Dynamic Lateral Earth Pressure Research Articles

Numerical Investigation of Seismic Behaviour for a Flexible Cantilever Retaining Wall with Cohesive Backfill

In the seismic design of flexible cantilever walls retaining cohesive backfill soil, the common practice is to neglect the cohesion effect. Dynamic lateral earth pressure is typically evaluated based on approaches primarily intended for cohesionless soils or through analytical pseudo-static methods. Nevertheless, both experimental and theoretical evidence has demonstrated significant effects due to soil cohesion that are not accounted for by these methods. This study involved finite element modeling (FE) of a flexible cantilever wall with a height of 5.4m, supporting homogeneous cohesive backfill under initial static and seismic loadings. The calculated active earth thrust was then compared with values obtained experimentally and through conventional analytical methods. The obtained results indicate that the presence of soil cohesion significantly reduces seismic demands on flexible cantilever retaining walls, resulting in a substantial reduction of seismic active earth pressures and total seismic thrust by up to 50% and 52%, respectively. It enhances also the overall stability of the system by shifting the point of application of seismic thrust toward the base of the wall, thereby increasing the safety margin. In addition, it significantly decreases the wall displacement at the stem top, with reductions of up to 104% compared with the case involving cohesionless backfill. It was observed that the conventional methods recommended by some seismic regulations largely underestimate seismic active pressure.

Investigation on dynamic performance of soilbag cushion using shaking table tests

Soilbag cushion is one of the promising base isolation methods to reduce seismic energy transfer from ground to building structure. In this study, a series of shaking table tests were conducted comparatively on foundation models with soilbag cushion and sand cushion to evaluate their dynamic performance. The test results indicate that soilbag cushion could significantly reduce acceleration response and accumulated settlement compared to sand cushion. And the relatively smaller amplitude of dynamic lateral earth pressure measured on contact surface of soilbags within soilbag cushion also indicates its stability during oscillation. The advantages of soilbag cushion for energy dissipation and damping are more easily highlighted under the condition of high-acceleration, high-frequency or high uniformly distributed load. The dynamic performance of soilbag cushion is dependent on embedded depth and thickness. It is most effective for soilbag cushion to be arranged near the rigid footing of building structures; it is suggested that the number of layers of soilbag cushion be controlled on the premise of the designed ratio of the thickness to the width of soilbag cushion ranging from 0.125 to 0.4 for low- or middle-rise masonry buildings in practical engineering.

Numerical Study on the Reduction of Dynamic Lateral Earth Pressure on Retaining Wall using Waste Tyre

The performance of retaining under various loading circumstances is dependent on the kind of backfills employed; nonetheless, several lightweight fill materials such as EPS geofoam, geoboard, fly ash, waste tyre (in various forms), and so on are widely utilised as backfill materials. The key benefits of adopting lightweight materials are a lower overall lateral force on the wall and lateral displacement of the retaining wall. Because of the growing number of automobiles, disposing of discarded tyres has become a major issue. Waste tyres are increasingly being utilised in geotechnical applications such as embankment fill, retaining walls, machine foundations, and bridge abutments. According to prior research, shredded tyre inclusion with soil is employed as backfill material for earth-retaining constructions.The most important aspect of sectional design for retaining walls is the total lateral thrust. Literature indicates that the use of waste tyres in backfill decreases the overall lateral thrust whether used as sole backfill as tyre chips or a mixture of sand tyres or when used as a compressible inclusion between the wall and the backfill.In the present work, a numerical simulation was conducted using OPTUM G2 (a computational tool based on finite elements) to examine the effect of discarded tyres as backfill material on the total lateral earth pressure for an 8-meter-high wall. Maximum surcharge pressure of 20 kPa is applied to the backfilling.The use of discarded tyres as a backfill material significantly decreases total lateral earth pressure on the wall by 50-54% compared to walls backfilled with soil, according to the current study.

A comprehensive numerical analysis of EQ-induced lateral earth pressure on structures basement walls

Due to soil-structure interaction, dynamic lateral earth pressures on building embedded walls affect the dynamic performance of the building. Classic relations such as Mononobe-Okabe (M − O) and Seed & Withman (S–W) are applied to determine these dynamic lateral earth pressures in conventional design methods. Considering these relations' assumptions and their neglect of soil-structure interactions during an earthquake, using these relations may result in erroneous and inaccurate estimation of dynamic earth pressure. This paper attempts to understand this phenomenon better and estimate dynamic earth pressure on basement walls. Structure and soil mass are simulated simultaneously, using numerical models. Numerical (finite element) dynamic analyses are carried out for qualitative and quantitative evaluation of dynamic earth pressures on buildings with basements. Different excavation depths, ground topography, geotechnical parameters, and building stories above ground have been considered in these analyses. Finally, the soil-structure interaction response has been discussed using the obtained results, and approximate relations are derived to estimate the dynamic earth pressure.

