Ensaios de penetração dinâmica são ferramentas de investigação geotécnica de fácil execução e baixo custo. Estas características tornaram o ensaio SPT na técnica de investigação mais utilizada em diversos países como Canadá, Estados Unidos, Japão e principalmente, no Brasil. Em contrapartida, a penetração dinâmica de amostradores produz um complexo mecanismo de reação do solo, função da energia entregue ao sistema e da capacidade de absorção desta energia pelo próprio solo. Na prática de engenharia, este mecanismo é simplificado através do uso de abordagens empíricas. Pesquisas na década de 1970, realizadas por Schmeertmmann & Palacius (1979) e Schmertmmann (1979), avaliaram a energia inserida no sistema haste-amostrador objetivando a padronização do ensaio SPT para diferentes equipamentos e procedimentos. Pesquisas recentes de interpretação do ensaio utilizam conceitos de conservação de energia e trabalho realizado pelo amostrador ao penetrar no solo, visando equacionar a resistência mobilizada (eg. Oderebrecht, 2003; Odebrecht et al, 2005; Schnaid, 2005). Na presente pesquisa, são utilizados os conceitos de conservação de energia, associados com equações de equilíbrio dinâmico e com a teoria de expansão de cavidades (Vésic, 1972) para desenvolver uma rotina de simulação numérica capaz de modelar os principais mecanismos de reação do solo devido cravação de um amostrador. A partir da validação da rotina de simulação numérica para ensaios dinâmicos de distintas geometrias (ensaios SPT, ILPT, NALPT e RLPT), avalia-se a variabilidade da energia entregue ao solo devido às diferenças de compacidade do solo, eficiência do golpe, geometria do martelo, tipo e comprimento da composição de hastes. Destas simulações, é possível observar as diferenças de resultados entre ensaios de distintas geometrias de martelo e composição de hastes, concluindo-se que pequenas variações geométricas produzem diferenças no índice de resistência à penetração. Como conseqüência, sugere-se que a interpretação dos resultados depende de um método racional de análise capaz de incorporar estes efeitos à estimativa de propriedades de comportamento de solos. Na identificação dos mecanismos de ruptura para solos de diferentes compacidades foram desenvolvidas duas metodologias que permitem estimar a resistência ao cisalhamento de solos granulares a partir do índice de resistência à penetração medida em ensaios de penetração dinâmica. A primeira metodologia utiliza a rotina de simulação numérica desenvolvida através de uma análise do Problema do valor inverso, enquanto a segunda proposta utiliza os pressupostos do Teorema de Buckingham no estabelecimento de uma solução analítica que permita estimar o ângulo de atrito de pico de materiais granulares. As duas alternativas foram validadas através de estudo de casos, permitindo concluir que as soluções produzem estimativas de ângulo de atrito realistas, de mesma ordem de magnitude que outras abordagens difundidas no meio técnico e compatíveis com resultados de ensaios de campo e laboratório. / Dynamic penetration tests are simple, economic and easily performed geotechnical investigation tools. Due to these general characteristics, the test has been used systematically in many countries such as Canada, United States, Japan and Brazil. Despite the attractive conditions of performing a simple test, dynamic penetration of a any tool into a soil mass produces a complex soil reaction mechanism that depends on the energy delivered to the soil, as well as the capability of the soil to absorb this energy. Given this complexity a simple approach of interpreting the test by using empirical correlations has prevailed. In 1970, Schmeertmmann & Palacius (1979) and Schmertmmann (1979) develop the first rational methodology to compute the energy delivered to the rod-sampler system that has been incorporated to engineering practice by normalizing different practices in terms of a reference energy. Most recent researches of SPT test interpretation make uses of energy concepts and work to compute the mobilized soil-resistance due to the sampler penetration (e.g. Oderebrecht, 2003; Odebrecht et al, 2005; Schnaid, 2005). In present research these recent approaches are extended through the use of energy concepts associated with dynamic equilibrium equations and cavity expansion theory (Vésic, 1972). Constitutive equations have been incorporated to a numerical simulation routine able to reproduce the some of the most important processes of soil reaction during dynamic in cohesionless soil. The model validation for different dynamic penetration test geometries (SPT, ILPT, NALPT and RLPT) enabled the energy delivered to soil to be evaluated and the effects of soil density, blow efficiency, hammer geometry, rod type and length to be assessed. From a number of simulations, it was possible to describe the differences related typical geometrical changes (i.e. hammer length, rod cross section and length). Conclusions from the analysis are that small geometrical changes in hammer and rod characteristics - typically observed in different SPT practices - produce differences into the measured blow count. As consequence, it is suggested that interpretation of dynamic penetration test results will depend on a model capable of incorporating all these effects when attempting to derive soil constitutive parameters. This is one of the outputs of the present study that lead to the development of two rational methodologies to assess the internal friction angle of cohesionless soils from dynamic penetration blow count. The first one uses the numerical simulation routine as a Inverse Boundary Value problem while the second one uses the Buckingham’s Theorem to develop an analytical equations that correlates the N-SPT with the soil shear strength. Both methodologies have been validated by a series of case studies designed to demonstrate that the proposed solution produces friction angle values of the same order of magnitude of other approaches and compatible to measurements produced by laboratory and in situ tests.

