Note: reference is made by several documents in this page to programs developed by the U.S. Army Corps of Engineers. These cannot be downloaded from this site; however, they are available here.
Barry R. Christopher, Ph.D., P.E., Charles Schwartz, Ph.D., P.E. and Richard Boudreau, P.E.
This is the Reference Manual and Participants Workbook for the FHWA NHI’s Course No. 132040 – Geotechnical Aspects of Pavements. The manual covers the latest methods and procedures to address the geotechnical issues in pavement design, construction and performance for new construction, reconstruction, and rehabilitation projects. The manual includes details on geotechnical exploration and characterization of in place and constructed subgrades as well as unbound base/sub-base materials. The influence and sensitivity of geotechnical inputs are reviewed with respect to the requirements in past and current AASHTO design guidelines and the mechanistic-empirical design approach developed under NCHRP 1-37A, including the three levels of design input quality. Design details for drainage features and base/sub-base material requirements are covered along with the evaluation and selection of appropriate re-mediation measures for unsuitable subgrades. Geotechnical aspects in relation to construction, construction specifications, monitoring, and performance measurements are discussed.
Roy E. Olson
The term consolidation is used to describe a process whereby fluid is forced out of the void spaces in a soil to allow the soil to decrease in volume. The term is also used in a more general way to include swelling as well as compression. The term one-dimensional consolidation refers to a consolidation process in which both fluid flow and deformation occur along a single axis. In field problems, this axis is vertical. Because soils are not infinitely permeable, time is needed for escape of pore fluid; thus, consolidation is a time-dependent process.
Nearly all practical analyses are performed using what we will term the “classical method”. When this method is applied, the total compression is first calculated using a suitable one-dimensional stress-strain curve for the soil, and then the time rate of compression is calculated using Terzaghi’s theory. This theory, and a number of simple extensions of it, is reviewed in this report.
The report goes on to describe a program FD31 which implements this theory and solves the equations using finite-difference methods.
Engineer Manual EM 1110-1-1905
30 October 1992
This manual presents guidelines for calculation of the bearing capacity of soil under shallow and deep foundations supporting various types of structures and embankments. This information is generally applicable to foundation investigation and design conducted by Corps of Engineer agencies.
Principles for evaluating bearing capacity presented in this manual are applicable to numerous types of structures such as buildings and houses, towers and storage tanks, fills, embankments and dams. These guidelines may be helpful in determining soils that will lead to bearing capacity failure or excessive settlements for given foundations and loads.
Bearing capacity is the ability of soil to safely carry the pressure placed on the soil from any engineered structure without undergoing a shear failure with accompanying large settlements. Applying a bearing pressure which is safe with respect to failure does not ensure that settlement of the foundation will be within acceptable limits. Therefore, settlement analysis should generally be performed since most structures are sensitive to excessive settlement.
Robert L. Parsons, Ph.D., P.E., Derek H. Foster, and Stephen A. Cross, Ph.D., P.E., University of Kansas
Unanticipated settlement of compacted earth fill has been a continuing problem for embankments managed by KDOT. This report contains the results of an investigation of current compaction specifications, with particular emphasis on the Type B compaction specification that relies on visual verification of compaction by sheepsfoot roller walkout.
This investigation consisted of two parts: a field investigation of existing embankments with varying levels of performance and a telephone survey of other DOT’s to determine the status of compaction specifications. Eight embankments constructed between 1994 and 2000 were selected for undisturbed field sampling. Two borings were drilled in each embankment and Shelby tube samples were collected for testing at regular intervals. Samples of the cuttings were also collected for testing.
A telephone survey of all state DOT’s was conducted to assess current practice with regard to specifications for compaction of fills. Thirty-two states, including Kansas, responded to the survey. It was determined that a number of compaction and moisture specifications are currently in use, however there were common themes among the specifications.
Based on the results of this research it is recommended that KDOT specify a relative compaction standard and a moisture content range based on the optimum moisture content for compaction of embankments. It is recommended that the compaction standard be at least 95 percent of maximum density as determined by KT-12 (AASHTO T 99), or an equivalent relative compaction based on modified effort (AASHTO T 180). It is also recommended that the specified moisture range be centred about optimum or a point slightly above optimum, as the average moisture content of the existing embankments is slightly above optimum.