Seismic ground motion induced lateral earth pressures on basement walls

Research on the dynamic lateral earth pressures acting on basement walls induced by seismic ground motions has appeared in the literature in the last few years to examine the apparent inconsistency between the theoretical pressures and the pressures suggested by basement wall good performance of during large earthquakes. This inconsistency suggested that the current methods would yield excessive lateral earth pressures. In this paper, a two dimensional plane strain finite element model of a 2-story concrete basement wall was used to examine the dynamic lateral earth pressures. The seismic ground motion was the N-S component of the 1992 Erzincan earthquake motion record. The assumed soil profile was a sands deposit overlying a reflecting bedrock layer. The observed time history outputs were the wall acceleration in horizontal direction, the lateral earth pressures, and the associated lateral thrust. The outputs were examined further to evaluate the amplification of wall acceleration, the different time history pattern of wall acceleration and lateral thrust, the influence of limiting soil tensile strength, the time difference for peak wall acceleration and peak lateral thrust, and a discussion on phase difference. The results suggested that the complex interaction could not be represented by typical simple peak input acceleration – soil pressure relationships.

Laboratory evaluation of dynamic behavior of steel-strip mechanically stabilized earth walls

To investigate the influence of the peak acceleration, the loading duration, and the strip length on the dynamic behavior of steel-strip reinforced soil walls (SSWs), in terms of the dynamic reinforcement load distribution and the dynamic lateral earth pressure behind the surface, a series of 1-g shaking table tests was performed on five reduced-scale reinforced soil wall models. It was observed that the maximum axial force of the strips (Tmax) is mobilized at the intersection of the failure plane with strips in all rows. It was also discovered that, in the upper half of the walls, the Tmax values decrease with a decreasing strip length, while this trend is reversed in the lower half of the walls. Additionally, a proper convergence was found between the Tmax/H·γs·SV·SH and L/H′ ratio at different levels of acceleration and duration, so that Tmax/H·γs·SV·SH can be defined as a function of the L/H′ ratio and the seismic parameters for different rows of strips. On the other hand, it was observed that the values of earth pressure predicted by conventional methods under static and seismic conditions are too conservative and these methods predict the position of the resultant lateral force higher than the actual point.

Experimental study on seismic response of soil-nailed walls with permanent facing

A series of 1-g shaking table tests were performed on five reduced-scale soil-nailed wall models to investigate the influence of peak acceleration, loading duration, and nail length on seismic response of the soil-nailed walls in terms of the distribution of shear modulus (G) and damping ratio (D) in soil-nailed mass, the axial force distribution along the nails and the distribution of dynamic lateral earth pressure behind the surface. It was found that the seismic response of walls highly depends on the length of nails and input motion parameters. By introducing a new non-dimensional parameter (Gglobal) for soil-nailed walls, it was observed that the values of G, G/G0, and D are strongly dependent of confining pressure, L/H ratio, and shear strain levels, so that the variation trend of these parameters with γ is well expressed as an exponential equation with a high correlation coefficient. Additionally, a proper convergence was found between Tmax/H.γs.SV.SH and L/H ratio at different levels of acceleration and duration, so that Tmax/H.γs.SV.SH can be defined as a function of L/H ratio and seismic parameters for different rows of nail. Also, It was discovered that the values of predicated earth pressure by conventional methods in static and seismic conditions are too conservative and these methods predict the location of the resultant lateral earth pressure higher than the actual point.