Orientador: Antonio Jose da Silva Maciel / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-06T18:35:35Z (GMT). No. of bitstreams: 1 Albiero_Daniel_M.pdf: 5056205 bytes, checksum: 94067cb876fadf926d673b4af8cc5f8c (MD5) Previous issue date: 2006 / Resumo: Este trabalho foi desenvolvido no campo experimental da Faculdade de Engenharia Agrícola da UNICAMP e teve como objetivo avaliar o novo sistema de preparo de solo Conservacionista em Faixas com "Paraplow" Rotativo, dando ênfase para a aplicação em sistemas de plantio voltados para agricultura familiar. A avaliação foi dividida em três grupos: caracterização da ferramenta como conservacionista; caracterização geométrica da faixa bem preparada; e determinação da configuração operacional ótima para a agricultura familiar. Foi utilizada a técnica de análise dimensional que através do planejamento experimental à ela atrelado define o elenco dos principais parâmetros a serem medidos e importantes para as respectivas determinações, caracterizações e comprovações. Com estes parâmetros definidos, em um total de vinte e dois parâmetros foram realizados o experimento em campo em um delineamento experimental totalmente aleatório, onde foi realizado o experimento com oito tratamentos, onde cada tratamento disposto em uma linha experimental com cinco pontos de coletas de dados antes, e cinco pontos de coleta de dados após a passagem da ferramenta. Para este arranjamento foram feitas duas repetições para cada parâmetro totalizando dezesseis linhas experimentais, perfazendo um total de dez pontos avaliados para cada tratamento. Com os dados coletados foi possível realizar as análises através da: estatística descritiva básica, análise dimensional e análise de variância. Os resultados obtidos demonstram claramente que o "Paraplow" Rotativo é uma ferramenta de preparo de solo conservacionista. As avaliações operacionais indicam que esta ferramenta acoplada a um motocultor de 12 cv é adequada a utilização pela agricultura familiar, tendo capacidades de campo compatíveis com as necessidades das pequenas propriedades. Comparações entre as metodologias da Análise Dimensional e a Análise de Variância de uma via simples, demonstram a superioridade da Análise Dimensional em estudos de dinâmica do solo e avaliações de máquinas de preparo de solo / Abstract: This work was developed in the experimental field of Agricultural Engineering CoI: of State University of Campinas, and it had as objective to evaluate the new system of tillage in strip conservationist with Rotary "Paraplow", it was given emphasis for application in seeding systems appropriate for small fanns. The evaluation was divide( three groups: characterization of tool as conservationist; geometric characterization of st determination of operation configuration for small fanns. It was used the dimensional analysis method for to define the experimental plannin, having been determined which parameters should be measured. These parameters, in a tota twenty two, they were arrangement in a experimental design completely random, where t were realized the experiment with eight treatments, each treatment was allocated in experimental strip, with five points of obtaining data, before and after the action of the tI for these arrangement were made two repetitions for each parameter, totalizing sixt experimental strips, with ten point of obtaining data for each treatment. With these data it ' possible to realize the analysis through: descriptive statistical; dimensional analysis; . variance analysis. The results demonstrate that the Rotary "Paraplow" is a tool of soil till conservationist. The evaluations show that this tool coupled with tiller with 12 cv appropriated for small fanns, it have been compatible field capacity with the needs of sn fanns. Comparisons between the methodologies of dimensional analysis and the varia: analysis of one way, showed the superiority of the dimensional analysis in studies of ~ dynamics and evaluations of soil tillage machines / Mestrado / Maquinas Agricolas / Mestre em Engenharia Agrícola

Research performed on the subject of dynamic soil-structure interaction (SS) concerning railway bridges is presented in this thesis with the focus on simply supported railway bridges supported by shallow foundations in soil strata on bedrock. The research aims to obtain insight into the SSI of high-speed railway bridges and to provide recommendations on how to model the soil-bridge system from a design perspective. A three-dimensional (3D) simply supported soil-bridge model was first developed and the effects from model assumptions made on the soil-foundation system was evaluated in a 3D setting (paper I). The soil-foundation system was then refined and a model assumptions study was performed in order to evaluate the effects of model assumptions on impedance functions, including the influence of the permanent load acting on the soil-foundation system (paper II). Finally, a study of the assembled soil-bridge system was performed in an extensive parametric study including a set of 2D bridge models in combination with