A Computer Program to Calculate the Magnitude of Settlement of a Multi-Layered Soil System (MAGSET-II)
Vincent Partyka, David M. Jubenville and Robert L. Schiffman
University of Colorado
GESA Report Number D-76-9
This program utilizes Terzaghi’s one dimensional consolidation theory, simplified to apply to a two-dimensional condition, for estimating settlements in cohesive soils. The program applies a vertical stress influence factor, due to the loading, to the effective stress history. Some very complex loadings can be accounted for, such as: unloading due to excavation,temporary and/or permanent changes in water table, live loads applied to the structure, and loadings due to adjacent structures or construction. There are two built in methods to account for strain influence or allows the user to enter a set of influence factors. Also, for granular soils, three methods are available for estimating settlements. These are due to Meyerhof, d’Appolonia and Schmertmann.
Reed L Mosher and N. Radhakrishnan
U.S. Army Corps of Engineers
Instruction Report K-80-5
This report documents and gives example runs of three computer programs for performing settlement analysis of foundations and embankments. The programs are I0016, MAGSETII and FD31.
EMBANK: A Microcomputer Program to Determine One-Dimensional Compression Settlement Due to Embankment Loads
Dr. Alfredo Urzua
The objective of this report is to introduce a microcomputer program for computing one-dimensional compression vertical settlement due to embankment loads. The program follows the equations presented by Lambe & Whitman (1969), Ladd (1973), and Poulos & Davis (1974). For the case of a strip symmetrical vertical embankment loading, the program superimposes two vertical embankment loads. For the increment of vertical stresses at end of fill, the program internally superimpose a series of 10 rectangular loads to create the end-of-fill condition. The report presents the equations and analytical procedures utilized by the program and examples of the capabilities of the user-friendly data entry form. The computer program is coded in the Turbo Pascal 4.0 language and takes full advantage of the stand-alone, (single-user) characteristics of the IBM-PC through the use of “friendly” input menus and data-checking routines.
The code implements copyrighted portions of the microcomputer programs SAF-I and STRESS developed by PROTOTYPE Engineering, Inc., Winchester, MA, and uses the screen editor Turbo Magic From Sophisticated Software.
Jeb S. Tingle
U.S. Army Engineer Research and Development Centre
Recent military operations in the Balkans and Southwest Asia have demonstrated the need to develop solutions for rapidly constructing temporary roads in the theater of operations. Loose sands and very soft soils have historically provided obstacles to efficient military manoeuvre. The U.S. Army Engineer Research and Development Centre (ERDC) has conducted a series of research projects over the last seven years to evaluate commercial-off-the-shelf technology for constructing temporary roads. These projects included two problematic subgrade types, loose sand and soft soil. These projects have evaluated a variety of products including geosynthetics, lightweight fill, and matting. This paper describes various systems for rapidly constructing temporary roads over loose sand or soft subgrade soils. This paper summarizes results from numerous full-scale test sections designed to evaluate the performance of expedient road systems under realistic traffic conditions. Each system’s performance is summarized, and specific recommendations are provided for material use. A comparative analysis is included to present tradeoffs in performance, cost, weight, volume, and installation rate. This paper represents the state-of-the-art in temporary road construction for military applications.
Steve L. Webster, Jeb S. Tingle
U.S. Army Corps of Engineers
Waterways Experiment Station
Technical Report GL-98-10
The field experiment evaluating the lightweight mats presented in this report was conducted in the Hangar 4 Test Facility during the period June through September 1997 by the U.S. Army Engineer Waterways Experiment Station Vicksburg, MS. Traffic was applied to the lightweight mats using a 5-ton military truck loaded to a gross vehicle weight of 41,600 lb. The field traffic experiment was performed to evaluate the potential of each mat as an expedient road surfacing when placed over sand subgrades and trafficked with wheeled military vehicles. A summary of each material investigated and its performance is presented in this report An analysis of the field data was conducted to determine the potential of these expedient surfacings under actual loading conditions.