Assessment of racking deformation of rectangular underground structures by centrifuge tests

Seismic safety of buried structures has become increasingly important over the past two decades, especially after the destructive earthquakes such as in Kobe, Japan (1995), Kocaeli, Turkey (1999) and Chi-Chi, Taiwan (1999). Some of the embedded structures including pipelines, subways and tunnels collapsed or suffered severe damage in those earthquakes due to inappropriate design. The main difficulty in seismic design is the incorporation of soil–structure interaction effect governed by the relative stiffness (flexibility ratio) between the soil and the embedded structure. This study aims to clarify the effect of flexibility ratio on the dynamic response of rectangular structures buried in dry sand. For that purpose, a series of dynamic centrifuge tests were conducted on two types of box-shaped models with different rigidities under various harmonic motions. The results reveal that the magnitude of dynamic lateral earth pressure and sidewall deformation is highly dependent on the flexibility ratio of the embedded structure. Based on the flexibility ratios, racking deformations observed in centrifuge tests and racking deformations estimated through analytical approaches were evaluated in a comparative manner.

Shake table lateral earth pressure testing with dense c-ϕ backfill

Dynamic lateral earth pressure is recorded during ten shake table testing events. In these tests, peak input acceleration at the base of the retaining wall varied in the wide range of 0.13–1.20g in order to include scenarios of relevance to recently observed strong earthquake excitations. The results shed light on the influence of soil cohesion and the effect of small wall movements on the magnitude and distribution of earth pressure. In accordance with field practice, a commonly encountered dense sand backfill with a small percentage of fines (SP-SM) is used. Inside a large soil container, earth pressure is measured against a rigid wall (backfill height H=1.7m) that is allowed to undergo limited translation/rotation due to the imparted dynamic excitation (up to 10mm or 0.006H at 1.2g base acceleration). In this particular series of experiments, favorably low dynamic pressures were recorded at backfill accelerations of up to about 0.7g in light of: (i) the relatively high soil strength (including cohesion) that precluded a limit equilibrium type failure in the backfill, and (ii) the high soil stiffness coupled with the small value of observed wall translation/rotation (as much as 3mm or 0.0018H at ground surface). In tests with instants of very high acceleration (in the range of 1g), the corresponding dynamic earth pressure is found to be of much significance for practical applications. Lateral thrusts recorded during these instants of strong shaking compare well with limit equilibrium predictions that include the soil cohesion intercept. Exclusion of the cohesion intercept results in substantial over-prediction of the measured lateral forces.

Constructability optimal design of reinforced concrete retaining walls using a multi-objective genetic algorithm

The term "constructability" in regard to cast-in-place concrete construction refers mainly to the ease of reinforcing steel placement. Bar congestion complicates steel placement, hinders concrete placement and as a result leads to improper consolidation of concrete around bars affecting the integrity of the structure. In this paper, a multi-objective approach, based on the non-dominated sorting genetic algorithm (NSGA-II) is developed for optimal design of reinforced concrete cantilever retaining walls, considering minimization of the economic cost and reinforcing bar congestion as the objective functions. The structural model to be optimized involves 35 design variables, which define the geometry, the type of concrete grades, and the reinforcement used. The seismic response of the retaining walls is investigated using the well-known Mononobe-Okabe analysis method to define the dynamic lateral earth pressure. The results obtained from numerical application of the proposed framework demonstrate its capabilities in solving the present multi-objective optimization problem.

Earthquake-induced pressures on discontinuous piling support on Santiago gravel

Discontinuous anchored piling support (anchored soldier piles without lagging) is one of the most frequent earth-retaining systems used in temporary deep excavations in Santiago, Chile. The main advantages of using discontinuous piling support are their relatively low cost and ease of installation. This system is particularly efficient on stiff soils with deep groundwater table, conditions usually found in Santiago. This paper presents a numerical investigation of the characteristics of earthquake induced lateral pressures on discontinuous pile-supported excavations in Santiago gravel. An equivalent bi-dimensional plane-strain model was developed on the basis of a more refined 3D model in order to quantify the influence of the “arching effect” on the dynamic lateral earth-pressures. The dynamic response was studied for a suite of Chilean ground motion recorded on rock in order to evaluate the variability of the dynamic pressures and their influence on the piles' internal forces. These results are then compared against some simplified design recommendations.

Full-scale shake table investigation of bridge abutment lateral earth pressure

During strong seismic excitation, passive earth pressure at the abutments may provide resistance to longitudinal displacement of the bridge deck. The dynamic pressure component may also contribute to undesirable abutment movement or damage. Current uncertainty in the passive force-displacement relationship and in the dynamic response of abutment backfills continues to motivate large-scale experimentation. In this regard, a test series is conducted to measure static and dynamic lateral earth pressure on a 1.7 meter high bridge abutment wall. Built in a large soil container, the wall is displaced horizontally into the dense sand backfill, in order to record the passive force-displacement relationship. The wall-backfill system is also subjected to shake table excitation. In the conducted tests, lateral earth pressure on the wall remained close to the static value during the low to moderate shaking events (up to about 0.5g). At higher levels of input acceleration, a substantial portion of the backfill inertial force started to clearly act on the wall.

