Coefficient Of Lateral Earth Pressure Research Articles

Experimental Study on At-rest Lateral Earth Pressure Coefficient of Cemented Clay

The determination of lateral earth pressure is of practical importance and plays an important role in the design of retaining structures. Test results of at-rest lateral stress, coefficient of earth pressure at rest and its change law of an artificially cemented clay were presented in this paper. A K0 consolidometer was utilized to measure the at-rest lateral stress and vertical compression of the specimen. The test material was a Lianyungang marine clay and was mixed with a special kind of Portland cement that was designed for ocean engineering. The cement contents were 4, 6, 8, 10 and 12% by weight of dry soil particles and the curing time was 7, 14, 28, 60 and 90 days. The test results indicate that the at-rest lateral stress of cemented clay is different from that of uncemented clay. And at-rest lateral stress decreases rapidly with an increase in cement content and curing time. However, the lateral stress increases sharply when the applied load exceeds the vertical yield stress, which causes a corresponding change in K0.

A numerical approach on side resistance of drilled shafts embedded in sandy soils

ABSTRACT This study numerically investigates the side resistance of drilled shafts (bored piles) in sand using FLAC2D computer program. The results of the equations available in the literature are compared with the results of the present numerical study. A series of analyses is also conducted to assess the effects of various soil and pile parameters on the magnitude of side resistance of bored piles embedded in sand. Furthermore, the coupling (combined) effect of coefficient of lateral earth pressure with friction angle, and the coefficient of lateral earth pressure with a unit weight of soil on side resistance are investigated. The results show that the maximum effect of K0 on side resistance occurs around the soil friction angle of 40° and 45°. Also, the effect of K0 on side resistance is approximately constant by increasing the soil unit weight. Finally, a correction factor for coefficient of lateral earth pressure is determined.

A Note on the Compressibility and Earth Pressure Properties of EPS Beads-Rigid Particulates Composite

In past decade, the application of lightweight composite materials has received great attention in geotechnical engineering discipline. This paper evaluates the effect of expanded polystyrene (EPS) beads on the compressibility and lateral earth pressure of completely rounded particulates presented by virtual steel pellets. EPS beads were added to steel pellets at 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% by weight. A series of tall oedometer tests have been carried out to investigate the compressibility and “at rest” lateral earth pressure. Tests were conducted under five different overburden pressure (100 kPa, 150 kPa, 200 kPa, 250 kPa and 300 kPa). As well, a series of passive earth pressure tests have been conducted using a physical modelling of retaining wall in laboratory scale. The test results revealed that for a given overburden pressure, the volume compressibility and “at rest” lateral earth pressure coefficient increase as the EPS content increases. However, the internal friction angle and passive lateral earth pressure coefficient exhibited reduction by an increase of the EPS beads content.

A Statement on the Stress Field of Pipe-Soil Structure

Abstract In this study, stress analyses of buried flexible pipes were carried out using a newly designed experimental setup for the method of photoelasticity. Several universal tests using a Dynamical Mechanical Analyzer and the parallel plate test in a polariscope were performed to obtain the mechanical and optical properties of a ring that is made from a thin plate of optically sensitive Araldite, which modeled the pipe cross section. Additionally, the mechanical properties of soil used in the experiment have been determined by unconsolidated-undrained triaxial compression tests and specifically developed photoelastic tests. This test method, which provided satisfactory results for estimating the coefficient of lateral earth pressure, can be used as a fast method to obtain this coefficient for general cases. From the buried ring experiment, the distributions of the circumferential stresses along the inner surface and the absolute value of the Tresca stresses along the outer surface of the ring were calculated by some precise photoelastic measurements. Comparing the results with those from the parallel plate test, the lack of design criteria were clarified. The buried ring experiment clarified that the pipe-soil structure keeps the field of elastic stress-strain that is due to a loading until a higher load is applied. The distributions of stresses were compared to those obtained from the finite element analysis of a half ring under the loads determined by Michell’s formulation.

