SPT and CPT Testing for Evaluating Lateral Loading of Deep Foundations

Current design software (FloridaPier, Com624P) requires p-y curves to estimate the foundation lateral load resistance. Input parameters used to develop these curves can be obtained from in situ [standard penetration test (SPT) and cone penetration test (CPT)] correlations. This paper presents an evaluation of predictions using input soil parameters from SPT and CPT correlations versus field measured values. A lateral load test database consisting of 24 SPT and 6 CPT data sets was developed. The comparisons showed that four different SPT correlations for ? coupled with three different k-values all produce similar R-values. (R-value = measured∕predicted × 100%). Therefore, little difference exists between the SPT correlation combinations, albeit the estimated k value has a greater effect on predicted deformation. Similar combinations of CPT correlations also show little effect among the commonly used correlations. SPT predictions are quite conservative at low load levels (R-values ≈ 53%) and remain conservative (R-values ≈ 87%) at high load levels. Also, the scatter (standard deviation) is high (≈40%). CPT evaluations gave unconservative predictions (R-values ≈ 105 to 154%). In addition, the scatter (standard deviation) is high (≈34 to 74%).     

Effects of Construction on Laterally Loaded Pile Groups

Full-scale lateral load tests on a group of bored and a group of driven precast piles were carried out as part of a research project for the proposed high-speed rail system in Taiwan. Standard penetration tests, cone penetration tests (CPT), and Marchetti Dilatometer tests (DMT) were performed before the pile installation. The CPT and DMT were also conducted after pile installation. Numerical analyses of the laterally loaded piles were conducted using p-y curves derived from preconstruction and postconstruction DMT and by applying the concept of p multipliers. Comparisons between preconstruction and postconstruction CPT and DMT data and evaluation of the results of computations show that the installation of bored piles softened the surrounding soil, whereas the driven piles caused a densifying effect.     

Load Testing and Settlement Prediction of Shallow Foundation

The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8?m (6?ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT-N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accounting for overconsolidation, provided better estimates than the hardening soil (hyperbolic-cap) model for all insitu test derived parameters.     

Estimation of Axial Load Capacity for Bored Tapered Piles Using CPT Results in Sand

Tapered piles in comparison to cylindrical piles can be beneficial in terms of the load capacity. In this paper, estimation of the load capacity for tapered piles using cone penetration test (CPT) resistance was investigated. Fourteen calibration chamber load tests using different pile types and six CPTs were conducted under various soil conditions. From the calibration chamber test results, the total, base, and shaft load capacities were analyzed in terms of soil conditions and taper angle. To evaluate CPT-based load capacity of tapered piles, normalized base and shaft resistances were obtained from normalized unit load-settlement curves. Based on the normalized base and shaft resistances, design equations that can be used to evaluate the base and shaft resistances of tapered piles were proposed. The proposed method is valid for sands of medium to dense conditions, while it may result in unconservative predictions for loose sands. To check the accuracy of the proposed method, field load tests using both cylindrical and tapered piles were conducted and compared with the predictions using the proposed method. A simplified approach using an equivalent cylindrical pile was also investigated and compared.     

Estimation of Footing Settlement in Sand

The settlement of foundations under working load conditions is an important design consideration. Well‐designed foundations induce stress‐strain states in the soil that are neither in the linear elastic range nor in the range usually associated with perfect plasticity. Thus, in order to accurately predict working settlements, analyses that are more realistic than simple elastic analyses are required. The settlements of footings in sand are often estimated based on the results of in situ tests, particularly the standard penetration test (SPT) and the cone penetration test (CPT). In this article, we analyze the load‐settlement response of vertically loaded footings placed in sands using both the finite element method with a nonlinear stress‐strain model and the conventional elastic approach. Calculations are made for both normally consolidated and heavily overconsolidated sands with various relative densities. For each case, the cone penetration resistance qc is calculated using CONPOINT, a widely tested program that allows computation of qc based on cavity expansion analysis. Based on these analyses, we propose a procedure for the estimation of footing settlement in sands based on CPT results.     

Horizontal Bearing Capacity of Piles in a Lateritic Soil

The behavior of pile foundations subjected to horizontal loading is typically evaluated using horizontal load tests. Although load tests are valuable to understand site-specific soil-structure interaction phenomena, validated predictive methods are also useful during the design phase. In this study, the results from horizontal load tests are compared with methods which predict the horizontal bearing capacity of piles using in situ measurements of soil behavior. Specifically, several horizontal load tests were performed in order to evaluate the behavior of two 12-m long Strauss piles and four bored piles with similar length, all installed in a lateritic soil profile. Two prediction methods were evaluated using p-y curves computed from the results of Marchetti’s dilatometer test (DMT) results. The predictive methods using the p-y curves from the DMT showed good agreement with the behavior observed in the pile loading test.     