Laboratory Impulse Tests for Soil-Underground Structure Interactions

Abstract The dynamic lateral earth pressures resulting from underground detonation can cause severe damage to underground structures. The shock exerted on an underground structure caused by an underground explosion will vary with the detonation depth, the intensity of detonation force, and distance of detonation source from the underground structure. This paper describes four large-scale impulse tests on a 1-m-high pro-totype subsection of an underground structure subjected to controlled impulsive lateral loadings propagating through a 0.75-m-thick backfill soil. The response of the subsection to the impulsive loading is carefully monitored utilizing an extensive instrumentation program. The test results provide insight into the phenomenon of shock wave propagation caused by an impulsive loading emanating from an underground source adjacent to the underground structure. The tests indicated that the damaging effect of impulse loading increased with surcharge pressure (depth) until a threshold surcharge pressure is reached above which the damaging effect of impulse loading decreased.

Experimental developments for studying static and seismic behavior of retaining walls with liquefiable backfills

The effects of earthquakes on cantilever retaining walls with liquefiable backfills were studied. The experimental techniques utilized in this study are discussed here. A series of centrifuge tests was conducted on aluminum, fixed-base, cantilever wall models retaining saturated, cohesionless backfills. Accelerations on the walls and in the backfill, static and excess pore pressures in the soil, and deflections and bending strains in the wall were measured. In addition, direct measurements of static and dynamic lateral earth pressures were made. In some tests, sand backfills were saturated with the substitute pore fluid metolose. Modeling of model type experiments were conducted. The experimental measurements were found internally consistent and repeatable. Both static and dynamic earth pressure measurements were determined to be reliable. It was also observed that for the test configuration adopted, a special boundary treatment such as the use of duxseal is optional. Static and seismic modeling of models were also successful, which indicated that the assumed scaling relations were essentially correct.

Geotechnical Study for Evaluating Stability and Restoration Work at the 1,000 Year Old Archaeological Site of Ayla, Gulf of Aqaba, Kingdom of Jordan

Geotechnical Investigations at the site of ancient Ayla in Aqaba, Jordan, show that soils are predominantly granular, with archaeological fill overlying beach sand, which in turn overlies a coarser sand and gravel. Except for the wadi area, ground water occurs about 3 m below the existing ground level. The bearing capacity of the foundation is 3.5 kg/cm 2 for the dense granular materials that represent the probable founding layer of the existing walls, and 2.0 kg/cm 2 for the weaker silty/clayey zone. Back analysis yields a safe wall height of at least 6.0 m. Therefore, no stability problems are present. Tilting and sinking were noted in some portions of the exterior walls as a result of dynamic lateral earth pressures caused by a major earthquake incident in 1067 A.D. Thus, wall-foundation support is recommended during archaeological excavations; and permanent excavations for exposing the walls should be limited to about 3 m by the western wall, and about 2.5 m by the eastern wall. Stones used in the construction of ancient Ayla consist of precut sandstone, siltstone, mudstone and granite. Weathering effects were clearly noted on the exposed stones on the walls. The replacement stone should consist of sandstone blocks located 35 km north of Aqaba. Wall restoration includes replacement of mortar in the inner walls and disintegrated stone pieces in the external walls. Existing mortars consist primarily of a brown silty mixture and a gray mixture, but also a mixture of fine gravel, and a lime/gypsum binder. The major chemical constituents of the original mortar are 18 percent SiO 2 , 23 percent CaO, and 34 percent SO 3 . X-ray diffraction peaks indicate the presence of gypsum, calcite and quartz. Comparative analysis data gave 7 percent CaCO 3 , 53 percent sand, and 40 percent solubles as average values for the constituents. Two sand sources were identified for the mortar mix; recommended mortar for restoration was a mix of lime, sand, and ash, with ratios of 1:3:1.5.