a set of shallow foundations in soil strata on bedrock (paper III). A supplementary section related to paper III was also added in this thesis, showing the effects of the substructure mass. The model assumptions made when creating the soil-foundation model and the soil-bridge model can be very important and must be made with care. The permanent load acting on the soil-foundation systems of shallow foundations may alter the impedance functions significantly. The substructure mass may alter the behavior of the soil-bridge system depending on its magnitude, and neglecting it gives inaccurate results. The 3D effects of SSI do not cause high vibrations due to modes other than the first bending mode, and assuming a 2D bridge model is generally acceptable. The effects of SSI on the soil-bridge systems with shallow soil strata are largely dependent on the ratio between the natural frequency of the bridge and the fundamental frequency of the soil. Depending on the value of this ratio, the effect of including SSI in bridge models may contribute to the bridge obtaining a negligible, conservative, or non-conservative response, as compared to the bridge with the assumption of non-flexible supports. / Forskning i syfte att utröna effekten av dynamisk jord–struktur-interaktion (SSI)på järnvägsbroar presenteras i denna avhandling med huvudfokus på fritt upplagdabroar med stöd av plattgrundlagda fundament i jordar på fast berggrund. Forsknin-gen syftar till att ge förståelse för interaktionen mellan jord och järnvägsbroar samtatt ge rekommendationer på hur systemet kan modelleras ur ett designperspektiv.En tredimensionell (3D) fritt upplagd jord–bromodell utvecklades först och effek-terna av modellantaganden gjorda på jord–grundläggningssystemet utvärderadesi en 3D miljö (artikel I). Jord–grundläggningssystemet förfinades och en studiegenomfördes för att utvärdera effekterna av modellantaganden på impedansfunk-tioner, inklusive påverkan av den permanenta belastningen som verkar på jord–grundläggningssystemet (artikel II). Slutligen utfördes en omfattande parametriskstudie av det sammansatta jord–brosystemet där en uppsättning tvådimensionella(2D) bromodeller kombinerades med en uppsättning jordar (artikel III). Ett kom-pletterande avsnitt relaterat till artikel III lades till i denna avhandling som visareffekterna av massan av underbyggnaden på jord–brosystemet.De modellantaganden som görs vid skapandet av jord–grundläggningsmodeller ochjord–bromodeller kan vara mycket viktiga och bör utföras med varsamhet. Den per-manenta belastningen som verkar på jord–grundläggningssystemet kan väsentligtförändra impedansfunktionerna. Massan av underbyggnaden kan vidare ändra re-sponsen i jord–brosystemet, beroende på dess storlek, och att försumma den kan gefelaktiga resultat. De 3D effekterna av SSI orsakar inte höga vibrationer på grundav andra moder än den första böjmoden, och att anta en 2D bromodell är såledesgenerellt sett motiverat.Effekterna av SSI på jord–brosystemet i grunda jordar beror till stor del av kvotenmellan brons naturliga frekvens och jordens fundamentala frekvens. Beroende påvärdet på denna kvot kan effekten av att inkludera SSI i bromodeller bidra till attbron får en försumbar, konservativ, eller icke-konservativ respons, i jämförelse medbron med antagandet om fasta upplag. / <p>QC 20200903</p>

The use of geophysical testing methods has considerable potential to be a cost effective and accurate technique to assess near-surface soil conditions. Multi channel analysis of surface waves (MASW) test is a geophysical non-intrusive test that uses the dispersive characteristic of Rayleigh waves to estimate low strain shear modulus and damping coefficient of near-surface soil. Also, this technique is used to detect underground voids. Recently, MASW technique has gained more attention, partly because of its ease of use and partly because of the significant improvements in data acquisition systems. The theories of MASW test consider the effect of horizontal soil layering, though the effect of lateral inhomogeneities (i. e. cavities and voids), inclined layering and inverse layering (i. e. a layered system in which the top layers are stiffer than the bottom ones) are not addressed properly in these theories. <br /><br /> The objective of this dissertation is to investigate the effect of lateral inhomogeneities on the propagation of Rayleigh waves in an elastic half-space excited by a transient loading. The results can be applied to locate underground cavities using MASW test and to improve the MASW analysis techniques. In lieu of theoretical solutions, two and three dimensional numerical models are constructed to simulate the MASW test. To assure the quality of the obtained data, numerical models are calibrated with Lamb solution. Voids with different sizes and embedment depths are inserted in the medium. Responses along the surface as well as inside the medium are recorded and analyzed in time, frequency, spatial and frequency-wave number domains. Different material types and sources are used to generalize the results. Afterwards, the