Donggyu Park

Experimental Investigation on the Coefficient of Lateral Earth Pressure at Rest of Silty Sands: Effect of Fines

The coefficient of lateral earth pressure at rest (K0) is an important state variable of soils and is often estimated using Jakys K0 equation, which is based on the internal friction angle (φ′). When fines are contained in sand, the effect of the fines content needs to be properly taken into account for the φ′-based estimation of K0, as the strength characteristics change because of changes in particle interlocking and contact conditions. In this study, an experimental testing program was established to measure and analyze K0 and its correlation to shear strength characteristics of sand–silt mixtures focusing on the effect of silt content. Thin-wall oedometer tests, triaxial tests, and other property tests were conducted to obtain K0 values and characterize the test materials. The values of K0 became higher as the relative density and silt content decreased, which was found because of decreasing particle interlocking and friction angle. Jakys K0 equation using the peak strength tended to underestimate K0 at lower relative densities, whereas the K0 matched closely to measured values for higher relative densities. The K0 correlation based on the mobilized inter-particle strength was proposed and was applicable to various sand conditions. The calculated results using the proposed K0 correlation matched the measured results well, confirming the effectiveness of the proposed method.

Estimation of Ultimate Lateral Load Capacity of Piles in Sands Using Calibration Chamber Tests

Current practice for the estimation of the ultimate lateral load capacity of piles is typically based on the vertical effective stress σ′v, while the effect of the lateral effective stress σ′h is not specifically considered. In the present study, calibration chamber lateral pile load tests are conducted to investigate the load response and ultimate lateral load capacity Hu of laterally loaded piles under various soil and stress conditions. In order to determine Hu from load-deflection curves, different criteria are explored and analyzed. From the test results, it is shown that Hu increases significantly with increasing σ′h for a given σ′v. It is also found that lateral deflection of pile at ultimate state tends to increase as the relative density and lateral stress increase. On the basis of the test results, the lateral stress correction factor reflecting the effect of the lateral effective stress σ′h on Hu is proposed. From the test results, it is seen that the proposed procedure using the lateral stress correction factor produces more realistic estimation of Hu. Case examples are selected from the literature and used to compare results measured and predicted using the proposed approach.

Groundwater Effect Factors for the Load-Carrying Behavior of Footings From Hydraulic Chamber Load Tests

The presence of groundwater level (GWL) causes changes in stiffness and strength of soil, affecting the bearing capacity and settlement of shallow foundations. In the present study, the load-carrying capacity and settlement of footings in sands under various GWL conditions were investigated. For this purpose, a series of model footing load tests and cone penetration tests (CPTs) were conducted using the hydraulically controlled chamber system. Different GWL and soil conditions were considered in the tests. The load-carrying capacity of footings became lower with increasing GWL, which was most significant within the depth of GWL (dw) equal to footing width (1.0B). Larger reductions in the bearing capacity with GWL were observed for looser soils with lower relative density. Based on the test results, design equations and correlation parameters for the GWL effects on the bearing capacity and settlement were proposed as a function of GWL, applied load, and relative density. It was confirmed that the existing CPT-based correlations to footing bearing capacity are valid and applicable for soils with GWL.