Estimating Liquefaction-Induced Lateral Displacements Using the Standard Penetration Test or Cone Penetration Test

A semiempirical approach to estimate liquefaction-induced lateral displacements using standard penetration test (SPT) or cone penetration test (CPT) data is presented. The approach combines available SPT- and CPT-based methods to evaluate liquefaction potential with laboratory test results for clean sands to estimate the potential maximum cyclic shear strains for saturated sandy soils under seismic loading. A lateral displacement index is then introduced, which is obtained by integrating the maximum cyclic shear strains with depth. Empirical correlations from case history data are proposed between actual lateral displacement, the lateral displacement index, and geometric parameters characterizing ground geometry for gently sloping ground without a free face, level ground with a free face, and gently sloping ground with a free face. The proposed approach can be applied to obtain preliminary estimates of the magnitude of lateral displacements associated with a liquefaction-induced lateral spread.     

Construction Effect on Load Transfer along Bored Piles

The load transfer behavior along bored piles is affected by details of pile construction particularly those imposing stress and moisture changes to the surrounding soils. An investigation involving moisture migration tests, in situ horizontal stress measurements, and borehole shear and pressuremeter tests shows clear effects of construction that lead to subsequent changes in soil properties. The construction of bored piles in Singapore and the region often involves casting of concrete either in unsupported “dry” boreholes or in “wet” boreholes filled with water. It is necessary to differentiate these two extreme construction conditions in bored pile design. Based on triaxial compression and pressuremeter tests on the residual soil of the Jurong Formation in Singapore, the variation of soil modulus with shear strain can be described by a hyperbolic function. A procedure is recommended for assessing the combined effect of stress relief and soaking on soil modulus by introducing a modulus reduction factor. Modulus degradation curves from pressuremeter tests with the borehole conditions properly simulated are found capable of producing load transfer curves that are comparable to those deduced in the field.     

CPT-DMT Correlations

Although the cone penetration test (CPT) and flat-plat dilatometer test (DMT) have been used for over 30 years, relatively little has been published regarding comprehensive correlations between the two in situ tests. This paper presents preliminary correlations between the main parameters of the CPT and DMT. The key to the proposed correlations is the recognition that the main DMT parameters are normalized and hence, should be correlated with normalized CPT parameters. The suggested correlations are developed and evaluated using published records and existing links to various other parameters as well as comparison profiles. The suggested correlations may guide future more detailed correlations between these two in situ tests.     

Undrained Lateral Pile Response in Sloping Ground

Three-dimensional finite element analyses were performed to study the behavior of piles in sloping ground under undrained lateral loading conditions. Piles of different diameter and length in sloping cohesive soils of different undrained shear strength and several ground slopes were considered. Based on the results of the finite element analyses, analytical formulations are derived for the ultimate load per unit length and the initial stiffness of hyperbolic p-y curves. New p-y criteria for static loading of piles in clay are proposed, which take into account the inclination of the slope and the adhesion of the pile-slope interface. These curves are used through a commercial subgrade reaction computer code to parametrically analyze the effect of slope inclination and pile adhesion on lateral displacements and bending moments. To validate the proposed p-y curves, a number of well documented lateral load tests are analyzed. Remarkable agreement is obtained between predicted and measured responses for a wide range of soil undrained shear strength and pile diameter, length, and stiffness.     

Validation and Application of Empirical Liquefaction Models

Empirical liquefaction models (ELMs) are the standard approach for predicting the occurrence of soil liquefaction. These models are typically based on in situ index tests, such as the standard penetration test (SPT) and cone penetration test (CPT), and are broadly classified as deterministic and probabilistic models. No objective and quantitative comparison of these models have been published. Similarly, no rigorous procedure has been published for choosing the threshold required for probabilistic models. This paper provides (1) a quantitative comparison of the predictive performance of ELMs; (2) a reproducible method for choosing the threshold that is needed to apply the probabilistic ELMs; and (3) an alternative deterministic and probabilistic ELM based on the machine learning algorithm, known as support vector machine (SVM). Deterministic and probabilistic ELMs have been developed for SPT and CPT data. For deterministic ELMs, we compare the “simplified procedure,” the Bayesian updating method, and the SVM models for both SPT and CPT data. For probabilistic ELMs, we compare the Bayesian updating method with the SVM models. We compare these different approaches within a quantitative validation framework. This framework includes validation metrics developed within the statistics and artificial intelligence fields that are not common in the geotechnical literature. We incorporate estimated costs associated with risk as well as with risk mitigation. We conclude that (1) the best performing ELM depends on the associated costs; (2) the unique costs associated with an individual project directly determine the optimal threshold for the probabilistic ELMs; and (3) the more recent ELMs only marginally improve prediction accuracy; thus, efforts should focus on improving data collection.     

