Fawad Niazi

Dissolution and chemical weathering of carbonate rocks have complex effects on their mechanical properties, accelerating their rate of deterioration that can lead to early failure under external stresses. To investigate the effects of acidic solutions on the mechanical properties of inherently low-porosity karstic limestone, compression tests were performed on sound and weathered samples exposed to different corrosive environments and for different durations. The tested samples exhibited a general increase in porosity and decrease in peak strength and Young's modulus for higher acidity and exposure duration. To establish links between these mechanical changes and those at the micro-scale, microstructures and mechanisms of deformation were also studied. As indicators of the sample degradation, the distribution, orientation and intensity of the fractures in the tested samples and their twinning density were used. Based on these parameters, it was found that chemical erosion influe...

Abstract The UniCone direct piezocone method by Eslami and Fellenius (1997) for evaluating the axial capacity of pile foundations is reviewed and improved means of evaluating the soil resistance factors are recommended. This method uses all three piezocone penetration test (CPTu) readings in a soil behavioral type (SBT) classification chart and provides estimations of axial pile capacity for a wide variety of pile types installed in different assortments of geomaterials. In this paper, the earlier method is improved using a dataset of 153 pile load tests and CPTu soundings from 52 worldwide sites. An alternative soil classification system using the CPT material index I c is used to provide improved correlations of higher reliability via continuous functions for estimating the side and base capacity components of driven and jacked piles, and drilled shafts. An analysis is also included to test the performance of the newly proposed design formulations. Finally, a simplified flowchart is presented for convenient application of the enhanced expressions.

A massive landslide created a natural dam on two tributaries of Jhelum River near the town of Hattian Bala in Kashmir in October 2005. The landslide was triggered by a 7.6 Mw earthquake. The resulting unconsolidated dam and water impoundment upstream carried hazard potential of downstream damage to both infrastructure and population due to potential flooding caused by its breach. Comprehensive investigations and monitoring were implemented to analyse dam stability. Fresh topographic profiles were generated. Samples of the matrix materials were utilized in the laboratory investigations including grain-size analysis, laboratory electrical resistivity and permeability tests at varying densities and degrees of saturation, and sediment concentration assessment in the seepage discharge. A noninvasive geophysical method was employed together with new topographic information to develop transient subsurface pictures and to assess the advancement of seepage fronts within the dam body. Interna...

This manual provides guidance on how to use the cone penetration test (CPT) for site investigation and foundation design. The manual has been organized into three volumes. Volume 1 covers the execution of CPT-based site investigations and presents a comprehensive literature review of CPT-based soil behavior type (SBT) charts and estimation of soil variables from CPT results. Volume 2 covers the methods and equations needed for CPT data interpretation and foundation design in different soil types, while Volume 3 includes several example problems (based on instrumented case histories) with detailed, step-by-step calculations to demonstrate the application of the design methods. The methods included in the manual are current, reliable, and demonstrably the best available for Indiana geology based on extensive CPT research carried out during the past two decades. The design of shallow and pile foundations in the manual is based on the load and resistance factor design (LRFD) framework. ...

Cone penetration tests (CPT) are used to evaluate the nonlinear axial load-displacement-capacity performance of a large driven pile from the EURIPIDES project. The 0.76-m diameter pile was driven open-ended in dense sands at Eemshaven, The Netherlands, and tested in static compression and tension at three successive penetration depths: 30.5m, 38.7m and 47.0m. The profiles of four independent readings with depth [total tip resistance (qt), sleeve friction (fs), mid-face porewater (u1) pressure, and shear wave velocity (Vs)], provided by seismic piezocone tests (SCPTu) were utilized to evaluate the soil engineering parameters at the site. These parameters were employed in a rational manner for the axial capacity evaluations. Other direct CPT methods that allow the SCPTu readings for pile capacity evaluations were also utilized to obtain unit pile side friction (fp) and end bearing (qb). The Vs readings enable the determination of the small strain shear modulus (Gmax) profile that prov...

