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Finite element analyses of gravity earth retaining structures founded on soilRegalado, Levi R. 24 October 2005 (has links)
The safety of gravity earth retaining structures is usually evaluated with regard to: (1) overturning about the toe, (2) sliding along the base and (3) bearing failure of the foundation. Conventional equilibrium methods are utilized in these analyses, which are performed using assumed earth loads based on simplified earth pressure theories. Recent finite element studies performed on gravity retaining walls founded on rock revealed that the use of conventional methods may lead to overly conservative results. The effects of soil-structure interaction result in a greater degree of wall stability than conventional approaches would indicate.
This research examines the behavior of gravity earth retaining structures founded on soil. Two methods of analyses were used in these studies : (1) the Following Load method, which does net account for soil-structure interaction effects, and (2) the Backfill Placement method, which does account for soil-structure interaction effects. A procedure called the “Alpha Method” for 2D soil elements was developed for the purpose of improving the post-failure stress-strain behavior of the backfill and foundation soils and incorporated in the finite element program (SOILSTRUCT) utilized in the analyses.
A series of analyses demonstrated the effectiveness of the Alpha Method in controlling overshoot and providing good estimates of collapse loads on wall-foundation systems. Following Load analyses indicated that walls on soil become unstable by bearing capacity rather than overturning or sliding. These results also provided the basis for modifications to Vesic’s bearing capacity theory, which extended the applicability of the theory to the conditions encountered in retaining wall problems. The Backfill Placement analyses showed that there are significant differences in behavior between walls founded on rock and walls founded on soil. These analyses also led to new insight into the factors that affect the shear forces within the backfill and which contributes to the stability of the wall. / Ph. D.
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Multi-hazard modelling of dual row retaining wallsMadabhushi, Srikanth Satyanarayana Chakrapani January 2018 (has links)
The recent 2011 Tōhoku earthquake and tsunami served as a stark reminder of the destructive capabilities of such combined events. Civil Engineers are increasingly tasked with protecting coastal populations and infrastructure against more severe multi-hazard events. Whilst the protective measures must be robust, their deployment over long stretches of coastline necessitates an economical and environmentally friendly design. The dual row retaining wall concept, which features two parallel sheet pile walls with a sand infill between them and tie rods connecting the wall heads, is potentially an efficient and resilient system in the face of both earthquake and tsunami loading. Optimal use of the soil's strength and stiffness as part of the structural system is an elegant geotechnical solution which could also be applied to harbours or elevated roads. However, both the static equilibrium and dynamic response of these types of constructions are not well understood and raise many academic and practical challenges. A combination of centrifuge and numerical modelling was utilised to investigate the problem. Studying the mechanics of the walls in dry sand from the soil stresses to the system displacements revealed the complex nature of the soil structure interaction. Increased wall flexibility can allow more utilisation of the soil's plastic capacity without necessarily increasing the total displacements. Recognising the dynamically varying vertical effective stresses promotes a purer understanding of the earth pressures mobilised around the walls and may encourage a move away from historically used dynamic earth pressure coefficients. In a similar vein, the proposed modified Winkler method can form the basis of an efficient preliminary design tool for practice with a reduced disconnect between the wall movements and mobilised soil stresses. When founded in liquefiable soil and subjected to harmonic base motion, the dual row walls were resilient to catastrophic collapse and only accrued deformation in a ratcheting fashion. The experiments and numerical simulations highlighted the importance of relative suction between the walls, shear-induced dilation and regained strength outside the walls and partial drainage in the co-seismic period. The use of surrogate modelling to automatically optimise parameter selection for the advanced constitutive model was successfully explored. Ultimately, focussing on the mechanics of the dual row walls has helped further the academic and practical understanding of these complex but life-saving systems.
