Development of p-y Criteria for Drilled Shafts in Loess

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General Information
Solicitation Number: 746
Status: Solicitation withdrawn
Date Posted: Dec 27, 2002
Last Updated: Nov 17, 2003
Solicitation Expires: Dec 27, 2003
Partners: KS
Lead Organization: Kansas Department of Transportation
Financial Summary
Commitment Start Year: 2003
Commitment End Year: 2005
100% SP&R Approval: Pending Approval
Commitments Required: $450,000.00
Commitments Received: $90,000.00
Contact Information
Lead Study Contact(s): Rodney Montney
rodney@ksdot.org
Organization Year Commitments Technical Contact Name Funding Contact Name Contact Number Email Address
Kansas Department of Transportation 2004 $45,000.00 James Brennan Rodney Montney 785-291-3844 rodney@ksdot.org
Kansas Department of Transportation 2005 $45,000.00 James Brennan Rodney Montney 785-291-3844 rodney@ksdot.org

Background

Highway bridge foundations are designed for lateral loads resulting from wind, traffic, earth pressures, and occasionally extreme event loadings (at waterways or in seismic areas). In many cases the lateral loading controls the diameter and reinforcing required for a drilled shaft foundation. The most common method in use today utilizes the p-y approach in which the soil resistance is modeled as a series of nonlinear elastic springs acting against a pile or drilled shaft foundation. This approach has a long history of use for foundation design and is implemented effectively via computer codes such as LPILE and FLPIER.

The key feature of this approach is the development of nonlinear p-y curves (p= soil resistance, y = displacement) for modeling the soil behavior. Empirical correlations of p-y response to soil strength and stiffness parameters have been developed for a variety of soil types from observation of the results of instrumented field load tests. The use of empirical correlation with field tests is both a blessing and a curse: a blessing because the results are very reliable for those soils for which correlations have been developed thanks to the basis in full scale field tests; a curse because there exists great uncertainty when dealing with soil or rock formations in which there are no correlation full scale instrumented field tests.

Loess is a type of soil for which there has not been a thorough and systematic development of a p-y criterion for design of laterally loaded deep foundations. Loess is an aeolian (wind-blown) deposit of predominantly silt sized particles and is often cemented to various degrees. This soil is widespread across the Midwest, especially Kansas, Nebraska, Missouri, Iowa, and in many areas of the lower Mississippi River valley (Mississippi). There is a need for research to develop rational p-y correlations for loess soil so that highway bridge foundations can be designed with reliability and cost effectiveness in these soils.

Objectives

The purpose of the proposed research is to develop a rational and reliable criterion for p-y curves in loess soil for use in design of drilled shaft foundations for highway bridges. Consistent with the p-y approach for design, this criterion should be based upon carefully conducted full scale field loading tests, and correlated with conventional laboratory and/or in-situ tests which are widely available and commonly conducted as part of a bridge foundation investigation.

Scope of Work

The following tasks are proposed to accomplish this objective:

1. Review available research information regarding the behavior of loess for laterally loaded deep foundations, the availability and effectiveness of various in-situ and laboratory strength tests for characterizing loess, and the applicability of this information to the problem of laterally loaded drilled shaft foundations in loess.

2. Develop plans for field lateral loading tests of drilled shafts at four locations, including site selection, site characterization (borings and tests), and development of specific plans for load testing at each site. Tentative plans are as follows:

3. A site in the Kansas City area will serve as the focus for a major testing program including a range of variables such as cyclic loading, rapid loading, and diameters of three and four feet.

4. Three additional sites will be selected to provide simple static lateral load tests for a range of differing soil conditions in the general geologic setting characterized as loess. It is expected that one site in northern Kansas would be utilized, one site in western Kansas, and one site yet to be determined. The fourth site is intended to represent loess in a differing environment from the other three sites, such as in Missouri, Nebraska, or Mississippi (and depending upon project participants and funding levels.)

5. Conduct the field testing program at each of the test sites. Tests are expected to consist of static lateral loading tests at each site, tentatively planned for a pair of 3-foot diameter by 25-foot deep shafts. These would be heavily reinforced and instrumented to provide information on the subsurface response of the test shaft and soil resistance. At the Kansas City site additional tests are planned for larger (4-foot) diameter shafts, for shafts subjected to repetitive cyclic loading, and for shafts subjected to rapid lateral loading using the Statnamic device. All of the test sites will include soil borings with lab classification and triaxial strength tests and in-situ tests such as pressuremeter and borehole shear. Other in-situ tests which may be promising in developing reliable correlations with p-y curves will be evaluated and considered for inclusion in the study.

6. Analyze the field load test to develop a criterion for p-y curves which can reliably correlate the observed soil resistance with the site characterization across the range of conditions encountered in the four sites used for this research. The p-y criterion developed as part of this research will be implemented into a new release of LPILE as an available subroutine for computation of p-y curves in loess. This development is an important feature of the research and will allow immediate implementation of the results of the research into practice.

7. Produce a final report documenting all of the research including the testing and results, along with a detailed presentation of the p-y criterion produced as a result of the research. The report will provide documentation so that the research can be readily implemented by other researchers and in other software packages which may be used for design. It is also anticipated that a final presentation will be made to project sponsors.

Comments

This solicitation was also made on the national RAC listserv on 25 Oct 2002. A $90,000 commitment is requested from each partner.

