Horizontal Coefficient Research Articles

Composite Consolidation Coefficient Analysis of Soft Soil with Drainage Water

The consolidation coefficient is the most basic parameter to calculate the consolidation rate of soil layer, and the horizontal consolidation coefficient controls the radial water flow into the drainage well. Based on the background of the soft soil in Shantou, Guangdong Province, a series of experimental studies on the consolidation characteristics were carried out by using the modified consolidation instrument. And the concept of the composite consolidation coefficient of the drained water body was put forward. The composite consolidation coefficient reflects the consolidation characteristics of soft soil with drainage water, The test results showed that: 1) The consolidation test with drainage plate is basically consistent with the load compression curve, but its consolidation rate is fast, which is reflected by the composite consolidation coefficient. 2) In the consolidation test of water bodies with drainage, the vertical consolidation coefficient and radial consolidation coefficient are calculated by “three-point method”, and then the composite consolidation coefficient is obtained. The composite consolidation coefficient decreases with the increase of drain spacing ratio, effective drainage diameter and drainage height, which is basically consistent with the theoretical formula. 3) The vertical consolidation coefficient and radial consolidation coefficient decrease with the increase of the diameter of the sample, and the difference is obvious when the load is large. The large-size model with a diameter of 100 mm and a height of 100 mm is about 1.35 times of the vertical consolidation coefficient of the conventional consolidation test.

Simplified solution to analyse seismic stability of reinforced soil wall

ABSTRACT The normalized tensile reinforcement force for the seismic stability of reinforced soil walls using some rigorous methods considering the pseudo-static seismic forces is mostly used by the earlier researchers in the design of retaining walls backfilled with cohesive soil. Few studies have been presented using horizontal slice method without taking effect of the seismic acceleration in vertical direction. In the present study, a simplified solution has been presented using the pseudo-static equilibrium of the reinforced soil wall taking the effect of seismic accelerations in the horizontal and in the vertical direction. The seismic stability analysis presented here accounts the required total reinforcement strength in terms of the maximum value of reinforcement force coefficient and the critical inclination of failure plane. Taking some geometrical values of retaining wall and soil characteristics based on the literature, a detailed and comparative parametric study presented here accounts the effect of cohesion of the backfill, angle of internal friction of soil, horizontal seismic coefficient, vertical seismic coefficient and surcharge loading.

Interpretation of horizontal permeability from piezocone dissipation tests in soft clays

Piezocone is a common site investigation tool where a cone penetrometer is pushed into ground. In fine-grained soils, the penetrometer can be stopped to measure pore pressure decay, known as dissipation testing. Conventionally the horizontal coefficient of consolidation has to be first determined before the hydraulic conductivity can be estimated. This study uses the modified Cam-clay soil model to numerically simulate dissipation tests. A total of 90 calculations are performed to derive a new dimensionless time factor that easily and directly evaluates horizontal permeability for both standard and non-standard dissipation curves. The proposed equation is validated with field data.

A Robust Watermarking Scheme Based on the Mean Modulation of DWT Coefficients

In an endeavor to deal with image copyright infringement, robust watermarking approaches are commonly used. However, most of the existing approaches either present a limited robustness or rely on highly computational algorithms, thereby limiting the efficiency of these solutions. In this paper, a novel blind and robust watermarking method is presented. First, the vertical and horizontal subbands coefficients, resulting from the wavelet transformation, are scrambled using a chaotic sequence and then gathered into individual blocks. Next, the mean value of each block is modulated according to watermark bit. At the extraction stage, based on the sign of the blocks’ mean, a blind watermark extractor is suggested. The imperceptibility, security, complexity, and robustness of the proposed approach have been evaluated and compared with state of the art solutions. Experimental results prove that the proposed approach successfully satisfies the watermarking requirement and outperforms existing methods against both geometric and signal processing attacks.

Effect of surcharge loading rate and mobilized load ratio on the performance of vacuum–surcharge preloading with PVDs

The results from three laboratory model tests performed under various vacuum and surcharge loads with PVDs are reported. Different SLRs were adopted to investigate the effect on the consolidation of dredged soil. To measure the lateral displacement, a refitted inclinometer was developed and tested. In the tests, the settlement, lateral displacement, and vane shear strength were measured, and the degree of consolidation (DOC), horizontal coefficient of consolidation (Ch), and bearing capacity were calculated. The results indicate that larger SLR values promote consolidation. The largest vane shear strength, settlement, and Ch values were all obtained under the highest SLR, and the bearing capacity under this SLR was more than double that under the lowest SLR. The DOC was found to increase with the growth of the SLR. However, considering the vacuum pressure was higher in Case-III, the influence of SLR on reinforcement effect may not be so significant.

