Showing papers on "Lateral earth pressure published in 2010"

Seismic Earth Pressures on Cantilever Retaining Structures

Abstract: An experimental and analytical program was designed and conducted to evaluate the magnitude and distribution of seismically induced lateral earth pressures on cantilever retaining structures with dry medium dense sand backfill. Results from two sets of dynamic centrifuge experiments and two-dimensional nonlinear finite-element analyses show that maximum dynamic earth pressures monotonically increase with depth and can be reasonably approximated by a triangular distribution. Moreover, dynamic earth pressures and inertia forces do not act simultaneously on the cantilever retaining walls. As a result, designing cantilever retaining walls for maximum dynamic earth pressure increment and maximum wall inertia, as is the current practice, is overly conservative and does not reflect the true seismic response of the wall-backfill system. The relationship between the seismic earth pressure increment coefficient (ΔK AE ) at the time of maximum overall wall moment and peak ground acceleration obtained from our experiments suggests that seismic earth pressures on cantilever retaining walls can be neglected at accelerations below 0.4 g. This finding is consistent with the observed good seismic performance of conventionally designed cantilever retaining structures.

Field Tests on Pile-Supported Embankments over Soft Ground

Abstract: When designing embankments over soft soils, geotechnical engineers face many challenges. These include potential bearing failure, intolerable settlement, and global or local instability. Pile-supported embankments have been emerged as an effective alternative successfully adopted worldwide to solve these problems. This paper focuses on three cases in which pile-supported embankments were used for constructing highways in the eastern coastal region of China. Each case provides a description of the soil profile, construction procedure, and field monitoring of the settlements, earth pressures, and pore-water pressures. Field monitored data from contact pressures acting on the piles and the soils, to the settlements of the piles and the soils are reported and discussed. The development of the earth pressures both on the piles and the soils shows that there was a significant soil arching in the embankment, and the measured earth pressures acting on the piles are much higher than that acting on the soils betwee...

Validated Simulation Models for Lateral Response of Bridge Abutments with Typical Backfills

Abstract: Abutment-backfill soil interaction can significantly influence the seismic response of bridges. In the present study, we provide numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. Those tests involve well-compacted clayey silt and silty sand backfill materials. The simulation methods considered include a method of slices approach for the backfill materials with an assumed log-spiral failure surface coupled with hyperbolic soil stress-strain relationships [referred to as “log-spiral hyperbolic (LSH) model”] as well as detailed finite-element models, both of which were found to compare well with test data. Through parametric studies on the validated LSH model, we develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall defl...

Seismic response of underground utility tunnels: shaking table testing and FEM analysis

Abstract: Underground utility tunnels are widely used in urban areas throughout the world for lifeline networks due to their easy maintenance and environmental protection capabilities However, knowledge about their seismic performance is still quite limited and seismic design procedures are not included in current design codes This paper describes a series of shaking table tests the authors performed on a scaled utility tunnel model to explore its performance under earthquake excitation Details of the experimental setup are first presented focusing on aspects such as the design of the soil container, scaled structural model, sensor array arrangement and test procedure The main observations from the test program, including structural response, soil response, soil-structure interaction and earth pressure, are summarized and discussed Further, a finite element model (FEM) of the test utility tunnel is established where the nonlinear soil properties are modeled by the Drucker-Prager constitutive model; the master-slave surface mechanism is employed to simulate the soil-structure dynamic interaction; and the confining effect of the laminar shear box to soil is considered by proper boundary modeling The results from the numerical model are compared with experiment measurements in terms of displacement, acceleration and amplification factor of the structural model and the soil The comparison shows that the numerical results match the experimental measurements quite well The validated numerical model can be adopted for further analysis

Large-Scale Passive Earth Pressure Load-Displacement Tests and Numerical Simulation

Abstract: Passive earth pressure is recorded in two different tests, using a 6.7-m long, 2.9-m wide soil container. In these tests, sand with 7% silt content is densely compacted behind a moveable test wall to a supported height of 1.68 m (5.5 ft). Lateral load is applied to the vertical reinforced concrete wall section, which displaces freely along with the adjacent backfill in the horizontal and vertical directions. The recorded passive resistance is found to increase until a peak is reached at a horizontal displacement of 2.7–3% of the supported backfill height, decreasing thereafter to a residual level. In this test configuration, a triangular failure wedge shape is observed, due to the low mobilized wall-soil friction. Backfill strength parameters are estimated based on this observed failure mechanism. From these estimates, along with triaxial and direct shear test data, theoretical predictions are compared with the measured passive resistance. Using the test data, a calibrated finite-element model is employed...