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Gelžbetoninių atraminių sienų išramstymo būdų įvertinimas / Evaluation of the methods of the supporting on reinforced concrete retaining wallsMajauskas, Evaldas 16 June 2010 (has links)
Atramines sienas (toliau – AS) veikia įvairios apkrovos dėl kurių susidaro neleistinos deformacijos, atsiranda plyšiai, atraminės sienos pasvyra, siekiant jas apsaugoti nuo tolimesnio svyrimo ir griūties AS būtina stiprinti. Remiantis literatūros apžvalga pastebėta, kad nėra detaliai aptarti žemutinio bjefo (toliau – ŽB) atraminių gelžbetoninių (toliau – g/b) sienų stiprinimo būdai, todėl detalesniems tyrimams pasirinkti 4 hidromazgai (toliau – HTS), kurių atraminėms sienoms reikalingas stiprinimas. Darbo tikslas – įvertinti tinkamiausią gelžbetoninių atraminių sienų stiprinimo išramstant būdą. Siekiant parinkti tinkamiausią išramstymo būdą atlikti palyginamieji ekonominiai bei konstrukciniai skaičiavimai. Pagal ekonominių ir konstrukcinių skaičiavimų rezultatus nustatyta, kad ekonomiškiausias išramstymo būdas – įrengiant monolitines sijas ir „šukas“. / Retaining walls are under the influence of a number of loads, which results in unacceptable deformation, cracks appear and load-bearing walls lean on one side. Retaining walls should be strengthened in order to protect them from further collapse and loping. According to literary review, it is noticed that there is no detailed analysis of the lower pool retaining angled reinforced concrete wall-building techniques. This was the reason why 4 hydroschemes were chosen for more detailed researches in order to determine which retaining walls need strengthening. The aim of this work is to assess the most appropriate angled retaining wall building method. In order to select the most appropriate way of strengthening, comparative economic and structural calculations are done. In accordance with economic and structural results of calculations, it is found that the most economical way of building is a monolithic installation of beams and “combs”.
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Atraminių sienų skerspjūvio mažėjimas veikiant nepalankiems aplinkos poveikiams / Reduction of cross–section of retaining walls under the influence of negative environmental impactsPupelis, Vytas 16 June 2010 (has links)
Žemių užtvankų žemutinio bjefo atraminės sienos (toliau – AS) yra veikiamos nepalankių klimatinių poveikių, vandens, grunto slėgio ir kt. apkrovų. Veikiant agresyvioms aplinkoms ir apkrovoms atsiranda pažaidos, kurios ardo atraminę sieną bei mažina konstrukcijos laikomąją galią. Darbo tikslas – įvertinti nepalankių aplinkos poveikių įtaką atraminių sienų skerspjūvio sumažėjimui. 2007–2010 metais mokslinių ekspedicijų metu įvertinta 21 hidromazgo atraminių sienų būklė. Apžiūrėtos Kauno, Panevėžio, Utenos ir Marijampolės apskričių hidromazgų atraminės sienos, fiksuotos svarbiausios pažaidos. Detaliau ištirta Antanavo hidromazgo atraminė siena, įvertintas sienos skerspjūvio sumažėjimas dėl nepalankių aplinkos poveikių. Pagal tyrimų duomenis pasiūlyti pažaidų, mažinančių atraminių sienų skerspjūvį, remonto būdai. / Retaining walls of lower head–water of ground dams are influenced by negative climatic impacts, water, ground pressure and other loads. Upon the effect of aggressive environment and loads, deteriorations occur destroying the retaining wall as well as reducing the bearing capacity of the constructions. The aim of the work is to evaluate reduction of cross–section of retaining walls as a result of negative environmental impacts. Through the period 2007–2010 on scientific expeditions the condition of retaining walls of 21 hydroshemes was assessed. Retaining walls of hydroschemes in the counties of Kaunas, Panevezys, Utena and Marijampole have been examined, the most significant deteriorations were fixed. Retaining wall in Antanavas hydropower station was examined in detail; reduction of cross–section of retaining wall due to the influence of negative environmental impacts was assessed.
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A finite difference soil-structure interaction study of a section of the Bonneville Navigation Lock buttress diaphragm wall utilizing pressuremeter test resultsMcCormack, Thomas C. 01 January 1987 (has links)
The P-y curve, used in current practice as an efficient Iine-load vs. soi displacement model for input into the finite difference method of laterally loaded pile analysis, is extended in this study for use with cohesionless soils in diaphragm wall analysis on the Personal Computer with the BMCOL7 program. An analogous W-y curve is proposed, an elastic-plastic model with line-load limits developed from classical earth-pressure theories.
A new formula for predicting a horizontal walI modulus for cohesionless soiIs from the pressuremeter modulus is developed for use in predicting the displacements on the W-y curves. The resulting modulus values are shown to yield reasonable displacements values.
A new procedure for modeling preloaded tie-back anchors and staged excavation for diaphragm walIs was developed, utiIizing multiple computer runs, updated the W-y curves, and superposition of deflections.
These new developments were applied to a parametric study of a deflection-critical section of the new Bonnevilie Nav-Lock Buttress Diaphragm Wall, for which extensive high-quality pressuremeter test results were available. Deflection curves of the wall are presented, showing the effect of variations in anchor preload, walI cracking, anchor slip, at-rest pressure, and soiI modulus.
The results indicate that preloading will reduce wall deflections by at least 4-fold, but that wall cracking can potentially double deflections. Safety factors against passive soil failure were determined to be about 5 at anchor preload, and more than 40 after fulI excavation.
