Effect of Coarse Content on Compaction Test

The compaction is a mechanism to densify the loose soils. The maximum soil densification can be achieved by optimization of the desirable optimum moisture content (OMC) and maximum dry density (MDD). The maximum dry density and the optimum moisture content were affected by several parameters. The coarse content (CC) is one of these parameters. This paper studied the effect of the coarse content on the compaction parameters (MDD, OMC). Several sand-kaolin mixtures had coarse content ranged from 30 % to 80 % and moisture content ranged from 12% to 20% were used to inspect the relationship between CC, specific gravity (Gs), MDD, OMC, and bulk density. The results presented five empirical correlations with coefficient of determination (R2 ≥ 0.98) between CC, Gs, MDD, OMC and bulk density. The comparison between the current study and previous researchers indicated that both soil type and moisture content have significant effect on the efficiency of the empirical correlation equations between the maximum dry density, specific gravity, and coarse content. The results indicated a linear relationship between coarse content toward maximum dry density and specific gravity where both MDD and Gs increased with an increase CC. In contrary, the results showed non-linear relationship between optimum moisture content and coarse content where OMC decrease with an increase CC.

Soil Densification Effect on The Seismic Response of Structures Taking into Consideration Soil-Structure Interaction

Soil compaction is a considerable construction activity to ensure safety and durability, notably in the transportation industry. This technique of compaction increases soil bulk density and soil strength, while decreases porosity, aggregate stability index, soil hydraulic conductivity, and nutrient availability, thus reduces soil health. Consequently, it lowers crop performance via stunted aboveground growth coupled with reduced root growth. Therefore, if the characteristics of the soil are changed, it will affect the response of the structures. In this work, the effect of improving soil characteristics by compaction techniques on the dynamic response of foundations and structures, taking into consideration the effect of soil-structure interaction was determined. The dynamic response of foundations is presented by the impedances functions, which are determined numerically by the CONAN program, based on the cone method. In addition, the response of the structure will be presented according to the lateral displacement in each level of it. This motion vector is a function of the forces in each level; for this, the equivalent static method was applied, which allows to calculate the seismic force at the base and its distribution on the height of the structure. The results obtained show the efficiency of soil densification on the seismic response of MDOF frames.

Performance Assessment of Composite Skirted Ground Reinforcement System in Liquefiable Ground Under Repeated Dynamic Loading Conditions

Occurrence of earthquake generates both horizontal and vertical ground motions. In saturated sands, combination of generated ground motions and pore water pressures induces soil liquefaction. In this study, a composite skirted ground reinforcement system was developed to mitigate generation of pore water pressure in liquefiable soils and also to attenuate incoming ground motions to the foundation. The composite system contains Poly Urethane foam as an isolation barrier for ground motion attenuation with stone columns for improving both soil densification and drainage. The performance of this composite reinforcement system was evaluated under repeated acceleration loading conditions to estimate its efficiency. For testing, saturated ground model having 40% and 60% relative density was prepared and investigated with and without the composite reinforcement system. Test results showed that, the developed skirted ground reinforcement system effectively mitigates the interaction of incoming ground motions with the foundation and also improves the re-liquefaction resistance of soil compared to that of unreinforced ground.

Calculating the Dynamic Impedances of Foundations and their Effect on the Seismic Response of Structures: Analytical and Numerical Study

This study evaluates the movement of a frame built on soft soil under seismic excitation taking into account soil-structure interaction. First, the study was evaluated using the finite element method, then, by using a substructure method which modelled the soil using springs and dampers in a linear and nonlinear study. Rheological models were determined using impedance functions, calculated using a numerical program CONAN. These dynamic impedances are shown in the displacement vector of a three-degrees-of-freedom frame, which was calculated on the basis of lateral forces distributed over the structure height using the equivalent static method. In this regard, two different calculation norms were chosen; RPA2003 and UBC97. Finally, a parametric study was carried out, based on the effects of soil densification and the foundation geometry on the response of the RC frame.

Liquefaction and Reliquefaction Resistance of Saturated Sand Deposits Treated with Sand Compaction Piles

To mitigate liquefaction and its associated soil deformations, ground improvement techniques were adopted in field to reinforce saturated sand deposits. Sand Compaction Pile (SCP) is one such popular proven treatment to improve liquefaction resistance of sandy deposits. Installation of sand compaction piles improves soil density and rigidity which further enhance seismic resistance against liquefaction and this was well evident from past field observations. However, studies involving SCP performance during repeated shaking events were not available/limited. In this study, using 1-g uniaxial shaking table a series of shaking experiments were performed on SCP treated and untreated sand deposits having 40% and 60% relative density subjected to repeated incremental acceleration loading conditions(i.e. 0.1g – 0.4g at 5 Hz frequency).Parameters such as improvement in soil resistance and relative density, generation and dissipation of excess pore water pressures, maximum observed foundation settlement and soil displacement and variation in cyclic stress ratio were evaluated and compared. Seismic response of liquefiable sand deposits found to be improved significantly due to SCP installation together with occurrence of continuous soil densification under repeated loading. The experimental observations suggested that SCP can perform better even at repeated shaking events.

Lateral Extent and Environmental Effects of Dynamic Compaction in a Coastal Area of Southern Iran

ABSTRACT The lateral extent, depth of densification, and environmental effects of dynamic compaction (DC) were investigated for a very loose to loose silty sand layer with thickness varying from 6 to 12 m in a coastal area in southern Iran. Cone penetration testing (CPT) was done at different distances from the center of the point of impact before and after DC. The increase in cone resistance at different distances is plotted versus dimensionless distance X/D (X = distance from center point of impact and D = diameter of tamper), and equations are proposed to describe them. The amount of soil densification decreased progressively until the distance from the center of the tamper increased to about 3.3 times the diameter of the tamper, beyond which there was no densification. The peak partial velocity (PPV) measured at different distances from the center point of impact was used to determine the environmental effect caused by the impact of the tamper. Equations describing the relationship between the weight of the tamper, tamper drop height, distance from the center point of impact, and PPV for this site are proposed.