Effectiveness study of prefabricated vertical drain using vacuum preloading and surcharge preloading

Prefabricated vertical drain is a method of soil improvement in order to accelerate consolidation settlement. In line with the development of knowledge, vacuum preloading was used to replace embankment preloading to produce stress in soil. This research will compare the effectiveness of vacuum preloading against the embankment preloading through the analysis of the degree and time of consolidation. The prediction of settlement is manually calculated using 1 dimension consolidation Terzaghi’s theory method, while the finite element method by PLAXIS 2D Program and ASAOKA method from settlement on the field. The horizontal coefficient of consolidation used is based on the result of back calculation using ASAOKA’s chart. The ratio of coefficient consolidation (Ch/Cv) obtained for vacuum preloading is 5.9 and for embankment preloading is 2.21-4.25. The analysis show that the vacuum preloading method can cut the consolidation time up to 74% comparing the embankment preloading method.

Accurate and reliable reversible data hiding using sequential encoding techniques

SummaryReversible data hiding facilitates images to be authenticated and by eliminating the digital watermark. Histogram Shifting Based Reversible Data Hiding (HSRDH) is presented in the previous research, which aims to decrease the performance with low quality when recreating the images. However, embedding patches could be hacked where it does not concentrate on the security threats. This issue is resolved using Sequential Encoding Based Reversible Data Hiding (SEB‐RDH) method. Here, initially input image is transformed into Haar wavelet using discrete wavelet transform. This wavelet is decomposed by utilizing 1D wavelet transformation; Haar wavelet is processed, and after that, by means of utilizing 2D wavelet transformation, the result of 1D wavelet transformation is decomposed once more. Horizontal coefficients are separated and embedded with the normalized input image. This type of data hiding enlarged the compression size and acts as a guard from the hackers who could not hack the protected data contents. This technique guarantees the enlarged reconstruction image accurateness in the receiver side. It is implemented in Matlab simulation environment, and it is confirmed that the SEB‐RDH displays 15.8% improved PSNR rate after that the previous technique HSRDH and 26.5% improved MSE rate compared with the previous HSRDH technique.

Verification of the preloading design of soft clay with prefabricated vertical drains by full-scale field instrumentation and numerical modelling

ABSTRACT Preloading with surcharge and prefabricated vertical drains (PVDs) was used to construct road and rail embankments on a 26-m-thick soft clay layer across Boubyan Island, Kuwait. Given the variations in the horizontal and vertical coefficients of consolidation (Ch and Cv, respectively) measured in the laboratory, the preliminary analysis predicted that the time to reach 90% consolidation may vary from three months to one year. To validate these predictions, a full-scale pilot project that included an instrumented section under a surcharge load with PVDs was carried out. Back analysis of the consolidation parameters was carried out by an observational method and numerically by finite element modelling. The results indicated that 98% consolidation was achieved in 367 days. The numerical model of the heave due to surcharge removal and settlement due to reloading predicted 70 mm of heave and minimum primary and secondary consolidation for a service period of 20 years.

Horizontal coefficient of consolidation from inward- and outward-flow tests

Vertical drains are widely used to accelerate the consolidation of soft clay deposits when preloading is used as a ground-improvement technique. Barron's theory is generally used for the design of vertical drains. One of the important input parameters required in Barron's theory is the coefficient of horizontal consolidation, ch. A reliable estimate of chis, therefore, necessary for proper design. The values of chcan be determined by the radial-consolidation test, using either a central sand drain or a porous plastic peripheral drain. This paper compares the results of the radial-consolidation tests conducted using a 100 mm dia. Rowe consolidation cell under radially inward or radially outward flow conditions. The influence of the diameter of the sand drain (namely, 10, 15 or 50 mm) was also studied. It was found that the radially outward-consolidation test gave lower values of chcompared to the radially inward test. Also, it was observed that the measured values of chdecreased as the perimeter of the drainage boundary increased.