The load-settlement (Q-s) response of deep foundations is influenced by the soil stiffness. One of the most common methods of installing these foundations is the process of driving, which changes the in-situ soil stress and stiffness regime. The stiffness further reduces in a non-linear manner as the loads and shearing strains increase within the soil. The decay in the stiffness of the soil surrounding an axially loaded pile varies with depth. While variety of methods are available to predict the non-linear Q-s response of piles in relatively simpler soil profiles, only selected methods can handle the case of multi-layered soils, where the stiffness properties vary between layers. As an alternative, the Randolph analytical pile solution is exploited for: (1) developing a new modulus reduction scheme from the back-analysis of load tests on driven piles that also accounts for plasticity of the soil, (2) devising a methodology for generating modulus reduction curves for individual laye...

The understanding of the variation of mechanical properties and microstructural changes of rocks due to chemical weathering is critical for prospection, extraction and storage of energy resources in the subsurface. Uniaxial and triaxial compression tests were conducted on fresh and chemically weathered oolitic limestone samples submerged in acidic solutions with pH5 and pH3 values for 30 and 50 days each. Results show that both, acid concentration and exposure period have a significant influence not only in changes of effective porosity, Young’s modulus and peak strength, but also in the development of stress-induced microstructures. While the change in effective porosity increased and the Young’s modulus decreased with exposure time, the peak strength decreased with exposure time and decreasing pH. Micro-fracturing, twinning, and rigid body rotation were the main mechanisms of the deformations observed. The highest density of microcracks and twinned grains were observed in samples ...

Initiating at the small-strain shear modulus (Gmax), the mechanical nonlinear stress-strain-strength behavior of soil manifests in the form of modulus reduction, typically expressed in normalized form as Gop/Gmax. Here, Gop is the operative shear modulus – a reduced stiffness value corresponding to strain levels that the soil is experiencing. Assessment of Gop is critical to reliable predictions of load-related deformations within the soil. Among the various categories of loading, deep foundations and pilings exhibit a typical mechanism of axial load transfer to the foundation soil. For friction type piles, the stiffness reduction mostly takes place along the pile shaft-soil interface. Within the framework of an analytical solution, the back analyses from the results of load tests on pile foundations, together with the knowledge of pile geometries and soil parameters, provide an outline for evaluation of Gop at different load increments. This paper explains the methodology employed ...

Ever since the use of the cone penetration test (CPT) in geotechnical practice, attempts have been made to correlate CPT parameters with pile capacity components of unit end bearing (qb) and unit shaft resistance (fp), thus deriving multiple CPT-based pile design methods. These methods focus on "capacity" only without consideration to complete axial pile load-displacement (Q-w) response. Estimated capacities from these methods also exhibit considerable scatter without any consensus on their consistency. In addition, load-displacement curves obtained from axial load tests on highly expensive and extensively instrumented piles can exhibit different shapes. Nevertheless, a single value from the curve so obtained dictates the design capacity. Currently, there are at least 42 different criteria defining capacity with considerable variation in the values obtained thereof. The Randolph elastic solution, which provides a framework for analytical evaluation of pile load-displacemen...

Ever since the use of cone penetration testing (CPT) in geotechnical site investigations, efforts have been made to correlate its readings with the components of static axial pile capacity: unit base resistance (qb) and unit shaft resistance (fp). Broadly, the pile capacity analysis from CPT data can be accomplished via two main approaches: rational (or indirect) methods, and direct methods. The rational methods require a two-step approach, whereby CPT data are first used to provide assessments of geoparameters that are further utilized as input values within a selected analytical framework to enable the evaluation of the pile capacity components. In contrast, direct CPT methods use the measured penetrometer readings by scaling relationships or algorithms in a single-step process to obtain fp and qb for full-size piling foundations. The evolution of the CPT from mechanical to electrical to electronic versions and single-channel readings (i.e., measured tip resistance, qc) to the pie...