combined effect of void and layered systems on the surface responses are studied. To verify the results, experimental field and laboratory data are presented and the trends are compared to the numerical results. <br /><br /> It is found that the void starts to vibrate in response to the Rayleigh wave excitation. Due to the vibration of the void energy partitioning occurs. Part of the incident energy is reflected in the form of Rayleigh wave. Another part is converted to body waves, and spread into the medium. The transferred part of the energy is attenuated and has smaller amplitudes. Finally, a part of energy is trapped in the void region and bounces back and forth between the void boundaries, until it damps. The trapped energy is associated to higher modes of Rayleigh waves and excited Lamb waves. The effect of trapped energy is seen as a region in the vicinity of the void with concentrated energy, in frequency domain. The extents of this region depends on the void size, and the frequency content of the incident energy. Thus, in some cases it is possible to correspond the size of the model to the extents of the region with energy concentration. <br /><br /> A new technique is proposed to determine the location of a void, and estimate its embedment depth. The technique is called Attenuation Analysis of Rayleigh Waves (AARW), and is based on the observed damping effect of the void on the surface responses. For verification, the results are compared to experimental field and laboratory data. The observations are in good agreement with the observed numerical results. Further, the AARW technique showed to be a promising tool for void detection.

The use of geophysical testing methods has considerable potential to be a cost effective and accurate technique to assess near-surface soil conditions. Multi channel analysis of surface waves (MASW) test is a geophysical non-intrusive test that uses the dispersive characteristic of Rayleigh waves to estimate low strain shear modulus and damping coefficient of near-surface soil. Also, this technique is used to detect underground voids. Recently, MASW technique has gained more attention, partly because of its ease of use and partly because of the significant improvements in data acquisition systems. The theories of MASW test consider the effect of horizontal soil layering, though the effect of lateral inhomogeneities (i. e. cavities and voids), inclined layering and inverse layering (i. e. a layered system in which the top layers are stiffer than the bottom ones) are not addressed properly in these theories. <br /><br /> The objective of this dissertation is to investigate the effect of lateral inhomogeneities on the propagation of Rayleigh waves in an elastic half-space excited by a transient loading. The results can be applied to locate underground cavities using MASW test and to improve the MASW analysis techniques. In lieu of theoretical solutions, two and three dimensional numerical models are constructed to simulate the MASW test. To assure the quality of the obtained data, numerical models are calibrated with Lamb solution. Voids with different sizes and embedment depths are inserted in the medium. Responses along the surface as well as inside the medium are recorded and analyzed in time, frequency, spatial and frequency-wave number domains. Different material types and sources are used to generalize the results. Afterwards, the combined effect of void and layered systems on the surface responses are studied. To verify the results, experimental field and laboratory data are presented and the trends are compared to the numerical results. <br /><br /> It is found that the void starts to vibrate in response to the Rayleigh wave excitation. Due to the vibration of the void energy partitioning occurs. Part of the incident energy is reflected in the form of Rayleigh wave. Another part is converted to body waves, and spread into the medium. The transferred part of the energy is attenuated and has smaller amplitudes. Finally, a part of energy is trapped in the void region and bounces back and forth between the void boundaries, until it damps. The trapped energy is associated to higher modes of Rayleigh waves and excited Lamb waves. The effect of trapped energy is seen as a region in the vicinity of the void with concentrated energy, in frequency domain. The extents of this region depends on the void size, and the frequency content of the incident energy. Thus, in some cases it is possible to correspond the size of the model to the extents of the region with energy concentration. <br /><br /> A new technique is proposed to determine the location of a void, and estimate its embedment depth. The technique is called Attenuation Analysis of Rayleigh Waves (AARW), and is based on the observed damping effect of the void on the surface responses. For verification, the results are compared to experimental field and laboratory data. The observations are in good agreement with the observed numerical results. Further, the AARW technique showed to be a promising tool for void detection.