Experimental studies on soft marine clay under combined vacuum and surcharge preloading with PVD

ABSTRACT A large-scale three-dimensional cell is designed, manufactured and assembled for applying designated vacuum and surcharge preload and allows for the measurement of settlement and excess porewater pressure. Six experiments were performed with post- and pre-installation of prefabricated vertical drain to study the effect of smear on reconstituted samples of Mumbai marine clay. The effective stresses (40–180 kPa) are applied with six different combinations of surcharge preload (20–80 kPa) and vacuum pressure (0–100 kPa). The study concluded that the coefficient of radial consolidation (c h) increases from 4.60% to 20.07% higher than one-dimensional coefficient of consolidation. The addition of vacuum pressure tends to increase the horizontal coefficient of consolidation leads to shorten the preloading time by 15–63% depending on the vacuum pressure magnitude. The increase in shear strength due to vacuum pressure is more significant than a surcharge preload. Abbreviation: PVD: Prefabricated Vertical Drain

Effect of Soil Amplification on Seismic Earth Pressure Using Pseudo-Dynamic Approach

The study of seismic earth pressure is essential for the design of a retaining wall in the earthquake-prone regions. Pseudo-static and pseudo-dynamic approaches are widely used for cohesionless soil backfill without considering the effect of soil amplification. Soil amplification is a very important factor for the calculation of seismic active earth pressure and should not be ignored in the design in the earthquake-prone regions. In this paper, a generalized formulation has been presented to compute the seismic active earth pressure distribution on the inclined retaining wall back-face. The retaining wall supports the inclined cohesionless soil backfill. A parametric study has been conducted to study the effect of various parameters like soil friction angle, the inclination of wall back-face, the inclination of soil backfill, wall friction angle, soil amplification, horizontal and vertical seismic coefficients. The results of the present study have been compared with the available results of an earlier study. The study highlighted the effect of model parameters on seismic earth pressure.

Prefabricated Vertical Drain (PVD) and Deep Cement Mixing (DCM)/Stiffened DCM (SDCM) techniques for soft ground improvement

Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the smear zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent smear effect due to non-uniform consolidation is also discussed in addition to the smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced deep mixing method, namely Stiffened Deep Cement Mixing (SDCM) pile is introduced to improve the flexural resistance, improve the field quality control, and prevent unexpected failures of the Deep Cement Mixing (DCM) pile. The SDCM pile consists of DCM pile reinforced with the insertion of precast reinforced concrete (RC) core. The full scale test embankment on soft clay improved by SDCM and DCM piles was also analysed. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC cores, and, at lesser extent, increasing sectional areas of the RC cores in the SDCM piles. In addition, the lateral movements decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC cores in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.

Non-monotonic piezocone dissipation curves of backfills in a soil-bentonite slurry trench cutoff wall

Pore pressure dissipation during piezocone testing provides a unique tool for estimating the hydraulic properties of in-situ backfills in soil-bentonite (SB) slurry trench cutoff walls. Six tests were performed in an SB slurry trench cutoff wall located in Jiangsu Province, China. The pore pressure dissipation curves obtained are non-monotonic, which, as far as the authors are aware, is reported for the first time in SB cutoff walls. The non-monotonic dissipation curves are attributed to the redistribution of excess pore pressures between the base soil clods and the rest of the backfill around the cone. Four existing interpretation methods are adopted to analyze the measured non-monotonic piezocone dissipation curves. The horizontal coefficients of consolidation (ch) of the backfills obtained by three methods are close to each other and in agreement with the results of fixed-ring consolidometer tests, while the other method gives a high overestimate. The hydraulic conductivities (kh) of the backfills are also estimated by four methods, three based on dissipation test results and one based on piezocone penetration data. kh estimated by consolidation theory are close to the results of flexible wall permeameter tests. Two empirical expressions for dissipation tests give relatively low kh, but the method based on penetration gives kh much larger than the laboratory test results.

