Settlement Of Backfill Research Articles

Seismic Resilience of Geogrid Reinforced Concrete Earth-Retaining Wall of Various Incremental Panels Based on Physical and Numerical Modelling

Seismic Resilience of Geogrid Reinforced Concrete Earth-Retaining Wall of Various Incremental Panels Based on Physical and Numerical Modelling

Numerical investigation on the behaviour of Post-Tensioned Mechanically Stabilised Earth Walls (PT-MSEW)

Numerical investigation on the behaviour of Post-Tensioned Mechanically Stabilised Earth Walls (PT-MSEW)

Centrifugal model test study on deformation characteristics of deep, thick fillings in giant karst cave tunnels under different construction processes

Centrifugal model test study on deformation characteristics of deep, thick fillings in giant karst cave tunnels under different construction processes

Seismic performance of mechanically stabilized earth walls with Sand-Crumb rubber backfills of varying proportion

The applicability of crumb rubber mixed with sand as alternative fill material in mechanically stabilized earth (MSE) walls is investigated in the current study. Shaking table tests have been conducted to analyze the dynamic response of model geogrid reinforced earth walls subjected to three different base input motions. Eight different sand-crumb rubber mixture combinations were used as backfill. The outcomes of this study provide quantitative results on how base excitation amplitudes could influence the seismic behavior of the MSE walls in the presence of sand-rubber backfill. The results have been analyzed in terms of deformation and rotation of the wall, settlement of backfill, acceleration amplification, and earth pressure response. Wall displacement and backfill settlement was found to reduce with the addition of rubber in the sand. The maximum displacement at the top of the wall was found to reduce by 45% at a rubber content of 30% for high peak ground acceleration (PGA) input motion. Two-wedge failure was observed with the failure envelope inclined at an angle of 49° from the vertical. Apart from this, the strain in the geogrid was decreased with an increase in the rubber content. Hence, the rubber content of 30% mixed with sand can be considered an optimum percentage to control the dynamic performance of MSE walls. In the end, a cost-benefit analysis was conducted, and it was found that using rubber as a partial substitute for sand backfill reduces the overall cost of the project. This research will also promote the use of recyclable rubber as a construction material in highway construction.

Evaluating Finn-Byrne Model in Liquefaction Analysis of Quay Wall and Cantilevered Retaining Wall Models

Two centrifuge tests on a quay wall and a cantilevered retaining wall with saturated granular backfills were simulated using Finn-Byrne model. Capabilities of Finn-Byrne model in liquefaction analysis of the quay wall and the cantilevered retaining wall were evaluated. The quay wall model subjected to a horizontal acceleration time history and the cantilevered retaining wall model subjected to a horizontal and a vertical time history. The constitutive model is a linear elastic – perfectly plastic model. Hooke’s elasticity and Mohr-coulomb criterion for the yield surface were assumed for the backfill material behavior. The excess porewater pressure generation, acceleration, wall lateral displacement, lateral earth pressures, deformation pattern, and backfill settlements were monitored and compared with centrifuge tests’ results. The results showed that the adopted model is suitable for stability and displacement analyses of the quay walls and cantilevered retaining walls. However, a care should be taken when assessing the backfill settlements and dynamic earth pressure behind the wall stem. The rest of the results showed a good agreement with the centrifuge tests’ results.

Dynamic Characteristics of Reinforced Soil Retaining Wall with Composite Gabion Based on Time Domain Identification Method

A series of shaking table tests was carried out on the dynamic performance and working mechanism of a gabion reinforced soil retaining wall under seismic load. The test results show that the panel presents the deformation mode of middle and upper bulging at the contact point between the rigid box and the retaining wall The settlement of top backfill is relatively uniform, and there is basically no differential settlement, the natural frequencies at different positions and heights inside the retaining wall are basically the same, and the natural frequencies are stable between 22.61 and 23.04 Hz below 0.8 g. The damping ratio decreases with the increase in wall height, and the damping ratio at each stage after vibration is greater than that before vibration. The seismic earth pressure is nonlinearly distributed. The measured value of the lower part of the retaining wall is smaller than that calculated by the Seed–Whitman method with an increase in peak acceleration, and the measured value of the upper part of the retaining wall is larger than the theoretical calculation results. The position of the resultant action point of seismic earth pressure is greater than 0.33 times the wall height specified by the Mononobe–Okabe method.

