This report presents an overview of the DMT equipment, testing procedure, interpretation and design applications. It is a statement on the general practice of dilatometer testing and is not intended to be a standard.

The Flat Dilatometer Test (DMT) in Soil Investigations - A Report by the ISSMGE Committee TC16

When pile driving is difficult and (or) economically not viable, cast-in-place piles are indispensable. Tapered piles, which have top cross-sections larger than the bottom cross-sections, have the potential for substantial advantages over conventional straight-sided piles. This paper investigates the construction and performance of innovative drilled concrete tapered piles. A full-scale pile load-testing program was conducted to evaluate the axial compressive capacity of drilled concrete tapered piles in frictional soil. One straight and three tapered augers were designed and manufactured to produce six piles. The piles that were constructed and tested included four tapered and two straight piles. The testing results showed that tapered piles with a taper angle varying between 0.95° and 1.91° had a load carrying capacity up to 50% higher than the straight-sided piles with equal volume. It should be noted, however, that the experimental results are site specific. Moreover, an analytical expression was deve...

Compression testing and analysis of drilled concrete tapered piles in cohesive-frictional soil

This paper provides commentary on the many uses of the flat dilatometer test (DMT) developed by Marchetti in 1975. The test has been used as a simple but repeatable means of obtaining information about a wide variety of soil properties and parameters. It is an expedient indexing tool for site stratification and evaluation of soil properties. The test is used to analyze soils primarily in North America, Europe, and Southeast Asia. The initial statistical trends were based on data from only eleven natural soils found primarily in Italy. Even so, the original empirical correlations have proved useful in obtaining approximate parameters for geotechnical analysis and design. A number of comparative studies, modified relationships, and new correlations have since become available in foreign soils, and several of these are reviewed in the present paper. The possibility of adopting generalized expressions for data reduction and the interpretation of soil properties is explored, particularly for evaluating the lateral stress coefficient, K sub 0, in clays from the dilatometer index K sub D. The test is useful for determining soil type, classification, and consistency for clays, silts, and sands. It provides information about stress history, undrained shear strength, shear modulus, consolidation, and pore water pressure to name just a few of the many soil parameters determined by the test.

Commentary on Marchetti Flat Dilatometer Correlations in Soils

The problems of granulometric stability related to particle migration phenomena (i) at the contact between materials affected by different grain size or (ii) through widely or gap graded soils (i.e. suffusion) are well recognized, as shown by several historical dams incidents. For a complete simulation of these phenomena and their evolution towards possible limit conditions (i.e. clogging, blinding, complete erosion), the (space and time) variability of soils granulometric properties (i.e. voids volume, porosity, permeability, flow velocity, local piezometric gradients, flow direction,…), as well as the particles erodibility and deposition, must be taken into account. The available empirical and analytical (derived from “continuum” mechanics) methods to analyze particle migration phenomena generally don’t considerer the coupled effects of these micro-structural (at the grain scale), meso-structural (porosity, permeability) and hydraulic variables. Thus, a numerical procedure allowing to simulate coupled 1D seepage and particle migration processes, by taking into account the mutual dependency of the above cited governing variables, has been developed and applied to carry out detailed analyses and review of available, selected experimental data.

Modeling of Soil Migration Phenomena in Embankment Dams

The dilatometer was first introduced by Marchetti in 1975. This new in situ device has a very large potential in evaluating some important soil properties. The knowledge of drainage conditions during penetration is an important part of the test results. Unfortunately, the dilatometer by itself cannot measure the pore pressure generated during penetration. Therefore, in order to determine what the drainage conditions were, a piezoblade was designed. This new piezometer has the same shape as a dilatometer. Many dilatometer and piezoblade tests were performed and the dilatometer's first pressure readings were compared to the generated excess pore pressures. From the test results, it appears that the maximum effect of generated excess pore pressure in very overconsolidated soil is about 40% of the dilatometer's first pressure reading.

Dilatometer Testing in Highly Overconsolidated Soils

Closure of "Dilatometer Testing in Highly Overconsolidated Soils"

This review of tied-back wall design examines different factors of safety, and then the effect of free length is demonstrated through wall analyses using the STABL computer program. Many types of searches to determine the most critical failure surface are discussed. It is noted that the FHWA Design Manual Publication DP-68-IR and STABL Program perform compatibly when designing tied-back walls. The number of tiebacks and spacing of soldier piles should be determined from the FHWA Design Manual but the final design load should be obtained using the STABL Program if the slope is unstable. These and other observations are noted.

Alireza Boghrat

Papers

Dilatometer Testing in Highly Overconsolidated Soils

Closure of "Dilatometer Testing in Highly Overconsolidated Soils"

Use of stabl program in tied-back wall design

Closure of "Use of STABL Program in Tied-back Wall Design"