Journal of Geotechnical and Geoenvironmental Engineering

Field measurements of settlement and lateral deformation obtained from three deep excavation sites constructed in mixed ground profiles are presented and analyzed. Settlement measurements were obtained throughout the construction process, categorized in three stages as: (1) preexcavation (i.e., preliminary site work and support wall installation); (2) main excavation and bracing/anchor installation; and (3) postexcavation (i.e., removal of bracing as basement construction proceeds). Maximum preexcavation stage settlements of $0.03\mathrm{\%}{H}_w$ to $0.06\mathrm{\%}{H}_w$ (where $H_w=\text{wall}$ or trench depth) were measured at two sites, with the maximum settlements occurring adjacent to the wall during its installation. Maximum ground surface settlements during the main excavation stage ranged from about $0.15\mathrm{\%}{H}_e$ to $0.30\mathrm{\%}{H}_e$ (where $H_e=\text{final}$ excavation depth) and the distribution of ground settlement extended to a distance of $1.5H_e$ to $2.0H_e$ from the wall. Maximum settlements occurred at distances of about $0.3H_e$ to $0.5H_e$ from the wall at two sites where the wall consisted of concrete cast in situ (concrete diaphragm and concrete secant pile walls), creating a significant reverse curvature in the settlement distribution. The maximum postexcavation stage settlements ranged from $0.07\mathrm{\%}{H}_e$ to $0.10\mathrm{\%}{H}_e$ for the three sites, representing roughly 10 to 60% increases in settlement over the main excavation settlements, depending greatly on the specific support removal methods as well as the basement floor construction details employed at an individual site. Lateral deflections during the main excavation stage were consistent with trends reported in the literature, ranging from $0.12\mathrm{\%}{H}_e$ to $0.23\mathrm{\%}{H}_e$ , while lateral movement during postexcavation stage ranged from $0.03\mathrm{\%}{H}_e$ to $0.09\mathrm{\%}{H}_e$ . Finally, the settlements measured during the main and postexcavation stages are related to the support system stiffness.

The behavior of step tapered bored piles in sand, under static lateral loading, was examined by field tests at one site in Kuwait. A total of 14 bored piles including two instrumented piles were installed for lateral loading. The soil profile consists of medium dense sand with weak cementations and no groundwater was encountered in the boreholes. Laboratory tests were carried out to determine the basic soil characteristics and the strength parameters. Both the ultimate lateral capacity and the deflections at applied loads were examined. The results indicate increased lateral load carrying capacity and decreased deflections at different applied loads for the step tapered piles due to the enlargement or strengthening of the upper section of the piles. The advantages of using this type of pile is emphasized including the cost saving resulting from an economical design.

The undrained bearing capacity of foundations on or near slopes is commonly calculated using empirical equations or from design charts which have been produced based on limit equilibrium or upper bound plasticity calculations. Many of the available methods do not take account of important parameters that affect the undrained bearing capacity factor, such as the distance of the footing from the slope, the slope height, or the soil properties. This paper presents finite element analyses of strip footings on or near undrained soil slopes performed in order to investigate the influence of the various parameters that affect undrained bearing capacity. The results of the analyses are compared to available methods. It is found that while some of these methods compare well with the finite element results for certain combinations of geometrical parameters and soil properties, they cannot produce sufficiently accurate results as they either do not take account of all of the affecting parameters or are generally not conservative. Based on the finite element results, design charts, equations, and a design procedure are proposed for the calculation of the undrained bearing capacity factor $N_c$ as a function of the undrained shear strength and the bulk unit weight of the soil, the footing width, the distance of the footing from the slope, the slope angle and the slope height.

In Australia, very few rail tracks have been constructed directly on deep estuarine deposits. In recent years, Kooragang Island has become a major export terminal and most coal trains need to cross the main lines at Sandgate to enter Kooragang Island. In this study, a rail track built on up to 30 m of thick soft estuarine soil was stabilized with relatively short vertical drains to consolidate the soil just beneath the track, and no additional preloading surcharge was provided, except the weight from the trains. The initial soil compression was caused by the passage of trains with a speed restricted at 40 km/h. From this study, it is shown that prefabricated vertical drains significantly decrease the buildup of excess pore-water pressure during cyclic loading, and also continue to dissipate excess pore-water pressure during the rest period. A preliminary finite-element analysis was employed to examine the performance of vertical drains, and a Class A prediction was obtained in terms of lateral and vertical displacements. The monitored settlement and lateral displacement results are presented and discussed. The study shows that relatively short vertical drains are sufficient for providing stability for rail tracks, without the need for driving deep vertical drains through the entire soft soil depth.

In order to investigate the influence of water on compression characteristics of decomposed granite soils, single-particle crushing and one-dimensional compression tests were carried out on three types of decomposed granite soils as well as on quartz-rich silica sand under both dry and wet conditions. Results showed that the initial crushing strength of a single particle was reduced and strength variability increased due to the weakening effects induced by the presence of water. Moreover, it was observed that the one-dimensional compression behavior of decomposed granite soil was related to the initial crushing strength. Finally, the magnitude of initial crushing strength was also affected by the degree of weathering of the soil.