Centrifugal Model Test and Simulation of Geogrid Reinforced Backfill and EPS Interlayer on Bridge Abutment

In this paper, the use of geotechnical centrifuge and numerical modeling techniques to investigate the influence of geogrid reinforcement and EPS interlayer on the lateral earth pressure and the backfill surface settlements behind gravity abutment and pile-supported abutment is reported. According to the principle of equal strain, the abutment back structure, foundation, backfill material, grid and interlayer material were simulated, and the centrifugal model test for two types of abutments was carried out with a model scale of n = 62.5, 40, respectively. The tests showed that the reinforcement of the geogrid could reduce the surface settlement of backfill and the lateral earth pressure of the backfill on the back of abutment. After setting the EPS interlayer, the influence of abutment displacement on earth pressure could be eliminated, and the earth pressure of the backfill material on the abutment back was significantly reduced. The “interlayer + geogrid” structure further reduced the earth pressure of backfill material on the abutment back. The existence of the EPS interlayer adjusted the strain distribution of the reinforced material, significantly increasing the strain of the reinforced material near the abutment, which was conducive to the reinforcement effect. The above research conclusions could provide a basis for the design and practical application of abutment backfill materials.

Integral bridge abutments in response to seasonal temperature changes: State of knowledge and recent advances

Expansion and contraction of integral abutment bridges due to temperature changes force integral bridge abutments (IBAs) to move toward and away from the backfill, thus increasing horizontal earth pressures behind the abutments and inducing bending moments on pile foundations. This paper presents the state of knowledge and recent advances in understanding the behavior of IBAs in response to temperature changes including abutment movement, pile response, and horizontal earth pressure behind the abutment, examines the effect of bridge skew on the behavior, and discusses possible measures to mitigate temperature change-induced problems for IBAs. Field data show that both bending moments of piles near the bottom of abutments and axial loads of piles fluctuated with temperature. Redistribution of dead loads among bridge components due to planar temperature gradients and earth pressure changes behind the abutment contributed to axial load fluctuations in piles. Magnitude and distribution of horizontal earth pressures behind the abutment depend on factors such as abutment movement and abutment movement mode. Most of the current design methods overestimated the horizontal earth pressures at the bottom of the abutment during bridge expansion. Compressible inclusions placed behind the abutment, geosynthetic-reinforced backfill, and lightweight backfill in place of typical aggregate backfill are helpful to reduce horizontal earth pressures behind the abutment at high temperatures and temperature change-induced backfill settlements.

Short- and long-term behavior of EPS geofoam in reduction of lateral earth pressure on rigid retaining wall subjected to surcharge loading

Retaining walls are subjected to dead loads from backfill and adjacent structures, live loads and other loads from the vicinity of the structure. Retaining walls need to withstand earth pressure generated from above mentioned loads satisfactorily throughout their service life. Lateral earth thrust on retaining walls can be minimized by placing a compressible inclusion, such as, EPS geofoam, between the backfill and retaining wall. The present study is aimed at understanding both short- and long-term influence of EPS geofoam on surcharge induced lateral earth pressures on retaining walls through 1-g model studies. Four densities of geofoam in the range of 10–25 kg/m 3 and three thicknesses of geofoam in the range of 25–75 mm were used in the present study. Lateral earth pressure at several locations along the height of the wall were monitored using earth pressure cells. Geofoam compression and backfill settlements under the surcharge load were also quantified using image analysis. From the series of model tests, it was observed that with the use of geofoam, lateral earth pressure on retaining wall was reduced under both short- and long-term loading conditions. However, higher reduction was observed under long-term loading. • Geofoam is highly beneficial in reducing the earth pressures on rigid non-yielding retaining walls. • The main advantage of provision of geofoam is that the earth pressures will continuously decrease with elapsed time. • Lateral earth pressure on retaining wall with geofoam reduces for repetitive loading, irrespective of density of geofoam. • Percentage of geofoam compression along the height of wall decreases with increase in density & thickness of geofoam. • Percentage lateral thrust reduction ( I T ) on retaining wall is observed in the range of 55–78% from short-term static tests. • I T achieved using EPS15 and EPS20 is almost same, but geofoam compression and backfill settlements are higher for EPS15. • Compressive creep sustained geofoam is more efficient in reducing the lateral earth pressure on retaining wall. • Percentage lateral thrust reduction from pseudo-long-term static tests was 2.4–8.1% higher than that of short-term tests.