The response of deep foundations to axial loading can be evaluated from the profiles of four independent readings provided by the seismic piezocone test (SCPTu): qt, fs, u2, and Vs. The multiple penetrometer readings are used for direct capacity evaluations and the Vs measurements enable the evaluation of the fundamental soil stiffness (Gmax). Together, this permits the derivation of the load-settlement response by integrating Randolph elastic solutions with G/Gmax reduction schemes. Back-analyses of pile load tests applied within the framework of elastic solutions and SCPTu data also enable generation of site-specific stiffness reduction trends that can be applied with care for predictions for similar soil and pile conditions. A review of selected direct capacity methods is presented along with case studies of driven piles in clayey soils in Ireland, Scotland, Quebec, and Utah.

Landslide dams are complex geomorphologic features which usually exist temporarily at the interface between hill-slope and the valley-floor. These temporary natural features have a potential of downstream damage resulting from possible failure. Brief accounts of two such landslide dams are presented along with a summary of the investigations conducted to study their failure potentials: South Fork Castle creek landslide dam near Mount St. Helens, Washington, USA and Hattian Bala landslide dam near Muzaffarabad, Kashmir. Although, these natural features formed in different parts of the world with different geologic settings, the case history of the earlier served as basis for formulating the investigation methodology for the stability study of the later. The comprehensive site investigations include topographic profiling, sampling of the matrix material for laboratory investigations (index properties, geomaterials classification, permeability and internal erosion potential assessments...

On Oct. 8, 2005, debris from an earthquake triggered landslide blocked two tributaries of Jhelum River at their confluence, near Muzzafarabad, Pakistan, creating lakes. Spillways construction reduced the volume of water in small lake. Large lake kept filling till Apr. 2007, when its surface elevation reached the spillway level. Inundation upstream of this natural dam can cause substantial downstream damage in case of failure. Results of a study are presented, aimed at evaluating the ingress of water into the dam body through seepage from large lake by utilizing hydrological data. Desired results could not be obtained due to data inadequacies; yet, a practical method was evolved which can be applied to the study of similar scenarios.

On Oct. 8, 2005, an earthquake triggered a landslide which blocked two tributaries of the Jhelum River, namely the Karli and Tang channels at their confluence, near Hattian Bala, Azad Kashmir, creating two lakes. Construction of spillways for the two lakes reduced the ...

ABSTRACT Starting with the fundamental small-strain shear modulus (Gmax), the mechanical nonlinear stress-strain-strength behavior of soil manifests itself in the form of stiffness reduction under loading. Back analyses of 105 pile load tests combined with a knowledge of soil parameters at the site and pile geometries provide a framework for evaluation of operational stiffnesses at different levels of loading. This paper explains the framework for obtaining the operational stiffnesses from pile load tests and presents stiffness reduction curves (G/Gmax) in terms of logarithm of pseudo-strain (w/d), where w = pile displacement and d = pile diameter. The result affords an approach to evaluating the nonlinear load-displacement response of piles without resort to evaluating the pile capacity. The framework utilizes the Randolph elastic pile model to generate stiffness reduction curves from top-down axial compression load tests, tension tests, and O-cell configurations.

ABSTRACT The Osterberg cell (O-cell) type of bidirectional pile load testing is a modern full-scale proofing method in the realm of performance-based pile design. It is done at considerable cost, not possible on small to medium size projects. An economical approach of utilizing the flexible and approximate analytical solution, proposed by Randolph, has frequently been adopted in the past for evaluating the pile settlements under static unidirectional top-down axial compression loading. In order to extend this solution for O-cell loadings, following adaptations are warranted: (1) appropriate modifications to handle the loadings in two directions, and (2) development of non-linear stiffness reduction model, derived from the back-analysis of O-cell pile load tests. Accordingly, a modified analytical solution is presented for the two common cases of O-cell loading arrangements. Using these modified sets of solutions and a well-documented database of O-cell load tests on drilled shaft foundations from different sites, two stiffness reduction models have been developed. The shear wave velocity readings obtained from the hybrid geophysical-geotechnical seismic piezocone tests afford the evaluation of fundamental shear stiffness modulus (Gmax) profiles. These profiles together with the re-arranged modified solution were applied to the axial loads vs. displacements (Q – w) from the database of load tests to back-figure the applicable operational shear stiffness (G) values. Additional sensitivity analyses indicate that pile geometry and soil stiffness profile are the two most significant factors affecting the outcome of this solution. A comprehensive set of step-by-step example calculations is included to explain the procedure for implementing the solution.