Effects of Disturbance on Undrained Strengths Interpreted from Pressuremeter Tests

Although the cylindrical cavity expansion theory should provide a sound basis for obtaining the undrained shear strength of clays from pressuremeter tests, the interpreted strengths are often inconsistent with data measured in high-quality laboratory tests. This paper investigates how the pressuremeter results are affected by disturbances that inevitably occur during device installation. The installation of self-boring and displacement-type pressuremeters is simulated using strain path analyses, with realistic effective stress-strain-strength properties described by the MIT-E3 model. Derived strengths obtained from the simulated expansion of displacement-type pressuremeters tend to underestimate the in situ∕cavity expansion strength by amounts that depend on the relative volume of soil displaced, the time delay prior to testing, and the initial overconsolidation ratio of the clay. Interpretation procedures using the simulated contraction curves give much more reliable estimates of the true undrained shear strength. The simulated disturbance effects of self boring lead to derived peak shear stresses that are significantly higher than the reference undrained shear strengths. This overestimate depends on the volume of soil removed during installation and is enhanced when the finite membrane length is included in the analyses. Self-boring pressuremeter data from a well-documented test site in Boston confirm the general character of the predicted pressuremeter stress-strain behavior. The theoretical analyses underestimate the peak strengths derived from self-boring pressuremeter (SBPM) expansion tests, but match closely the measured postpeak resistance in the strain range of 3–6% (saddle point condition). Saddle point strengths are similar in magnitude to the shear strengths measured in laboratory undrained triaxial compression tests at this site. The current predictions are not able to explain the very high shear strengths derived from the SBPM contraction curves.     

New Structure-Based Model for Estimating Undrained Shear Strength

This paper presents an experimental study of the strength in anisotropic clays by means of centrifuge model, cone penetration, and vane shear tests. To understand the effects of void ratio, overconsolidation ratio, and testing rate on the undrained shear strength (Su) of anisotropic Speswhite clay, a new centrifugal testing technique is designed to obtain constant overconsolidation ratio (OCR) profiles with varying void ratios (e), called the “descending gravity test.” The parameters controlling the generation of peak shear strength are quantified. As a result of this function, a new material and rate-dependent surface is defined in the e-OCR-Su space, which is identified as a “structural state capacity surface” since it relates the anisotropic structure to structure inherent capacity and properties. A new function for the estimation of excess pore pressure (uex) generated by cone penetration is found. By combining the strength and pore pressure functions a new model is proposed, called the “CU model.” The CU model is a structure-based model that provides reliable estimates of shear strength for in situ saturated clays using the knowledge of void and overconsolidation ratios. Finally, by combining Su-e-OCR and uex-e-OCR relationships, it estimates the void ratio and OCR profiles of anisotropic clays from piezocone penetration test results.     

Liquefaction Resistance of Clean and Nonplastic Silty Sands Based on Cone Penetration Resistance

Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy in the assessment of the likelihood of liquefaction at a site affects the safety and economy of the design. In this paper, curves of cyclic resistance ratio (CRR) versus cone penetration test (CPT) stress-normalized cone resistance qc1 are developed from a combination of analysis and laboratory testing. The approach consists of two steps: (1) determination of the CRR as a function of relative density from cyclic triaxial tests performed on samples isotropically consolidated to 100 kPa; and (2) estimation of the stress-normalized cone resistance qc1 for the relative densities at which the soil liquefaction tests were performed. A well-tested penetration resistance analysis based on cavity expansion analysis was used to calculate qc1 for the various soil densities. A set of 64 cyclic triaxial tests were performed on specimens of Ottawa sand with nonplastic silt content in the range of 0–15% by weight, and relative densities from loose to dense for each gradation, to establish the relationship of the CRR to the soil state and fines content. The resulting (CRR)7.5-qc1 relationship for clean sand is consistent with widely accepted empirical relationships. The (CRR)7.5-qc1 relationships for the silty sands depend on the relative effect of silt content on the CRR and qc1. It is shown that the cone resistance increases at a higher rate with increasing silt content than does liquefaction resistance, shifting the (CRR)7.5-qc1 curves to the right. The (CRR)7.5-qc1 curves proposed for both clean and silty sands are consistent with field observations.     

