When a rigid shaft such as a jacked pile or the sleeve of a cone penetrometer penetrates soil, the soil mass at the shaft tip fails. This failed soil mass flows around the shaft surface and creates a disturbed soil zone. The soil in this zone, which is at a failure or critical state (CS), flows and behaves like a viscous fluid. During continuous penetration, the shaft surface is subjected to an additional viscous shear stress above the static shear stress (interfacial solid friction). The total resistance on the shaft in motion is due to the static and viscous shear components. Current methods of calculating the penetration resistance in soils are based on static interfacial friction, which determine the force required to cause failure at the shaft-soil interface and not the viscous drag. The main aim of this research is to understand the viscous soil resistance on penetrating shafts in clays.This research consists of two components. First, a theoretical analysis based on creeping flow hydrodynamics is developed to study the viscous drag on the shaft. The results of this analysis reveal that the size of the CS zone, the shear viscosity of the soil and velocity of the shaft influence the viscous drag stress. Large increases in viscous drag occur when the size of the CS zone is less than four times the shaft radius.Second, a new experimental procedure to estimate the shear viscosity of clays with water contents less than the liquid limit is developed. Shear viscosity is the desired soil parameter to estimate viscous drag. However, there is no standard method to determine shear viscosity of clays with low water contents (or Liquidity Index, LI). Soils can reach CS for water contents in the plastic range (LI<1) and exhibit viscous behavior. The fall cone test is widely used to interpret the index (liquid and plastic limit) and strength properties of clays. In this study the existing analysis of the fall cone test is reexamined to discern the viscous drag as the cone penetrates the soil. This reexamination shows that the shear viscosity of clays with low water contents (LI<1.5) can be estimated from time-penetration data of the fall cone. Fall cone test results on kaolin show that the shear viscosity decreases exponentially with an increase in LI.The results of this research can be used to understand practical problems such as jacked piles in clays, cone penetrometer sleeve resistance and advancement of casings in soil for drilling or tunneling operations.

<p> The base and shaft resistance of steel pipe piles installed in silica sand is affected by several factors; these include but are not limited to: shaft resistance degradation, shaft surface roughness, installation method, pile geometry, soil density and particle size, and setup.  This thesis focuses on the first four factors, while also considering the effect of soil density within each factor. Several of the pile design formulas available do not consider the effects of shaft resistance degradation due to load cycles during installation of jacked and driven closed-ended pipe piles, plug formation and evolution during driving of open-ended pipe piles, the degree of corrosion or pitting corrosion on the shaft surface of a pile and its potential impact on setup, and the geometry of the tip of the pile. To assess the impact on pile capacity of some of these factors, a series of static compression load tests were performed in a controlled environment in a calibration chamber with a scaled down instrumented model pile. The air-pluviation technique with different combination of sieves assembled in a large-scale pluviator was used to prepare F-55 sand samples of different density in the calibration chamber. Slight changes were made to the experimental setup to study each factor: sand sample density, driving energy, mode of installation, and geometry and shaft roughness of the model pile.</p> <p><br></p> <p>The results from the experiments confirmed that each of these factors affects the pile resistance. Some of the important conclusions were:</p> <p><br></p> <p>i. The shaft resistance of the model pile is about 2.4 times greater for jacked piles than for driven piles in dense sand, due to the greater shaft resistance degradation in driven piles. </p> <p>ii. Despite the effect of degradation, the shaft resistance of the non-displacement model pile which had no loading cycles was a ratio of 0.37 to that of the driven model pile in medium dense sand and 0.60 in dense sand, due to the absence of displacement.</p> <p>iii. An increase in the surface roughness of the jacked model piles from smooth to medium-rough resulted in an increase of the shaft resistance, which had a ratio of 7.75 to the smooth pile in dense sand and 3.05 in medium dense sand. An increase from smooth to rough resulted in an increase of the shaft resistance, which had a ratio of 8.00 to the smooth pile in dense sand and 4.26 in medium dense sand.</p> <p>iv. Although rougher interfaces produce greater interface friction angles than smooth interfaces with sand, once a limiting value of surface roughness is reached, shearing occurs in a narrow band in the sand in the immediate vicinity of the model pile, with the shaft resistance depending on the critical-state friction angle of the sand. This means the shaft resistance will not increase further with changes in pile surface roughness, due to the fact that the internal critical-state friction angle of the sand has been reached in the shear band during loading.  </p> <p>v. During installation, the conical-based pile had a higher penetration per blow compared to the flat based pile from 0 to 25.6<em>B</em> in medium dense sand and 0 to 20<em>B</em> in dense sand (<em>B</em> = base diameter). After the pile was installed beyond 25.6<em>B</em> in medium dense and 20<em>B</em> in dense sand, the penetration per blow was identical. </p> <p>vi. The base resistance of a conical-based model pile was about 0.76 times that of a flat-based model pile in dense sand and 0.56 in medium dense sand. </p> <p>vii. Jacked piles had similar base resistance ratio of about 0.93 to 0.95 of driven piles in dense sand and 0.98 to 1.05 in medium dense sand. However, they had a much higher shaft resistance ratio of about 1.67 to 2.07 in dense sand and 1.44 to 1.50 in medium dense sand. </p>