Use of Deep Cement Mixing to Reduce Settlements at Bridge Approaches

Differential settlements between a bridge and the backfill behind the abutment have been a major problem in the construction of expressway embankments over a soft clay foundation. Deep cement mixing (DCM) columns with varying lengths were used to reduce such differential settlements along the Fu-Xia Expressway, Fujian Province, China. The performance and the feasibility of the DCM method were investigated in a trial embankment constructed prior to the actual construction. This paper presents the results of the instrumentation including total settlements, multipoint settlements, soil pressures on both the DCM columns and soil surface, pore-water pressures, and lateral movements obtained from in situ monitoring. The strength of the soil-cement from laboratory mix tests and from in situ quality control tests on DCM columns is presented in the paper. Study results indicate that DCM columns with varying lengths were a simple and effective method to reduce the total and differential settlements from a soft clay foundation at a bridge approach.     

Probabilistic Foundation Settlement on Spatially Random Soil

By modeling soils as spatially random media, estimates of the reliability of foundations against serviceability limit state failure, in the form of excessive differential settlements, can be made. The soil’s property of primary interest is its elastic modulus, E, which is represented here using a lognormal distribution and an isotropic correlation structure. Prediction of settlement below a foundation is then obtained using the finite element method. By generating and analyzing multiple realizations, the statistics and density functions of total and differential settlements are estimated. In this paper probabilistic measures of total settlement under a single spread footing and of differential settlement under a pair of spread footings using a two-dimensional model combined with Monte Carlo simulations are presented. For the cases considered, total settlement is found to be represented well by a lognormal distribution. Probabilities associated with differential settlement are conservatively estimated through the use of a normal distribution with parameters derived from the statistics of local averages of the elastic modulus field under each footing.     

Load-Settlement Response of Rectangular and Circular Piles in Multilayered Soil

Traditionally, analyses developed for circular piles have also been used for rectangular piles by replacing in calculations the rectangular pile with a circular pile of equivalent area. In this paper, we present a settlement analysis that applies to piles with either rectangular or circular cross sections installed in multilayered soil deposits. The analysis follows from the solution of the differential equations governing the displacements of the pile-soil system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. Pile displacements and vertical soil displacements calculated using this analysis match well those from finite-element analysis. A parametric study highlights some important insights for rectangular and circular piles in multilayered soil. A user-friendly spreadsheet program (ALPAXL) was developed to facilitate the use of the analysis. Examples illustrate the use of the analysis in design.     

Nonlinear Cone Penetration Test-Based Method for Predicting Footing Settlements on Sand

This paper presents centrifuge data from model footing tests on dry sand, where a high resolution optical displacement measurement technique was employed to record subsurface soil displacements beneath the centerline of loaded strip footings. These measurements allow derivation of vertical strain profiles, which are then used to estimate operational soil stiffness values. The stiffness values, which were assessed assuming a dependence on cone penetration test tip resistance and initial vertical effective stress level, are shown to degrade rapidly with increasing strain level. Despite such nonlinearity, the experimental strain data can be represented using an updated form of the well known Schmertmann strain influence profile. Settlements calculated using this profile are shown to be in agreement with subsurface settlements when appropriate soil stiffness values are employed.     

Simplified Model for Wall Deflection and Ground-Surface Settlement Caused by Braced Excavation in Clays

Accurate prediction of ground-surface settlement adjacent to an excavation is often difficult to achieve without using accurate representation of small-strain nonlinearity in a soil model within finite-element analyses. In this paper a simplified semiempirical model is proposed for predicting maximum wall deflection, maximum surface settlement, and surface-settlement profile due to excavations in soft to medium clays. A large number of artificial data are generated through finite-element analyses using a well-calibrated, small-strain soil model. These data, consisting of wall displacements and ground-surface settlements in simulated excavations in soft to medium clays, provide the basis for developing the proposed semiempirical model. The proposed model is verified using case histories not used in the development of the model. The study shows that the developed model can accurately predict maximum wall deflection and ground-surface settlement caused by braced excavations in soft to medium clays.     