Small-Strain and Large-Strain Modulus Measurements with a Consolidation Device

Abstract By using a back-pressure saturated, constant rate-of-strain consolidation device with bender elements (BP-CRS-BE), values of large-strain constrained modulus (M) and small-strain shear modulus (Gmax) were obtained from tests performed on kaolinite soil specimens. The methodology and procedures that were utilized to obtain values of M, Gmax, large-strain shear modulus (G), drained Poisson’s ratio (ν), horizontal effective stress (σh′), vertical effective stress (σv′), specific volume (v), coefficient of lateral earth pressure during unloading (K0,UL), and drained friction angle (ϕ′) are discussed herein. The following five observations were made. (1) The Gmax values increased with increasing values of σv′ and decreased with increasing values of the overconsolidation ratio (OCR). (2) The Gmax values that were obtained by utilizing correlations and the large-strain BP-CRS-BE testing data (identified as GmaxCRS,p′), which were back-calculated by considering the modulus reduction, matched the Gmax values that were obtained from the bender element measurements within the BP-CRS-BE device (Gmax,BE). (3) The ν values increased with increasing σv′ values but decreased with the increasing void ratio (e) values. (4) The K0,UL values increased with increasing OCR values. (5) The ϕ values that were calculated for the soil that was tested within the BP-CRS-BE device by using the K0,UL-OCR data that were obtained from the BP-CRS-BE device (21.2°, 16.0°, and 24.7°) were similar to the ϕ′ values that were obtained from modified Mohr-Coulomb diagram from triaxial tests on the same soil (20.7°).

Mechanized tunneling induced ground movement and its dependency on the tunnel volume loss and soil properties

SummaryThis study investigates the ground movements due to mechanized tunnel excavation by applying two‐dimensional finite element analyses. To assess the contribution of the compressibility and plasticity of the soil on the ground movements, different constitutive models are employed to describe the soil behavior. The influence of volume loss around the tunnel on the surface volume loss is investigated, and a quadratic correlation between them is proposed. Consequently, the empirical Gaussian distribution curve, which is generally used to determine the tunneling induced settlement trough, is improved by applying the proposed quadratic correlation between surface volume loss and tunnel volume loss. Furthermore, the settlement trough width parameter has been derived by a linear function of tunnel volume loss as well. The proposed equations are validated via a case study of centrifuge tests from the literature. The results show that the proposed modification enhances the empirical solution by having better knowledge on the model parameters. Additionally, tunnel overburden and coefficient of lateral earth pressure at rest (K0) are taken into account to study their influence on the tunneling induced surface settlements. Finally, global sensitivity analysis is applied to evaluate the relative importance of corresponding model parameters in terms of their influence on the ground movements.

Lagged settlement in sandy cobble strata and earth pressure on shield tunnel.

Lagged settlement is a typical accident induced by shield construction in sandy cobble strata. This paper analyzed the process and mechanism of lagged settlement, results show that all phases are in accord with the characteristics of ellipsoid theory of particle flows. Based on this theory, a method for calculating coefficient of lateral earth pressure and loosened earth pressure is proposed in this research. For the coefficient of lateral earth pressure, the boundary of loosened ellipsoid is divided into two parts, the arch zone and the excavation zone, and the lateral pressure coefficients are derived respectively according to the stress state. For loosened earth pressure on tunnel, the Terzaghi earth pressure theory and Protodyakonov earth pressure theory are adapted in different conditions according to the state of loosened cobble soil. Theories developed in this study can be applied on determination of shield excavation parameters, as well as calculation of loosened earth pressure and control of tunnel support.

Stress path dependent small strain stiffness of Shanghai clay

The soil small strain stiffness plays an important role in many geotechnical applications such as machine foundations, deep excavations and earthquake ground response analysis. In this study, the small strain stiffness of saturated intact Shanghai clay specimen is measured in a hollow cylinder apparatus. The lateral earth pressure coefficient at rest is measured first during the one-dimensional consolidation. After consolidation, the very small strain stiffness is obtained by shear wave measurement using bender elements, while the degradation of small strain stiffness with strain is investigated by quasi-static loading with high resolution linear variable displacement transducers (LVDT). The effect of stress path on the small strain stiffness is also investigated. The results show that the small strain stiffness is nonlinear and significantly depends on the stress path.

Simplified Method for Calculating Active Earth Pressure Against Rigid Retaining Walls for Cohesive Backfill

The horizontal slice element method for calculating active earth pressure against rigid retaining walls has been extended to the cohesive backfill. The formula of the nonlinear distribution of active earth pressure is derived satisfying the reciprocal theorem of shear stress. According to the Mohr-Coulomb theory, the lateral active earth pressure coefficient can be determined. In order to check the accuracy of the proposed equation; the predictions from the equation are compared with both existing full-scale test results and values from other studies. The comparisons between calculated and measured values show that the proposed equations provide satisfactory results.

