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.

Experimental and analytic investigations were performed to examine the influences of wall height, backfill behavior, and compaction on the magnitudes of backfill loads on rigid retaining walls. Measurements of lateral and vertical backfill loads were made during tests using the Virginia Tech instrumented retaining wall facility. The tests were performed with two soils, moist Yatesville silty sand and dry Light Castle sand. Two hand-operated compactors, a vibrating plate compactor and a rammer compactor, were used to compact the backfill. The backfill height was 6.5 feet in all of the tests. Analyses of backfill loads were made using a compaction- induced lateral earth pressure theory and a vertical shear force theory. The compaction-induced lateral earth pressure theory was revised from a previous theory. The revisions improved the accuracy with which the theory models the hysteretic stress behavior of the backfill during compaction. The theory was also extended to include the pore pressure response of moist backfill in a rational manner. A vertical shear force theory was also developed during this research. The theory is based on consideration of backfill compressibility and mobilization of interface shear strength at the contact between the backfill and the wall. The theory provides a useful basis for understanding how wall height, backfill compressibility, wall-backfill interface behavior, and compaction-induced lateral pressures affect the vertical shear forces on rigid walls. Studies were also made to investigate the cause of erratic pressure cell readings. An important cause of drift in pressure cell readings was found to be moisture changes in the concrete in which the pressure cells were mounted. It was found that this problem could be mitigated by applying a water-seal treatment to the face of the wall. Both the vibrating plate compactor and the rammer compactor were instrumented to measure dynamic forces and energy transfer during compaction. The force applied by the vibrating plate compactor was about one-quarter of the manufacturer’s rated force. The force applied by the rammer compactor was about twice the manufacturer’s rated force. The transferred energy measurements provided a basis for relating laboratory and field compaction procedures. / Ph. D.

A retaining wall is subject to various limit states such as sliding, overturning and bearing capacity, and it can fail by anyone of them. Since a great deal of uncertainty is involved in the analysis of the limit states, the use of detenninistic conventional safety factors may produce a misleading result. The main objective of this study is to develop a procedure for the optimum design of a retaining wall by using the reliability theory. Typical gravity retaining walls with four different heights were selected in this study. The walls were designed first to satisfy the conventional design criteria, and later the safety indices inherent in the walls were computed by using Advanced First Order Second Moment method. With the safety indices the probabilities of failure for the three limit states were calculated and the probabilistically optimized design could be achieved by using the probability of failure. The influence of the coefficient of variation on the probability of failure was investigated. The ratios of base width to wall height which lead to the optimum design were obtained through a parametric study. / Ph. D.

Previous laboratory and field experimental studies of earth pressures exerted on retaining structures and laboratory studies of the at-rest earth pressure coefficient are summarized. The current methods used to evaluate the earth pressures due to compaction are reviewed. The design features of a new instrumented oedometer developed to investigate the effect of number of load cycles on the at-rest earth-pressure coefficient are presented along with the results of a series of tests on Monterey sand #0/30. The Instrumented Retaining Wall Facility developed to provide a means of obtaining experimental measurements of the earth pressures exerted on retaining structures is described. The instrumented wall of the facility is seven feet high and ten feet long and is instrumented to measure horizontal and vertical forces, horizontal earth pressures, horizontal deformations, and temperature. A description of the microcomputer-based data-acquisition system and the software used to record the test results is included. The results of four tests where Yatesville silty sand was compacted in layers in the Instrumented Retaining Wall Facility are presented. The experimental results are compared with the results of similar studies by others and to an analytical method used to estimate compaction-induced earth pressures. / Ph. D.

The objective of this study was to investigate the accuracy of the procedures employed in the conventional equilibrium method of analysis of gravity-earth-retaining structures founded on rock, using the finite element method of analysis. This study was initiated because a number of existing large retaining structures at various navigation lock sites in the United States that show no signs of instability or substandard performance have been found not to meet the criteria currently used for design of new structures. The results of following load analyses show that when the loss of contact along the base of a wall is modeled in the finite element analysis, the calculated values of effective base contact area and maximum contact pressure are somewhat larger than those calculated using conventional equilibrium analyses. The values of the mobilized base friction angle calculated using both methods are in precise agreement. Comparisons between the results of backfill placement analyses using the finite element method and the conventional equilibrium analyses indicate that conventional analyses are very conservative. The finite element analyses indicate that the backfill exerts downward shear loads on the backs of retaining walls. These shear forces have a very important stabilizing effect on the walls. Expressed in terms of a vertical shear stress coefficient (Kᵥ - r_xy/σᵥ), this shear loading was found to range in value from 0.09 to 0.21, depending on the geometrical features and the values of the material parameters involved in the problem. Another important factor not considered in the conventional equilibrium method is that the displacements of the wall have a significant influence on the distribution of both the stabilizing and destabilizing forces exerted on the wall. In general, as the wall moves away from the backfill, the lateral forces exerted on the wall by the backfill decrease, and the lateral forces exerted on the front of the wall by the toe fill increase. / Ph. D.

Thesis (MScEng)--Stellenbosch University, 2013. / Durability and impermeability in a water-retaining structure are of prime importance if the structure is to fulfill its function over its design life. In addition, serviceability cracking tends to govern the design of water retaining structures. This research concentrates on load-induced cracking specifically that due to pure bending and to direct tension in South African reinforced concrete water retaining structures (WRS). As a South African design code for WRS does not exist at present, South African designers tend to use the British codes in the design of reinforced concrete water-retaining structures. However, with the release of the Eurocodes, the British codes have been withdrawn, creating the need for a South African code of practice for water-retaining structures. In updating the South African structural design codes, there is a move towards adopting the Eurocodes so that the South African design codes are compatible with their Eurocode counterparts. The Eurocode crack model to EN1992 (2004) was examined and compared to the corresponding British standard, BS8007 (1989). A reliability study was undertaken as the performance of the EN1992 crack model applied to South African conditions is not known. The issues of the influence of the crack width limit and model uncertainty were identified as being of importance in the reliability crack model.

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.

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.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Concrete water retaining structures (WRS) in South Africa are under scrutiny due to the numerous durability problems that they have experienced lately; despite the efforts by local and national authorities in conserving these structures. At the heart of these problems are the creep and shrinkage phenomena. While shrinkage is the reduction of concrete volume with time, creep is defined as the time-dependent increase of concrete strain under constant or controlled stress. Both phenomena are affected by conditions to which WRS are exposed hence their accurate prediction is required. Numerical models have been developed to calculate the extent to which concrete creeps or shrinks over time. The objective of this thesis is to identify which of these models is better equipped to be used in South African WRS design. This is achieved through a systematic method that involves an investigation into the contents of these models and a statistical comparison of model calculations to WRS representative data. In partnership with reputable universities, a pioneer experimental creep and shrinkage data base is created in this project from which the WRS related data is selected. While investigating the contents of the numerical models, their applicability to South African WRS is identified and the integrity of model contents is assessed. Indeed, a few irregularities are found in the process and are presented in this thesis. The model calculations are statistically compared to data in the form of individual experiments as well as in the form of groups of experiments with similar concretes to find the ideal prediction model for different types of concretes as well. Also pioneered in this project is a weighted criteria and point system in which the findings of the model content assessment and statistical evaluations are incorporated. It is based on this system that conclusions are drawn and the most suitable prediction model for WRS design in South Africa is selected.

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”.