Numerical Analysis of Geosynthetic-Reinforced and Pile-Supported Earth Platforms over Soft Soil

Geotechnical engineers face several challenges when designing structures over soft soils. These include potential bearing failure, intolerable settlement, large lateral pressures and movement, and global or local instability. Geosynthetic-reinforced and pile-supported earth platforms provide an economic and effective solution for embankments, retaining walls, and storage tanks, etc. constructed on soft soils; especially when rapid construction and/or strict deformation of the structure are required. The inclusion of geosynthetic(s) in the fill enhances the efficiency of load transfer, minimizes yielding of the soil above the pile head, and potentially reduces total and differential settlements. A numerical study has been conducted to investigate pile-soil-geosynthetic(s) interactions by considering three major influence factors: the height of the fill, the tensile stiffness of geosynthetic, and the elastic modulus of pile material. While current methods have not fully addressed important effects of the geosynthetic stiffness and pile modulus on the soil arching ratio, numerical results suggested that the stress concentration ratio and the maximum tension in geosynthetic increase with the height of the embankment fill, the tensile stiffness of geosynthetic, and the elastic modulus of the pile material. The distribution of tension force in the geosynthetic reinforcement indicated that the maximum tension occurs near the edge of the pile.     

An Automatic Newton‐Raphson Scheme

This article presents an automatic Newton‐Raphson method for solving nonlinear finite element equations. It automatically subincrements a series of given coarse load increments so that the local load path error in the displacements is held below a prescribed threshold. The local error is measured by taking the difference between two iterative solutions obtained from the backward Euler method and the SS21 method. By computing both the displacement rates and the displacements this error estimate is obtained cheaply. The performance of the new automatic scheme is compared with the standard Newton‐Raphson scheme, the modified Newton‐Raphson scheme with line search, and two other automatic schemes that are based on explicit Euler methods. Through analyses of a wide variety of problems, it is shown that the automatic Newton‐Raphson scheme is superior to the standard Newton‐Raphson methods in terms of efficiency, robustness, and accuracy.     

Approximate Displacement Influence Factors for Elastic Shallow Foundations

Displacement influence factors for calculating the magnitudes of drained and undrained settlements of shallow foundations are approximated by simple numerical integration of elastic stress distributions within a spreadsheet. Influence factors for circular foundations resting on soils having homogeneous (constant modulus with depth) to Gibson-type (linearly increasing modulus) profiles with finite layer thicknesses are obtained by summing the unit strains from incremental vertical and radial stress changes. The effects of foundation rigidity and embedment are addressed by approximate modifier terms obtained from prior finite-element studies. Results are compared with closed-form analytical and rigorous numerical solutions, where available. A new solution for Gibson soil of finite thickness is presented.     

Prediction of Ground Movements due to Pile Driving in Clay

This paper evaluates theoretical predictions of ground movements caused by the installation of driven (or jacked) piles in clay. The predictions are based on an approximate analysis framework referred to as the shallow strain path method that simulates undrained pile penetration from the stress-free ground surface. Large strain conditions close to the pile are solved numerically, and closed-form analytical expressions are obtained from small strain approximations at points further away. These results show that, for closed-ended cylindrical piles of radius R and embedment L, the normalized displacements δL∕R2 are functions of their dimensionless position x∕L. In contrast, for a planar sheet pile or unplugged open-ended pile, the far-field soil displacements at x∕L depend only on the wall thickness w; i.e., δ∕w = f[x∕L]. The proposed analyses show favorable agreement with data from a variety of available sources including field measurements of (1) building movements caused by installation of large pile groups; (2) uplift of a pile caused by driving of an adjacent pile within a group; and (3) spatial distributions of ground movements caused by installation of a single pile (both cylindrical closed-ended and sheet pile wall), including a particularly detailed set of measurements in a large laboratory calibration chamber. The comparisons show that the proposed analysis is capable of reliably predicting the deformations within the soil mass but generally underestimates the vertical heave measured at the ground surface. Further investigation suggests that this discrepancy may be related to the occurrence of radial cracks observed at the ground surface during pile installation and is consistent with tensile horizontal strains computed in the shallow strain path method analyses.     