The influence of phase on the calculation of pseudo-static earth pressure on a retaining wall

Centrifuge modelling tests show clearly the phase change in lateral acceleration in the backfill behind a retaining wall as shear waves propagate from the base of the model towards the ground surface. However, design calculations for the dynamic lateral earth pressure on a retaining wall which use a pseudo-static approach assume that the backfill experiences a uniform acceleration throughout. Researchers have agreed that the total lateral earth pressure calculated using this approach is approximately correct, but have disagreed over the distribution of the dynamic increment of pressure. The Paper presents an analysis which takes into account a finite shear wave velocity in the backtill, thus allowing for the phase change in a prototype structure. The phase change does not have a significant influence on the magnitude of the total earth pressure, but it has a marked effect on the distribution of the dynamic increment. The resultant pressure is seen to act at a point above one third of the height of the wall. The maximum dynamic earth pressure and the peak bending moment on the wall are approximately in phase with the acceleration at mid-depth, and therefore this acceleration may be the most appropriate value to use for design. The effect of a non-uniform shear modulus distribution is considered, as is the effect of amplification of acceleration on the distribution and magnitude of earth pressure. Ampliication of acceleration has an influence similar in character to the effect of increasing the acceleration coefftcient in a uniform acceleration field. Centrifuge model test data analysed using this approach show good agreement if the amplification of motion is taken into account. Des essais de modèle à la centrifugeuse indiquent clairemeat le changement de phase de l'accélération latérale dans le remblai derrière un mur de soutènement pendant que les ondes de cisaillement se propagent à partir de la base du modèle vers la surface du terrain. Les calculs classiques pour la pression latérale dynamique des terres sur un mur de soutènement qui emploient un méthode pseudostatique admettent cependant que le remblai entier subit une accélération uniforme. Les rechercheurs reconnaissent que la pression latérale totale des terres calculée par cette méthode est approximativement correcte, mais ne sont pas d'accord sur la distribution de l'incrément dynamique de pression. L'article présente une analyse qui inclut une vélocité finie de l'onde de cisaillement dans le remblai. Le changement de phase darts une structure prototype eat ainsi pris en compte. Le changement de phase est pratiquement sans influence sur la valeur totale de la pression des terres, tandis qu'il prod un effet marqué sur la distribution de l'incrément dynamique. On observe que la pression résultante s'applique au-dessus du tiers de la hauteur du mur. La pression maximale dynamique des terres et le moment maximal de flexion sur le mur se trouvent approximativement en phase avec I'acclélération a mi-profondeur, de sorte que cette accélération peut représenter la valeur la plus convenable à employer dans les calculs de murs. L'article considère l'effet d'une distribution non-uniforme du module de cisaillement aussi bien que l'effet de I'amplification de l'accélération sur la distribution et la valeur de la pression des terres. L'amplification de l'accélération exerce une influence analogue à l'effet l'augmentation du coefficient d'accélération darts un champ d'accélération uniforme. Lea données d'essais sur modèle en centrifugeuse analysées par cette méthode sont satisfaisantes, à condition que l'amplification du mouvement soit prise en compte.

Dynamic responses of buried pipelines during a liquefaction process

Dynamic response analysis for buried pipelines were performed based on the Rayleigh—Ritz method using the Hamilton's principle for the formulation. The critical evaluations of the soil's parameters were made during the process of soil liquefaction, which include variations of dynamic soil and water pressures, subgrade reactions, and damping coefficient. The analytical results were compared with model experiments in a shaking table. The analytical results were approximately 60 to 100% larger than the experimental measurements. One of the reasons of the discrepancy might be attributed to some conservative assumptions used in assessing the dynamic lateral earth pressure. It was also found that rigorous evaluation of damping during liquefaction process is significantly critical for the accurate analysis.

Determination of earthquake loads on structures — Research and development required

This paper discusses the research and development work required in three aspects of seismic analysis, i.e. modal combination criteria in the response spectrum analysis, the techniques in modeling and simulating structures, systems and components, and the determination of dynamic lateral earth pressure during an earthquake. In the seismic analysis of structures, the lumped mass method is commonly used. For this method, the thin wall beam theory approach and the rigidity approach used in determining the effective shear areas and the distributions of translational shears are discussed. In the analysis of structures, either the time history or response spectrum method is used. When the response spectrum modal analysis method is used, the exact phase angle relation among maximum modal responses is not defined; therefore, a logical combination criterion must be established. The criterion for closely spaced modal responses to obtain system response is also mentioned. Finally, the significantly different lateral earth pressures on basement walls of embedded structures obtained using the Mononobe-Okabe method and the finite element method are also discussed. Hopefully, through further research and development work in these areas, safe and economic design can be achieved.