Enhanced Integration of Shear Wave Velocity Profiling in Direct-Push Site Characterization Systems Alexander V. McGillivray 370 Pages Directed by Dr. Paul W. Mayne Shear wave velocity (VS) is a fundamental property of soils directly related to the shear stiffness at small-strains. Therefore, VS should be a routine measurement made during everyday site characterization. There are several lab and field methods for measuring VS, but the seismic piezocone penetration test (SCPTu) and the seismic dilatometer test (SDMT) are the most efficient means for profiling the small-strain stiffness in addition to evaluating large-strain strength, as well as providing evaluations of the geostratigraphy, stress state, and permeability, all within a single sounding. Although the CPT and DMT have been in use for over three decades in the USA, they are only recently becoming commonplace on small-, medium-, and large-size projects as more organizations begin to realize their benefits. Regrettably, the SCPTu and the SDMT are lagging slightly behind their non-seismic counterparts in popularity, in part because the geophysics component of the tests has not been updated during the 25 years since the tests were envisioned. The VS measurement component is inefficient and not cost effective for routine use. The purpose of this research is to remove the barriers to seismic testing during direct-push site characterization with SCPTu and SDMT. A continuous-push seismic system has been developed to improve the integration of VS measurements with SCPTu and SDMT, allowing VS to be measured during penetration without stopping the progress of the probe. A new type of portable automated seismic source, given the name RotoSeis, was created to generate repeated hammer strikes at regularly spaced time intervals. A true-interval biaxial seismic probe and an automated data acquisition system were also developed to capture the shear waves. By not limiting VS measurement to pauses in penetration during rod breaks, it is possible to make overlapping VS interval measurements. This new method, termed frequent-interval, increases the depth resolution of the VS profile to be more compatible with the depth intervals of the near-continuous non-seismic measurements of the SCPTu and the SDMT.

The budgeting of water fluxes in the soil is an extremely complex problem, and is compounded by subsurface controls and environmental forces which modify the soil water dynamics. Of the controlling factors, the underlying geology and the soil media are vital components and are often misinterpreted. The geology and soil media components have been neglected mostly because of the difficulty in monitoring the dominant processes that are linked to the water balance in the subsurface. Until recently, hydrometry has been the dominant method of measuring and monitoring the subsurface water balance. Hydrometric measurements have included water content measurement by Time Domain Reflectometry (TDR), soil water potential measurements through tensiometry and groundwater water level monitoring. Hydrometry is still the preferred method of monitoring soil water dynamics, but measurements are generally localised and lateral accumulations and fluxes of water are difficult to interpret. Using geophysical methods and instrumentation to define soil water dynamics could have numerous advantages over conventional hydrometric methods. Among the geophysical techniques dedicated to image the near surface, Electrical Resistivity Tomography (ERT) surveying has been increasingly used for environmental, engineering and geological purposes during the last decade. The aim of this study is to determine if ERT observations could yield the accuracy required to define vertical and lateral soil water dynamics. The ERT instrumentation uses an electrical current that is inserted into the subsurface through various electrode arrangements and a resulting resistance is determined at the take-out electrodes. With the aid of a modelling package these resistance values are reproduced into a pseudosection of underlying resistivity distribution which is influenced by the moisture conditions of the subsurface medium. This geophysical method is primarily used for geological studies but by doing repeated surveys with the same electrode positioning, moisture fluctuation monitoring could be realised. Use of the ERT technique is at the forefront of soil water dynamics monitoring. The main objective of this study is to propose that the ERT instrumentation could be a more efficient and more informative method of studying soil water dynamics than the traditional soil water dynamics monitoring equipment, particularly to define lateral fluxes and accumulation of subsurface water. The study site is a well instrumented transect in the Nkuhlu Exclosures in the Kruger National Park, South Africa, where ongoing soil water dynamics are monitored. The