Behavior of an Atypical Embankment on Soft Soil: Field Observations and Numerical Simulation

This paper compares the behavior of an embankment with nonsymmetric geometry built on soft soil with that predicted numerically using four elastoplastic soil models. Two of these models are based on isotropic conditions (Modified Cam-Clay on its own or in association with Von Mises) and two other are derived from anisotropic conditions (Melanie on its own or conjugated with Mohr Coulomb). The performance of the models, whose parameters are derived from experimental data, is checked against triaxial tests results. For the embankment, the measured and computed displacements and excess pore pressure are compared, with the isotropic models performing best. The maximum horizontal displacements versus settlements, the change in excess pore pressure versus vertical stress, the extent of the yield domain and the contours of the effective vertical and horizontal stress increments are also examined. The numerical results are explained based on the characteristics of the numerical models, namely the size and shape of the yield surface. The embankment, despite its nonsymmetric geometry, exhibits some similarities with typical behavior.     

Soil Isolation for Seismic Protection Using a Smooth Synthetic Liner

A synthetic liner consisting of a nonwoven geotextile over an ultrahigh molecular weight polyethylene, geotextile/UHMWPE, placed within a soil profile can dissipate seismic energy transmitted to the overlying soil layer and structure. This concept of soil isolation can be an effective and inexpensive way of reducing seismic ground motions through slip displacements. Shaking table tests on soil layers isolated using cylindrical and tub-shaped liners were conducted using harmonic and earthquake base excitations. The results show that an isolation liner can significantly reduce the accelerations at the surface of the isolated soil mass. Accompanying such a reduction in accelerations are slip displacements that manifest around the perimeter of the isolated soil. Because of the curved nature of the liner, permanent slips are minimized by the restoring effect of the gravitational forces of the isolated soil mass. Analytical results under field scale conditions indicate that a soil isolation liner can dramatically reduce the peak and spectral accelerations of a vertically propagating shear wave. Such a reduction can provide seismic protection to a structure founded on soil-isolated ground.     

Wall and Ground Movements due to Deep Excavations in Shanghai Soft Soils

An extensive database of 300 case histories of wall displacements and ground settlements due to deep excavations in Shanghai soft soils were collected and analyzed. The mean values of the maximum lateral displacements of walls constructed by the top-down method, walls constructed by the bottom-up method (including diaphragm walls, contiguous pile walls, and compound deep soil mixing walls), sheet pile walls, compound soil nail walls, and deep soil mixing walls are 0.27%H, 0.4%H, 1.5%H, 0.55%H, and 0.91%H, respectively, where H is the excavation depth. The mean value of the maximum ground surface settlement is 0.42%H. The settlement influence zone reaches to a distance of about 1.5H to 3.5H from the excavation. The ratio between the maximum ground surface settlement and the maximum lateral displacement of a wall generally ranges from 0.4 to 2.0, with an average value of 0.9. The factors affecting the deformation of the wall were analyzed. It shows that there is a slight evidence of a trend for decreasing wall displacement with increasing system stiffness and the factor of safety against basal heave. Wall and ground movements were also compared with that observed in worldwide case histories.     

高线精轧机润滑系统的污染与防治

通过对油品污染物的产生及危害的分析，对过滤器、油箱采取一定的防治措施，合理使用油水分离器，并对油液进行定期检测，来保证润滑系统的正常工作。     

Coupled Slosh Dynamics of Liquid-Filled, Composite Cylindrical Tanks

The present paper concerns the hydrodynamic coupling of fluid with laminated composite cylinders under small displacements. A numerical model using finite-element technique is presented to study the dynamics of inviscid, incompressible liquid inside thin-walled, flexible, composite cylindrical tanks. The finite-element equations of motion for both the tank wall and the fluid domain are formulated and numerically integrated using Newmark's predictor–multicorrector algorithm. Both fluid transients and structure dynamics problems are dealt with separately before solving for the coupled interaction problems. The solution procedures are applied to both rigid and flexible fluid-tank systems to demonstrate the effect of tank flexibility on the slosh characteristics and the structural response.     

Response of Inhomogeneous Seabed around Buried Pipeline under Ocean Waves

Recently, considerable efforts have been devoted to the phenomenon of wave-seabed-pipeline interaction. However, conventional investigations for this problem have been concerned with a uniform seabed, despite the strong evidences of variable permeability and shear modulus. In this paper, a finite-element model is proposed to investigate the wave-induced pore pressure, effective stresses, and soil displacements in the vicinity of a buried pipeline in a porous seabed with variable permeability and shear modulus. The numerical results indicate that the inclusion of variable permeability and shear modulus significantly affects the wave-induced soil response around the pipeline. The influence of the variable permeability and shear modulus and geometry of the pipe on the wave-induced soil response around a buried pipeline are also detailed.     

