Two-layered Ground Research Articles

Proposed Correlation to Evaluate the Bearing Capacity of a Two-Layered Ground

Proposed Correlation to Evaluate the Bearing Capacity of a Two-Layered Ground

Stochastic-Deterministic Assessment of Electric Field Radiated by Base Station Antenna above a Two-Layered Ground

The paper deals with stochastic-deterministic modelling of radiated electric field by base station antennas (BSAs) operating in GSM frequency range. Within the framework of deterministic analysis, the total electric field above a two-layered lossy ground is obtained by considering the incident and reflected ray in the far field zone. The influence of nonhomogeneous lower medium is taken into account via two approaches: Fresnel plane wave reflection coefficient (FRM) and simplified reflection coefficient stemming from Modified Image Theory (MIT). Antenna height, relative conductivity, and permittivity of each ground layer, as well as the thickness of the upper ground layer, are considered as input parameters with inherent uncertainty. To quantify the uncertainty of output electric field, deterministic models are treated as black boxes by two stochastic methods, Monte Carlo (MC) and Stochastic Collocation (SC), respectively. Stochastic mean and standard deviation of the output are computed, and sensitivity analysis is carried out in order to analyze the impact of input parameters’ variations on the resulting electric field variance. The presented results expose weakness and strength of the two stochastic methods, particularly identifying the cases when the preferred SC method fails to converge. Furthermore, sensitivity analysis reveals that despite the smallest variation around its respective average value, the antenna height has the highest impact on the output variance at observation points in the vicinity of the antenna. However, as the distance from the antenna increases, the 1st layer depth and its relative electric permittivity become the most significant parameters.

Seismic response of shallow circular tunnels in two-layered ground

The effect of ground stratification on the seismic response of circular tunnels is investigated, as most practice-oriented studies consider homogeneous ground. A finite element plain-strain model of a circular tunnel cross-section embedded in a two-layered ground is used to highlight the influence of stratification on the tunnel׳s seismic response. The layers interface was placed at the crown, centre and invert level.It is proved that ground stratification has an important role in the lining seismic forces. When the tunnel is fully embedded in one of the layers, the seismic lining forces may vary significantly in comparison with the single-layer case. If the tunnel intercepts both layers, maximum lining forces aggravation occurs when the lower layer is very stiff.

A tunnel face failure mechanism for layered ground, considering the possibility of partial collapse

A recent rotational face collapse mechanism is extended to compute critical pressures, in the context of the upper-bound limit analysis, for tunnels in layered (or stratified) ground. The mechanism can consider both (i) cases in which contacts between layers intersect the tunnel face; and (ii) cases in which they are located above the tunnel crown. In addition, the mechanism is extended to address partial collapse in a two-layered ground (with a softer-top and a stronger-bottom), without the need to scale mechanisms that were derived for global collapse. A 3D numerical model is employed to validate the predictions of the limit analysis mechanism, demonstrating that it provides, with a significantly reduced computational effort, good predictions of critical pressure, of the type of collapse (global or partial), and of its geometry. The mechanism is then employed to conduct parametric studies of the influence of several geometrical and mechanical parameters on face instability, considering the possibility of partial collapse, of tunnels in layered soils. Results show that a weak material in the upper section of the tunnel face can lead to a significant increase of the collapse pressure; it also makes a partial collapse possible. They also show that, when partial collapse is not critical and a constant face pressure is considered, the lower layer has a stronger influence on the computed values of collapse pressure. Finally, the results of the proposed mechanism are compared to a recent limit analysis solution for layered soils.

Bearing Capacity of Two-Layered Artificial Ground with Firm Crust and Weak Subgrade Under Circular Pressure

Classical bearing capacity expressions can not afford variant engineering requests, since they were deducted under hypotheses of strip footing on homogeneous soil. An often met case was taken into account that circular footing on two-layered ground, which has firm crust and weak subgrade. Weighted method and layered method were used in capacity deduction, respectively. The former counts layered soils as single layer of weighted structure and material parameters. But it is restricted to conditions with close strength to each layer. The latter is preferred in engineering calculation, which regards the whole bearing capacity as subgrade’s capacity under the influence of the upper layer. Thus the issue is transformed to K. Terzaghi model plus stress reduction and dispersion effects. At last, the expressions gained from both methods and finite element analysis (FEA) were used in an example calculation, respectively. It approves layered calculating method and suggests the corresponding security coefficient based on elastoplastic FEA results.

