Rockfill Slopes Research Articles

Calibration of Adjustment Coefficient of the Viscous Boundary in Particle Discrete Element Method Based on Water Cycle Algorithm

The viscous boundary has a direct influence on the accuracy of structural dynamic response analysis, and the absorbing effect of the viscous boundary is controlled by the adjustment coefficient. Therefore, a calibration model of the viscous boundary’s adjustment coefficient based on the water cycle algorithm is established for the particle discrete element to improve the accuracy of dynamic response analysis. First, the traditional viscous boundary theory is utilized to realize the viscous boundary’s application method in the particle discrete element via programming. This avoids the reflection and superposition of seismic waves at the boundary and makes the structural dynamic response with the particle discrete element more real and accurate. Second, for the complex and time-consuming adjustment coefficients determination, a calibration model based on the water cycle algorithm and Latin hypercube sampling is established for the adjustment coefficients in the particle discrete element method. Finally, this calibration model is employed for the seismic response analysis of a rockfill slope, the maximum velocity of rock in this rockfill slope being about 1.30 times that of a seismic wave. Comparing the rockfill slope response with fixed and viscous boundaries, the calibration’s accuracy and the viscous boundary’s feasibility are demonstrated, further expanding the research and application of the particle discrete element method in dynamic response analysis.

Evaluation of the effects of protective measures implemented in high-rockfill slope engineering based on the discrete element model

There has to date been no quantitative analysis of the anti-sliding effects of protective measures implemented in high steep rockfill slope engineering under conditions of instability, despite the importance of this analysis for engineering design, improvement to engineering measures, and promotion of hazard warning and management. This study established a discrete element model (DEM) of a high steep rockfill slope based on an engineering project. Numerical simulation was used to investigate the anti-sliding effect of concrete retaining wall height on the high rockfill slope under conditions of instability, with a focus on the distributions of rock before and after slope instability, rock displacement, the quantity of rock crossing the concrete retaining wall, and the quantity of rock reaching the riverbed. The trajectory of rolling rock changes in velocity under different concrete retaining wall heights, and the resistance to rolling rock by the retaining wall were analyzed. Movement trajectories and velocity time-history curves of rolling rock suggested that a higher concrete retaining wall could enhance slope stability under long-term operation. Quantitative analyses determined the optimum height of the concrete retaining wall. The method proposed in this study could provide guidance for effective protective measures in high steep rockfill slope engineering.

Study on the Early Warning Methods of Dynamic Landslides of Large Abandoned Rockfill Slopes

The excavation of large-scale underground projects produces a large amount of rubble waste material that is temporarily deposited near the project site, which forms a large-scale waste rockfill artificial slope. The slope has a granular structure, thus, during excavation and trans-shipment, surface shallow landslides may frequently occur. Existing contact monitoring methods such as buried sensors and GPS (Global Position System) are difficult to apply to the monitoring of rockfill landslides. Therefore, there are no appropriate early warning methods for waste rockfill slope landslides during dynamic transfer. Here, we used ground-based interferometric synthetic aperture radar to monitor the deformation of a rockfill slope during the excavation and transfer processes as a proposed method for the early warning against landslides on rockfill slopes during dynamic construction based on the radar interference measurement results. Through data cleaning and data interpolation, the line of equal displacement was generated, and the cross-sectional area of the equal displacement bodies of landslides was calculated. In addition, we established a four-level early warning grading standard, with the rate of change of the cross-sectional area of the equal displacement body as the early warning index, and realized real-time dynamic early warning of waste rockfill landslides during excavation and transportation. Finally, five landslide examples were used to verify the proposed warning method. The results show that the warning method can make an early warning 8–14 min before the occurrence of landslide, which can effectively avoid the appearance of catastrophic events.

