Evaluation of uplift interpretation criteria for drilled shafts in gravelly soils

2012 ◽  
Vol 49 (1) ◽  
pp. 70-77 ◽  
Author(s):  
Yit-Jin Chen ◽  
Tsu-Hung Chu
Keyword(s):  
Drilled Shafts ◽  
Load Test ◽  
Drilled Shaft ◽  
Specific Design ◽  
Interpretation Criteria ◽  
Interpretation Criterion ◽  
Gravelly Soils ◽  
Load Tests ◽  
Drilled Shaft Foundations ◽  
Shaft Failure

Representative interpretation criteria are examined in this paper to evaluate the capacity of drilled shaft foundations under axial uplift loading in gravelly soils. A large number of uplift shaft load tests for gravelly soils are used for analysis, and the interpretation criteria are applied to these load test data to establish a consistent uplift interpretation criterion. The statistical results show that the smaller the uplift displacement, the higher the coefficient of variation. In general, the displacements required to mobilize shaft failure load in gravelly soils are larger than those in non-gravelly soils. Based on these analyses, the relative merits and interrelationships of these criteria are established. Specific design recommendations for the evaluation of uplift drilled shaft capacity are given.

Evaluation of lateral interpretation criteria for rigid drilled shafts

2011 ◽  
Vol 48 (4) ◽  
pp. 634-643 ◽  
Author(s):  
Yit-Jin Chen ◽  
Song-Wei Lin ◽  
Fred H. Kulhawy
Keyword(s):  
Test Data ◽  
Failure Load ◽  
Limit State ◽  
Drilled Shafts ◽  
Load Test ◽  
Ultimate Limit State ◽  
Interpretation Criteria ◽  
Drilled Shaft Foundations ◽  
Shaft Failure ◽  
Ultimate Limit

Representative criteria are examined to evaluate the “interpreted failure load” or “capacity” of rigid drilled shaft foundations under lateral loading. Field lateral load test data are used for this analysis, consisting of both drained and undrained databases. It was found that a hyperbola describes the load–displacement data well and that the normalized undrained curve is stiffer, higher, and more sharply curving than the drained curve. The initial elastic region ends at approximately 1%B (where B is the shaft diameter),which represents serviceability limit state (SLS) conditions. The final region begins at about 4%–5%B, which represents ultimate limit state (ULS) conditions. Also, the QL method is most appropriate for interpreting the “failure load” because it is the only method that incorporates actual soil-shaft failure mechanisms as part of the interpretation, is the least variable, and has the lowest coefficient of variation (COV). Further detailed recommendations are given for assessing the load test data.

Evaluation of Tip Capacity Analysis Model for Drilled Shafts in Gravelly Soils

2013 ◽  
Vol 284-287 ◽  
pp. 1320-1324
Author(s):  
Yit Jin Chen ◽  
Maria Cecilia M. Marcos ◽  
T.H. Chu ◽  
H.W. Wu
Keyword(s):  
Bearing Capacity ◽  
Drilled Shafts ◽  
Load Test ◽  
Engineering Practice ◽  
Capacity Analysis ◽  
Drilled Shaft ◽  
Analysis Model ◽  
Overburden Pressure ◽  
Static Compression ◽  
Gravelly Soils

This paper examines an analysis model for predicting the tip capacity of drilled shaft foundations under gravelly soils. Forty one static compression load test data are utilized for this purpose. Comparison of predicted and measured results demonstrates that the prediction model greatly overestimates the tip capacity of drilled shafts. Further assessment on the model reveals a greater variation in three coefficients; the effective overburden pressure ( ), the overburden bearing capacity factor (Nq); and the bearing capacity modifier for soil rigidity (ζqr). These factors are modified from the back-analysis of the drilled shaft load test results. Varying effective shaft depths are considered for the back-calculation to explore their effects on capacity behavior. Based on the analyses, the recommended effective shaft depth for the evaluation of effective overburden pressure is limited to 15B (B=shaft diameter). The Nq and ζqr are enhanced while maintaining their basic relationship with the soil effective friction angle, in which the Nq increases and ζqr decreases as increases. Specific design recommendations for the tip bearing capacity analysis of drilled shafts in gravelly soils are given for engineering practice.