The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.

This paper extends a previously developed method of the writers by using a pseudostatic approach to conduct seismic stability analysis for potential translational failures of multilayer lined landfills. Assuming that the designed seismic coefficient, $k_s$ , is known, the factor of safety against translational failure for lined landfills can be calculated from the new developed equations. The critical interface with the seismic yield coefficient, $k_y$ , is generally located at different interfaces along the back slope and along the base. The failure surface is seen to transfer from one interface to another with changes of dimensions of the top width, depth, and front slope of the waste mass. Using this method, a waste filling sequence can be generated so as to maintain the $k_y$ -value above a stipulated value during landfill operations. It is important to ensure that the minimum $k_y$ -value at the critical interface is always equal to or greater than a targeted value during the waste filling sequence and after closure corresponding to the different geometric dimensions of the waste mass.

The present paper discusses the application of a high-cycle accumulation (HCA) model originally developed for sand for the prediction of permanent deformations in an unbound granular material (UGM) used for base and subbase layers in pavements. Cyclic triaxial tests on precompacted samples of an UGM have been performed in order to validate and calibrate the model. The stress amplitude, the initial density, and the average stress were varied. The test results are compared to those of air-pluviated samples of sand (subgrade material). Some significant differences in the behavior of both materials under cyclic loading are outlined. It is demonstrated that the functions describing the intensity of accumulation can be maintained for an UGM with different material constants, but that the flow rule must be generalized in order to describe the anisotropy. Recalculations of the laboratory tests show a good prediction of the modified HCA model.

Under embankment dams and dykes, horizontal groundwater seepage prevails. If the subsoil is layered, and if some coarse layers are not appropriate filters for finer layers, there can be contact erosion at the interface between fine and coarse soils. In order to study contact erosion threshold, some base-soil and coarse-soil combinations were submitted to a flow parallel to the interface between the coarse soil and the base soil. Critical velocities and critical hydraulic gradients were measured for various base soils. Using effective base-soil grain diameter, an empirical expression for critical velocity was proposed that is well adapted for silts or sand/clay mixtures as well as for sands. The mass of eroded soil was measured relative to the flow velocity for each base-soil/coarse-soil setup. The shear stress applied to the interface between base soil and coarse soil was derived from the hydraulic gradient. Using an empirical relationship between applied shear stress and measured eroded mass, erosion rate was estimated for each base-soil/coarse-soil setup.

Application of a pressure membrane extractor (PME) to establish soil-water characteristic curve (SWCC) of fine-grained soils, in 0–1,500 kPa range, is well established. However, this technique requires testing of several identical specimens, corresponding to same or different pressure(s), and their subsequent removal from the PME chamber for moisture content determination. This turns out to be a cumbersome process and even the results are considered less accurate, by the research fraternity. This is mainly due to the fact that removal of the specimen before equilibration time may not incorporate the influence of the applied pressure, precisely. This calls for the development of an alternate technique that can be employed for measuring the instantaneous moisture content of the specimen when it is pressurized, sequentially, without removing it from the PME chamber. In this context, the utility of electrical measurements (i.e., the voltage) across two points in the specimen for determining moisture content was investigated and its details are presented in this paper. This technique has been found to be quite promising and hence can be employed for acquisition of the data which would yield the moisture content of the specimen, without removing it from the PME chamber, easily and quickly. Validity of the methodology has been demonstrated by comparing the obtained SWCC vis-à-vis those obtained by conducting studies using a dewpoint potentiameter, WP4, and by employing the fitting function and a pedo-transfer function available in the SoilVision database.

In this paper, two Taiwan case studies are used to investigate the potential application of the borehole ground-penetrating radar (BGPR) technique. The first case located an unknown buried pipe which had to be dug out prior to underground excavation work. The second case identified the existence of reinforcing bars inside the foundation piles. These missing reinforcing bars potentially threaten the safety of a planned bridge. The results of these studies clearly demonstrate the capability of BGPR to effectively identify the existence of underground targets and thereby provide necessary information for engineering work.

The enhancement of local soils with cement for the construction of stabilized pavement bases, canal lining, and support layer for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, as well as the need of a spoil area. The present research aims to quantify the influence of the amount of cement, the porosity, and the voids/cement ratio in the assessment of unconfined compressive strength $\left(q_u\right)$ and splitting tensile strength $\left(q_t\right)$ of an artificially cemented sand, as well as in the evaluation of $q_t/q_u$ relationship. A program of splitting tensile tests and unconfined compression tests considering three distinct voids ratio and seven cement contents, varying from 1 to 12%, was carried out in the present study. The results show that a power function adapts well $q_t$ and $q_u$ values with increasing cement content and with reducing porosity of the compacted mixture. The voids/cement ratio is demonstrated to be an appropriate parameter to assess both $q_t$ and $q_u$ of the sand-cement mixture studied. Finally, the $q_t/q_u$ relationship is unique for the sand-cement studied, being independent of the voids/cement ratio.