Analysis of La Dehesa paleo-landslide. Central Pre-Andes of Argentina

The main objective of this paper is to consider the influence of Quaternary faults as likely triggering factor for rockslides occurrence in the Central Pre-Andes, a region with intense shallow seismic activity. A rockslide deposit was selected as study case, placed in the western flank of La Dehesa and Talacasto (DT) range (31°3′37″ S and 68°46′ 8″ W). Applied methodology includes the characterization of main discontinuities, reconstruction of the topography using a high-resolution digital elevation model, safety factor calculation along the sliding surface and, Newmark displacements estimation for three different hypothetical seismic scenarios, recreated from existing neotectonic local information. Equilibrium-limit method's results confirm that study case, La Dehesa rockslide (LDR), had a stable and safe slope's configuration under static conditions. However, a seismic horizontal coefficient between 0.2 and 0.3 decreases safety factor below the safety threshold. Newmark's displacements for different seismic reconstructed scenarios varies between 4.1 and 15.9 cm, values that agreed with a coherent failure process, likely triggered by Pleistocene to Holocene seismogenic sources in Central Pre-Andes. LDR trigger could be assigned mainly to an earthquake related to La Dehesa Quaternary fault (LDF) activity; however, similar movements produced by neighboring faults should not be discarded. LDR triggering related to climatic conditions is despised. Finally, the methodology presented in this work is easy to reproduce and may be applied to other rockslides located in the mountainous areas of the Central Pre-Andes of Argentina.

Redistribution Principle Approach for Evaluation of Seismic Active Earth Pressure Behind Retaining Wall

The knowledge of seismic active earth pressure behind the rigid retaining wall is very essential in the design of retaining wall in earthquake prone regions. Commonly used Mononobe–Okabe (MO) method considers pseudo-static approach. Recently there are many pseudo-dynamic methods used to evaluate the seismic earth pressure. However, available pseudo-static and pseudo-dynamic methods do not incorporate the effect of wall movement on the earth pressure distribution. Dubrova (Interaction between soils and structures, Rechnoi Transport, Moscow, 1963) was the first, who considered such effect and till date, it is used for cohesionless soil, without considering the effect of seismicity. In this paper, Dubrova’s model based on redistribution principle, considering the seismic effect has been developed. It is further used to compute the distribution of seismic active earth pressure, in a more realistic manner, by considering the effect of wall movement on the earth pressure, as it is displacement based method. The effects of a wide range of parameters like soil friction angle (ϕ), wall friction angle (δ), horizontal and vertical seismic acceleration coefficients (kh and kv); on seismic active earth pressure (Kae) have been studied. Results are presented for comparison of pseudo-static and pseudo-dynamic methods, to highlight the realistic, non-linearity of seismic active earth pressure distribution. The current study results in the variation of Kae with kh in the same manner as that of MO method and Choudhury and Nimbalkar (Geotech Geol Eng 24(5):1103–1113, 2006) study. To increase in ϕ, there is a reduction in static as well as seismic earth pressure. Also, by keeping constant ϕ value, as kh increases from 0 to 0.3, earth pressure increases; whereas as δ increases, active earth pressure decreases. The seismic active earth pressure coefficient (Kae) obtained from the present study is approximately same as that obtained by previous researchers. Though seismic earth pressure obtained by pseudo-dynamic approach and seismic earth pressure obtained by redistribution principle have different background of formulation, the final earth pressure distribution is approximately same.

Verification of numerical simulation of suspended matter distribution under marine dumping process

The several of finite-difference schemes in flat and spatial statement of the dumping processes have been observed. Verification of numerical experiments and model’s calibration is the important phases of mathematical simulation. The results of calculation by fundamental solution are the single corrected source for numerical simulation without data in situ. The several of finite-difference schemes in flat and spatial statement of equation for unsteady turbulent diffusion have been proposed.
 The comparison of numerical simulation with calculations based on the fundamental formulas and also with data in situ was done. It was established that the explicit finite-difference scheme is more preferably for the short time intervals. The results of numerical simulation by this scheme correspond with calculation by fundamental formula for the flat statement if coefficient Courant = 0,25 and using comparison of calculations with time shift equal the step of the finite-difference schemes.
 The deviation of numerical experiment result from the direct investigations is not more then 10 – 15% under condition of small current velocity and small windy waves for the short distances from the dumping place. It was established that for these conditions are possible to calculate the horizontal coefficient of turbulent diffusion by Karaushev’s formula.

Three-dimensional limit analysis of seismic stability of tunnel faces with quasi-static method

Based on the existing research results, a three-dimensional failure mechanism of tunnel face was constructed. The dynamic seismic effect was taken into account on the basis of quasi-static method, and the nonlinear Mohr-Coulomb failure criterion was introduced into the limit analysis by using the tangent technique. The collapse pressure along with the failure scope of tunnel face was obtained through nonlinear limit analysis. Results show that nonlinear coefficient and initial cohesion have a significant impact on the collapse pressure and failure zone. However, horizontal seismic coefficient and vertical seismic proportional coefficient merely affect the collapse pressure and the location of failure surface. And their influences on the volume and height of failure mechanism are not obvious. By virtue of reliability theory, the influences of horizontal and vertical seismic forces on supporting pressure were discussed. Meanwhile, safety factors and supporting pressures with respect to 3 different safety levels are also obtained, which may provide references to seismic design of tunnels.

