Mohammad Yamin

Analysis Method for Drilled Shaft–Stabilized Slopes Using Arching Concept

The use of drilled shafts to stabilize an unstable slope has gained popularity in highway applications, mainly because it is a structural fix that does not require additional right-of-way. An analysis method for determining the factor of safety of a drilled shaft or slope system and for determining the earth thrust on the drilled shafts for structural design is introduced. The concept of the analysis is cast in the limiting equilibrium approach via the method of slices, while incorporating the drilled shaft–induced arching effects as the soil mass moved downslope and around the drilled shafts. The mathematical equations based on the limiting equilibrium calculation, together with the load transfer factor for accounting for the drilled shaft–induced arching effects, are presented. The three-dimensional finite element model parametric study using ABAQUS program was used to derive the semiempirical equations for quantifying the arching effect. A UASLOPE computer program was written to incorporate these algorithms for applications to real cases. A case study of a fully instrumented and monitored slope stabilization project, ATH-124, in Ohio, is presented. The analysis of the slope at the project site using finite element modeling and the computer code UASLOPE is presented, together with field-monitored data. On the basis of field monitoring data and the comparison between the finite element analysis results with the computer code UASLOPE results, the suggested analysis and design approach appears to be reasonable.

Solutions for Soil-Pile-Soil Forces in Pile Stabilized Slopes

This paper introduces a mathematical procedure to analyze slope/pile systems. Limiting equilibrium method of slices is extended to account for the pile in the slope. Force and moment equilibrium for each individual slice is satisfied. The proposed procedure allows two separate predefined failure slip surfaces (one in the upslope side and the other in the downslope side) with a unique factor of safety for each slip surface. An illustrative example is presented to elucidate the use of the solution in comprehending the interrelationships among the pile location, the desired factor of safety of the slope/pile system, and the interactive soil/pile forces.

Design of Drilled Shafts for Slope Stabilization

A design method for using the drilled shafts to stabilize an unstable slope is presented in this paper. The method is based on the concept that the presence of drilled shafts in a slope reduces the driving forces on the down slope side of the drilled shafts due to the soil arching by which the earth pressure was transferred to the drilled shafts. The presented design procedure allows for optimization of the drilled shafts size, shaft location, shaft fixity (the necessary rock-socket length), and the spacing between the drilled shafts for a given unstable slope with known slip surface to achieve the desired target FS of the slope/drilled shafts system.

LESSON FROM INSTRUMENTED SLOPE STABILIZATION PROJECT USING DRILLED SHAFTS

A case study of a slope stabilization project using a single row of rock socketed drilled shafts is presented in this paper. The design method, instrumentation program, and slope/drilled shafts monitoring results are presented. The slope is instrumented with inclinometers to obtain soil movement, piezometers to observe the GWT line, and soil pressure cells to measure earth pressures in different zones. Two drilled shafts are instrumented with an inclinometer in each one to measure the shaft deflection. Furthermore, strain gages and pressure cells were also embedded in the drilled shafts to measure the strain in the longitudinal reinforcement and contact earth pressures at the contact interface between the shaft and the soil. Observations and conclusions regarding the effectiveness of drilled shafts in stabilizing the reconstructed roadway embankment are presented.

Lateral earth pressures acting on circular shafts considering soil-structure interaction

Abstract Nowadays, there is a significant demand on developing and expanding the existing infrastructure which necessitates the implementation of fast and cost effective construction methods such as the secant pile walls. The secant pile walls constructed in a circular plan layout to form a vertical shaft provide unique advantages such as compression ring behaviour. Compression rings act as a single-unit system in resisting lateral earth pressure and converting loads from all directions to compressive forces which can be resisted only by low concrete strength. Secant pile walls require stringent drilling tolerances to be achieved in order to behave as a compression ring and to perform as an effective groundwater cut-off wall. This paper presents a parametric study that investigates various aspects of the behaviour of circular shafts constructed using secant pile walls. The aspects that are studied include the identification of the magnitude and distribution of earth pressures exerted on circular shafts by the retained material. The distribution of surcharge pressures on the shaft walls is also studied. The results showed that the surcharge pressures on the wall increased with increasing width of surcharge area; for example, the maximum surcharge pressure increased by at least 60% when surcharge width increased from W = 3 m to W = 48 m. In addition, the results indicated a decrease of the maximum surcharge pressure on the wall by almost 22% when shaft radius decreased from R = 5 m to R = 3 m for Soil 1. Unlike what is observed in plane strain conditions, distance between the surcharge and shaft wall was seen to have a small effect on the magnitude of maximum pressures. The results also showed that the theoretical estimate of pressures underestimated the calculated values at larger depths and that the horizontal extent of the spread of pressure around the shaft was significantly influenced by the type of soil as well as width of surcharge. The outcomes of this study address practical design concerns and are considered to be of interest to those involved in design and construction of vertical shafts.

Evaluation of shear geophones in MASW testing

Abstract Dynamic properties such as wave velocities and damping ratios are required for dynamic analyses of sites. Wave velocities in field are typically evaluated by MASW (Multichannel Analysis of Surface Waves). MASW is favoured due to its ability to resolve hidden layers and better characterisation of shallow depths. Vertical geophones that measure vertical component of motion are typically used in MASW. Shear geophones that measure the horizontal component of motion are increasingly being used in seismic surveys; however, their ability to measure Raleigh velocities in MASW testing has not been evaluated. This study presents the results of numerical simulations and experimental program that evaluates the suitability of shear geophones in MASW. The shear wave velocity profiles from vertical and horizontal components of particle motion due to Raleigh wave propagation are computed and compared. The results of this study suggest that shear geophones can be used in lieu of vertical geophones in MASW testing. Simultaneous measurements of horizontal and vertical components of particle motion can become a promising technique in future to isolate surface waves and enhance Raleigh modes using correlation techniques.