The performance of pile foundations under axial compression loading can be rationally evaluated within an elastic continuum framework using field results from seismic piezocone tests (SCPTu). The SCPTu is an optimal means for collection of subsurface information because it captures up to 5 independent readings in one sounding: tip resistance (qt), sleeve friction (fs), tip or mid-face porewater pressure (u1) and/or shoulder porewater pressure (u2), and shear wave velocity (Vs). The meas-urements obtained are at opposite ends of the stress-strain-strength curves: the peak strength and stress state for capacity interpretations and the small-strain stiffness (Gmax) for evaluating the initial deformations. Using a versatile Randolph-type elastic pile model, the approach can be applied to evaluate the axial response of pile load tests. The axial load distribution within the shaft is also evaluated. A case study is presented illustrating application of this approach on a bored cast in sit...

The response of deep foundations to axial loading can be evaluated from the profiles of 4 independent readings provided by the Seismic Piezocone Tests (SCPTu): qt, fs, u1 or u2, and Vs. Established correlations are used to assess geotechnical parameters at the site for pile capacity evaluations. Alternatively, CPT readings are used for direct capacity evaluations. Vs readings enable estimation of the soil stiffness (Gmax), allowing derivation of the load-settlement response by integrating elastic solutions with the Gmax softening schemes. A review of selected methods is presented relevant to the EURIPIDES case study illustrating the application of SCPTu results for the response evaluation of driven pipe piles in dense sands.

ABSTRACT The axial load-displacement-capacity response of drilled shaft foundations can be evaluated during the analysis and design stage using an elastic continuum framework and results from in-situ testing methods, in particular, the seismic piezocone test (SCPTù). The SCPTù is an optimal and economical means for collection of geotechnical data because the same sounding provides up to five separate measurements with depth: cone tip resistance (qt), sleeve friction (fs), porewater pressure (u2), time rate of consolidation (t50), and shear wave velocity (Vs). Moreover, the SCPTù provides information on soil behavior at both ends of the stress-strain-strength curves, namely the peak strength and geostatic stress state for evaluating axial pile capacity and the small-strain stiffness (Gmax = t∙Vs2) for the initial soil-pile deformations. Using a Randolph-type analytical elastic pile model, the approach can handle either traditional top down compression loading by dead-weight or reaction beam systems, or the more recent Osterberg cell that juxtaposes base and side resistances in opposite directions. A case study involving O-cell tests on a drilled shaft in Piedmont residuum and partially-weathered rock in Atlanta are presented.

ABSTRACT Piezocone penetration test (CPTu) readings of total tip resistance (qt), corrected sleeve friction (fst), and shoulder porewater pressure (u2) in fine-grained soils can be modeled using spherical cavity expansion (SCE) theory and critical state soil mechanics (CSSM) concepts. The predicted profiles can be fitted to the measured CPTu response using input of soil parameters: preconsolidation stress, total unit weight, effective friction angle, rigidity index (IR), and compressibility parameters (Cc and Cs). This paper presents application of such a formulation for CPTu representation obtainable using a hybrid SCE-CSSM model to a variety of clays sites which have been field tested by CPTu. These deposits have known profiles of fundamental geotechnical information and compressibility parameters determined from laboratory tests, and shear stiffness (Gmax) obtained from field measurement of shear wave velocity (Vs). Undrained shear strength (su) evaluated via critical-state concepts are used together with Gmax to evaluate IR over a range of applicable strains.

... Geotechnical soil parameters for the evaluation of this deep foundation were conveniently obtained from a 100-m deep seismic piezocone tests made at the site with four ... The use of CPT for calculating axial capacity of drilled shafts. Ph. ... Nonlinear soil stiffness in routine design. ...