Soil Mechanics

This document is considered by many to be the best single reference on soil mechanics, even though it is now more than a quarter century old.

We offer two versions of this document, take a careful look before downloading:

• UFC 3-220-10N, technically the currently issued document on the subject
• NAVFAC DM 7.01, 1 September 1986. The current document has no different information than DM 7.01, and the version presented here is far superior in graphics and text quality than UFC 3-220-10N

Many thanks to J. Ledlie Klosky for furnishing the improved version of DM 7.01.

Checklist and Guidelines for Review of Geotechnical Reports and Preliminary Plans and Specifications

FHWA ED-88-053
August 1988
Revised February 2003

A set of review checklists and technical guidelines has been developed to aid engineers in their review of projects containing major and unusual geotechnical features. These features may involve any earthwork or foundation related activities such as construction of cuts, fills, or retaining structures, which due to their size, scope, complexity or cost, deserve special attention. The review checklists and technical guidelines are provided to assist generalist highway engineers in:

• Reviewing both geotechnical reports and plan, specification, and estimate (PS&E) packages;
• Recognizing cost-saving opportunities
• Identifying deficiencies or potential claim problems due to inadequate geotechnical investigation, analysis or design;
• Recognizing when to request additional technical assistance from a geotechnical specialist.

At first glance, the enclosed review checklists will seem to be inordinately lengthy, however, this should not cause great concern. First, approximately 50 percent of the review checklists deal with structural foundation topics, normally the primary responsibility of a bridge engineer; the remaining 50 percent deal with roadway design topics. Second, the general portion of the PS&E checklist is only one page in length. The remaining portions of the PS&E checklist apply to specific geotechnical features – such as pile foundations, embankments, landslide corrections, etc., and would only be completed when those specific features exist on the project. Third, the largest portion of the checklists deals with the review of geotechnical reports, with a separate checklist for each of eight geotechnical features. The checklist for each geotechnical feature is only one to two pages in length. Therefore, on most projects, reviewers will find that only a small portion of the total enclosed checklist needs to be completed.

Critical State Soil Mechanics

Andrew Schofield and Peter Wroth
Cambridge University, England

This book is about the mechanical properties of saturated remoulded soil. It is written at the level of understanding of a final-year undergraduate student of civil engineering; it should also be of direct interest to post-graduate students and to practising civil engineers who are concerned with testing soil specimens or designing works that involve soil.

The authors' purpose is to focus attention on the critical state concept and demonstrate what they believe to be its importance in a proper understanding of the mechanical behaviour of soils. They have tried to achieve this by means of various simple mechanical models that represent (with varying degrees of accuracy) the laboratory behaviour of remoulded soils. They have not written a standard text on soil mechanics, and, as a consequence, they have purposely not considered partly saturated, structured, anisotropic, sensitive, or stabilized soil. They have not discussed dynamic, seismic, or damping properties of soils; they have deliberately omitted such topics as the prediction of settlement based on Boussinesq’s functions for elastic stress distributions as they are not directly relevant to the authors' purpose.

Durability/Corrosion of Soil Reinforcement Structures

Victor Elias
FHWA-RD-89-186
December 1990

This report is intended to provide criteria in evaluating potential corrosion losses when using coated or uncoated steel reinforcements, and in determining aging and construction damage losses when using geosynthetic reinforcements. To monitor in-situ corrosion rates of bare or galvanized steel reinforcements, remote electrochemical measurement equipment has been developed, evaluated and demonstrated on 7 field sites. The prototype equipment has been delivered to FHWA for further use.

Dynamic Compaction

Robert G. Lukas
Geotechnical Engineering Circular #1
FHWA-SA-95-037
March 1995

This manual provides state-of-the-practice methods and techniques to assist the highway engineer in the planning, design, and construction monitoring of dynamic compaction to improve the load supporting capacity of weak foundation soils. Guidelines are presented for:

• completing a preliminary evaluation to determine if dynamic compaction is appropriate for the site and subsurface conditions
• detailed design for site improvement
• preparation of a specification
• construction monitoring

Two case histories of actual projects are presented to demonstrate the use of the guidelines.

Engineering Use of Geotextiles

UFC 3-220-08FA
16 January 2004

Supercedes:
TM 5-818-8, 20 July 1995 (still available)

This manual covers physical properties, functions, design methods, design details and construction procedures for geotextiles as used in pavements, railroad beds, retaining wall earth embankment, rip-rap, concrete revetment, and drain construction. Geotextile functions described include pavements, filtration and drainage, reinforced embankments, railroads, erosion and sediment control, and earth retaining walls. This manual does not cover the use of other geosynthetics such as geogrids, geonets, geomembranes, plastic strip drains, composite products and products made from natural cellulose fibers.