Recent FHWA national surveys revealed that State Departments of Transportation (DOTs) have safely and economically constructed highway bridges supported on spread footings bearing on competent and improved natural soils as well as engineered granular and MSE fills, and that many State DOTs may be missing an opportunity to save time and costs by not doing so more often. The goal of this report is to promote the consideration and use of spread footings on soils when appropriate to support highway bridges. Initially, perceived obstacles in using spread footings are identified. Then, the report presents recommendations to address these obstacles and a guidance to help State DOTs implementing these recommendations that are centred around: 1) deployment of AASHTO and FHWA technical resources; 2) highlighting practices of State DOTs that
actively use spread footings, especially for selection of spread footings; 3) a performance review of bridges constructed with spread footings bearing on soils; and 4) LRFD implementation for spread footings. State DOTs’ concerns with using spread footings on engineered and MSE fills and with integral abutments are addressed. Consideration of load tests on spread footings, instrumentation programs for bridges with spread footings, and
deployment of adequate subsurface investigation and construction programs are recommended. The main concern of State DOTs that do not consider spread footings is excessive settlement of bridges. This report advances a rational procedure for settlement analysis of bridges supported on spread footings bearing on soils. This procedure and the results of the national surveys demonstrate that bridges with spread footings on soil can
perform very well with respect to settlement. Development of LRFD design bearing resistances for footings on various types of soils is discussed. Based on the previous recommendations, the report finally provides a technical resource for State DOTs to develop LRFD guidance that would allow selection of spread footings in design when appropriate, and development of accurate and economical design methods for spread footings.
Spread footings are most often less expensive than deep foundations. In an effort to improve the reliability of spread footings, this research project was undertaken. The results consist of
- A user friendly microcomputer data base of spread footings, case histories and load tests.
- The performance of five large scale square footings in sand.
- An evaluation of the current accuracy of settlement and bearing capacity prediction methods.
- Observations on the scale effect, the zone of influence, the creep settlement, and soil heterogeneity.
- A new and simple method to predict the complete load settlement curve for a footing as well as several correlations.
- Evaluation of the WAR test, a dynamic test for spread footings.
Albert F. Di Millio
A visual inspection was made of the structural condition of 148 highway bridges supported by spread footings on compacted fill throughout the State of Washington. The approach pavements and other bridge appurtenances were also inspected for damage or distress that could be attributed to the use of spread footings on compacted fill. This review, in conjunction with detailed investigations of the foundation movement of 28 selected bridges, was used to evaluate the performance of spread footings on compacted fills. It was concluded that spread footings can provide a satisfactory alternative to piles especially when high embankments of good quality borrow materials are constructed over satisfactory foundation soils. None of the bridges investigated displayed any safety problems serious functional distress. All bridges were in good condition and many were found t o be in very good condition. In addition to the performance evaluation, cost effectiveness analyses and tolerable movement correlation studies were made to further substantiate the feasibility of using spread footings in lieu of expensive deep foundation systems. Cost analyses showed spread footings were 50-65 percent cheaper than the alternate choice of pile foundations. Foundation movement studies showed that these bridges have easily tolerated differential settlements of 1-3 inches (25-75 mm) without serious distress.
Naresh C. Samtani, PE, PhD, Edward A Nowatzki, PE, PhD and Dennis R. Mertz, PE, PhD
Revised December 2017
The FHWA believes that spread footings on soils are underutilized because designers encounter one or more of the following obstacles: (a) limited knowledge of AASHTO/FHWA technical references that pertain to spread footings on soils to support bridges; (b) limited knowledge of adequate performance data for spread footings; (c) unrealistic tolerable settlement criteria; (d) overestimation of loads used to calculate settlement; and (e) the use of conservative settlement prediction methods. These obstacles have resulted in institutional biases and overly conservative and excessively costly institutional processes that lead to the unnecessary use of costlier deep foundation systems. The primary goal of this report is to promote the use of spread footings bearing on competent natural soils, improved soils, and engineered fill materials as a routine alternative to deep foundations for support of bridges by addressing the factors identified above. Documented performance data is used to make this case.
The report also presents powerful concepts such as construction-point analysis and angular distortions to demonstrate the efficacy of using spread footings. Implementation of these concepts requires only that conventional computations be taken one step further without any requirement for advanced computational skills. The report presents sources of information that agencies and designers can use as references in their project applications. The report contains comprehensive appendices that treat in detail many of the topics discussed in the report. For example, one such appendix provides an introduction to Load and Resistance Factor Design (LRFD) that permits a rational approach to the consideration of spread footings on soils as a feasible alternative to deep foundations.
Bonus: We also have the program VDISPL, a Windows implementation of the vertical displacement program shown in the manual.