Lateral Earth Pressure Coefficient and Lateral Earth Pressure against Retaining Walls

Lateral Earth Pressure Coefficient and Lateral Earth Pressure against Retaining Walls

Constrained Compression Models for Tire-Derived Aggregate-Sand Mixtures Using Enhanced Large Scale Oedometer Testing Apparatus

Tire derived aggregates have recently been in wide use both in industry and engineering applications depending on the size and the application sought. Five different contents of tire derived aggregates (TDA) were mixed with sand thoroughly to ensure homogeneity. A series of large scale oedometer experiments were conducted to investigate the compressibility properties of the mixtures. Tire shreds content, TDA aspect ratio, skeletal relative density and overburden pressure are studied parameters. Constrained deformation modulus and coefficient of earth pressure at rest are measured parameters. All tests were conducted at seven overburden pressure levels. It was concluded that deformability of TDA-sand mixture increases with soft inclusion. Overburden pressure and skeletal relative density are also important parameters which render more rigidity and less lateral earth pressure coefficient accordingly. TDA size or aspect ratio was shown to have minor effect at least for the constrained strain conditions encountered in current study. An EPR-based parametric study and also sensitivity analyses based on cosine amplitude method revealed quantitative evaluation of the relative importance of each input parameter in varying deformation and lateral earth pressure coefficient as the outputs.

Analysis of the effect of groundwater on soil arch in shield tunneling

The soil arch above tunnel face should be considered in the calculation of the minimum support pressure on tunnel face. It is not clear that the effect of water on the soil arch at present. Various model tests are carried out to analyze the differences of the soil arch above tunnel face between dry sand and saturated sand. Tests are performed with a variety of impact factors such as sand particle size, cover depth, and water conditions. Test results showed that the forming process of soil arch is delayed by groundwater and the arch height can be changed. Based on the finite element simulation, it can be concluded that there are two factors which affect the soil arch in water. The first one is groundwater and the other one is internal friction angle. At last, it can be concluded that the lateral earth pressure coefficients of the prism above tunnel face should be revised because the soil arch is affected by groundwater.

Monitoring Ground Improvement Using the Seismic Dilatometer in Christchurch, New Zealand

This article illustrates the use of the seismic dilatometer test (SDMT) in combination with the piezocone test (CPTu) to monitor the effects of ground improvement by different techniques at seven test sites in Christchurch, New Zealand. The results of SDMTs carried out in treated soils and in adjacent natural soils are compared in order to assess the effectiveness of different ground improvement techniques (Rammed Aggregate Piers, Low Mobility Grout, Stone Columns, Deep Soil Mixing) aimed at reducing the liquefaction susceptibility. Moreover, the article presents the variation of significant parameters obtained from parallel SDMT and CPTu soundings in treated versus natural soils. SDMT and CPTu results are also used in combination to estimate the overconsolidation ratio and the at-rest lateral earth pressure coefficient (K0) before and after the treatment. The effectiveness of the different ground improvement techniques is also evaluated in terms of the variation of the before and after integral liquefaction vulnerability indicators, such as the liquefaction potential index and the liquefaction severity number, which are calculated using different methods based on CPTu, the DMT horizontal stress index (KD), and the shear wave velocity (VS) for a design earthquake. The results confirm that the DMT, as well as the CPTu, is sensitive to changes in stress/density in sands and silty sands and is, therefore, well suited to detecting improvements in these soils, while VS provides less evident results.

Numerical investigation of the mechanical behavior of deformed segmental tunnel linings, strengthened by epoxy-bonded filament wound profiles

Large deformations of shield tunnels may be the consequence of a long period of operation or of nearby pit construction. To reduce them, a novel strengthening method was recently proposed. It makes use of epoxy-bonded filament wound profiles (FWP). Full-scale tests were performed to prove the effectiveness of this method. The present paper contains a report on a comprehensive parametric study of the influence of several design parameters, such as, for example, the mechanical properties of the bond between the FWP and a segment of the tunnel and Young’s modulus of the FWP, on the increase of the load-carrying capacity of the structure. Several tests were conducted to obtain these parameters. The influence of the lateral earth pressure coefficient of the surrounding soil and of the geometry of segmental tunnel linings on the strengthening benefits was also investigated. The parametric study was based on a numerical model, established in the course of this research. It was validated by comparing the numerical results with the experimental results and by demonstrating the model’s capacity to describe the experimentally observed failure mechanism of the strengthened structure. Based on this analysis, an optimum combination of design parameters for the proposed strengthening method is suggested to ensure its safety, reliability, and effectiveness.

