soil displacements is essential to prevent damage to nearby aboveground and underground structures in densely populated urban areas. This study develops a device for modeling DOT shield tunneling based on transparent soil technology and image processing technique and investigates soil displacement during the construction process of the DOT shield tunnel, which is considered in the uniform convergence mode (UCM) of soil loss. Meanwhile, the soil displacement under the non-uniform convergence mode (NCM) is analyzed contrastively using a two-dimension particle flow code (PFC2D). The results show that horizontal displacements increase gradually when the shield tail passes the monitoring face, while settlements increase rapidly. The maximum horizontal displacement of the surface and the maximum surface settlement under NCM are slightly larger than those under UCM. A trapezoid-shaped failure pattern of soil is experienced at three tunnel depths. The maximum soil displacement under NCM is 1.93, 2.10, and 2.05 times, respectively, as much as that under UCM, corresponding to H/D (the ratio of the tunnel depth to the tunnel diameter) = 1.0, 1.5, and 2.0. The soil arch effect above DOT tunnels arises as the DOT tunnel depth increases. Moreover, the experimental and numerical results are adopted to assess the validity of the proposed model, which indicates that the proposed model is close to the test results of the disturbance zone on DOT tunnels.

A new method of acceleration of consolidation using a cylindrical cavity expansion in presence of vertical drains

The purpose of this paper is to investigate the acceleration of consolidation through a new method composed by a cylindrical cavity expansion (CCE) combined with vertical drains (VD). In fact, the cylindrical cavity applies a radial displacement in the soil. Excess pore pressures will be consequently generated and the consolidation process will occur at the vicinity of the cavity wall. The dissipation of excess pore pressures can be enhanced in presence of VD installed at a radial distance r d from the center of the cylindrical cavity. During cavity expansion, the variation of excess pore pressures and incremental stresses are analyzed. The subsequent consolidation around the CCE in the presence of VD is solved using the Finite Difference Method (FDM) with taking into account the effect of the CCE installation. This effect is described by a decrease in horizontal permeability within a disturbed zone. Obtained results show that the proposed system of consolidation i.e., composed by a CCE combined with VD, greatly accelerates the consolidation of soil. Furthermore, the effects of the extent of the disturbed zone and the soil permeability reduction have a significant influence on the consolidation of the soil. The application of the proposed method to the case of “Tunis Rades La Goulette Bridge” is presented and discussed.

Drilling and Grouting Works for Pressurised Groundwater Conditions of the Semmering Base Tunnel

The Semmering Base Tunnel (SBT), with a total length of 27.3 km, is one of the leading construction projects of the Baltic-Adriatic Railway Network. The tunnel connects the two federal provinces of Lower Austria and Styria and cuts through the eastern part of the Alps. The construction lot SBT 1.1-Tunnel Gloggnitz is characterized by a complex geological- and hydro-geological architecture containing alternating competent geological structures, major fault zones, and corresponding geological transition zones. There are three main water-bearing formations at the construction lot SBT 1.1: (a) Karst-prone blocky limestone with an initial water pressure of 10 bar. The discontinuities form a highly permeable interconnected joint network with a significant storage coefficient of the groundwater table. (b) Massive to blocky dolomite with an initial water pressure of 25 bar. The systematic discontinuities and disturbed zones of subsidiary structures with karst form a permeable, interconnected joint network. (c) The transition zone of the limestone to base structure marks the most challenging area for consolidation- and sealing grouting. Weak fault rocks characterize transition zones with intense fracturing. However, as subjected to high groundwater pressure of 10 bar, these zones are associated with the potential of flowing ground conditions. Based on the overall project requirements, specific drilling- and grouting methods and materials for pre-excavation grouting have been established and successfully implemented in the construction process. The innovations include a Standpipe-Packer substituting a conventional steel standpipe, a specifically cased drilling system with grouting inserts to prevent erosion within the borehole and allow for defined grouting. In addition, this Grouting-Pipe system replaces standard tube-à-manchettes and controls the flushing while drilling with preventers. Finally, a combined cement-polyurethane grout mix (Hybrid Grout) was implemented to stabilize the grout. The implementation of these measures will be discussed in detail, and their benefits to the construction process will be highlighted.

Investigations of effect of underground excavations using hydrologic and tracer transport modeling

Understanding the effect of underground excavations and barrier capability of the near field are relevant to the geologic disposal of nuclear waste. For a repository in crystalline host rock characterization of the naturally fractured rock and the excavated disturbed zone are of importance to the study of migration of radionuclides. Excavations could weaken the repository components that are part of the engineered barrier system. Permeable excavated disturbed zones could also develop around the repository walls that could create conduits for radionuclides away from the repository. Experimental hydrology and tracer transport data from the Mizunami Underground Research Laboratory in Central Japan have been used to develop a site-scale model for the study area. Upscaled permeability and porosity data of a previously developed discrete fracture network model were used. In this study development and utilization of the model is presented. The model was used to reproduce hydrology and non-reactive transport in the modeling area. The modeling work includes prediction of inflow of water into the research tunnel during excavation of tunnel parts and related draw-down. The modeling work also includes prediction of pressure recovery and changes in tracer distribution as a result of water filling of a tunnel chamber. Modeling results were successfully compared with the project hydrology and tracer concentration histories. Modeling results of inflow and recovery were complementary and together with fracture characterization combined to give a better constraint on the system. The study provides experimental and modeling methods to study the effect of excavations in an underground research laboratory.

Finite element modelling of helical pile installation and its influence on uplift capacity in strain softening clay

This study investigated the effect of helical pile installation in undrained softening clay using a coupled Eulerian-Lagrangian (CEL) finite element modelling approach. A previously published strain softening soil constitutive model was used to evaluate soil disturbance. The influence of two key strain softening parameters was considered to assess installation-induced soil disturbance. The CEL-predicted remoulded soil strength field was then imported into a finite element limit analysis (FELA) to evaluate the subsequent influence on uplift capacity. The CEL results showed that helical pile installation caused a significantly disturbed zone of soil that measured approximately 1.4 helix diameters in plan and extended the full length of the pile. When the disturbed soil strength field was imported into FELA calculation, it was found that the solutions reported in previous literature had significantly overestimated the ultimate uplift capacity for softening clay. The numerical output informed the development of a new closed-form analytical approach to predict uplift capacity considering the influence of the installation process. The design method was shown to provide a high-fidelity representation of the numerical results.

Relationship of isotopic variations with spring density in the structurally controlled springs and related geosystem services in Alaknanda Valley, Garhwal Himalaya, India

As a traditional water source, springs are vital for Himalayan communities and it is essential to consciously focus on springs conservation. We report oxygen isotopes (δ18O) of spring water before, within, and after the tectonically active zones of the Alaknanda Valley, Uttarakhand. Higher variation of δ18O in the spring waters is found in highly tectonically disturbed zone i.e., Zone-2 with δ18O range − 4.9‰ to − 9.0‰ compared to tectonically less disturbed zones: Zone-1 and Zone-3 with δ18O value range − 7.9‰ to − 9.9‰ and − 7.4 to − 10.2‰ respectively. We hypothesize that the highly active thrust zones (Zone-2) with increased permeability compared to other Zones, manifested as greater spring density, results in higher water recharge in Zone-2. Very high to high spring density stretches are dominant in Zone-2 compared to Zone-1 and Zone-3. Stretches in Zone-2 with high spring density formed due to its highly tectonically active nature leads to the higher isotopic variation in Zone-2. The study also identifies the geosystem services provided by thrust zones as water resources to the local people and need of conservation modalities to manage the spring water resources in the thrust zones.