Earth retaining walls with backfill possessing cohesion - Numerical analyses of seismic behavior

Results of a parametric finite element study are presented regarding the seismic response of gravity earth retaining walls with backfill possessing cohesion (c-φ soil). The response of the “wall-backfill” system was studied for the cases of a 4.0 m and 7.5 m walls under both harmonic and actual (recorded) earthquake base excitations of varying intensities. The paper constitutes an extension of the Athanasopoulos-Zekkos et al. (2013) [2] study which provided a validation of the numerical model used in the analyses (based on comparisons to centrifuge testing results) and considered only cohesionless backfill material. The results indicate that the presence of backfill possessing a small to moderate amount of cohesion is beneficial regarding the kinematic response of the system: reduction of lateral wall displacements (up to 60%) and rotation (up to 40%) as well as reduction (or complete avertment) of the backfill settlements. On the other hand, the inertial response of the cohesion possessing system may range from beneficial (increase of phase difference between wall inertia and soil thrust, decrease of residual seismic earth thrust on the wall) through neutral (independence of seismic earth thrust magnitude from the presence of cohesion) to detrimental (aggravation of the backfill amplification of motion, movement of the point of application of resultant thrust towards the top of the wall). It is concluded that only low values of backfill cohesion (5 kN/m2 to 15 kN/m2) may be beneficial for the seismic response of the “wall-backfill” system.

Seismic fragility of approach backfill differential settlement for statewide bridges in California

This study develops the first-of-its-kind seismic fragility models for estimation of approach backfill differential settlement for statewide bridges in California. Seismic compression analysis is carried out through a multi-step framework that estimates seismic-induced shear strain profiles for backfills, converts them to volumetric strains, and computes soil settlement through depth integration. As a crucial step, three independent methods are advanced on a uniform basis to estimate soil shear strains under earthquake loading: a simplified one-dimensional (1D) Static approach, a 1D Dynamic method from site response analysis, and a two-dimensional (2D) Dynamic method that accounts for the trapezoidal shape of the bridge embankment. Subsequently, seismic fragility models are derived using the multiple-stripe analysis (MSA) approach that convolves the seismic demands of backfill settlement with capacity models for several broad groupings of approach-slab designs having different abutment and abutment-foundation types, and abutment-connection details. A survey of California's bridge inventory provides stochastic data inputs that quantify various sources of uncertainties in backfill profile, embankment geometry, and both approach slab and abutment designs. Finally, a combined fragility model is developed by considering an equal methodological contribution from each mentioned approach. The final fragility models suggest that the lowest differential-settlement fragility is achieved by combining regular abutments on spread footings with long-length approach slabs connected to the bridge abutment, while the worst case occurs where bridge abutments on deep foundations are not connected with abutting pavements. The proposed seismic fragility models offer a sound basis for first-order estimation of approach-fill differential settlement which may lead to reduced ride quality, traffic speed reductions, and in extreme cases, temporary roadway closure. These represent one of many seismic fragility models for the full range of bridge components needed for prioritizing seismic retrofit measures, facilitating post-hazard inspections and repair actions, as well as assessing the network mobility for resilience quantification.

Mitigation of seasonal temperature change-induced problems with integral bridge abutments using EPS foam and geogrid

Expansion of bridge girders in summer moves integral bridge abutments toward backfill, causing high lateral earth pressures behind the abutment. Some backfill material slumps downward and toward the abutment when the abutment moves away from the backfill due to bridge girder contraction in winter. Placement of geogrids within the backfill can increase stability of the backfill while placement of compressible inclusions (e.g., Expanded Polystyrene (EPS) foam) can reduce lateral earth pressures behind the abutment caused by bridge girder expansion. In this study, six physical model tests were conducted with 30 abutment top movement cycles due to simulated seasonal temperature changes to study the performance of integral bridge abutments with different mitigation measures. The test results showed that geogrid reinforcements caused higher maximum lateral earth pressures at the same abutment movement, but geogrids with wrap-around facing significantly reduced the backfill surface settlements. The combination of the EPS foam and geogrids could minimize lateral earth pressure increase and backfill settlement. The EPS foam reduced the abutment toe outward movement when the abutment top was pushed against the backfill; however, the mitigation effects by the EPS foam was limited due to its small thickness and relatively high elastic modulus in this study.