Soil arching in highway piled embankments subjected to moving shakedown limit loads

Shakedown analysis provides the loading variation limit of a structure, under which the plastic deformation occurred in first loading cycles will cease to further develop and the structure will respond purely elastically to the remaining load cycles. This paper investigated the arching in highway piled embankments under moving shakedown limit loads, which was calculated by the shakedown solutions. The shakedown solutions for materials obeying Mohr–Coulomb criterion was firstly presented based on Melan’s shakedown theorem, which utilised elastic stress fields obtained from the full three-dimensional (3D) finite element (FE) method. Finally, the shakedown limit load for pure rolling condition (i.e. only normal load) was applied onto the surface of pavement as a moving vehicle load. The FE results under moving shakedown limit loads captured similar trend with those under the static loads in terms of settlement and vertical stress, but gave the normalised settlement and vertical stress 33 and 24% larger. The soil arching remained existed in the highway piled embankments under moving shakedown limit loads, but was reduced. The inclusion of moving shakedown limit loads increased the vertical stress of the embankment and thus resulted in a reduction of the maximum value of lateral earth pressure coefficient by approximately 38%.

Practical criteria for assessment of horizontal borehole instability in saturated clay

Horizontal borehole instability raises concern due to negative impacts on success of drilling, reaming and pipe installation during Horizontal Directional Drilling. Shear failure (blow-out) and tensile failure (hydraulic fracture) are the two main failure mechanisms controlling borehole instability in saturated clay. Criteria for categorizing shear failure versus tensile failure are given which are functions of the ratio of undrained shear strength to vertical effective stress Su/σv′ and the Lateral Earth Pressure Coefficient at Rest K0′. Given that Su/σv′ and K0′ can be expressed as a function of soil parameters like friction angle, Over Consolidation Ratio (OCR) and Liquidity Index (LI), new forms of these criteria are developed for situations where Su/σv′ and K0′ cannot be obtained directly. It is confirmed that tensile failure generally controls in brittle clays like heavily overconsolidated and/or low liquidity index materials. Cases from the laboratory and the field as reported in the literature are used to examine the effectiveness of the new criteria, with inconsistency between theory and the physical evidence explained.

Effect of the lateral earth pressure coefficient on settlements during mechanized tunneling

Tunnel excavation leads to a disturbance on the initial stress balance of surrounding soils, which causes convergences around the tunnel and settlements at the ground surface. Considering the effective impact of settlements on the structures at the surface, it is necessary to estimate them, especially in urban areas. In the present study, ground settlements due to the excavation of East-West Line 7 of the Tehran Metro (EWL7) and the Abuzar tunnels are evaluated and the effect of the lateral earth pressure coefficient (K0) on their extension is investigated. The excavation of the tunnels was performed by TBMs (Tunnel Boring Machines). The coefficient of lateral earth pressure (K0) is one of the most important geotechnical parameters for tunnel design and is greatly influenced by the geological characteristics of the surrounding soil mass along the tunnel route. The real (in-situ) settlements of the ground surface were measured experimentally using leveling methods along the studied tunnels and the results were compared with evaluated settlements obtained from both semi-empirical and numerical methods (using the finite difference software FLAC3D). The comparisons permitted to show that the adopted numerical models can effectively be used to predict settlements induced by a tunnel excavation. Then a numerical parametric study was conducted to show the influence of the K0 values on the ground settlements. Numerical investigations also showed that the shapes of settlement trough of the studied tunnels, in a transverse section, are not similar because of their different diameters and depths of the tunnels.

Lateral Earth Pressure Coefficient of Soils Subjected to Freeze–Thaw

Artificial frozen soils (AFS) have been used widely as temporary retaining walls in strata with soft and water-saturated soil deposits. After excavations, frozen soils thaw, and the lateral earth pressure penetrates through the soils subjected to freeze–thaw, and acts on man-made facilities. Therefore, it is important to investigate the lateral pressure (coefficient) responses of soils subjected to freeze–thaw to perform structure calculations and stability assessments of man-made facilities. A cubical testing apparatus was developed, and tests were performed on susceptible soils under conditions of freezing to a stable thermal gradient and then thawing with a uniform temperature (Fnonuni–Tuni). The experimental results indicated a lack of notable anisotropy for the maximum lateral preconsolidated pressures induced by the specimen’s compaction and freeze–thaw. However, the freeze–thaw led to a decrement of lateral earth pressure coefficient K0, and K0 decrement under the horizontal Fnonuni–Tuni was greater than that under the vertical Fnonuni–Tuni. The measured K0 for normally consolidated and over-consolidated soil specimens exhibited anisotropic characteristics under the vertical Fnonuni–Tuni and horizontal Fnonuni–Tuni treatments. The anisotropies of K0 under the horizontal Fnonuni–Tuni were greater than that under the vertical Fnonuni–Tuni, and the anisotropies were more noticeable in the unloading path than that in the loading path. These observations have potential significances to the economical and practical design of permanent retaining walls in soft and water-saturated soil deposits.

