Predicting settlements of shallow foundations

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    Predicting settlements of shallow foundations is the No. 1 application of the DMT, especially in sands, where undisturbed samples cannot be retrieved. Many world experts consider DMT one of the best presently available tool for predicting settlements, notoriously not well predicted by conical probes.

    Settlements are generally calculated, both in sands and in clays, by means of the one-dimensional formula.

    settlements formula

    Where Dsv is calculated according to Boussinesq and MDMT is the constrained modulus by DMT. In clays the predicted settlement is the primary settlement (net of immediate and secondary).


    The validity of the method has been confirmed by a large number of observed agreement between measured and DMT-predicted settlements. (see e.g. summaries of comparisons by Schmertmann 1986, Monaco et al. 2006, Failmezger 2015).


    Settlements estimates are useful, for instance, when the designer has to choose between a shallow foundation and a piled foundation.

    Settlements Calculation using “DMT Settlements”

    A computer program for calculating settlements according to Eq. 1 is freely available. The DMT Settlements Software is freely downloadable in the section SOFTWARE.

    The validity of the method has been confirmed by a large number of observed agreement between measured and DMT-predicted settlements. (see e.g. summaries of comparisons by).

    Settlements estimates are useful, for instance, when the designer has to choose between a shallow foundation and a piled foundation.

    dimensional method settlements
    • (a) Blades cause penetration distortions lower than axy-cylindrical probes.
    • (b) Modulus by a mini load test relates better to a modulus than a penetration resistance.
    • (c) Availability of the parameter KD, providing stress history information (note that DMT is a 2-parameter test. It is fundamental to have both: ED and KD). The availability of at least two measurements is indispensable, if deformation properties have to be investigated.
    • (d) The soil is loaded at a lower, more appropriate, strain level.
    settlements distortions in clay
    Distortions caused by probes of different shape
    settlements shear modulus

    The dilatometer modulus ED should not to be used, as such, for predicting settlements, because ED is only slightly sensitive to Stress History, while the operative modulus increases considerably with Stress History. ED must first be corrected for Stress History:

    MDMT = ED × RM (KD, ID)  (2)

    where ED is the dilatometer modulus and RM is a correction factor applied to ED depending primarily on the stress history index KD (Marchetti 1980). As to the operative Young’s modulus E, if required, it can be estimated from Mdmt using the theory of elasticity (E 0.8-0.9 MDMT).

    Incorporating stress history information in the settlement calculation, using KD, is not a refinement, but a necessity. The availability of the parameter KD is important. There are not many alternatives to KD for obtaining in situ information on stress history. On the other hand if the investigation is carried out with probes of modest sensitivity to stress history, the benefits of stress history are ignored, leading to a settlement overprediction and a more expensive design.

    1. Not rarely M estimated in situ are higher than M estimated in the laboratory, due to sample disturbance. E.g. Schmertmann (1988) compared M obtained by different methods at Sunshine Skyway Bridge, Tampa Bay in Florida. On the average, M estimated by DMT was 200 MPa, by laboratory oedometers 50 MPa, back calculated from observed settlements 240 MPa. The laboratory oedometers were in this case 4 times too soft, possibly due to sample disturbance and stress relief. On the other hand already Terzaghi and Peck, in their 1967 book, had warned that even a good oedometer of OC clay may 2 to 5 times softer than in situ. In sands in situ estimates of M are even more useful, due to the difficulty of recovering undisturbed samples in sand.
    2. Eq. (1), based on linear elasticity, provides a settlement proportional to the load, and is unable to provide a non linear prediction. The predicted settlements is meant to be the settlement in working conditions
    3. Immediately after a DMT is completed, the predicted settlements may give an idea of the proper type of foundation. E.g. in case of buildings, very roughly, if the predicted settlement is < 3 cm (or possibly 4 or 5 cm), then a shallow foundation can be adopted, otherwise a deep foundation has to be adopted. In general the entity of settlements has a significant economical consequence. Accurate estimates may permit a more economical design.
    4. M can also be predicted as M = a Qc. The problem is that a depends on stress history or OCR, a missing information if only Qc is available. The range of variation of a is quite wide (a = 2 to 20).

    Citations by world experts on settlements

    Lambrecht and Leonards (1978)

    Prestressing increased the modulus by one order of magnitude, while Qc had only a slight increase.

    Robertson (1986)

    CPT predictions of soil modulus from the cone resistance can be rather poor, especially for overconsolidated soils, with a large potential error.

    Jamiolkowski (Isopt-1 1988)

    Without Stress History it is impossible to select a reliable E (or M) from Qc (similar statement by Terzaghi, Leonards, Schmertmann…)

    Leonards & Frost (1988)

    Correlations between penetration resistance and soil modulus will seriously overestimate settlements if the deposit has been prestressed.

    Schnaid (2009)

    Correlations between cone tip resistance and soil stiffness are unreliable.

    Been SOA at CPT (2010)

    If purpose is parameters, CPT cannot be used in isolation – must be supplemented by laboratory or other methods. CPT can easily mislead in terms of soil type, strength and particularly modulus.

    Powell (BRE) (2012)

    The scarce ability to predict modulus is a well known weakness of CPT.

    Schmertmann (1986)

    A DMT sounding can usually provide the data needed for the calculation of expected settlements with an accuracy adequate for most practical purposes.

    Leonards (1988)

    It has been argued that, at the present time, the Marchetti dilatometer is the most generally applicable practical tool for sensing soil compressibility.

    Geopac Quebec (1992)

    Settlements predicted by PMT and DMT were very similar, but cost and time for DMT were a fraction of PMT.

    Woodward & McIntosh (1993)

    Use of modulus from DMT permitted considerable savings. Using DMT, the structure was able to be constructed successfully on a shallow foundation system without utilizing more expensive and time consuming soil improvement techniques.