project aims to compare the ERT data to fiR data on a daily basis, over a period of three weeks, during the rain season, monitoring event based wetting and the subsequent drying phases of the soils in a 2-dimensional section. The project and its fmdings are shown to be valuable to the hydrological interpretation of the subsurface water balance. The application is shown to be particularly important to ecohydrology, in the monitoring of soil water dynamics in a 2-dimensional transect and understanding how the natural cycles of water distribution and plant uptake are linked together. The study demonstrates that ERT can be used to observe changes in the water storage and lateral fluxes within a transect which supports varying vegetation and ecologies. The linking of water fluxes in the hydrology cycle to uptakes and controls in the ecosystem has been developed into the research focus known as ecohydrology The use of the ERT instrument can only benefit this research focus in the future. The study demonstrates that ERT instrumentation can be used to provide valuable understanding of subsurface water dynamics and in turn the effects on ecohydrology. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Tagungsband des Ohde-Kolloquiums 2014. Die Fachtagung fand am 26.03.2014 an der TU Dresden statt.

In this study, dynamic response of Akk&ouml / pr&uuml / Dam under earthquake motions is analyzed and the permanent displacements are evaluated. Initially, the critical slip surface of the dam and the corresponding yield acceleration are determined by using the computer program SLOPE. Then, by employing the finite element program SAP2000, static analyses are performed to obtain the mean effective stresses which are used in the determination of dynamic material properties of the dam. Four different scenario earthquakes having a magnitude of 7 are used in the dynamic analyses. Two of those scenarios are taken from European Strong Motion Database and the others are generated by XS artificial earthquake generation program prepared by Erdik (1992). Dynamic analyses of the dam are carried out by the finite element program TELDYN. Permanent displacements of the critical slip surface are calculated by utilizing the Newmark method. Consequently, for an earthquake having a magnitude of M=7 and a peak ground acceleration of 0.20g, the maximum permanent displacement of the dam is found to be 15.90 cm. Furthermore, the permanent displacements of the dam are calculated under base motions having different peak ground acceleration values and it is observed that the rate of increase in the amount of permanent displacements is greater than the increase in the amount of peak ground accelerations.

Species which play particularly important roles in ecosystem patterns and processes are recognised as keystone species or ecosystem engineers. The conservation of these species is critical for the maintenance of the ecological role they play in ecosystem function. The aardvark, Orycteropus afer, is known to play a role in biopedturbation through digging for refuges and for prey, and as a consequence of these digging activities is expected to serve the role of an ecosystem engineer and keystone species. This study aimed to describe and quantify the ecological patterns and processes driven by the aardvark through their digging activities, within the eastern Karoo, and thereby evaluate the significance of aardvarks as ecosystem engineers and keystone species in a semi-arid environment. The landscape pattern (dig abundance and distribution) and soil displacement of aardvark forage and refuge digs in a semi-arid Karoo landscape, as well as the ecological processes (generating fertile, seed retention hotspots) driven by aardvark forage digs was measured. Refuge digs occurred in the highest densities in areas characterised by a specific suite of soil, vegetation and elevation features, while forage digs occurred in high abundance in most habitats measured, and were likely driven by prey availability. Forage digs served as litter and seed retention hotspots, with accelerated decomposition rates of litter as a function of increased soil moisture in digs. The functional processes (i.e. resource capture, shelter for plants and animals, germination sites, soil aeration, organic turnover, mineralization rates, fertile soil displacement and transport) driven by aardvark digs are not restricted to refuge digs. Forage digs occurred in most habitats measured and their functional role is unique and perhaps greater across the landscape in comparison to refuge digs. The aardvark has a disproportionate effect in ecosystems, in terms of its refuge and forage digs relative to its abundance and therefore its role as a keystone species and ecosystem engineer is confirmed. Conservation and protection of this species is therefore essential to maintain its important role in ecosystem function.