Load-settlement response of circular footing resting on reinforced layered system

Removal of unsuitable soil and replacement with a strong material is one of the oldest and simplest ground improvement techniques. During this process, a layered soil system with a strong layer overlying a weak layer is achieved. Studies on the load-settlement response of footing on such layered system are limited. An experimental study is carried out to obtain the load-settlement response of a model circular footing resting on (a) unreinforced aggregate layer overlying a sandy soil layer, and (b) geogrid-reinforced aggregate layer overlying a sandy soil layer. A large-scale test chamber of size equal to 1m x 1m x 1m is used to perform the experiments. Actuator of 10T capacity is used to apply the loads in a displacement-rate controlled mode. A plate vibrator is used to prepare uniform sand and aggregate layers inside the test chamber. Relative density equal to 70% is maintained for both the layers during the entire test program. The improvement in the load carrying capacity of model footing with the increase in the thickness of aggregate layer and with the introduction of geogrid reinforcement in the aggregate layer is proposed in the study

Settlement of Embankment Constructed with Geofoam

Expanded polystyrene (EPS) geofoams are being widely used in civil engineering. They are mainly used to construct embankments over weak sub soils because of their light weight property. Embankment constructed with geofoam as fill material typically consists of geofoam blocks with a load distribution slab and a soil cover above it. Settlement of such embankments is critical in the design due to high compressibility of geofoam. In this paper, finite difference program (FLAC—fast lagrangian analysis of continua) is used to obtain the settlements at the top of embankment due to applied loading. Live loads as per ASSHTO specifications are applied on the embankment. The numerical model is also used to analyze the vertical stresses on geofoam due to applied loading. Parametric studies are performed for various thicknesses of soil cover above geofoam (30 cm, 75 cm, and 100 cm), and for two different values of elastic modulus of geofoam (1 MPa and 10 MPa)

Modeling Reinforcement-Soil Interactions under Oblique or Transverse Forces-A Review

The pullout resistance of the reinforcement is an important parameter in the design of reinforced earth structures. The existing design procedures consider the pullout resistance due to only axial pull. However, the kinematics of failure clearly establishes that the reinforcement is displaced obliquely. In this paper, a review on the physical modeling of sheet reinforcement subjected to an oblique force applied at one end of the reinforcement is presented. The review ranges from simple physical models that consider linear normal stress-deformation of the fill material and rigid plastic behavior of shear stress-displacement at soil-reinforcement interface to more sophisticated models that consider nonlinear behavior for both normal stress-deformation of the fill and shear stress-displacement of soil-reinforcement interface. The effects of various parameters on the reinforcement-soil interaction are also highlighted. Review shows that the pullout resistance of the reinforcement is higher when subjected to the oblique force compared to that for an axial pullout

Compaction Quality Control of Earth Fills Using Dynamic Cone Penetrometer

Quality control for compaction of earth fills is commonly performed by measuring the in situ density using the sand cone method. In situ density measurements from sand cone testing are highly operator-dependent; in addition, the test procedure is tedious and time-consuming. In this study, a dynamic cone penetrometer (DCP) was used to perform quality control (QC) of earthworks by measuring penetration resistance in compacted soil. DCP tests were performed on three test pads specially constructed using different soil types - clayey sand with gravel, clayey sand, and silty sand. The test results were expressed in terms of a dynamic penetration index (DPI), defined as the depth of penetration of the cone per hammer blow. Correlations are developed between DPI and compacted density for the three soil types considered. In order to meet the criterion of compacted density equal to or greater than 98% of the maximum density from a laboratory standard Proctor test, DPI values are found to range from 5 to 8 mm/blow, corresponding to 250 mm penetration of cone on tested soil types. The effect of the fall height of the hammer on the measured DPI is also studied by performing DCP tests for two fall heights, 575 and 450 mm. DPI values are found to increase by 11-26% when the height of the fall increases from 450 to 575 mm, for the highest energy level considered in the study. It is also found that DPI is very sensitive to the moisture content and in situ density of compacted layers. The DCP device provided quick test results and was simple to operate on any subgrade layer; hence, the frequency of QC tests can be increased, leading to an improvement in the overall quality of compaction of earthworks