Effect of Geometrical Properties on Mechanical Behavior of Cantilever Pile Walls (CPW): Centrifuge Tests

Cantilever Pile Wall (CPW) is one of the cost-effective retaining structures supporting excavations. In this study, a series of nine centrifuge tests in 70 g acceleration were conducted to study the influence of different geometrical properties including pile space ratio (S/D; S: pile center to center spacing and D: diameter of the pile) and pile embedment depth ratio (L/H; L: length of the pile and H = excavation depth) on the wall lateral displacement, pile bending moment and backfill settlement. Centrifuge results revealed that a decrease in pile space and an increase in the embedment depth of piles reduced backfill settlements of CPW. The maximum bending moment approximately occurred in the same depth of excavation irrespective of piles’ space and embedment ratios. Furthermore, the maximum lateral displacement of CPW considerably decreased as the embedment depth ratio reaches a value of about 1.7. In this regard, increasing the value of L/H from 1.4 to 1.6 led to an impressive decline in wall lateral displacement about 68.7%, but this decline was just 3% while L/H was increased from 1.6 to 2. However, more increase in embedment depth of pile slightly increased the maximum bending moment of the piles. Moreover, the evaluation of these experiments provided a deeper understanding of the behavior of CPW. Additionally, safety factors of CPW models were calculated with conventional slice methods which showed an impressive agreement with centrifuge test results.

An analytical solution to estimate the settlement of tailings or backfill slurry by considering the sedimentation and consolidation

A common and important task in mining industry is to estimate the settlement or final volume of the tailings or backfill associated with sedimentation and self-weight consolidation. Up to now however, most existing analytical solutions were developed by only considering the settlement induced by consolidation. In this paper, the process of shrinkage tests has been compared with those of sedimentation and consolidation. It was shown that the pore water and particles movement in the sedimentation are very similar to that in the normal shrinkage. The void ratio at the end of sedimentation is thus for the first time considered to be equal to the void ratio at desaturation onset of shrinkage tests. An analytical solution was then proposed to estimate the settlement of tailings or backfill by considering the sedimentation and consolidation. To validate the proposed analytical solution, tailing deposition tests were conducted in two molds to simulate the tailings impoundment and underground mine stope. The required parameters were obtained through shrinkage and consolidation tests. Good agreements were obtained between the measured settlements and those calculated by the proposed solution. The proposed solution can thus be considered as validated and used to evaluate the settlement of tailings or backfill slurry.

Evolution of active arching in granular materials: Insights from load, displacement, strain, and particle flow

Abstract The progressive failure of active soil arching in a quasi-static particle flow was investigated to elucidate the deformation behavior and load evolution mechanism. A transparent trapdoor test apparatus and self-developed particle image velocimetry system were used to capture the soil mass displacement field. Disturbed region and active region were introduced to characterize the displacement patterns evolution for both shallow and deep conditions. Meanwhile, the evolution of the surface settlement, horizontal displacement, and volumetric change of backfill as the trapdoor receding were quantified. The shear band propagation was interpreted considering the dilatancy behavior. In addition, the vorticity reveals local rotation characteristics in the shear region. Afterwards, i) the evolution mechanism of arching was speculated from macro-and microscopic perspectives. ii) The critical displacement for mobilizing the minimum load was discussed. These results can provide a profound understanding for mathematical modelling that is expected to illustrate the progressive development of active arching with displacement.

Study on Comprehensive Treatment Technology of High-speed Railway Passing Through Giant Karst Tunnel

In the mountainous areas of Southwest China, a karst landscape is well developed. There, exposed giant karst caves in the construction of high-speed railway tunnels cause great construction difficulties and safety risks for the tunnel crossing. In this paper, the study object is the project on giant karst cave of the Qianjiang–Changde railway high-mountain tunnel. After the karst cave was revealed, unmanned aerial vehicle detection, three-dimensional laser scanning, and blasting vibration monitoring were used to study the stability of the karst cave. It was found that the karst cave has a higher risk of falling rocks. On the basis of careful consideration of construction, operation safety, and economy, the “backfill cave ballast + grouting to reinforce on the upper part” scheme was determined for the treatment of the karst cave. During the process of disposal, the surface and layered settlement of backfill were monitored, in which it showed that the surface settlement control was reasonable, and the settlement mainly came from the bottom of the grouting layer, the top of non-grouting backfill, and original accumulation. To prevent the risk of falling rocks, we performed permanent safety protection of the wall and the roof for the karst cave and temporary safety protection of the mobile scaffold. Finally, the backfill treatment of the giant karst cave of high-mountain tunnel was smooth, the settlement after construction was controllable, and it met the design requirements.