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance (qt) and penetration pore-water pressure at the shoulder (u2). Parametric studies for normalized cone tip resistance (Q = qcnet/σv0′) and normalized excess pressures (Δu2/σv0′) as a function of overconsolidation ratio (OCR = σvy′/σv0′) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter (Bq = Δu2/qcnet). The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δu2/σv0′ space is superior to Q–Bq space when evaluating piezocone data for a range of soil types. Still, there are zones of overlap for silty soils and heavily overconsolidated clays, thus requiring that supplementary information to Q and Δu2/σv0′ be obtained in unfamiliar geologies, including variable rate penetration tests, dissipation tests, CPT friction ratio, or soil sampling.     

p-y Criterion for Rock Mass

Drilled shafts socketed in rock mass have been used frequently as a foundation system to support both vertical and lateral loads. Traditionally, the lateral interaction between the drilled shaft and the surrounding rock medium has been characterized by means of nonlinear p-y curves; however, there is a lack of well verified p-y criterion for rock mass. In this paper, a hyperbolic p-y criterion is developed based on both theoretical derivations and numerical (finite element) parametric analysis results. The methods for determining pertinent rock parameters needed for constructing the proposed p-y curves are presented in the paper. Two full-scale lateral load tests on large diameter, fully instrumented drilled shafts socketed in rock conducted by the writers, together with additional four load test results reported by Gabr et al. were used to validate the applicability of the proposed hyperbolic p-y curves for rock mass. The comparisons between the computed shaft responses (both deflections and bending moments) and the actual measured responses are considered acceptable.     

CPT-Based Evaluation of Liquefaction and Lateral Spreading in Centrifuge

Two series of centrifuge model tests were conducted using Nevada sand. Four saturated models placed in a mildly inclined laminar box and simulating a 6-m-thick deposit were shaken inducing liquefaction effects and lateral spreading. The sand was deposited at a relative density, Dr = 45 or 75%; two of the 45% models were subjected to overconsolidation or preshaking. The second series involved in-flight measurements of static cone tip penetration resistance, qc, simulating the standard cone penetration test (CPT) 36-mm cone. Values of qc increased with Dr, overconsolidation, and preshaking. A normalized resistance, qc1N, was assigned to each of the four liquefaction/lateral spreading models. Increases in Dr, overconsolidation, and preshaking decreased liquefaction and ground deformation, but relative density alone captured these effects rather poorly. Conversely, qc1N predicted extremely well the liquefaction and lateral spreading response of the four models, confirming Seed’s hypothesis to explain the success of penetration-based seismic liquefaction charts. The depth to liquefaction measured in the four centrifuge models is consistent with the field CPT liquefaction chart.     

Wedge Failure Analysis of Soil Resistance on Laterally Loaded Piles in Clay

A fundamental study of pile-soil systems subjected to lateral loads in clay soil was conducted by using experimental tests and a lateral load-transfer approach. The emphasis was on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. A framework for determining the p-y curve on the basis of both theoretical analysis and experimental load test results is proposed. The proposed p-y method is shown to be capable of predicting the behavior of a large-diameter pile under lateral loading. The proposed p-y curves with an improved wedge model are more appropriate and realistic for representing a pile-soil interaction for laterally loaded piles in clay than the existing p-y method.     

Modeling Lateral Soil-Pile Response Based on Soil-Pile Interaction

Although most designers prefer the p-y curve method as compared to elastic continuum or finite-element analysis of laterally loaded pile behavior, the profession has reached a state where it is time that closer scrutiny be given to the traditional “Matlock-Reese” p-y curves used in the analysis. The traditional p-y curves were derived from a number of well-instrumented field tests that reflect a limited set of conditions. To consider these p-y curves as unique is questionable. As important as such curves have been to advancing the practice from elastic to nonlinear beam on elastic foundation analysis, such calibrated∕verified p-y curves reflect the specific field test conditions (particularly the pile properties) encountered. As presented in this paper, there are additional influences such as pile bending stiffness, pile cross-sectional shape, pile-head fixity, and pile-head embedment that have an effect on the resulting p-y curves. It is argued that strain wedge (SW) model formulation can be used to characterize such effects. SW model analysis predicts the response of laterally loaded piles and has shown very good agreement with actual field tests in sand, clay, and layered soils. The advantage of the SW model is that it is capable of taking into account the effect of changes in soil and pile properties on the resulting p-y curves.     

Retesting of Liquefaction and Nonliquefaction Case Histories from the 1976 Tangshan Earthquake

A field investigation was performed to retest liquefaction and nonliquefaction sites from the 1976 Tangshan earthquake in China. These sites were carefully investigated in 1978 and 1979 by using standard penetration test (SPT) and cone penetration test (CPT) equipment; however, the CPT measurements are obsolete because of the now nonstandard cone that was used at the time. In 2007, a modern cone was mobilized to retest 18 selected sites that are particularly important because of the intense ground shaking they sustained despite their high fines content and/or because the site did not liquefy. Of the sites reinvestigated and carefully reprocessed, 13 were considered accurate representative case histories. Two of the sites that were originally investigated for liquefaction have been reinvestigated for cyclic failure of fine-grained soil and removed from consideration for liquefaction triggering. The most important outcome of these field investigations was the collection of more accurate data for three nonliquefaction sites that experienced intense ground shaking. Data for these three case histories is now included in an area of the liquefaction triggering database that was poorly populated and will help constrain the upper bound of future liquefaction triggering curves.