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Behaviour and analysis of embedded cantilever wall on a slopeOng, Chin Chai January 2007 (has links)
[Truncated abstract] The feasibility of using interlocked light gauge sheet piles to form a deep cross-sectional wall embedded in a residual slope or with a berm support is explored. This thesis compares the performance of a large section modulus sheet pile wall as an alternative to a concrete diaphragm wall, acting as an embedded cantilever wall on a slope (ECWS) by means of experimental centrifuge tests, numerical models and analytical methods. Abaqus (Hibbitt, Karlsson and Sorensen Inc, 1997) was used to conduct extensive numerical trials on the structural performance of the sheet pile wall model prior to the actual physical testing. The Abaqus results showed that the integrity of the interlock and reduced modulus action (RMA) due to slippage along the interlocked joint did not cause premature buckling of the thin wall even at the ultimate load. Further, a comparative study using centrifuge tests on 1:30 scaled models and Plaxis analysis demonstrated that under the worst condition with high water table, the rigid sheet pile wall of 1.32 m cross-sectional width carried a higher ultimate surcharge load with a much lower top of wall deflection, compared to a more flexible 0.6 m thick cracked concrete diaphragm wall. The analysis of the wall/soil/slope interactions for an ECWS involves many inter-dependent variables in addition to the complications of considering an adjacent slope or a berm support. It is difficult for existing analytical approaches to take all these factors into account, and some form of numerical analysis, calibrated through field data and results from centrifuge model tests is necessary. From the observations of the centrifuge tests and finite element analysis, major assumptions about the failure of a stiff ECWS in a rotational mode were deduced and adopted in the proposed limiting equilibrium method (Leq). The plane strain Leq ECWS Abstract ii analysis is based on the framework of minimum upper bound limiting equilibrium with planar failure planes and a Mohr-Coulomb soil model. As compared to the traditional limit equilibrium analysis, the Leq method is a fully coupled analysis using the shear strength reduction technique (SSR). New formulations are proposed for the development of horizontal active and passive pressure distributions based on the experimental and FE models. The proposed active pressure profile used is derived by combining the Coulomb and Krey method, and empirically back-figured to curve-fit the centrifuge tests by Morris (2005). The proposed passive pressure profile of a rigid rotational wall in failure is adjusted to allow for an adjacent slope or berm support through a presumed elasto-plastic deformation instead of a linear rigid translation of the passive wedge. ... A parametric study was later undertaken using the Leq method to develop a series of non-dimensionalised graphs to study and draw summarised conclusions on the behaviour of the ECWS. The final conclusions on the comparative study of the centrifuge tests, Plaxis and Leq analyses demonstrated that the alternative light gauge steel sheet pile performed very well as an ECWS. A key factor in the performance of the sheet pile wall was attributed to the large 1.32 m cross-sectional width of the interlocked sections. This provided high bending stiffness and high moment stability from shear stresses acting on the back and front faces of the wall.
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Optimum Design Of Retaining Structures Under Static And Seismic Loading : A Reliability Based ApproachBasha, B Munwar 12 1900 (has links)
Design of retaining structures depends upon the load which is transferred from backfill soil as well as external loads and also the resisting capacity of the structure. The traditional safety factor approach of the design of retaining structures does not address the variability of soils and loads. The properties of backfill soil are inherently variable and influence the design decisions considerably. A rational procedure for the design of retaining structures needs to explicitly consider variability, as they may cause significant changes in the performance and stability assessment. Reliability based design enables identification and separation of different variabilities in loading and resistance and recommends reliability indices to ensure the margin of safety based on probability theory. Detailed studies in this area are limited and the work presented in the dissertation on the Optimum design of retaining structures under static and seismic conditions: A reliability based approach is an attempt in this direction.
This thesis contains ten chapters including Chapter 1 which provides a general introduction regarding the contents of the thesis and Chapter 2 presents a detailed review of literature regarding static and seismic design of retaining structures and highlights the importance of consideration of variability in the optimum design and leads to scope of the investigation. Targeted stability is formulated as optimization problem in the framework of target reliability based design optimization (TRBDO) and presented in Chapter 3. In Chapter 4, TRBDO approach for cantilever sheet pile walls and anchored cantilever sheet pile walls penetrating sandy and clayey soils is developed. Design penetration depth and section modulus for the various anchor pulls are obtained considering the failure criteria (rotational, sliding, and flexural failure modes) as well as variability in the back fill soil properties, soil-steel pile interface friction angle, depth of the water table, total depth of embedment, yield strength of steel, section modulus of sheet pile and anchor pull. The stability of reinforced concrete gravity, cantilever and L-shaped retaining walls in static conditions is examined in the context of reliability based design optimization and results are presented in Chapter 5 considering failure modes viz. overturning, sliding, eccentricity, bearing, shear and moment failures in the base slab and stem of wall. Optimum wall proportions are proposed for different coefficients of variation of friction angle of the backfill soil and cohesion of the foundation soil corresponding to different values of component as well as lower bounds of system reliability indices.