Required Unfactored Strength of Geosynthetic in Reinforced Earth Structures

Abstract: Current reinforced earth structure designs arbitrarily distinguish between reinforced walls and slopes, that is, the batter of walls is 20° or less while in slopes it is larger than 20°. This has led to disjointed design methodologies where walls employ a lateral earth pressure approach and slopes utilize limit equilibrium analyses. The earth pressure approach used is either simplified (e.g., ignoring facing effects), approximated (e.g., considering facing effects only partially), or purely empirical. It results in selection of a geosynthetic with a long-term strength that is potentially overly conservative or, by virtue of ignoring statics, potentially unconservative. The limit equilibrium approach used in slopes deals explicitly with global equilibrium only; it is ambiguous about the load in individual layers. Presented is a simple limit equilibrium methodology to determine the unfactored global geosynthetic strength required to ensure sufficient internal stability in reinforced earth structures. This approach allows for seamless integration of the design methodologies for reinforced earth walls and slopes. The methodology that is developed accounts for the sliding resistance of the facing. The results are displayed in the form of dimensionless stability charts. Given the slope angle, the design frictional strength of the soil, and the toe resistance, the required global unfactored strength of the reinforcement can be determined using these charts. The global strength is then distributed among individual layers using three different assumed distribution functions. It is observed that, generally, the assumed distribution functions have secondary effects on the trace of the critical slip surface. The impact of the distribution function on the required global strength of reinforcement is minor and exists only when there is no toe resistance, when the slope tends to be vertical, or when the soil has low strength. Conversely, the impact of the distribution function on the maximum unfactored load in individual layers, a value which is typically used to select the geosynthetics, can result in doubling its required long-term strength.

Seismic Rotational Displacements of Gravity Walls by Pseudodynamic Method with Curved Rupture Surface

Abstract: This paper presents the use of pseudodynamic method to compute the rotational displacements of gravity retaining walls under passive condition when subjected to seismic loads. The concept of Newmark sliding block method for computing the rotational displacements under seismic condition and the limit equilibrium analysis have been combined in this paper to evaluate the performance of a gravity retaining walls under seismic conditions. One of the main features of the paper is the adoption of a new procedure to evaluate seismic passive earth pressure considering composite curved rupture surface (which is the combination of arc of a logarithmic spiral and straight line) and the dynamic nature of earthquake loading, which is useful to predict rotational displacements accurately. It also determines the threshold seismic acceleration coefficients for rotation using Newmark’s sliding block method. It is shown that the assumption of planar failure mechanism for rough soil-wall interfaces significantly overestimate...

Influence of existing tunnel on mechanical behavior of new tunnel

Abstract: By quantifying the displacement and crack propagation during the excavation of a new tunnel constructed near an existing tunnel, the influence of the size of the existing tunnel, the distance between tunnel centers, and the earth pressure coefficient, K on the mechanical behavior of existing and new tunnels was investigated and analyzed. A series of experimental model tests was performed and analyzed. It was found that the displacements decreased and stabilized as the distance between tunnel centers increased depending on the size of the existing tunnel. Consequently, a 3.0D distance between tunnel centers for Model Test I and 1.2D for Model Test II are required conservatively to avoid the tunnels being influenced by each other. It was also found that regardless of the distance between tunnel centers, displacements are reduced and hence the stability of the pillar can be secured as the earth pressure coefficient increases. This fundamental insight provides the basis for a more rational design of closely spaced twin tunnels.

Can Soil Arching Be Insensitive to ϕ

Abstract: Arching is a common phenomenon that is encountered in backfilling behind retaining walls, trenches, or underground voids in the mine. Marston’s equation has been widely used and modified for computing stresses within backfills, duly accounting for the reduction in stresses due to arching. A critical appraisal of Marston’s equation and its improved forms reveal that the average vertical stress within the soil backfill at any depth is governed by the product of earth pressure coefficient K and wall-backfill frictional coefficient μ , which does not vary significantly with variation in friction angle ϕ of the granular soil backfill. The average normal stress depends on the value assumed for δ/ϕ and whether the lateral earth pressure coefficient has been assumed as Ka , K0 , or KKrynine . Therefore, it is not necessary to direct any effort toward determining the friction angle of the backfill precisely. Rather, attention should be paid to the value of δ/ϕ and the appropriate expression for K . Thus, it can be...