Load and Resistance Factor Design, Cost, and Risk: Designing a Drilled-Shaft Load Test Program in Florida Limestone

2003 ◽  
Vol 1849 (1) ◽  
pp. 98-106 ◽  
Author(s):  
Michael C. McVay ◽  
Ralph D. Ellis ◽  
Bjorn Birgisson ◽  
Gary R. Consolazio ◽  
Sastry Putcha ◽  
...  
Keyword(s):  
Laboratory Data ◽  
Resistance Factor ◽  
Load Test ◽  
Drilled Shaft ◽  
Load Testing ◽  
Load Tests ◽  
Factor Design ◽  
Drilled Shaft Foundations ◽  
Load And Resistance Factor ◽  
The Cost

Currently there are few if any guidelines on estimating the number of load tests in the design of drilled-shaft foundations in Florida limestone. For instance, for many sites there may be a similar number of field load tests but a significantly different number of design shafts. Moreover, little if any information exists on risk or reliability versus cost of drilled-shaft foundations or on the cost of field load testing. The collection of a large database of drilled-shaft tests (more than 25 with Osterberg and Statnamic devices), in situ laboratory data, drilled-shaft construction costs, and field load testing costs for Florida limestone is reported on. From the field load tests, the average unit skin friction for various sites was found, as well as the predicted values based on the Florida Department of Transportation recommended design approach. Next, using load and resistance factor design (LRFD), the resistance (ϕ) values were found for various reliabilities (risk or probability of failure). Once the factored design loads were known (from plans), drilled-shaft lengths were estimated on the basis of the computed LRFD ϕ-values for different reliabilities (i.e., risk). From the linear length of the designed shaft as well as the expected cost per meter, a plot of total foundation cost versus reliability (risk) was generated for each site. On the basis of the latter plot, acceptable risk, and the cost of field load testing (bid and itemized), the designer can identify the cost savings of load testing and the appropriate number of tests to be performed.

Comparison of Measured and Predicted Skin Friction Values for Axially Loaded Drilled Shaft Foundations in Gravelly Soils

2005 ◽  
Author(s):  
Abdalla M. Harraz ◽  
William N. Houston ◽  
Kenneth D. Walsh ◽  
Courtland R. Perry ◽  
Sandra L. Houston
Keyword(s):  
Skin Friction ◽  
Drilled Shaft ◽  
Gravelly Soils ◽  
Axially Loaded ◽  
Drilled Shaft Foundations

Reliability Evaluation of AASHTO Design Equations for Drilled Shafts

1997 ◽  
Vol 1582 (1) ◽  
pp. 60-67
Author(s):  
William M. Isenhower ◽  
James H. Long
Keyword(s):  
Data Base ◽  
Reliability Evaluation ◽  
Drilled Shafts ◽  
Drilled Shaft ◽  
Factors Affecting ◽  
First Order ◽  
Axial Capacity ◽  
Moment Methods ◽  
First Order Second Moment ◽  
Load Tests

A reliability evaluation of the AASHTO design equations for drilled shafts is described. The evaluation computed the variance of a data base containing load tests to failure on 30 straight-sided drilled shafts using first-order, second-moment methods applied to the AASHTO design equations. The computed variance was compared with the measured variance of the data base. The measured variance was found to exceed the computed variance for approximately 75 percent of the load tests. This is believed to result from important factors affecting the axial capacity of the drilled shaft not being included in the AASHTO design equations. It is speculated that the missing factors are related to common variations in construction practices for drilled shafts.

Load tests on drilled shaft foundations in moderately strong to strong limestone

2015 ◽  
Vol 9 (1) ◽  
pp. 2-10
Author(s):  
M. L. Race ◽  
R. A. Coffman
Keyword(s):  
Drilled Shaft ◽  
Load Tests ◽  
Drilled Shaft Foundations

scholarly journals Side Resistance of Drilled Shafts Socketed into Rocks for Serviceability and Ultimate Limit States

2020 ◽  
Vol 5 (3) ◽  
pp. 156-165 ◽  
Author(s):  
Yit-Jin Chen ◽  
Cheng-Chieh Hsiao ◽  
Anjerick Topacio
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Factor Versus ◽  
Drilled Shafts ◽  
Load Test ◽  
Limit States ◽  
Interpretation Criteria ◽  
Side Resistance ◽  
Ultimate Limit ◽  
Adhesion Factor

This study evaluates the analysis models of side resistance in rock sections by utilizing a wide variety of load test data. Available analytical models including the empirical adhesion factor versus the rock’s uniaxial compressive strength and its root are analyzed and compared statistically to determine the optimum relationships. The interpretation criteria for the L1 and L2 methods are used to analyze the load test results for serviceability and ultimate limit states, respectively. The analysis results show that the relationship model with the empirical adhesion factor versus the root of the rock’s uniaxial compressive strength exhibits better correlation than the one with the rock’s uniaxial compressive strength. Moreover, the general coordinate axes regression equation demonstrates better reliability than the semi-logarithmic and full logarithmic axes equations for both limit states. Based on these analyses, specific design recommendations for the side resistance of drilled shafts socketed into rocks are developed and provided with the appropriate statistics to verify their reliability.