Documents Attached
Title File/Link Type Privacy Download
Development of p-y Criteria for Drilled Shafts in Loess 746.pdf Solicitation Public

Development of p-y Criteria for Drilled Shafts in Loess

General Information
Solicitation Number: 746
Status: Solicitation withdrawn
Date Posted: Dec 27, 2002
Last Updated: Nov 17, 2003
Solicitation Expires: Dec 27, 2003
Partners: KS
Lead Organization: Kansas Department of Transportation
Financial Summary
Commitment Start Year: 2003
Commitment End Year: 2005
100% SP&R Approval: Pending Approval
Commitments Required: $450,000.00
Commitments Received: $90,000.00
Contact Information
Lead Study Contact(s): Rodney Montney
rodney@ksdot.org
Commitments by Organizations
Agency Year Commitments Technical Contact Name Funding Contact Name Contact Number Email Address
Kansas Department of Transportation 2004 $45,000.00 James Brennan Rodney Montney 785-291-3844 rodney@ksdot.org
Kansas Department of Transportation 2005 $45,000.00 James Brennan Rodney Montney 785-291-3844 rodney@ksdot.org

Background

Highway bridge foundations are designed for lateral loads resulting from wind, traffic, earth pressures, and occasionally extreme event loadings (at waterways or in seismic areas). In many cases the lateral loading controls the diameter and reinforcing required for a drilled shaft foundation. The most common method in use today utilizes the p-y approach in which the soil resistance is modeled as a series of nonlinear elastic springs acting against a pile or drilled shaft foundation. This approach has a long history of use for foundation design and is implemented effectively via computer codes such as LPILE and FLPIER.

The key feature of this approach is the development of nonlinear p-y curves (p= soil resistance, y = displacement) for modeling the soil behavior. Empirical correlations of p-y response to soil strength and stiffness parameters have been developed for a variety of soil types from observation of the results of instrumented field load tests. The use of empirical correlation with field tests is both a blessing and a curse: a blessing because the results are very reliable for those soils for which correlations have been developed thanks to the basis in full scale field tests; a curse because there exists great uncertainty when dealing with soil or rock formations in which there are no correlation full scale instrumented field tests.

Loess is a type of soil for which there has not been a thorough and systematic development of a p-y criterion for design of laterally loaded deep foundations. Loess is an aeolian (wind-blown) deposit of predominantly silt sized particles and is often cemented to various degrees. This soil is widespread across the Midwest, especially Kansas, Nebraska, Missouri, Iowa, and in many areas of the lower Mississippi River valley (Mississippi). There is a need for research to develop rational p-y correlations for loess soil so that highway bridge foundations can be designed with reliability and cost effectiveness in these soils.

Objectives

The purpose of the proposed research is to develop a rational and reliable criterion for p-y curves in loess soil for use in design of drilled shaft foundations for highway bridges. Consistent with the p-y approach for design, this criterion should be based upon carefully conducted full scale field loading tests, and correlated with conventional laboratory and/or in-situ tests which are widely available and commonly conducted as part of a bridge foundation investigation.

Scope of Work

The following tasks are proposed to accomplish this objective:

1. Review available research information regarding the behavior of loess for laterally loaded deep foundations, the availability and effectiveness of various in-situ and laboratory strength tests for characterizing loess, and the applicability of this information to the problem of laterally loaded drilled shaft foundations in loess.

2. Develop plans for field lateral loading tests of drilled shafts at four locations, including site selection, site characterization (borings and tests), and development of specific plans for load testing at each site. Tentative plans are as follows:

3. A site in the Kansas City area will serve as the focus for a major testing program including a range of variables such as cyclic loading, rapid loading, and diameters of three and four feet.

4. Three additional sites will be selected to provide simple static lateral load tests for a range of differing soil conditions in the general geologic setting characterized as loess. It is expected that one site in northern Kansas would be utilized, one site in western Kansas, and one site yet to be determined. The fourth site is intended to represent loess in a differing environment from the other three sites, such as in Missouri, Nebraska, or Mississippi (and depending upon project participants and funding levels.)

5. Conduct the field testing program at each of the test sites. Tests are expected to consist of static lateral loading tests at each site, tentatively planned for a pair of 3-foot diameter by 25-foot deep shafts. These would be heavily reinforced and instrumented to provide information on the subsurface response of the test shaft and soil resistance. At the Kansas City site additional tests are planned for larger (4-foot) diameter shafts, for shafts subjected to repetitive cyclic loading, and for shafts subjected to rapid lateral loading using the Statnamic device. All of the test sites will include soil borings with lab classification and triaxial strength tests and in-situ tests such as pressuremeter and borehole shear. Other in-situ tests which may be promising in developing reliable correlations with p-y curves will be evaluated and considered for inclusion in the study.

6. Analyze the field load test to develop a criterion for p-y curves which can reliably correlate the observed soil resistance with the site characterization across the range of conditions encountered in the four sites used for this research. The p-y criterion developed as part of this research will be implemented into a new release of LPILE as an available subroutine for computation of p-y curves in loess. This development is an important feature of the research and will allow immediate implementation of the results of the research into practice.

7. Produce a final report documenting all of the research including the testing and results, along with a detailed presentation of the p-y criterion produced as a result of the research. The report will provide documentation so that the research can be readily implemented by other researchers and in other software packages which may be used for design. It is also anticipated that a final presentation will be made to project sponsors.

Comments

This solicitation was also made on the national RAC listserv on 25 Oct 2002. A $90,000 commitment is requested from each partner.

Title Type Private
Development of p-y Criteria for Drilled Shafts in Loess Solicitation N

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