Soil Mechanics Fundamentals

Abstract: Preface The Authors 1. Introduction Soil Mechanics and Related Fields Dr. Karl von Terzaghi Uniqueness of Soils Approaches to Soil Mechanics Problems Examples of Soil Mechanics Problems Organization of Contents References 2. Physical Properties of Soils Introduction Origin of Soils Soil Particle Shapes Definitions of Terms with Three-Phase Diagram Particle Size and Gradation Summary References Problems 3. Clays and Their Behavior Introduction Clay Minerals Clay Shapes and Surface Areas Surface Charge of Clay Particles Clay-Water System. Interaction of Clay Particles. Clay Structures Atterberg Limits and Indices Activity Swelling and Shrinkage of Clays Sensitivity and Quick Clay Clay versus Sand Summary References Problems4. Soil Classification Introduction Unified Soil Classification System (USCS) AASHTO Classification System Summary References Problems 5. Compaction Introduction Relative Density Laboratory Compaction Test Specification of Compaction in the Field Field Compaction Methods Field Density Determinations California Bearing Ratio (CBR) Test Summary References Problems 6. Flow of Water through Soils Introduction Hydraulic Heads and Water Flow Darcy's Equation Coefficient of Permeability Laboratory Determination of Coefficient of Permeability Field Determination of Coefficient of Permeability Flow Net Boundary Water Pressures Summary References Problems 7. Effective Stress Introduction Total Stress versus Effective Stress Effective Stress Computations in Soil Mass Effective Stress Change due to Water Table Change Capillary Rise and Effective Stress Effective Stress with Water Flow Quicksand (Sand Boiling) Heave of Clay due to Excavation Summary References Problems 8. Stress Increments in Soil Mass Introduction 2:1 Approximate Slope Method Vertical Stress Increment due to a Point Load Vertical Stress Increment due to a Line Load Vertical Stress Increment due to a Strip Load Vertical Stress Increment under a Circular Footing Vertical Stress Increment under an Embankment Load Vertical Stress Increment under Corner of Rectangular Footing Vertical Stress Increment under Irregularly Shaped Footing Summary References Problems 9. Settlements Introduction Elastic Settlements Primary Consolidation Settlement One-Dimensional Primary Consolidation Model Terzaghi's Consolidation Theory Laboratory Consolidation Test Determination of Cv e-log sigma Curve Normally Consolidated and Overconsolidated Soils Final Consolidation Settlement for Thin Clay Layer Consolidation Settlement for Multilayers or a Thick Clay Layer Summary of Primary Consolidation Computations Secondary Compression Allowable Settlement Ground Improving Techniques Against Consolidation Settlement Summary References Problems 10. Mohr's Circle in Soil Mechanics Introduction Concept of Mohr's Circle Stress Transformation Mohr's Circle Construction Sign Convention of Shear Stress Pole (Origin of Planes) of Mohr's Circle Summary of Usage of Mohr's Circle and Pole Examples of Usage of Mohr's Circle and Pole in Soil Mechanics Summary Reference Problems 11. Shear Strength of Soils Introduction Failure Criteria Direct Shear Test Unconfined Compression Test Triaxial Compression Test Other Shear Test Devices Summary of Strength Parameters for Saturated Clays Applications of Strength Parameters from CD, CU, and UU Tests to In Situ Cases Strength Parameters for Granular Soils Direction of Failure Planes in Sheared Specimen Summary References Problems 12. Lateral Earth Pressure Introduction At-Rest, Active, and Passive Pressures At-Rest Earth Pressure Rankine's Lateral Earth Pressure Theory Coulomb's Earth Pressure Lateral Earth Pressure due to Surcharge Load Coulomb, Rankine, or Other Pressures? Summary References Problems 13. Bearing Capacity Introduction Terzaghi's Bearing Capacity Theory Generalized Bearing Capacity Equation Correction due to Water Table Elevation Gross versus Net Bearing Capacity Factor of Safety on Bearing Capacity Summary References Problems Numerical Answers to Selected Problems Subject Index Author Index Unit Conversion Table

Soil pressure balancing type tunnel shielding simulation experiment system

Abstract: The invention relates to a soil pressure balance type tunnel shield analog experiment system, a rectangular soil coelom with the upper part provided with an opening is internally provided with a shield machine model and filled with a simulated soil body, the axle wire of the shield machine model is overlapped with that of the soil coelom; the upper surface of the simulated soil body is covered with a layer of concrete cushion the upper surface of which is connected with a horizontal loading beam by more than two soil pressure jacks, the horizontal loading beam is connected with the bottom of the soil coelom by an anchor rope; and the simulated soil body is also internally embedded with a soil pressure box, a grating fiber optical sensor and a displacement meter, wherein, the soil pressurebox, the grating fiber optical sensor and the displacement meter are all electrically connected with a data acquisition and processing device. The system can simulate the influence of shield tunnel construction between subways of cities on the stratum and surrounding environment more conveniently, actually and effectively, and provide more actual and accurate experimental data for tunnel construction and design so as to guarantee the high-efficiency and safety of the shield tunnel construction of cities.