Impact of Layered Soil on Foundation Heat Transfer for Slab-On Grade Floors

This paper presents an analytical solution associated with the steady-periodic heat transfer for a typical slab-on-grade floor building foundation in contact with a nonhomogeneous soil medium. In particular, the solution accounts for the impact of the above-grade wall thickness on the ground-coupled heat transfer. The interzone temperature estimation profile (ITPE) technique is utilized to obtain the analytical solution to determine soil temperature distributions and to estimate foundation heat loss/gain from slab-on-grade floors. In this paper, the impact of the nonhomogeneous soil properties on the transient foundation heat transfer is investigated for various slab configurations and soil thermal properties. The presented solution presents the first ITPE analytical solution for building foundation coupled with layered soil medium. The results indicate that nonhomogeneous soil properties have a significant effect on soil temperature distribution and on total slab heat loss. In particular, it is found that an error of up to 20% in estimating total slab heat transfer can be incurred if homogeneous soil medium is considered instead of a two-layered ground.

Natural-frequency concept utilized in remote probing of the earth

The complete time-domain fields due to a vertical magnetic dipole on the surface of a two-layered earth model are derived in an analytical form using the natural-frequency concept. In these expressions, the displacement currents in the earth's layers are taken into consideration. The step responses of the induced voltage in a horizontal receiving loop is found to have definite diagnostic features for the ground beneath. These features are demonstrated by numerical results and shown by figures. The clear distinction between the step response of the homogeneous and the two-layered ground suggests that this response can be used for the detection of the stratification. PACS Nos.: 41.20.Jb, 42.25.Bs, 42.25.Gy, 44.05.+e

A STUDY ON RADIATION DAMPING OF RIGID FOUNDATION ON LAYERED BEDROCK

This paper presents results of theoretical analyses on in situ vibration test results of large-scale rigid foundations on bedrock, and estimation method of interaction characteristics of foundation on bedrock, where attention is paid to the layered structure of the bedrock. Stiffness and damping of the foundation estimated from theoretical analysis using ground material properties based on elastic wave detection proves to compare well with experimental ones. Using the results of parameter survey with two layered ground model, damping characteristics of the foundation on layered bedrock is shown to be estimated by simple two-layered ground model.

Consolidation of Multilayered Anisotropic Soils by Vertical Drains with Well Resistance

ABSTRACT Vertical drains are usually installed in alluvial weak subsoil consisting of several layers. Several existing solutions of centripetal consolidation considering the well resistance are available. Those are, however, inapplicable for multilayered ground. Taking well resistance into account, a numerical analysis method is presented in this study to solve the consolidation problem in multilayered anisotropic clayey subsoil in which vertical drains have been installed. The analytic results coincide well with the observed results obtained through a pair of in-situ consolidation tests. As a consequence of calculations for many cases of two-layered problems where both degree of heterogeneity and thickness ratio between the 1st and the 2nd layer differ from each other, it is indicated that the consolidation of a two-layered ground is significantly retarded than that of the single-layered ground whose coefficient of consolidation is equal to the mean value of the two-layered ground. A new procedure is next proposed for predicting the consolidation degree of multilayered ground using existing equations concerning single-layered centripetal consolidation. The accuracy of this procedure is discussed in comparison with the numerical results. The experimental results also reveal that the proposed procedure yields a sufficiently accurate consolidation curve for multilayered ground without the need for a computer.

Bearing Capacity of a Continuous Footing Set in Two-Layered Ground

The Meyerhof method to estimate the ultimate bearing capacity of a continuous footing set in homogeneous ground is extended to the case of two-layered ground where the base of the footing is set in the supporting layer overlain by the weak layer. The extended method takes into account the effect of the shearing strength of the weak layer on the bearing capacity of the footing base and gives more precise bearing capacity than the method which assumes the shearing strength of the weak layer to be zero.