Mehmet T. Tumay

Numerical analysis of the miniature piezocone penetration tests (PCPT) in cohesive soils

An analytical model to simulate the penetration of the piezocone penetrometer in cohesive soils is presented here. The elasto-plastic coupled field equations of the saturated cohesive soils (given by Voyiadjis and Abu-Farsakh) is used in this analysis. The numerical simulation of the piezocone penetration is implemented into a finite element program. The analytical model is used to analyze the miniature piezocone penetration tests (PCPT) conducted at LSU calibration chambers. Simulation of the piezocone penetration is done for two cases. In the first case, the soil–penetrometer interface friction is neglected, while in the second case, the soil–penetrometer interface friction is taken into consideration. The constraint approach is used to model the soil–piezocone interface friction in which the Mohr–Coulomb frictional model is used to define the sliding potential. Analysis is done for three different soil specimens with different stress histories. The results of the numerical simulations are compared with the experimental measurements of the miniature piezocone penetration tests (PCPT) in cohesive soil specimens conducted in LSU calibration chambers. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available prediction methods.

MINIATURE CONE PENETRATION TESTS IN SOFT AND STIFF CLAYS

An electric continuous intrusion miniature cone penetration test system was recently developed for roadway design and construction control of embankments. The system continuously advances a 2 sq cm electric miniature cone penetrometer by uncoiling a stainless steel push rod. Cone penetration testing advances a cylindrical probe into a soil sample and electronically measures the tip and sleeve resistance due to the intrusion. These resistance parameters are used to classify penetrated sediments and to estimate strength and deformation characteristics of soils. Field and laboratory testing programs were conducted on overconsolidated, normally consolidated, and compacted Louisiana clays. The field testing program consisted of cone penetration tests using both 2 and 15 sq cm electric cone penetrometers in conjunction with soil sampling, while laboratory tests included physical properties and strength characteristics of the investigated soils. Analyses of cone penetration tests were conducted to assess the repeatability and reliability, as well as confirming that the electric miniature friction cone (2 sq cm) output complies with the output of the 15 sq cm cone. The test data will provide the means to calibrate the miniature cone with respect to the commonly used cone penetrometers. It will be used to establish correlations between the miniature cone penetration test results and soil parameters determined in the laboratory and utilize them for roadway design and construction control of highway embankments.

Preparation of Large-Size Cohesive Specimens for Calibration Chamber Testing

This paper describes the design of an automated slurry consolidometer and calibration chamber system used to prepare largesize cohesive soil specimens for testing in-situ devices, model foundations, and ground anchors. A two-stage technique for the preparattion of homogeneous cohesive specimens subjected to a known stress history is described. Briefly summarized are the data acquisition/control system and the instrumentation details for monitoring the spatial pore pressure distributions in the specimen, the vertical and lateral stresses on the specimen, and specimen settlement during slurry consolidation and subsequent reconsolidation in the chamber. The specimens prepared were reproducible and of uniform quality as indicated by the settlement and pore pressure dissipation histories and by the water content results obtained from samples taken from chamber specimens. The homogeneity of the specimens is confirmed by the cone penetration test results.

Prediction of bearing capacity of friction piles in soft Louisiana soils by cone penetration test

A comparison of four different methods for predicting the axial compression capacity of single piles using cone penetration test (CPT) results is presented. Nineteen pile load tests and parallel CPT soundings conducted close to the piles were identified and documented from the Louisiana Department of Transportation and Development archives. Piles with different sizes and lengths were investigated. The four prediction methods selected were the Schmertmann method, the de Ruiter and Beringen method, the French Central Bridge and Pavement Laboratory (LCPC) method, and the Tumay and Fakhroo method. An evaluation scheme was performed using these methods to assess their capability to reliably predict the axial compression capacity of piles installed in soft Louisiana soils. The predicted pile capacities obtained by the different methods were compared with the measured pile capacities obtained from pile load tests. Analysis of the results showed that the Schmertmann, de Ruiter and Beringen, and Tumay and Fakhroo methods predicted the ultimate compression capacities of piles installed in soft Louisiana soils with a reasonable accuracy. The LCPC method underpredicted the measured capacities of these piles.

Determination of permeability of soils using the multiple piezo‐element penetrometer

The current method of determining the hydraulic properties of soils using piezocone penetration test (PCPT) requires the advancement of the piezocone penetrometer to the desired depth and holding (or arresting) it for the dissipation test. In order to obtain the hydraulic properties, one analyses the pore water dissipation test results by two-dimensional or three-dimensional radial drainage consolidation. This conventional procedure is methodologically simple and presents relatively reliable values of permeability compared to other field test methods. However, it is still challenging for field engineers and needs to be improved. The piezocone penetrometer intrudes into the ground with the speed of 2 cm/s. Thus, the test mechanism is a kind of strain-controlled condition with partial drainage. Therefore, the excess pore pressure during the piezocone penetration is a function of the permeability of the soil as well as the stress–strain parameters. Thus, with the proper coupled theory of mixtures which can take into account the coupling of solid and pore water flow, one can predict the permeability of the soil from the pore pressure response during PCPT. In this study, the coupled theory of mixtures of the soil grains and the pore water is used in order to predict the permeability of the soil from the excess pore pressure generated from the multiple piezo-element PCPT ‘on the fly’. An elasto-plastic, finite strain constitutive equation in an updated Lagrangian reference frame is used in this work. Using the proposed method, a reliable value of the permeability of soil is obtained conveniently without the use of the pore pressure dissipation tests. Copyright