Structural Behavior of a Pile-Supported Embankment

Abstract: The stress field in a pile-supported 3.9-m-high embankment was interpreted through three-dimensional finite-element modeling, and evaluated by field measurements involving strain gauges on the piles and earth pressure cells at the top and bottom of a 0.9-m-thick geogrid-reinforced platform. Analyses of the numerical results and the experimental data suggest that a vaultlike arch developed within the embankment, such that the vertical stress at the top of the platform was concentrated above the piles and virtually no vertical stress was measured between the piles. A similar situation existed within the platform, where an almost stress-free region between the piles was experimentally detected and numerically verified. From a structural point of view, a supporting skeleton was formed from a pile extension through the platform, a type of stress diffusion problem, and an arching effect appeared mainly in the embankment due to the very large stiffness of the piles in comparison to the surrounding media.

Pseudo-Dynamic Active Response of Non-Vertical Retaining Wall Supporting c-Φ Backfill

Abstract: Knowledge of seismic active earth pressure behind rigid retaining wall is very important. In this paper, the pseudo-dynamic approach, which considers the effect of both compression and shear wave propagation, is adopted to calculate the seismic active force supporting c-Φ backfill. Considering a planar rupture surface, the effect of wide range of parameters like inclination of retaining wall, wall friction and soil friction angle, shear wave and compression wave velocity, horizontal and vertical seismic coefficients are taken into account to evaluate the seismic active force. Results are presented in terms of seismic coefficients in tabular form and variation of pressure with depth.

Settlement evaluation of soft clay reinforced by stone columns, considering the effect of soil compaction

Abstract: This paper investigates the performance of stone columns in soft clay. Finite element analyses were carried out to evaluate settlement of soft clay reinforced with stone columns using 15-noded triangular elements using Plaxis software. A drained analysis was carried out using Mohr-Coulomb’s criterion for soft clay, stones, and sand. At the interface between the stone column and soft clay, interface elements have been used. The column installation was simulated for calculating the stresses due to compaction of soil. From numerical results, coefficient of lateral earth pressure after the installation of stone column and the settlement reduction ratio (SRR) of the soil has been estimated. On the bases of this analysis, variation of stress in soft soil after installation of column with distance from column is significantly reduced. The results are compared with those available in the literature and the advantages of the numerical analysis were highlighted.

Field Behavior of a Geogrid Reinforced Soil Retaining Wall with a Wrap-Around Facing

Abstract: The earth pressure and deformation characteristics of a geogrid reinforced soil retaining wall were monitored during and for a period of 1.5 years after construction. Both vertical and lateral soil stresses were recorded with vibrating-wire earth pressure cells, and the reinforcement deformations were measured using flexible displacement sensors. The maximum vertical foundation pressure along the wall’s reinforcements occurred at the center of the reinforcement, gradually decreasing towards the front and back ends. The measured lateral earth pressure within the reinforced soil wall is non-linear along the wall height, and the value is less than the theoretical active lateral earth pressure. The distribution of tensile strain along the reinforcements within the lower portion of the wall has two peak values. The potential failure surface of the wall closely follows the theoretical Coulomb failure surface of an unreinforced backfill.

Horizontal capacity of skirted circular shallow footings on sand

Abstract: Shallow footings are subjected to lateral forces induced by earthquake movements, wind loads, water wave pressure, lateral earth pressure, and transmitting power cables. In some structures such as water front structure, earth retaining structure and transmitting power structures, the lateral forces acting on the footings may be dominant. There has been little work studying the performance of skirted footings subjected to lateral loads. Twelve loading tests were performed on small scale circular skirted footing to shed some light on the performance of skirted footings when subjected to lateral loads. The effects of skirt length and the relative density of sand on the performance of the footing were investigated through laboratory testing program. Also a comparative experimental study between ultimate horizontal loads attained by skirted and unskirted footings with the same properties was conducted. From the accomplished laboratory tests it was found that the skirts changed the failure mode of circular shallow footings from sliding mechanism into rotational mechanism. Also the skirts attached to footings increased appreciably the ultimate horizontal capacity of shallow footings.