Mitigation of hunchbacked gravity quay wall displacement due to dynamic loading using shaking table tests

Abstract Five reduced-scale shaking table tests have been performed to investigate the deformation behavior of a block type quay wall under strong earthquakes. The quay wall was resting on a high relative density inclined seabed. The underlying seabed inclination and bottom block slopes have been considered as two parameters for mitigating the wall displacement. The experimental results indicated that the dominant mode of the wall failure under strong base acceleration was the sliding of the wall. Increasing the bottom block inclination (from 0 to 10°) significantly decreased the lateral displacement and the backfill settlements, which can increase the safety of port facilities. Since the high bottom inclination can cause the wall to overturn, a 7-degree angle was selected as the optimal degree for the presented wall model. Furthermore, it was observed that, making the bottom block inclined, without the seabed being inclined, did not effectively reduce the wall displacement.

Performance-based seismic fragility analysis of retaining walls based on the probability density evolution method

Seismic fragility analysis is an efficient way to study the seismic behaviour and performance of structures under the excitation of earthquakes of varying intensity, and an essential part of the seismic risk assessment of structures. A recently developed dynamic reliability methodology, the probability density evolution method (PDEM), is proposed for the dynamic reliability and seismic fragility analysis of a retaining wall. The PDEM can obtain an instantaneous probability density function of the seismic responses and easily acquire the seismic reliability of the structural system. An important advantage of the PDEM is its high efficiency relative to that of the Monte Carlo simulation method, which is often used in the reliability and fragility analysis of structures. The present study uses a typical gravity retaining wall to illustrate stochastic seismic responses and fragility curves that can be obtained by the PDEM. The combined uncertainties of the seismic force and soil properties are explicitly and systematically modelled by stochastic ground motions and random variables respectively. The performance of the retaining wall is analysed for different acceptable levels of backfill settlement. Additionally, seismic fragility curves are constructed without assuming the distribution of the seismic response.

Behaviour of Bamboo–Geogrid Reinforced Fly Ash Wall Under Applied Strip Load

This technical note presents results of model tests performed on bamboo geogrid reinforced fly ash walls under applied strip load. The effect of vertical spacing and length of bamboo geogrid mattresses and strips on the deformation behavior of the model walls was studied and discussed. The results demonstrated the effect of increase in length and coverage ratios and decrease in vertical spacing of reinforcements on the improved performance of the model walls, including increased failure surcharge pressure, reduced facing displacement and backfill settlement. The failure surcharge pressure compared with the unreinforced model wall was improved by 185.76 and 311.84% for bamboo geogrid strips and mattresses respectively when vertical spacing and length of reinforcement used were 20 and 65% of the wall height respectively.

Use of rubberised backfills for improving the seismic response of integral abutment bridges

Reuse of the 1.5 billion waste tyres that are produced annually is a one of the major worldwide challenges, as waste tyres are toxic and cause pollution to the environment. In recognition of this problem, this paper introduces the reuse of tyres, in the form of derived aggregates in mixtures with granulated soil materials, as previous studies indicated the potential benefits of these materials in the seismic performance of structures. The objective of the present research study is to investigate whether use of rubberised backfills benefits the seismic response of Integral Abutment Bridges (IABs) by enhancing soil-structure interaction (SSI) effects. Numerical models including typical integral abutments on surface foundation with nonlinear conventional backfill material and its alternative form as soil-rubber mixtures are analysed and their response parameters are compared. The research is conducted on the basis of parametric analysis, which aims to evaluate the influence of different rubber-soil mixtures on the dynamic response of the abutment-backfill system under various seismic excitations, accounting for dynamic soil-abutment interaction. The results provide evidence that the use of rubberised backfill leads to reductions in the backfill settlements, the horizontal displacements of the bridge deck, the residual horizontal displacements of the top of the abutment and the pressures acting on the abutment, up to 55, 18, 43 and 47 % respectively, with respect to a conventional backfill comprising of clean sand. Small change in bending moments and shear forces on the abutment wall is also observed. Therefore, rubberised backfills offer promising solution to mitigate the earthquake risk, towards economic design with minimal damage objectives for the resilience of transportation networks.