Evaluation of FEM Engineering Parameters from Insitu Tests

F.C. Townsend, J. Brian Anderson, and Landy Rahelison
Florida Department of Transportation RPWO-14
December 2001

The purpose of this study was to take a critical look at insitu test methods (SPT, CPT, DMT, and PMT) as a means for developing finite element constitutive model input parameters. The first part of the research examined insitu test derived parameters with laboratory triaxial tests at three sites: Saunder’s Creek, Archer Landfill, and SW Recreation Center. The triaxial tests on these sands were used to develop baseline input parameters. These parameters were verified by simulating the triaxial tests using two finite element codes. From these comparisons, the following conclusions were drawn:

1. FEM simulations of triaxial test stress-strain curves produced excellent results.
2. The hardening models (PLAXIS – Hardening Soil and PlasFEM – Sandler Dimaggio) simulated the non-linear behavior better than the Mohr-Coulomb or Drucker-Prager models.
3. In general, E50 triaxial test modulus values agreed with those estimated from DMT and PMT unloading tests, and
4. FEM simulations of field PMT curves using triaxial test based parameters were unsuccessful. It was necessary to increase the triaxial E₅₀ values by Ω = 1.3078e^0.0164pl R² = 0.8515, where Ω is the triaxial E₅₀ modulus multiplier and pl is the PENCEL limit pressure.

The second phase of this study was to predict the deformations of a cantilevered sheet pile wall (unloading case), and the deformations of a 2-m diameter shallow footing (loading case). Conventional analyses methods were compared with the FEM using insitu test derived input parameters. Conclusions were:

1. Conventional analyses (CWALSHT) under-predicted wall deformations unconservatively, while wall deflections were accurately predicted by using the Hardening Soil Model with input parameters estimated from SPT correlations and “curved matched” PMT values.
2. Fundamentally, the stress history of a soil profile, i.e., OCR or preconsolidation pressure, must be known for any settlement prediction either using conventional or finite element methods.
3. Of the conventional methods for estimating settlements (CSANDSET), only the SPT based D’Appolonia, and Peck and Bazaraa methods provided reasonable estimates of the observed settlement.
4. The conventional DMT method, which correlates OCR values, slightly overestimated measured settlements.
5. None of the insitu test derived input parameters (SPT, CPT, DMT, and PMT) coupled with FEM Mohr-Coulomb or Hardening Soil models, accurately predicted the shallow footing settlements

Evaluation of Soil Modification Mixing Procedures

Robert L. Parsons, Chad P. Johnson, and Stephen A. Cross
K-TRAN: KU-00-6
January 2001

Lime is routinely used as a soil modification agent in Kansas to improve the performance of subgrade soils with the primary goal of reducing volume change. Effective mixing of lime and soil is critical to ensuring that the expected improvements occur throughout the soil mass. The results are presented herein on the effectiveness of current soil-lime mixing and construction procedures for five soils treated with powdered quicklime or lime slurry.

A series of tests was performed on each soil as part of the evaluation process. Test procedures included field density determination, dynamic cone penetrometer, unconfined compression, lime content, pH, Atterberg limits, swell testing, and determination of the maximum unit weights and optimum moisture contents for the native soil and lime treated soil. The effect of significantly reducing the mellowing period for ease of construction was evaluated and determined to negatively affect subgrade compaction and strength due to high water contents remaining from the mixing process.

Additionally, the results of the testing showed that two passes with a rotary mixer were sufficient to effectively pulverize and mix the soil and lime to achieve modification. However, the results also suggested that there was the potential for additional strength gains with additional mixing. The consistency of lime distribution on a larger scale was also evaluated and determined to be adequate at the locations observed, although there was some evidence that the mixing of soil with lime in a slurry form appeared to yield a more consistent final product than mixing with powdered quicklime.

Several recommendations were proposed for consideration by KDOT for soil modification procedures. These included moving from a specified percentage of lime for all projects to a lime percentage based on soil testing.

Recommendations also included the introduction of a mellowing period after preliminary mixing to allow the lime more time to react with the soil to break down clay lumps and to give the soil time to dry to a water content closer to optimum. Also proposed for consideration was the adoption of National Lime Association specifications for final mixing, which include the use of AASHTO T-180 as the compaction standard and requiring rotary mixing during the final stage of mixing. Further evaluation of the performance of soils mixed with lime slurry compared with soils mixed with quicklime was recommended to determine if lime slurry yields a significantly better product.