Calibration of the microparameters of the discrete element method using a relevance vector machine and its application to rockfill materials

To accurately simulate the mechanical properties of rockfill materials under triaxial stress using the discrete element method (DEM), the microparameters of the rockfill material DEM model are calibrated based on the macroparameters of a constitutive model. For the calibration model, a refined 3-D numerical triaxial test is established to obtain the deformation curves of the rockfill under different confining pressures. Deformation curves with different microparameters in the contact model are then calculated by numerical triaxial tests to determine the macroparameters of the constitutive model. Then, a nonlinear relationship between the macroparameters of the E-B model and the microparameters of the contact bond model is built by a relevance vector machine. A memetic algorithm is employed to calibrate the microparameters of the rockfill, thereby establishing a calibration model based on a relevance vector machine and a memetic algorithm. Afterwards, a numerical triaxial test example of rockfill materials is used to verify the feasibility of this calibration model, and then the fabric microparameters under different confining pressures are analysed. In addition, to determine the influence region, a failure process of a rockfill slope is simulated with the calibrated microparameters of the DEM model. In summary, this calibration method substantially improves the numerical results, thereby enhancing the ability to determine the mechanical properties of construction materials and solve various problems in engineering.

Ön Yüzü Geomembran Kaplı Yüksek Bir KayaDolgu Barajın Deprem ve Geomembranda Yırtık Olması Durumunda Performansının Değerlendirilmesi

This paper presents stability and seepage evaluation of a high rockfill dam with a geomembrane seepage barrier by considering scenarios of a possible occurrence of a large earthquake due to the active faults in the region and also a seepage flow in the dam due to a possible rupture of the geomembrane liner. For this purpose, finite element transient seepage and pseudo static slope stability analyses were both carried out together to assess the critical potential failure surfaces and safety factors of the rockfill slopes. Therefore, pore water pressures on the failure surfaces were first calculated using the time varying (transient) numerical seepage analyses method which is essentially important to determine the time dependent variations of seepage paths and water pressures within the rockfill as well. In the analyses, it was determined that the most critical slope failure case is when a geomembrane liner tears at the time of the highest reservoir water elevation since the hydraulic head is maximum and causes the largest seepage pressure in the rockfill there. Analyses showed that if a strong earthquake struck the region, both the upstream and downstream slopes are safe with sufficiently high safety factors. In addition, in case of a possible tear and leakage on the geomembrane liner, the dam will also withstand well with 2.25 horizontal to 1 vertical slopes. However, it is recommended that constructing a downstream toe drain or a relief well will provide an additional safety measure against any heave occurrence or instability of the rockfill since the embankment and bedrock foundation are pervious causing high seepage pressures at the downstream toe of the dam.

The effect of size on the strength of coarse rock aggregates and large rockfill samples through experimental data

Testing the mechanical response of coarse granular materials requires very large and expensive laboratory equipments. During the 1960s, pioneering experimental programs were carried out on several rockfill dam materials, and those results are still a reference for engineers and researchers. However, only few experimental works have been reported to this day, and due to the scarcity of empirical data, the role of the size effect caused by grain crushing is not well known. To improve understanding of this rarely studied issue and the influence of individual particle strength, this paper analyzes the size effect on rock aggregate crushing strength and its connection with the shear envelope of rockfills. The suitability of the 4-parameter Weibull equation to describe size effects on the crushing strength reported in the literature is discussed. Furthermore, a Weibull statistical analysis was carried out for a wide number of experimental results on rock aggregates, where it has been observed that strength decreases with particle size. In parallel, the results of large triaxial tests on homothetic scaled rockfill samples of 250 and 1,000 mm in diameter reveal that the coarser the material, the higher the amount of grain breakage and the lower the shear strength. The impact of size effects obtained from the experiments is analyzed and discussed in terms of the factor of safety of rockfill slope stability. Furthermore, the results are compared with the only existing theoretical method that links the rock aggregate with the strength of the granular assembly. Good agreement between the empirical results and this theoretical method has been confirmed.

Electrical resistivity response due to variation in embankment shape and reservoir levels

The safety of the center-core type of fill dam structure was assessed by examining the effects of the distortion of electrical response verified in terms of two-dimensional (2D) apparent resistivity and its inverted sections from three-dimensional (3D) modeling for the embankment. The distortion effect is due to 2D interpretation of the 3D structure of the embankment. From the analysis, it was found that water level was correctly described by the resistivity section around the middle part rather than each side at the end of the embankment. This is due to the 3D terrain effect when the material of the embankment is assumed to be horizontally uniform. In addition, when the slope of the outer rock-fill section is set as uniform, the resistivity section is more similar for sharper center-core slopes. On the other hand, when the rock-fill slope is steep, the resistivity section shows the water level at a lower position than the real one, and the 3D distortion effect at the end of the embankment is enhanced.