Improvement of the Geotechnical Axial Design Methodology for Colorado's Drilled Shafts Socketed in Weak Rocks

2005 ◽  
Vol 1936 (1) ◽  
pp. 100-107 ◽  
Author(s):  
Naser M. Abu-Hejleh ◽  
Michael W. O'Neill ◽  
Dennis Hanneman ◽  
William J. Attwooll
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Design Methods ◽  
Drilled Shafts ◽  
Load Test ◽  
Empirical Methods ◽  
Weak Rocks ◽  
Rock Formations ◽  
Load Tests ◽  
Geotechnical Tests

Drilled shaft foundations embedded in weak rock formations support a large percentage of bridges in Colorado. Since the 1960s, empirical methods that entirely deviate from the AASHTO design methods have been used for the axial geotechnical design of these shafts. The margin of safety and expected shaft settlement are unknown in these empirical methods. Load tests on drilled shafts provide the most accurate design and research data for improvement of the design methods. Four Osterberg axial load tests were performed in Denver on drilled shafts embedded in soil-like claystone, very hard sandy claystone, and extremely hard clayey sandstone. An extensive program of simple geotechnical tests was performed at the load test sites, including standard penetration tests (SPT), unconfined compressive strength tests (UCT), and pressuremeter tests (PMT). Information on the construction and materials of the test shafts was documented, followed by thorough analysis of all test results. Conservative equations were suggested to predict the unconfined compressive strength and mass stiffness of weak rocks from SPT and PMT data. Colorado Department of Transportation (CDOT) and AASHTO–FHWA design methods for drilled shafts were thoroughly assessed. Design equations to predict the shaft ultimate unit base resistance ( qmax), side resistance ( fmax), and an approximate load–settlement curve as a function of the results of simple geotechnical tests were developed. The qualifications and limitations for using these design methods are presented (e.g., construction procedure, field conditions). Finally, a detailed strategic plan to identify the most appropriate design methods per LRFD for Colorado's drilled shafts was developed.

Innovative Method for Evaluating Drilled Shaft Foundations for St. Croix River Bridge

1998 ◽  
Vol 1633 (1) ◽  
pp. 84-93
Author(s):  
Michael W. O’Neill ◽  
Gary J. Person
Keyword(s):  
Drilled Shafts ◽  
Interface Roughness ◽  
Design Parameters ◽  
Lateral Stiffness ◽  
Test Results ◽  
Side Resistance ◽  
Major River ◽  
Load Tests ◽  
Drilled Shaft Foundations ◽  
A Site

To develop design parameters for axially loaded drilled shafts for the St. Croix River Bridge, a major river crossing at Oak Park Heights, Minnesota, load tests were conducted on half-scale sockets in the primary formation, the Franconia Sandstone, at a site on the west bank of the river. The test results were analyzed by using a procedure that considered dilatancy at the shaft-sandstone interface using the known normal, lateral stiffness of the rock, and several candidate interface roughness patterns. The normal stiffness was measured by splitting a short socket vertically with an Osterberg load cell, within the Franconia formation. The interface roughness patterns were varied until the load-deformation behavior of the axial socket test was matched. The production shafts will have larger diameters and will penetrate the formation to a shallower depth than the axial test socket. The lateral stiffness therefore was scaled to account for these effects, and the analytical method was used to determine values of side resistance that should be used for designing the production shafts.

scholarly journals A simplified numerical approach to the evaluation of residual shaft friction induced by concrete curing in drilled shafts on granular soils

2020 ◽  
Vol 13 (5) ◽  
Author(s):  
Augusto Bopsin Borges ◽  
Renato Vaz Linn ◽  
Fernando Schnaid ◽  
Samir Maghous
Keyword(s):  
Bearing Capacity ◽  
Plastic Material ◽  
Numerical Approach ◽  
Drilled Shafts ◽  
Load Test ◽  
Curing Process ◽  
Linear Elastic ◽  
Load Tests ◽  
Elastic Plastic Material ◽  
Shaft Friction

ABSTRACT: Conventional interpretation procedures of load tests on instrumented piles rely upon measurements of strains that assume as zero for strains measured at the instant immediately before starting the test as reference configuration. However, some experimental evidence shows that concrete in drilled shafts undergoes strains induced by the curing process comparable in magnitude to the strains measured during the load tests. It is therefore expected that mobilization of shaft friction takes place before the load test. Several authors have performed experimental and numerical analyses aiming to quantify the influence of those pre-load test concrete volumetric strains on the measured bearing capacity using different approaches. The present work aimed to establish a reference framework for the existing and future works on this topic. In order to assess the influence of concrete strains induced by curing process on the shaft friction before the start of the load tests in drilled shafts, several finite element numerical simulations are performed, considering the thermal, autogenous and drying strains. The analyses consider concrete as an isotropic linear-elastic material and the soil as an elastic-plastic material using the Mohr-Coulomb constitutive model natively implemented in the software ABAQUS. The results are interpreted focusing on the relevancy on the bearing capacity and load distribution along drilled shafts considering or not the strains induced by concrete curing.

Sign in / Sign up

Export Citation Format

Share Document