Other recommendations proposed for consideration included an evaluation of the benefits of making soil stabilization a goal of soil treatment and taking advantage of the benefits of including the stabilized layer as a component in the pavement design. Construction costs beyond those already incurred for modification should be relatively small and the additional structural benefits could yield significant savings.

Geotechnical Aspects of Pavements

Barry R. Christopher, Ph.D., P.E., Charles Schwartz, Ph.D., P.E. and Richard Boudreau, P.E.
FHWA NHI-05-037
May 2006

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/subbase 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/subbase material requirements are covered along with the evaluation and selection of appropriate remediation measures for unsuitable subgrades. Geotechnical aspects in relation to construction, construction specifications, monitoring, and performance measurements are discussed.

Geotextile Reinforcement of Low-Bearing-Capacity Soils:
Comparison of Two Design Methods Applicable to Thawing Soils

Karen S. Henry
USACE CRREL Special Report 99-7
June 1997

Thawing fine-grained soils are often saturated and have extremely low bearing capacity. Geosynthetics are used to reinforce unsurfaced roads on weak, saturated soils and therefore are good candidates for use in stabilization of thawing soils. To stabilize the soil, a geotextile is placed on it, then the geotextile is covered with aggregate. Design involves selection of aggregate thickness and geotextile. There are two commonly used design techniques for geotextile reinforcement of lowvolume roads, and the Army uses one of them. The theory and use of the two design methods for static loading (i.e., up to 100 vehicle passes) are presented and compared in this report. The design method not used by the Army offers the potential to reduce aggregate thickness over the geotextile because it accounts for the fact that the geotextile helps support the traffic load (when in tension) and confines the soil between the wheels and the subgrade. However, this alternative method appears to be unconservative with respect to stresses estimated at the subgrade surface. Thus, the current Army design technique should be used until more research is conducted. In the meantime, straightforward design curves for Army 10- and 20-ton trucks as well as vehicle loading and tire pressure information for a number of other vehicles are included in this report to help make the current design method easy to use. Future work should consider adopting a hybrid design method that provides realistic estimates of stresses at the subgrade and accounts for the tensile properties of geotextiles. In addition, aggregates other than the highquality crushed rock that is inherently assumed by each design method should be accounted for in new design development.

Introduction to Soil Moduli

Jean-Louis Briaud
Texas A&M University

The modulus of a soil is one of the most difficult soil parameters to estimate because it depends on so many factors. Therefore when one says for example:”The modulus of this soil is 10,000 kPa”, one should immediately ask: “What are the conditions associated with this number?” The following is a background on some of the important influencing factors for soil moduli. It is not meant to be a thorough academic discourse but rather a first step in understanding the complex world of soil moduli. In a first part, the modulus is defined. In a second part, the factors influencing the modulus and related to the state of the soil are described. In a third part, the factors related to the loading process are discussed. Fourth, some applications of soil moduli are presented. In a fifth and sixth part, the soil modulus is compared to the soil stiffness and to the soil coefficient of subgrade reaction respectively.

An Investigation of the Effects of Grain Crushing on the Engineering Analysis of Calcareous Sediments

Naval Civil Engineering Laboratory CR 83.020
December 1982

Sixteen specially prepared laboratory soil specimens were subjected to model pile driving to induce grain crushing about the pile perimeter and study the effects grain crushing has on the engineering analysis of calcareous sediments. Each specimen constituted a particular material, level of degree of cementation, and density. The parameters measured for each test were the pile driving resistance, pile pullout resistance, and grain size analysis curves determined before and after pile driving for areas next to and remote from the pile surface. The results of this experiment revealed that crushability depends on the interrelated effects of grain harness, pile penetration resistance t o driving, cement content, and soil density. A significant finding showed that the pile driving resistance is not a rational parameter in assessing pullout capacity for piles in calcareous sands.

Laboratory Investigation on Piles in Calcareous Settlements

Naval Civil Engineering Laboratory TN-1714
September 1982

Laboratory tests were performed, using a model pile, to determine what effect pile driving has on calcareous sand. Radiography was used to track the movement of lead shot in the sand during pile driving. Driving energy was also recorded. A test was done to measure the amount of grain crushing that occurs during pile driving. The result of this test shows that the side friction of piles in calcareous sand is low and does not increase with increasing blows. The reason for the low friction component is due to crushing the weak calcareous grains, which reduces the lateral pressures acting on the pile surface. Another test proved that the crushed calcareous sand does not reduce the soil-pile interface friction angle. Several innovative pile system concepts for improving the lateral load carrying capacity of piles in calcareous sand were developed.