Mechanisms of massive failure for flowthrough rockfill embankments

A modified wedge method for the analysis of the stability of a downstream slope of a flowthrough rockfill dam is presented. The results from this wedge analysis are compared with results from a conventional Bishop method of analysis, and both are compared with experimental measurements of the forces at incipient failure from model tests performed on simple granular embankments in hydraulic flumes. The proposed wedge method, based on a nonrotational failure mechanism, compared more favourably with experimental observations than did the Bishop method of analysis, based on a rotational failure mechanism. It is also concluded that the Bishop method is very conservative for the analysis of such rockfill slopes. Key words : rockfill embankment, slope failure, bursting forces, model slopes, non-Darcy flow.

Inquiry into rockfill slope stability analyses : V. F. B. De Mello, L. S. A. Kaimoto & M. Namba, Irrigation & Power Journal, 51(4), 1994, pp 23–40

Inquiry into rockfill slope stability analyses : V. F. B. De Mello, L. S. A. Kaimoto & M. Namba, Irrigation & Power Journal, 51(4), 1994, pp 23–40

Evacuateurs fondés sur remblai

The specific technical problems raised by spillways founded on earthfill are coming from foundation (low shear strength, strain, seepage), and downstream stilling basin. The typical spillways experienced are armoured rockfill slopes, concrete spillway chute and armoured earthfill. Each type is illustrated, in the discharges possible range, by significant works. A new type can be imagined with a graded chute partially dissipating hydraulic energy and possibly limiting downstream stilling basin requirements. This new type should probably be usable in the same range of discharges as the above experienced types.

886361 Casagrande resistance envelopes for rock and rockfill slopes having circular slip surfaces : Baikie, L D Can Geotech JV25, N1, Feb 1988, P42–49

886361 Casagrande resistance envelopes for rock and rockfill slopes having circular slip surfaces : Baikie, L D Can Geotech JV25, N1, Feb 1988, P42–49

Use of soft rockfill at Evretou Dam, Cyprus

Evretou Dam is a 72 m high rockfill dam with a vertical clay core, the embankment being constructed with rockfill derived from a weak reef limestone. This Paper describes the properties of this soft rockfill, together with the effect of these properties on the embankment design. The breakdown that occurs on handling, resulting in a composition of 25–40% sand sized material (0·075–2 mm) and up to 25% silt sized rock flour (less than 0·075 mm), means that the engineering properties of permeability and shear strength are intermediate between those of an earthfill and a hard rockfill. Instrumented performance of the rockfill is described, together with the interaction of the core and the rockfill shoulders. The embankment is founded on up to 40 m of alluvial deposits comprising interbedded silty sands and sandy gravels with many cobbles. The properties of this foundation are described where they affect the external rockfill slopes. Le barrage d'Evretou est une construction à noyau vertical d'argile avec remblai rocheux constitue par du calcaire récifal tendre. L'article décrit les propriétés de ce remblai rocheux tendre et leur influence sur la construction du barrage. La désagréation qui a lieu pendant les opérations produit une composition comprenant 25–40% de matière ayant les dimensions d'un sable (≥2 mm) et jusqu'à 25% de farine de rocher ayant les dimensions d'un limon (≥0·075 mm), ce qui indique que la perméabilitié et la résistance au cisaillement sont intermédiares entre celles d'un remblai en terre et celles d'un remblai rocheux. Une description est donée de la performance instrumentée du remblai rocheux et de l'interaction du noyau et des épaulements du remblai rocheux. Le barrage est fondé à 40 mètres de profondeur sur dep⊚cts alluvionnaires comprenant des sables limoneux et des graviers sablonneux avec beaucoup de galets. Les propriétés de cette fondation sont décrites en ce qui concerne leur influence sur les pentes externes du remblai rocbeux.

Casagrande resistance envelopes for rock and rockfill slopes having circular slip surfaces

A series of Casagrande resistance envelopes are presented for use in the preliminary design and evaluation of uniform rock and rockfill slopes. The influence of tension cracks on the safety factors for such slopes is examined. A comparison is also made between the safety factors obtained using the resistance envelope method and those obtained using published stability charts for rockfill slopes having nonlinear shear strength envelopes. Key words: rock, rockfill, slope, stability, Casagrande resistance envelope, safety factor.