On the Equilibration of Numerical Simulation of Internal Tide: A Case Study around the Hawaiian Ridge

AbstractTo investigate the equilibration of numerical simulation (ENS) of internal tide, a three-dimensional isopycnic coordinate internal tide model is applied to simulate the M2 internal tide on idealized topography and around the Hawaiian Ridge. An idealized experiment is carried out on a Gaussian topography, and the temporal variations of the baroclinic velocity and the baroclinic energy flux are analyzed, then ENS is studied, and two criteria are presented. Moreover, the impacts of four parameters [horizontal and vertical eddy viscosity coefficients, bottom friction coefficient, and damping coefficient (to parameterize the nonhydrostatic processes in the model)] on ENS during numerical simulations, the baroclinic velocity, the baroclinic tidal energy, and the baroclinic energy flux are investigated. It appears that ENS for the M2 internal tide is more sensitive to the horizontal eddy viscosity coefficient and the damping coefficient. To further examine the criteria of ENS, a numerical experiment is carried out to simulate the M2 internal tidal constituent near the Hawaiian Ridge. The simulated surface tide shows good agreement with results from the Oregon State University tidal model and TOPEX/Poseidon (T/P) observations. The simulation results indicate that a 50 M2 tidal period (25.88 days) run is capable of ensuring ENS for the M2 internal tide in this case. In short, this paper presents a method and two criteria for examining ENS for internal tides for modelers.

Stability Analysis of Gabion wall with Tieback in Seismic Regions

One of the most important issues in the construction of highways, mountain and urban roads is known as slope stabilization. If the necessary actions for protection are not considered, it could lead to problems and events such as landslides, settlements and even destruction of roads. There are many methods for stabilizing slopes such as Gabion walls and Tiebacks. This study can be used as the beginning of a new synthetic method where the Gabion wall is combined with Tiebacks. Gabion walls and tiebacks can be known as the most flexible methods of slope stabilization methods, because of this reason, if they can be combined with each other, it should show very good results in front of dynamic and even static forces. This combination is the novel point of this research. In this study at first, the gabion wall will be analysed in different loading conditions, and then to deal with earthquake dynamic forces the tiebacks will be used to increase the gabion walls stability.The software that is used in this study is GEO5 software, nowadays this software can be introduced as one of the best slope stability analysis software's. The results of this study showed that the designed gabion wall could be stable in dense silty gravel soil (GM) in 8.5-meter slope, and with magnitude of 0.25 horizontal coefficient of Manjil earthquake, but in the same geometry and material condition and impact of 0.4 magnitude horizontal coefficient of Bam earthquake it couldn't be stable alone. In this condition four rows of 18 meter tiebacks could stable the gabion wall very well. In this model, under loading condition 3 (with horizontal and vertical pseudo-static coefficient of Bam earthquake) that had the most vertical pseudo-static coefficient, the 23-meter tieback anchors with 12-degree inclination respect to horizontal could stable the considered gabion wall. This result could show that, the combination of gabion walls with tieback anchors gives a satisfactory result and it is an efficient and helpful method for stability of slopes in front of earthquake and dynamic forces.

Cavity Expansion Analysis to Predict Side Shear Set-Up in Clayey Soils

In this study, fifty driven piles located in the Santos Coastal Plain (“Baixada Santista”), Brazil, have been dynamically tested at various times after installation, indicating gain of capacity over time. The average side shear resistance, related to a low-OCR clayey layer – known as SFL soil , was evaluated over time, indicating side shear set-up within a relatively narrow range of values (between 2.0 and 2.5) approximately 20 days after installation. The cavity expansion theory, which considers an ideal cohesive soil, has been used to predict the effective radial stress over time, considering two main parameters: undrained shear strength and horizontal coefficient of consolidation. Finally, the average of measured pile shaft capacities were compared to the unit shear resistances predicted by the Method (effective stress method). The theoretical values of side shear set-up are fairly similar to the results of the analyzed load tests, which seems to support the viability of the presented method.