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Flat Dilatometer (DMT) downloadable papers. Prof. S. Marchetti silvano@marchetti-dmt.it   Tel +39 06 303.60.107 |
This is NOT a commercial site. |
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Abstract: A dilatometer test consists of pushing a flat blade located at the end of a series of rods. Once at the testing depth, a circular steel membrane located on one side of the blade is expanded horizontally into the soil. The pressure is recorded at specific moments during the test. The blade is then advanced to the next test depth. The main application of the DMT is to estimate Settlements and Operative Moduli, both in sands and clays, and the undrained shear strength in clay. Other design applications include: compaction control, detecting slip surfaces in slopes, liquefiability, laterally loaded piles and other geotechnical problems using the soil parameters for which the instrument provides estimates. Often DMT is requested by engineers in jobs where accurate predictions of settlements of foundations are needed or when a decision has to be taken about adopting a shallow or a deep foundation.
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Role of the DMT:
The most critical ingredients for a correct geotechnical design are, as today, the input soil parameters (we have plentiful "precise" computer programs).
Considering the disillusionment with "undisturbed" soil samples & laboratory testing (costly, uncertain quality, few data, time), the trend in the last decades has been towards in situ testing, that is often today the major portion of a geotechnical investigation (e.g. Schmertmann 1995, Powell 2001).
According to many eminent scientists (see e.g. State of the Art at the last Geotechnical World Conference 2009), the most practical and fast in situ tests - for everyday design - are CPT and DMT, the other methods being considered by these scientists too costly or complicated or slow.
CPT is faster than DMT, hence in many cases it is preferable and sufficient. However, in the frequent case that the design requires accurate settlement predictions, CPT may be not sufficient, as CPT often provides inaccurate settlement estimates (e.g. Robertson 1986, Leonards 1988, Jamiolkowski 1988, Schnaid 2009) and therefore DMT data, predicting well settlements, become preferable. DMT is also considerably more sensitive to stress history, which dominates soil behaviour (e.g. stress history is important for deformation analysis, for liquefaction evaluations etc.). The higher sensitivity to stress history is also the reason why DMT monitors the benefits of compaction twice as sensitively as CPT.
The DMT blade is also considerably more sensitive to horizontal stresses. Due to the flat shape, arching is negligible, as opposite to axi-symmetric probes, where arching obscures the horizontal stress.
Workshop on DMT and SDMT: 18 April 2012, Milano (Italy) - last minute subscription for the afternoon session (14:30-18:30), please call Simona (346.5946411) - no registration cost (view invitation). Click here for info on May 2011 workshop edition (Rome) and documentation handed to participants.
September 2011 DMT automatic acquisition
Editorial July 2010 Direct-push in situ tests : will they be the basis of our investigations ? Can direct-push replace lab? Notions emerged at CPT'10. Differences CPT - DMT.
August 2010 Sand liquefaction. Two recent papers (Tsai et al. 2009 and Kung and Tsai 2010), kindly signaled to the writer by Prof. Robertson, are believed to represent a breakthrough advancement in evaluating CRR (Cyclic Resistance Ratio) by DMT. Tsai's updated CRR-Kd curve (Tsai's Eqn. 8, or Fig. 11) is obtained as the translation of the large SPT & CPT liquefaction experimental base, in particular of the correlations CRR-Nspt and CRR-Qc1 (eqn. 4 and eqn. 11 in Youd & Idriss (2001). Such Tsai's CRR-Kd curve is the one that the writer would use today in engineering practice.
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Distinctive features of DMT:
Soil distortions. The dilatometer distorts the soil substantially less than other penetration tests. DMT and SDMT:
Cape Kennedy Space Center
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Documents
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DOWNLOADABLE PAPERS
Marchetti S. (1999) " The Flat Dilatometer and its applications to Geotechnical Design ", Lecture notes (90 pp) Intnl Seminar on DMT held at the Japanese Geot. Society, Tokyo, 12 Feb 1999 (pdf format 1.3 MB). Very detailed reference. Index: DMT equipment, Field equipment, Procedure, Derivation of parameters, Results, Distortions due to penetration, Comparisons with other tests, Coeff. of Consolidation & Permeability (clay), Settlements, Operative modulus, Detect slip surfaces in slopes, P-y curves for lat. loaded piles, Sand liquefaction, Compaction control, Pavement subgrade control, Subgrade Kh for anchored diaghrams, DMT for FEM.
READING HINTS . For a general overview, see the following comprehensive documents:
Readers unfamiliar with DMT: Totani et al. 2001 Bali, 6 pages (in Italian: Totani et al. 1999 Parma).
More detailed and extensive treatment : (a) In the form of paper : Marchetti 1997 Cairo and especially TC16 2001 Bali.
(b) In the form of a series of slides:
Marchetti 1999 Tokyo, Marchetti 2001 Torino. (c) In the form of Course Notes - User's Manual: Course Notes 2001 Bali
Papers (of the above list) grouped by topic - all downlodable
Settlements and compressibility: Schmertmann 86, Lacasse 86, Leonards 88, Hayes 90, Iwasaki 91, Geopac 92, Jendeby 92, Woodward 93, Steiner 94, Tanaka 98, Failmezger 98-2000, Failmezger et al. 99, Pelnik et al.99, Schnaid et al 2000, Tice & Knott 2000
PMT and DMT : Schmertmann 87 Digest 9, Geopac 92, Kalteziotis 91, Lutenegger 88 and 90, Wong 93, Sawada 95, Ortigao 96, Schnaid 2000
Ch and K by DMT: Robertson 88, Schmertmann 88, Marchetti 89, Totani 98
Liquefaction: Marchetti 82, Robertson 86 , Reyna 91, Tanaka 98, Milestones on liquefaction 98, TC16 2001
For personal or educational non-commercial use only.
The documents *.pdf, require Acrobat Reader, freely downloadable at : http://www.adobe.com/products/acrobat/readstep.html