Chapter 6 presents an approach to obtain seismic passive resistance behind gravity walls using composite curved rupture surface considering limit equilibrium method of analysis with the pseudo-dynamic approach. The study is extended to obtain the rotational and sliding displacements of gravity retaining walls under passive condition when subjected to sinusoidal nature of earthquake loading. Chapter 7 focuses on the reliability based design of gravity retaining wall when subjected to passive condition during earthquakes. Reliability analysis is performed for two modes of failure namely rotation of the wall about its heel and sliding of the wall on its base are considering variabilities associated with characteristics of earthquake ground motions, geometric proportions of wall, backfill soil and foundation soil properties. The studies reported in Chapter 8 and Chapter 9 present a method to evaluate reliability for external as well as internal stability of reinforced soil structures (RSS) using reliability based design optimization in the framework of pseudo static and pseudo dynamic methods respectively. The optimum length of reinforcement needed to maintain the stability against four modes of failure (sliding, overturning, eccentricity and bearing) by taking into account the variabilities associated with the properties of reinforced backfill, retained backfill, foundation soil, tensile strength and length of the geosynthetic reinforcement by targeting various component and system reliability indices is computed. Finally, Chapter 10 contains the important conclusions, along with scope for further work in the area. It is hoped that the methodology and conclusions presented in this study will be beneficial to the geotechnical engineering community in particular and society as a whole.
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Comparison Of Factor Of Safety Obtained From Limit Equilibrium Methods With Strength Reduction Factors In Finite Element ModelingEngin, Volkan 01 February 2012 (has links) (PDF)
Designing with Limit Equilibrium Methods involve a factor of safety (FS) in order to
maintain the stability and to keep the resisting structure away from limit state on
the safe side. Finite Element Program (such as Plaxis) on the other hand, instead of
an FS, reduces the shear strength of the soil by introducing a reduction factor that is
applied to tan
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Passive Earth Pressure Coefficients And There Applications In The Uplift Capacity Of AnchorsNayak, Sitaram 04 1900 (has links)
The problem of passive earth pressure is one of the important topics in Geotechnical engineering. At attempt is made in this thesis to generate passive earth pressure coefficients for general c-Φ soils using logarithmic spiral failure surface by limit equilibrium approach. Method of slices for the determination of passive force in c-Φsoils is presented and the method is extended to a typical problem of two layered soil system. The application of passive earth pressure coefficients has been demonstrated for pullout capacity of inclined strip anchors in sloping ground. A semi-empirical approach for the determination of displacement-related passive earth pressure is presented.
The thesis is organized in seven chapters. In Ch.2, a brief summary of relevant literature is presented along with the scope of the thesis. In Ch. 3, limit equilibrium approach for the determination of the passive earth pressure in soils is presented. The
passive earth pressure coefficients are developed for δ/Φ= - 1, - ¾ , -2/3, - ½, 0, ½, ¾
1; ψ = -60º, -45º, -30º, -20º, -10º, 0º,10º,20º,30º and 45º; i= -30º, -20º, -10º,0º,10º,20º and 30º where δ is the wall friction angle, Φ is the angle of internal friction, Ψ is the
inclination of the wall with the vertical and i is the ground inclination with the horizontal. Ch.4 deals with the method of slices. Satisfying all the three equilibrium conditions and using interstice friction as a variable, passive earth pressure coefficients are obtained for soils. Extension of the method to a two layered soil system is demonstrated by an illustrative example. A generalised approach for the determination of uplift capacity of inclined strip anchors in sloping ground subjected to surcharge is presented in Ch. 5. Expressions are provided for the determination of pullout capacity of deep anchors. Displacement-related passive earth pressure is discussed in Ch. 6. Using the earlier experimental observations on the passive earth pressure measurements with displacements, expressions have been fitted for the determination of displacement-related passive earth pressure for the three modes of rigid body movements viz., translation, rotation about the top and rotation about the bottom. The conclusions drawn from the present investigations are listed in Ch 7.
(Pl see the original document for abstract)
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A behavioral study of gabion retaining wallsSublette, William Robert January 1979 (has links)
No description available.
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