Estimation of Footing Settlement in Sand

The settlement of foundations under working load conditions is an important design consideration. Well‐designed foundations induce stress‐strain states in the soil that are neither in the linear elastic range nor in the range usually associated with perfect plasticity. Thus, in order to accurately predict working settlements, analyses that are more realistic than simple elastic analyses are required. The settlements of footings in sand are often estimated based on the results of in situ tests, particularly the standard penetration test (SPT) and the cone penetration test (CPT). In this article, we analyze the load‐settlement response of vertically loaded footings placed in sands using both the finite element method with a nonlinear stress‐strain model and the conventional elastic approach. Calculations are made for both normally consolidated and heavily overconsolidated sands with various relative densities. For each case, the cone penetration resistance qc is calculated using CONPOINT, a widely tested program that allows computation of qc based on cavity expansion analysis. Based on these analyses, we propose a procedure for the estimation of footing settlement in sands based on CPT results.     

Effects of the Erosion and Transport of Fine Particles due to Seepage Flow

The gradual erosion and transport of fine particles are among the possible consequences to the subsoil of a severe seepage flow, such as the seepage induced by the artificial lowering of the water table by means of pumping wells. The erosion, in turn, could induce local effects, in terms of reductions in the soil volume and variations in the soil mechanical characteristics, that could be non-negligible when working in an urban area. In this paper, some laboratory tests are presented aimed at investigating the erosion of fine particles from soil samples subjected to a controlled seepage flow. The phenomenon of erosion and transport is then modeled by combining, in a single governing equation, the conservation of mass of moving particles with a suitable law of erosion, which is calibrated on the basis of the seepage tests. This equation, coupled with the equation governing the seepage problem, permits one to evaluate the quantity of particles eroded and transported from the soil mass. The effects of the loss of fine material on the stress–strain distribution within the soil mass are estimated by a finite-element analysis. The proposed model is then adopted for the evaluation of the surface settlements induced by the water pumping from a drainage trench.     

Bridge Foundations for Hightstown Bypass

This paper presents a case history of the foundations for seven bridges supported on spread footings bearing on overconsolidated clay. Conventional methods of analysis were used to estimate the elastic and consolidation settlements of the foundations. The settlements were monitored during and after construction for approximately 300 to 500 days. While the settlements for all the piers were overpredicted, the predictions for the abutment settlements were in accord with predictions except for one bridge. The differential settlements from pier to abutment were underpredicted, with values after bridge deck placement that were up to one-half of the total or eventual differential settlements. Differential settlements from the start of construction were up to three-quarters of the total. The paper concludes that the overprediction of pier settlements and the reason for the relatively accurate abutment settlements are both related to inherent limitations in the methods of analysis used.     

Responses of Buildings with Different Structural Types to Excavation-Induced Ground Settlements

This paper compares the responses of buildings with different structural types on shallow foundations subjected to excavation-induced ground settlements and provides a better understanding of the complex soil-structure interaction in building response. Investigated structures include brick-bearing structures, open-frame structures, and brick-infilled frame structures. These structures are often encountered near a construction area, and the different structures may show very different behaviors to excavation-induced ground settlements. In this research, numerical studies were carried out to evaluate the responses of single brick-bearing walls and frame structures (both open and brick infilled) subjected to an identical progressive ground settlement and to provide key features of building responses in different soil conditions, structure conditions, and structural types. Each structure, which is four stories high, was modeled numerically with two different soil conditions, and the response was compared among other types of structures and between elastic and crackable conditions for the brick-bearing and brick-infilled frame structures. Comparison of building responses was investigated by using distortions and crack damages induced to the structures by excavation-induced ground settlements. The structures were modeled by using the two-dimensional (2D) universal distinct element code (UDEC 3.1) in which each brick unit was modeled as a separate unit, with the contacts between brick units having stiffness and strength characteristics of mortar. The numerical studies indicated that the structural response to excavation-induced ground settlements is highly dependent on structural type, cracking in a structure, and soil condition; therefore, their effects should be considered to better assess building response to excavation-induced ground settlements.