    Steiner (1994)

    An earthfill on a loose sandy-silt produced settlements substantially higher than anticipated based on conventional soil borings. DMT were then performed. “The DMT-predicted settlements agreed well with observed settlements”.

    Tice & Knott (2000)

    Good agreement was observed between DMT-predicted and measured settlements at the sandy site under Cape Hatteras Light Station.

    KCI Technologies Usa (2000)

    By DMT a more cost effective design can result, producing savings in construction cost.

    Crapps (2001)

    Users prefer DMT data over any other soils data to estimate settlements. A user with Law Engineering in Atlanta told me yesterday that the settlements are “always right on (meaning close to) the predictions from DMT”.

    Mayne (2004)

    Over two decades of calibration between the DMT and measured foundation performance records have shown its value & reliability in settlements computation.

    Failmezger & Bullock (2011)

    DMT is a static deformation test that strains the soil to intermediate strains. Tests are generally performed at depth intervals of 0.20 m. Tests typically take about 1 minute to perform. DMT is therefore the best choice of in-situ tests for settlement prediction of shallow foundations.

    Penna (2013)

    In my practical experience the DMT is the best approach for settlements prediction.

    Case History

    Cost savings by using DMT to redesign the foundation system

    Roger A. Failmezger, P.E., F. ASCE, D GE – In-Situ Soil Testing, L.C., Lancaster, Virginia, U.S.A.

    Project Name Cost Savings with DMT Redesign of Foundation System
    Westminister Village $100,000
    Ocean Landing Shopping Center $750,000
    Old Town Crescent $150,000
    Fox Run Village $100,000
    Monarch Landing $150,000
    MD Live! $2,000,000
    Towson Circle $200,000
    Retirement Community, Glen Mills, PA $150,000
    Xfinity Live! $500,000
    Obery Court $200,000
    Residences at Rivermarsh $100,000
    Residences at River Place $80,000
    Ocean Pines $200,000
    Four Seasons $100,000
    912 King Street-116 S Henry Street Mixed Use $500,000
    Dumfries Town Square $200,000
    Seacobeck Hall—Mary Wash- ington University $500,000
    Motown $150,000
    Richmond Area Collegiate Sci- ence Building $85,000
    Richmond Area Collegiate Re- search Building $150,000
    Food Processing Addition and Tank Farm $100,000
    13th and U Street $100,000
    55 M Street $150,000
    Alexan Dunn Loring Develop- ment $250,000
    Association of Manufacturing Technology Building $150,000
    Excelsior Parc Development $100,000
    Glenmont WMATA $150,000
    Halley Rise $150,000
    Howard Hughes HHMI Expan- sion $100,000
    I-64 Widening $500,000
    JHU-NIH-NCI $150,000
    Mark Center Plaza Building 5 $150,000
    Mosaic Parcel CE $100,000
    National Gateway Land Bay “E” West $250,000
    Potomac Yard Bay D $150,000
    Ripley Street Development $100,000
    Rock Spring Centre $250,000
    Route 7 over Dulles Toll Road $150,000
    Route 7 Widening $350,000
    Tysons Archstone $150,000
    Tysons Central $250,000
    Upper Rock Blocks G & H $100,000
    West Falls Church WMATA $150,000
    McWane Hall—Lynchburg Col- lege $100,000
    Brooktrout $50,000
    Mecklenburg Schools $100,000
    Abingdon Elementary School $225,000
    Abingdon Heights $400,000
    Fauquier High School $250,000
    Prince William Commons $400,000
    PWCPS Administration Bldg $225,000
    Warrenton Aquatic & Recrea- tion Facility $250,000
    Washington Center $350,000
    WMATA White Flint Parking Garage $625,000
    3800 Glenwood $350,000
    Homewood Suites $150,000
    Johnson County WWTP $1,000,000
    1011 M Street $200,000
    14th and W Street $200,000
    1600 7th Street $50,000
    300 8th Street $125,000
    A-1 Glass $100,000
    B-CC High School $350,000
    Carlisle $200,000
    Fairfax Blvd Center $100,000
    Forest Oak Middle School $100,000
    Grimke $1500,000
    Kilmer Place $50,000
    Liberty Tank $100,000
    Sumner Suites $125,000
    Windsor $50,000
    Wood Middle School $75,000
    Wootton $75,000
    14th and P Street $150,000
    Culpepper Farmers’ Coop $50,000
    Indian Head Water Tanks $75,000
    Portals Phase 3 $175,000
    Thomas Jefferson Library $75,000
    Avalon Mosaic Parcel H $800,000
    Cabin John Middle School $200,000
    Navy Federal Credit Union $100,000
    Cambridge Village $150,000
    Ben Oaks Water Tower $75,000
    Apple Greene Water Tower $50,000
    Oyster Bay Condos $100,000
    North Beach Various Parcels $50,000
    Fort Meade-DINFOS $200,000
    Fort Meade-Building #8605 $50,000
    Fort McNair-Building #48 $250,000
    535 Broadwater Road $50,000
    15 Judith Sound Circle $8,000
    318 Ironside Circle $50,000
    Courthouse Professional Build- ing $60,000
    Dahlgren Hotel $75,000
    Doc Stone MOB $40,000
    Hamptons at Hunton Park $60,000
    Kaeser Compressors Warehouse Expansion $80,000
    New Post Site $50,000
    Oakwood Estates $85,000
    Sophia and Hanover Streets $40,000
    1112 First Street Hotel $250,000
    Courthouse Village Bridge $250,000
    Arbor House $100,000
    William Square Hotel $250,000
    James Madison University— Phillips Hall $150,000
    1336 H Street $80,000
    Reston Crescent $90,000
    Total Cost Savings $21,258,000

    Other applications to design