CALIBRATION OF A MINIATURE CONE PENETROMETER FOR HIGHWAY APPLICATIONS

The electronic cone penetrometer is an important in situ investigation tool of choice for site characterization. Application of this proven concept of the cone penetration test (CPT) to highway design and construction control by miniaturization is described. A miniature cone penetrometer with a projected cone area of 2 cm2 has been developed and implemented in a continuous intrusion miniature cone penetration test system (CIMCPT). This device may be used for rapid, accurate, and economical characterization of sites and to determine engineering soil parameters needed in the design of pavements, embankments, and earth structures. The miniature cone penetration test (MCPT) gives finer details than the standard 10-cm2 cross-sectional area reference cone penetrometer. This makes the MCPT attractive for subgrade characterization, quality-control assessment, compaction control of embankments, and assessment of ground improvement effectiveness for transportation infrastructure. In situ calibration of the CIMCPT system was conducted at a highway embankment site in Baton Rouge, Louisiana. MCPT penetration profiles were compared with those obtained by using the standard cone penetrometer at the same site. The tip resistance of the MCPT was 10 percent higher than that of the reference CPT. The sleeve friction and friction ratio of the reference CPT were higher than that of the MCPT by 12 and 23 percent, respectively. Calibration was also performed to determine empirical cone factors required for estimating undrained shear strength from MCPT data.

Computerized Cone Penetration Test for Soil Classification: Development of MS-Windows Software

Computerized MS-Windows Visual Basic software of a cone penetration test (CPT) for soil classification was developed as part of an extensive effort to facilitate the implementation of CPT technology in many geotechnical engineering applications. Five CPT soil engineering classification systems were implemented as a handy, user-friendly, software tool for geotechnical engineers. In the probabilistic region estimation and fuzzy classification methods, a conformal transformation is first applied to determine the profile of soil classification index (U) with depth from cone tip resistance (qc) and friction ratio (Rf). A statistical correlation was established in the probabilistic region estimation method between the U index and the compositional soil type given by the Unified Soil Classification System. Conversely, the CPT fuzzy classification emphasizes the certainty of soil behavior. The Schmertmann and Douglas and Olsen methods provide soil classification charts based on cone tip resistance and friction ratio. However, Robertson et al. proposed a three-dimensional classification system that is presented in two charts: one chart uses corrected tip resistance (qt) and friction ratio (Rf); the other chart uses qt and pore pressure parameter (Bq) as input data. Five sites in Louisiana were selected for this study. For each site, CPT tests and the corresponding soil boring results were correlated. The soil classification results obtained using the five different CPT soil classification methods were compared.

Continuous Intrusion Miniature Cone Penetration Test System for Transportation Applications

The electronic cone penetrometer is an important investigation tool of choice for in situ site characterization. Application of this proven concept of the cone penetration test (CPT) to transportation applications is described. A miniature cone penetrometer with a projected cone area of 2 cm2 has been developed and implemented in a continuous intrusion miniature CPT system (CIMCPT). This device may be used for rapid, accurate, and economical characterization of sites as well as to determine engineering soil parameters needed in the design of pavements, embankments, and earth structures. The miniature CPT (MCPT) gives finer details than the standard 10-cm2 cross-sectional area reference cone penetrometer, which makes it attractive for subgrade characterization, quality control assessment, compaction control of embankments, and assessment of ground improvement effectiveness for transportation infrastructure. In situ calibration of the CIMCPT system was conducted at a highway embankment site in Baton Rouge, Louisiana. MCPT penetration profiles were compared with those obtained with the standard cone penetrometer at the same site. The tip resistance of the MCPT was 10 percent higher than that of the reference CPT. The sleeve friction and friction ratio of the reference CPT were higher than that of the MCPT by 12 and 23 percent, respectively. Calibration was also performed to determine empirical cone factors required for estimating undrained shear strength from MCPT data.

Low strain dynamic shear modulus of cemented sand from cone penetration test results

Low strain dynamic shear modulus property is generally used to subclassify soil strata, determine elastic settlements under geotechnical structures, and characterize the dynamic nature of soils. Several methods to interpret the dynamic shear modulus of sands from in situ friction cone test results have been developed. These methods used calibration chamber test data of clean sands. Therefore, these methods are not valid for interpreting the shear modulus of cemented sands. Introduced here is an interpretation method to estimate the shear modulus of cemented sand. Thirty-seven friction cone penetration tests (CPTs) were conducted on artificially cemented sand specimens of relative densities ranging from 45 percent to 85 percent and confining pressures ranging from 100 to 300 kPa in a laboratory stress-straincontrolled calibration chamber. Cementation levels of 1 and 2 percent were used in preparing cemented specimens. Resonant column tests were also conducted on the same sand with identical cementation lev...

Absorbed Energy and Compacted Cohesive Soil Performance

This technical note proposes a new concept of absorbed energy that is related to the soil structural formation for unsaturated cohesive soils. Results from limited preliminary laboratory tests indicate that such energy correlates reasonably well with unconfined compressive strength of soils, and it can be predicted by moisture content and dry unit weight of soils. The relationship between energy and engineering properties of soils can provide a basis to correlate different geotechnical engineering behaviors that have customarily been individually studied. Consequently, a new approach to interpret some traditional processes in geotechnical engineering, such as fill compaction and strength deterioration due to seasonal variation of moisture content, is suggested from the perspective of energy concept.