Groundwater Responses to Earth Tides: Evaluation of Analytical Solutions Using Numerical Simulation

Harmonic Earth tide components in well water levels have been used to estimate hydraulic and geomechanical subsurface properties. However, the robustness of various methods based on analytical solutions has not been established. First, we review the theory and examine the latest analytical solution used to relate well water levels to Earth tides. Second, we develop and verify a novel numerical model coupling hydraulics and geomechanics to Earth tide strains. Third, we assess subsurface conditions over depth for a range of realistic properties. Fourth, we simulate the well water level response to Earth tide strains within a 2D poroelastic layered aquifer system confined by a 100 m thick aquitard. We find that the non-linear inversion of analytical solutions to match two observations (amplitudes and phases) to multiple unknown parameters is sensible to the initial guess. We reveal that undrained, confined conditions are necessary for the analytical solution to be valid. This occurs for the dominant M$_2$ frequency at depths >50 m and requires specific storage at constant strain of S$_ϵ$ ≥ 10$^{−6}$ m$^{−1}$, hydraulic conductivity of the aquitard of k$_l$ ≤ 5 ⋅ 10$^{−5}$ ms$^{−1}$ and aquifer of k$_a$ ≥ 10$^{−4}$ ms$^{−1}$. We further illustrate that the analytical solution is valid in unconsolidated systems, whereas consolidated systems require additional consideration of the Biot modulus. Overall, a priori knowledge of the subsurface system supports interpretation of the groundwater response. Our results improve understanding of the effect of Earth tides on groundwater systems and its interpretation for subsurface properties

Multifactor analysis of specific storage estimates and implications for transient groundwater modelling

Specific storage (S$_S$) has considerable predictive importance in the modelling of groundwater systems, yet little is known about its statistical distribution and dependency on other hydrogeological characteristics. This study provides a comprehensive overview and compiles 430 values of S$_S$ from 183 individual studies, along with complementary hydrogeological information such as estimation methods, lithology, porosity, and formation compressibility. Further evaluation of different approaches to determine and utilize S$_S$ values for numerical groundwater modelling, along with the scale and source of uncertainty of different measurement methods, was carried out. Overall, S$_S$ values range across six orders of magnitude (from 3.2 × 10$^{–9}$ to 6 × 10$^{–3}$ m$^{–1}$) with a geometric mean of 1.1 × 10$^{–5}$ m$^{–1}$ and the majority (> 67%) of values are in the order of 10$^{–5}$ and 10$^{–6}$ m$^{–1}$. High S$_S$ values of ~10$^{–4}$ m$^{–1}$ were reported for glacial till and sandy lithologies, particularly for shallow and thin strata where leakage may obscure the estimation of S$_S$. A parallel assessment of 45 transient regional-scale groundwater models reveals a disconnect between findings of this study and the way S$_S$ is treated in practice, and that there is a lack of foundational S$_S$ data to conduct quantitative uncertainty analysis. This study provides the first probability density functions of S$_S$ for a variety of lithology types based on the field and laboratory tests collated from the literature. Log transformed S$_S$ values follow a Gaussian/normal distribution which can be applied to evaluate uncertainties of modelling results and therefore enhance confidence in the groundwater models that support decision making

Comparing methods of barometric efficiency characterisation for specific storage estimation

Groundwater responses to barometric pressure fluctuations are characterized using the concept of barometric efficiency (BE). For semiconfined and confined aquifers, BE values can be used to provide efficient, low-cost estimates of specific storage. This study compares, for the first time, eight existing methods of BE estimation. Comparisons were undertaken using data from the Peel region of Western Australia. Fourier analysis and regression deconvolution methods were used to estimate aquifer confinement status. The former approach was found to be robust and provided a quantitative basis for spatial comparisons of the degree of confinement. The latter approach was confounded by the presence of diurnal and/or semidiurnal signals. For wells at which semiconfined or confined responses were identified, frequency and time domain methods were used to estimate BE values. Most BE estimation methods were similarly confounded by diurnal and/or semidiurnal signals, with the exception of the Acworth et al. (2016) method. Specific storage values calculated from BE values were order-of-magnitude consistent with the results of four historical pumping tests. The methods implemented in this research provide efficient, low-cost alternatives to hydraulic testing for estimating aquifer confinement, as well as the BE and specific storage of semiconfined and confined aquifers. The frequency and duration of observations required by these methods are minimal; for example, typically requiring a minimum of four observations per day over a four month period. In some locations they may allow additional insights to be derived from existing groundwater hydrograph data

Technical note: Disentangling the groundwater response to Earth and atmospheric tides to improve subsurface characterisation

The groundwater response to Earth tides and atmospheric pressure changes can be used to understand subsurface processes and estimate hydraulic and hydro-mechanical properties. We develop a generalised frequency domain approach to disentangle the impacts of Earth and atmospheric tides on groundwater level responses. By considering the complex harmonic properties of the signal, we improve upon a previous method for quantifying barometric efficiency (BE), while simultaneously assessing system confinement and estimating hydraulic conductivity and specific storage. We demonstrate and validate this novel approach using an example barometric and groundwater pressure record with strong Earth tide influences. Our method enables improved and rapid assessment of subsurface processes and properties using standard pressure measurements

Otimização estrutural e geotécnica de um muro de contenção com o uso do Search Group Algorithm