U.S. Army Corps of Engineers
30 September 1990
This manual presents guidelines for calculation of vertical displacements and settlement of soil under shallow foundations (mats and footings) supporting various types of structures and under embankments. Soil is a nonhomogeneous porous material consisting of three phases: solids, fluid (normally water), and air. Soil deformation may occur by change in stress, water content, soil mass, or temperature. Vertical displacements and settlement caused by change in stress and water content are described in this manual.
Virginia R. Knowles
US Army Corps of Engineers
Technical Report ITL-91-1
The CSANDSET computer program calculates the settlement of shallow footings on sand from 15 different methods. This report provides a user’s guide for this program and a theoretical section discussing aspects of sand settlement computations. Factors presented include the SPT blow count and its correction, groundwater and embedment corrections, and elastic and empirical types of settlement methods. Each of the 15 settlement procedures is presented with a brief background summary and all related equations. Examples of hand calculated settlement by all the methods are shown in Appendix A and used for program verification.
This document is FHWA’s primary reference of recommended design and procurement procedures for shallow foundations. The Circular presents state-of-the-practice guidance on the design of shallow foundation support of highway bridges. The information is intended to be practical in nature, and to especially encourage the cost-effective use of shallow foundations bearing on structural fills. To the greatest extent possible, the document coalesces the research, development and application of shallow foundation support for transportation structures over the last several decades.
Detailed design examples are provided for shallow foundations in several bridge support applications according to both Service Load Design (Appendix B) and Load and Resistance Factor Design (Appendix C) methodologies. Guidance is also provided for shallow foundation applications for minor structures and buildings associated with transportation projects.
W.H. Perloff, G.Y. Baladi and M.E. Harr
Joint Highway Research Project #14
The distribution of stresses within and under long elastic embankments continuous with the underlying material is presented. The magnitude and distribution of stress in the foundation material in the vicinity of the embankment is significantly different from that predicted by the usual assumption of stress proportional to embankment height applied normal to the foundation. Influence charts for a variety of embankment shapes are given.
Reed L. Mosher and Michael E. Pace
U.S. Army Corps of Engineers
Instruction Report K-82-7
This user’s guide documents a computer program called CBEAR that can be used for analysis of the bearing capacity of shallow strip, rectangular, square or circular foundations on one- or two-layer soil systems. The bearing capacity can be computed considering the effects of:
- Embedment of the foundation;
- Inclination of the foundation base;
- Inclined loads;
- A sloping soil surface
- Eccentric loads in three dimensions;
- Submerged soil;
It contains a detailed description of the analysis procedures employed in the program, including extensive discussion of Vesic’s and Meyerhof’s methods for determining the bearing capacity of shallow foundations. It also included worked examples of problems the program was designed to solve.
User’s Guide: Computer Program for Determining Induced Stresses and Consolidation Settlements (CSETT)
Alexis E. Templeton
U.S. Army Corps of Engineers
Instruction Report K-84-7
This report documents CSETT, a computer program designed to compute consolidation settlement of compressible soils resulting from simple and complex loading conditions. The program provides ultimate settlement and time-rate of consolidation for the total soil mass specified and for the individual compressible soil layers within the soil mass. Additionally, it provides the in situ overburden pressures and the induced stresses.
Induced stresses are determined by integration of either Boussinesq or Westergaard point load equations over general shaped loaded regions. Loaded regions may consist of simple or complex geometric shapes for singular or multiple loads entered as two-dimensional pressure profiles, two-dimensional soil embankment profiles, or three-dimensional polygons.
Settlement computations are based on strain versus effective stress or void ratio versus effective stress relationships. The rate of consolidation is determined using Terzaghi’s one-dimensional consolidation theory. The program provides for analyses of multiple soil layers and a variety of drainage conditions.
Data can be input interactively or by entering a predefined data file. Data files are created using command words that identify corresponding data items. Interactive input can be accomplished by a question-and-answer session or by using command words. Output consists of a total settlement, settlement of individual layers, and degree of consolidation for each time and location specified by the user.
U.S. Army Corps of Engineers
The program computes the vertical stresses induced in a semi-infinite mass by a group of uniformly loaded rectangular areas. Under one program option the vertical foundation stresses caused by an embankment loading are approximated by assuming that the embankment is composed of a series of uniformly loaded rectangular areas lying on the top of one another. The program can handle up to 100 footing loads. The vertical stresses may be calculated by either Boussinesq or Westergaard solutions for vertical stresses.