Military Soils Engineering

U.S. Army FM 5-410
23 December 1992
Change 1, 4 June 1997

Construction in the theater of operations is normally limited to roads, airfields, and structures necessary for military operations. This manual emphasizes the soils engineering aspects of road and airfield construction. The references give detailed information on other soils engineering topics that are discussed in general terms. This manual provides a discussion of the formation and characteristics of soil and the system used by the United States (US) Army to classify soils. It also gives an overview of classification systems used by other agencies. It describes the compaction of soils and quality control, settlement and shearing resistance of soils, the movement of water through soils, frost action, and the bearing capacity of soils that serve as foundations, slopes, embankments, dikes, dams, and earth-retaining structures. This manual also describes the geologic factors that affect the properties and occurrences of natural mineral/soil construction materials used to build dams, tunnels, roads, airfields, and bridges. Theater-of-operations construction methods are emphasized throughout the manual.

This manual has an excellent treatment of basic geology as it relates to soil mechnics, a subject not well covered in most soils texts (including many of the documents on this website.) It is also, to our knowledge, unavailable from U.S. government sites that dispense these kinds of documents even though it was released to the public.

Performance Test for Geosynthetic-Reinforced Soil Including Effects of Preloading

Kanop Ketchart and Jonathan T.H. Wu
FHWA-RD-01-018
June 2001

A study was undertaken to investigate the behavior of Geosynthetic Reinforced Soil (GRS) masses under various loading conditions and to develop a simplified analytical model for predicting deformation characteristics of a generic GRS mass. Significant emphasis was placed on the effect of preloading. To conduct the study, a revised laboratory test, known as the Soil-Geosynthetic Performance (SGP) test, was first developed. The test is capable of investigating the behavior of a generic GRS mass in a manner mimicking the field placement condition, and the soil and geosynthetic reinforcement are allowed to deform in an interactive manner. A series of SGP tests was performed. Different soils and reinforcements were employed, and the soil-geosynthetic composites were subject to various loading sequences. The tests showed that preloading typically reduces vertical and lateral deformations of a generic soil mass by a factor 2 to 7, and that prestressing (preloading followed by reloading from a non-zero stress level) can further increase the vertical stiffness by a factor of 2 to 2.5. Correlations between the results of SGP tests and full-scale GRS structures were evaluated. It was found that the degree of reduction in settlement due to preloading could be assessed by the SGP test with very good accuracy. Finite element analyses were performed to examine the stress distribution in the SGP test. The importance of using small reinforcement spacing was evidenced by the stress distribution. A Simplified Preloading-Reloading (SPR) analytical model was developed to predict the deformation characteristics of a GRS mass subject to monotonic loading and preloading/reloading. The SPR model was shown to be able to accurately predict the results obtained from the SPG tests and numerical analysis of automated plane strain reinforcement (APSR) tests.

Soil Mechanics

Note: the software that accompanies this book is available here.

Arnold Verruijt
University of Delft, The Netherlands
2004

What do you think of the soil mechanics textbook you have (or had) has an undergraduate? Good or bad, one thing you didn't like about it -- the price! We are thus pleased to present a really first class textbook by a well known authority in geotechnial engineering. Topics include the following:

You can contact the author by clicking here.

A Summary of the Prevost Effective Stress Soil Model

Naval Civil Engineering Laboratory TR-913
September 1984

This report presents a summary of the Prevost effective stress soil model. A summary of the model formulation is given with its implementation into the DYNAFLOW finite element code. Test data are compared with code prediction. Several boundary value problems are solved as a demonstration of capability.

Use of Geogrids in Pavement Construction

U.S. Army ETL 1110-1-188
30 June 2002

Engineers are continually faced with maintaining and developing pavement infrastructure with limited financial resources. Traditional pavement design and construction practices require high-quality materials for fulfillment of construction standards. In many areas of the world, quality materials are unavailable or in short supply. Due to these constraints, engineers are often forced to seek alternative designs using substandard materials, commercial construction aids, and innovative design practices. One category of commercial construction aids is geosynthetics. Geosynthetics include a large variety of products composed of polymers and are designed to enhance geotechnical and transportation projects. Geosynthetics perform at least one of five functions: separation, reinforcement, filtration, drainage, and containment. One category of geosynthetics in particular, geogrids, has gained increasing acceptance in road construction. Extensive research programs have been conducted by the U.S. Army Engineer Research and Development Center (ERDC) and non-military agencies to develop design and construction guidance for the inclusion of geogrids in pavement systems. This document describes the use of geogrids in flexible pavement systems including design charts, product specifications, and construction guidance.