Soil Overconsolidation Changes Caused by Dynamic Replacement

In the dynamic replacement method (DR) the soil is improved by initially dropping a large weight (typically 8-20 t) pounder from a significant height up to 25 m. The created crater is filled with a stronger material (gravel, rubble, stone aggregate, debris), and the pounder is dropped once or multiple times again. The construction of dynamic replacement pillars influences the parameters of the adjacent soil. It results from the energy generated by dropping a pounder into the soil. In the current practice, these changes are not taken into the account during the design. This paper focuses on the changes of overconsolidation ratio (OCR) and in situ coefficient of lateral earth pressure (K) values estimated base on cone penetration test (CPTU) and Dilatometric test (DMT) performed at a test site. A single column was constructed and the ground around the column was examined using CPTU and DMT, performed at different distances from the column centre (2, 3, 4 and 6 m) and at different time intervals (during construction and 1, 8, 30 days later). The column was constructed in so-called transition soils (between cohesive and non-cohesive). While interpreting the results of the research, the authors addressed the matter of choosing the procedure of OCR and K indication for transition soils (in this case described as silts and/or sandy silts). Overconsolidation changes may differ depending on the chosen analysis procedure (for cohesive or non-cohesive soils). On the basis of the analysis presented in the paper and the observation of soil (acknowledged as cohesive according to macroscopic observations) during column excavation, it was decided that for more detailed analyses methods dedicated to cohesive soils should be applied. Generally, it can be stated that although the changes were complex, DR pillar formation process resulted in the increase of these parameters. The average increases of OCR and K values were 25% and 10% respectively. The post installation values are not significant from the engineering point of view, but they represent the influence of the formation process of only a single column. The described results indicate that Priebe’s column dimensioning method should be applied with caution, as it assumes the value K=1 which was not obtained in the described research. The results from the conducted tests indicate that different mechanisms occur during stone column formation with vibro-replacement and dynamic replacement. As the authors did not manage to find literature describing the results of K tests in the surrounding of a DR column, the presented results should be acknowledged as significant for designers who will apply the dynamic replacement method.

Progressive Development of Two-Dimensional Soil Arching with Displacement

Soil arching is a phenomenon describing stress redistribution due to relative movement between adjoining portions. It commonly exists when soil interacts with structure elements, such as tunnels, retaining walls, buried structures, and piles in pile-supported embankments. A yielding or ultimate state of soil (i.e., the shear stress in soil is equal to its shear strength) is mostly assumed in analytical models for soil arching. In reality, the level of shear stress and the shape of the slip surface in the soil depend on the magnitude of relative movement of the soil. In this study, a custom-made trapdoor test box was used to investigate the progressive development of soil arching with the trapdoor displacement. The dimensions of the test box was 1.76 m long, 0.46 m wide, and 1.48 m high, whereas the trapdoor had dimensions of 0.36 m wide and 0.46 m long. Earth pressures were installed on the top and sides of the trapdoor to monitor the development of soil arching with the displacement of the trapdoor. Furthermore, data from five references available in the literature were adopted to evaluate the progressive development of soil arching with the displacement for different geotechnical applications. Terzaghi’s method was used to calculate the two-dimensional soil arching ratios (i.e., the measured earth pressure divided by the overburden pressure) in all cases in this study using three different values of lateral earth-pressure coefficient (K), and the results were compared with the measured results. Terzaghi’s method calculated the soil-arching ratios reasonably well when the trapdoor displacement was equal to or larger than 10% of the trapdoor width. To facilitate the application of progressive development of soil arching with displacement in engineering practice, a simplified ground reaction curve (GRC) was proposed as three straight lines to represent the progressive development of two-dimensional soil arching with relative displacement. The methods for determining four required parameters were provided, and the proposed method was verified using three trapdoor test results from both this study and the literature.