TCC (graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Engenharia Civil.O muro de contenção é um sistema construtivo comumentemente utilizado em situações com instabilidade geotécnica. Aplicou-se, neste trabalho, o algoritmo de otimização meta-heurístico \textit{Search Group Algorithm} (SGA) para obtenção das funções objetivo independentes de peso e de custo em dois exemplos de muros de contenção cantilever. Foram consideradas as estabilidades geotécnicas de tombamento, deslizamento e capacidade de suporte da fundação, e os requisitos estruturais de esforços flexurais e cortantes em quatro seções críticas do muro para a formulação matemática do problema. As variáveis de projeto geométricas foram tomadas como contínuas e as variáveis de projeto estruturais como discretas. Não foi feita análise de função multiobjetivo neste problema, portanto foram avaliadas as funções de peso e custo separadamente. O objetivo do presente trabalho é avaliar a eficiência do SGA através dos valores minimizados de peso e custo em duas situações diferentes, as duas servem para comparar os resultados obtidos pelo SGA aos obtidos por Camp e Akin com o \textit{Big Bang-Big Crunch Algorithm} (BB-BC) e a segunda para ponderar o efeito da adição de uma chave de resistência translacional na base do muro. Nos dois exemplos é feita a análise de sensibilidade por variação paramétrica de sobrecarga, ângulo de inclinação do talude e ângulo de atrito interno do solo de aterro, e no primeiro exemplo é analisada a convergência do algoritmo proposto. Cada resultado foi obtido por 100 execuções do algoritmo e elencados em melhor função objetivo, média e desvio padrão.A retaining wall is a constructive system commonly used in situations where geotechnical instability occurs. A metaheuristic optimization algorithm, the Search Group Algorithm (SGA), was used to obtain the cost and weight objective functions from two examples of cantilever retaining walls. Geotechnical stability and structural requirements were considered in the mathematical formulation of the problem, wich are comprised by the overturning moments criteria, sliding resistance, soil bearing capacity and flexural and shear requirements in four critical sections. The geometric design variables were taken as continuous and the structural design variables were taken as discrete. The objective functions of cost and weight are independent, therefore multiobjective functions were not used. The objective of this work is to evaluate the efficiency of the SGA through the minimized values of weight and cost in two different situations, both of them aims to compare the results obtained by the use of the SGA to those obtained by Camp and Akin with the Big Bang-Big Crunch Algorithm (BB-BC) and the second to evaluate the effect of a base shear key. In both examples a sensitivity analysis is made with varying surcharge loads, backfill slope and internal friction angle of the retained soil and in the first example a convergence analysis of the proposed algorithm is made. Each result is obtained by 100 executions of the algorithm and listed as best objective funtion, mean value and standard deviation

Genetic Dissection of Cardiac Remodeling in an Isoproterenol-Induced Heart Failure Mouse Model.

We aimed to understand the genetic control of cardiac remodeling using an isoproterenol-induced heart failure model in mice, which allowed control of confounding factors in an experimental setting. We characterized the changes in cardiac structure and function in response to chronic isoproterenol infusion using echocardiography in a panel of 104 inbred mouse strains. We showed that cardiac structure and function, whether under normal or stress conditions, has a strong genetic component, with heritability estimates of left ventricular mass between 61% and 81%. Association analyses of cardiac remodeling traits, corrected for population structure, body size and heart rate, revealed 17 genome-wide significant loci, including several loci containing previously implicated genes. Cardiac tissue gene expression profiling, expression quantitative trait loci, expression-phenotype correlation, and coding sequence variation analyses were performed to prioritize candidate genes and to generate hypotheses for downstream mechanistic studies. Using this approach, we have validated a novel gene, Myh14, as a negative regulator of ISO-induced left ventricular mass hypertrophy in an in vivo mouse model and demonstrated the up-regulation of immediate early gene Myc, fetal gene Nppb, and fibrosis gene Lgals3 in ISO-treated Myh14 deficient hearts compared to controls

In situ estimation of subsurface hydro-geomechanical properties using the groundwater response to semi-diurnal Earth and atmospheric tides

Subsurface hydro-geomechanical properties crucially underpin the management of Earth\u27s resources, yet they are predominantly measured on core samples in the laboratory while little is known about the representativeness of in situ conditions. The impact of Earth and atmospheric tides on borehole water levels is ubiquitous and can be used to characterise the subsurface. We illustrate that disentangling the groundwater response to Earth (M₂) and atmospheric tidal (S₂) forces in conjunction with established hydraulic and linear poroelastic theories leads to a complete determination of the whole hydro-geomechanical parameter space for unconsolidated systems. Further, the characterisation of consolidated systems is possible when using literature estimates of the grain compressibility. While previous field investigations have assumed a Poisson\u27s ratio from literature values, our new approach allows for its estimation under in situ field conditions. We apply this method to water level and barometric pressure records from four field sites with contrasting hydrogeology. Estimated hydro-geomechanical properties (e.g. specific storage; hydraulic conductivity; porosity; shear, Young\u27s, and bulk moduli; Skempton\u27s and Biot–Willis coefficients; and undrained or drained Poisson\u27s ratios) are comparable to values reported in the literature, except for consistently negative drained Poisson\u27s ratios, which is surprising. Our results reveal an anisotropic response to strain, which is expected for heterogeneous (layered) lithological profiles. Closer analysis reveals that negative Poisson\u27s ratios can be explained by in situ conditions differing to those from typical laboratory core tests and the small strains generated by Earth and atmospheric tides. Our new approach can be used to passively, and therefore cost-effectively, estimate subsurface hydro-geomechanical properties representative of in situ conditions and it improves our understanding of the relationship between geological heterogeneity and geomechanical behaviour