Numerical Study of an Integral Abutment Bridge Supported on Drilled Shafts

Abstract: The majority of integral abutment bridges (IABs) in the United States are supported on steel H-piles to provide the flexibility necessary to minimize the attraction of large lateral loads to the foundation and abutment. In Hawaii, steel H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel H-piles in scour-susceptible soils has led to a preference for the use of concrete deep foundations. A drilled shaft-supported IAB was instrumented to study its behavior during and after construction over a 45-month period. This same IAB was studied using the finite-element method (FEM) in both two- (2D) and three dimensional (3D). The 3D FEM yields larger overall pile curvature and moments than 2D because in 3D, the high plasticity soil is able to displace in between the drilled shafts thereby “dragging” the shafts to a more highly curved profile while soil flow is restricted by plane strain beam elements in 2D. Measured drilled shaft axial ...

Quick preparation device and method of saturated soil sample

Abstract: The invention relates to quick preparation device and method of a saturated soil sample. Saturated clay is extruded by utilizing a load-vacuum combined consolidation principle so as to obtain a saturated clay sample with a low water content (the water content is lower than a plastic limit). The device comprises a sleeve, a base, a piston, a vacuum cavity and a fixing sleeve, wherein the sleeve is sequentially and respectively provided with a slide-fit piston, a cylindrical porous stone internally embedded with a horizontal pressure sensor and the fixing sleeve; the piston, the base and the sleeve are respectively provided with upper draining holes, lower draining holes and side draining holes; and a vacuum extraction hole is arranged on the vacuum cavity. The draining process of the saturated clay is accelerated under the extruding effect of the piston through the negative pressure (about 101.325kPa) condition of the vacuum cavity, and meanwhile, horizontal stress and vertical stress applied on the saturated clay are obtained through the horizontal pressure sensor and a vertical pressure sensor so as to further obtain a coefficient k0 of earth pressure at rest (a specific value of the horizontal pressure to the vertical pressure applied to the soil sample under the condition of no lateral deformation).

Estimation of Lateral Load Capacity of Rigid Short Piles in Sands Using CPT Results

Abstract: Conventional methods for the estimation of the ultimate lateral pile load capacity are typically based on certain expressions of the lateral soil resistance pu and assumed distributions of the lateral soil pressure mobilized along the pile embedded depth. When soils are nonhomogenous, however, the application of conventional methods represents significant difficulties due to the nonlinear and irregular variation of pu with depth. In this study, a cone penetration test (CPT)-based methodology for the estimation of the ultimate lateral pile load capacity Hu was proposed, which can take full account of entire soil profile through the CPT cone resistance qc . A normalized correlation between qc and pu was proposed with correlation parameters corresponding to different existing methods. In order to validate the proposed CPT-based methodology, case examples of laterally loaded piles in various soil conditions were prepared and used to compare values of Hu from original and proposed methods. Calibration chamber ...

Experimental Study and Numerical Simulation on Concrete Box Culverts in Trenches

Abstract: Concrete culverts in trenches have been widely used in expressways. Problems frequently take place because of improperly estimated vertical earth pressures on culverts. Different codes have been used in China to estimate the design load on culverts. In this study, a full-scale experiment and FEM simulation were conducted to evaluate the variation of vertical earth pressures and soil arching in backfill and to examine the accuracy of the methods recommended by different design codes including the prevailing Chinese General Code for Design of Highway Bridges and Culverts based on the linear earth pressure theory. The measured vertical earth pressures from the experiment were compared with those from the current theoretical methods. The variations of foundation pressure and settlement were also analyzed. The FEM simulation investigated the key influencing factors on the vertical earth pressures including the height of the embankment fill, the width of the trench, the slope angle of the trench, the dimensions of the culvert, the properties of the backfill, and the elastic modulus of the foundation soil. This research reveals that soil arch formed when the backfill on the culvert reached a certain height, but it was unstable. The coefficient of the vertical earth pressure on the top of the culvert was significantly different from that recommended by the Chinese General Code for Design of Highway Bridges and Culverts.

Out-of-Plane Flexural Performance of GFRP-Reinforced Masonry Walls

Abstract: The objective of this paper is to assess the out-of-plane flexural performance of masonry walls that are reinforced with glass fiber-reinforced polymers (GFRPs) rods, as an alternative for steel rebars. Eight 1 m×3 m full-scale walls were constructed using hollow concrete masonry units and tested in four-point bending with an effective span of 2.4 m between the supports. The walls were tested when subjected to increasing monotonic loads up to failure. The applied loads would represent out-of-plane loads arising from wind, soil pressure, or inertia force during earthquakes. One wall is unreinforced; another wall is reinforced with customary steel rebars; and the other six walls are reinforced with different amounts of GFRP reinforcement. Two of the GFRP-reinforced walls were grouted only in the cells where the rods were placed to investigate the effect of grouting the empty cells. The force-deformation relationship of the walls and the associated strains in the reinforcement were monitored throughout the t...