Lateral load tests of piles in sloping rock fill : Diaz, G M; Patton, B W; Armstrong, G L; Joolazadeh, M Proc of the Conference on Analysis and Design of Pile Foundations, San Francisco, California, 1–5 Oct 1984P214–P231. Publ New York: ASCE. 1984

A new container wharf constructed at the Port of Los Angeles features vertical prestressed concrete piles to provide both vertical and lateral support. A rockfill embankment used to allow a steeper under-wharf slope and a reduced wharf width resulted in the piles being embedded in the rockfill slope. Lateral load tests were performed on two production piles to evaluate the lateral load performance. Back-calculated p-y curves are compared to p-y curves calculated for cohesionless soils with a level surface.

Discussion: Stability of compacted rockfill slopes

Discussion: Stability of compacted rockfill slopes

Stability of compacted rockfill slopes : Charles, J A; Soares, M M GeotechniqueV34, N1, March 1984, P61–70

Stability of compacted rockfill slopes : Charles, J A; Soares, M M GeotechniqueV34, N1, March 1984, P61–70

Stability of compacted rockfill slopes

The Mohr failure envelopes for compacted rockfills exhibit significant curvature particularly at low and medium stresses. A computer program for circular arc slope stability analysis has been modified to accept these non-linear failure envelopes. A dimensionless stability number has been introduced to facilitate the production of charts for the rapid assessment of rock-fill slope stability. The effect of submergence on the stability of compacted rockfill slopes has been examined. Les courbes intrinsèques des remblais rocheux compactés montrent une courbure signifiante surtout à basses et moyennes contraintes. Un programme d'ordinateur pour l'analyse de la stabilité des pentes en arc de cercle a été modifié pour prendre encompte ces courbes intrinsèques non-linéaries. Un parameter de sécurité au renversement, sans dimensions a été introduit pour faciliter la production d'abaques pour l'évaluation rapide de la stabilité des pentes de remblais rocheux. L'effet de la submersion sur la stabilité des pentes de remblais rocheux compactés a été étudié.

Calculation of the protective facing of slopes of hydraulic structures with consideration of wind-wave refraction

1. Laboratory investigations to evaluate the oblique approach of waves to a rockfill slope, despite their limitedness (small scale of the model or investigation only at one gradient of the slope, equal to 1.5), show the economic expediency of taking into consideration wave refraction in such cases. 2. Equations (l)-(3) are recommended for calculation refraction and the mass of stone for protecting slopes from waves in the case of their oblique approach.

The influence of confining pressure on the shear strength of compacted rockfill

Large-scale drained triaxial compression tests have been carried out on heavily compacted samples of different types of rockfill over a range of confining pressures. The Mohr failure envelopes show pronounced curvature, particularly at low stresses. An assessment has been made of the significance of this for the stability of rockfill slopes where generally the shear strength of the rockfill at low stresses is of major importance. It is concluded that in many instances rockfill embankments could be built with slopes much steeper than those currently adopted and still have an adequate factor of safety against stability failure. Des essais de compression triaxiale drainés à grande échelle ont été réalisés sur des échantillons fortement compactés de différents types de remblai rocheux, suivant toute une gamme de pressions d'éntreinte latérale. Les courbes limites de Mohr présentent une courbure prononcée, notamment aux faibles contraintes. On etabli la signification de ce résultat vis-à- vis de la stabilité des talus de remblai rocheux dont la résistance au cisaillement pour de faibles contraintes est généralement predominante. On en a conclu que, dans bien des cas, il était possible de construire des talus de remblai rocheux avec une pente beaucoup plus raide que celle des talus couramment construits, le coefficient de sécurité relatif au glissement restant adequat.

Foundation Failures of Four Rockfill Slopes

Failures of four rockfill slopes were interpreted as large-scale shear tests on the foundation strata of stiff fissured clay. Analyses of the slope failures together with in situ and laboratory shear tests on the clay, have provided information on the relation between the strength in bulk of a stiff fissured clay and that measured by small-scale tests. Two of the failures were progressive while two were non-progressive. For the non-progressive failures and one of the progressive failures, the strength in bulk was approximately equal to the strength measured in small-scale field and laboratory tests. The strength in bulk found from the remaining progressive slide was, however, less than strengths measured in small-scale tests. At all four sites in situ effective horizontal stresses in the clay strata were about equal to the passive pressure resistance of the clay. This fact was used to provide an alternative assessment of the bulk strength of the clay.