1,721,020 research outputs found
Density specifications for hydraulic fills [Specifiche per la compattazione di riempimenti idraulici]
No full textA common problem with hydraulic fills arises during construction when acceptance criteria are considered. Contractual disputes are mainly related to degree of compaction and they arise largely because of poor specifications. A good specification is one that can be measured unambiguously in the field using reliable equipment. This paper describes the engineering process which should be followed during design and construction of hydraulic fills, starting from conceptual design all the way through to construction and subsequent use of the fill, focusing on the density requirements, specifications and acceptance criteria for density of the fill. It provides a methodology to specify the density of the fill, which will avoid most of the typical pitfalls related to hydraulic fills. This paper takes the CIRIA publication on Hydraulic Fills (Hydraulic Fill Manual for Dredging and Reclamation Works”, van’t Hoff and van der Kolff, 2012) as its starting point developing further considerations to supplement what is given in that document and in doing so tries to establish what is current best-practice
Sul comportamento di una fondazione mista in presenza di uno strato granulare interposto tra platea e pali.
No full textEffects of seismic input, fine crust and existing structure on liquefaction from centrifuge model tests
No full textThe results of dynamic centrifuge tests carried out to study the effects of seismic input, fine crust and existing structure on liquefaction triggering and manifestations are presented. The basic concept of the experimentation was to analyse the seismic behaviour of level ground, saturated, 14 m deep sandy deposits, homogeneous or stratified, subjected to increasing seismic excitations up to liquefaction, with or without a one degree of freedom structure on shallow foundations. The study was performed in the framework of the European project Horizon2020 “LIQUEFACT”
ISMGEO Large Triaxial Apparatus
No full textThe design of earth and rockfill dams is focused on ensuring the stability of the structure under a set of combined mechanical and hydraulic conditions that may occur both during construction and operative life of the dam. The prediction of the hydro-mechanical behavior of construction materials (which range from clayey soils to rockfill) is therefore fundamental. The most important characteristics to be studied are static and dynamic shear strength, shear stiffness at small and intermediate strain and compressibility of the construction materials. Testing of these properties is typically performed using the triaxial apparatus. However, testing large size materials such as rockfill requires the use of large triaxial specimens, whose diameter depends on the particles maximum dimension. Facilities capable of testing large grain size materials are few and sometimes neither the largest apparatuses are big enough to test particles as large as cobbles and boulders. ISMGEO large triaxial apparatus allows the execution of static and cyclic test on 300 mm diameter samples. The maximum particle dimension is 50 mm. Originally designed for testing the gravelly foundation soils of the Messina strait bridge, the apparatus has been recently up-graded in order reach a cell pressure of 2.5 MPa, thus allowing to reproduce the in situ stress conditions within particularly tall earth and rockfill dams. This paper describes the main features of the facility. Application examples are also shown. In particular, results of motononic compression test and cyclic tests are analyzed, with the main aim of evidencing the apparatus capabilities
Settlement prediction of shallow foundations for quality controls of sandy hydraulic fills
No full textThis paper describes a procedure for settlement prediction of shallow foundations on carbonate sands, but it is fully applicable and valid for siliceous sands. For practical purposes, the design of shallow foundations resting on medium dense and dense granular soils is typically governed by limiting settlement to tolerable values. Predicting foundation settlement is therefore important, but in standard practice it is necessarily based on indirect (and therefore often conservative) determinations of soil compressibility (or modulus), due to the intrinsic difficulties in obtaining direct measurements.While numerical analyses incorporating non-linear soil behaviour may be a preferred method for computing expected total and differential settlement of shallow foundations of given geometry and stiffness on sand under static loading, the method described in this paper consists of a simplified and expeditious method based on equivalent linear elasticity. The method uses: i) the elastic soil stiffness profile at small strain, E0(z) obtained from the shear wave velocity as the primary measurement of deformability and ii) the reduction in modulus as a function of strain magnitude, E(ε) to account for stiffness non-linearity. The beneficial effect on the soil initial stiffness of the applied footing load is also considered. The method was developed as an on-site tool for checking the compaction of hydraulic fills made of carbonate sand to form artificial islands, but its application can be extended to other natural and anthropogenic coarse-grained materials
Mechanical properties of a carbonate sand from a dredged hydraulic fill
No full text This paper focuses on the properties of a crushable, uncemented, carbonate sand, retrieved from an artificial island to be used for petroleum production offshore of the United Arab Emirates. The sand was dredged from an offshore borrow area, placed hydraulically within engineered bunds to create the island and densified by vibroflotation. The results of a comprehensive laboratory testing programme are summarised in this paper, providing a set of mechanical properties for carbonate sand. The laboratory programme included static, cyclic and dynamic tests, the results of which are interpreted in a critical state soil mechanics framework, including stress dilatancy. The results of this testing programme contribute to on-going research on the behaviour of carbonate sands under static and cyclic loading conditions. The results are also compared with selected data for other carbonate and siliceous sands, and highlight the behaviour of crushable, carbonate sands used as hydraulic fills. </jats:p
Consolidation settlement of coastal areas of the Emilia-Romagna region from cone penetration tests
No full textThis paper describes an attempt to develop and calibrate a simple tool to forecast the natural
subsidence of coastal Holocene deposits. An empirical correlation has been calibrated between the penetration
resistance measured by a static cone penetrometric tests and i) the normal compression line NCL of fine grained,
coastal deposits ii) the current void ratio and iii) the void ratio on the NCL at the site effective stress. The comparison
between the site void ratio and the normally consolidated void ratio can be used to roughly estimate if
the soil is overconsolidated, normally consolidated or under-consolidated/structured and, in the latter case, if the
fine layer is in the condition of further developing consolidation settlement to reach the self-weight equilibrium
Experimental and numerical investigations of a river embankment model under transient seepage conditions
Full text linkThe evaluation of riverbank stability often represents an underrated problem in engineering practice, but is also a topical geotechnical research issue. In fact, it is certainly true that soil water content and pore water pressure distributions in the riverbank materials vary with time, due to the changeable effects of hydrometric and climatic boundary conditions, strongly influencing the bank stability conditions. Nonetheless, the assessment of hydraulic and mechanical behavior of embankments are currently performed under the simplified hypothesis of steady‐state seepage, generally neglecting the unsaturated soil related issues. In this paper, a comprehensive procedure for properly defining the key aspects of the problem is presented and, in particular, the soil characterization in partially saturated conditions of a suitably compacted mixture of sand and finer material, typical of flood embankments of the main river Po tributaries (Italy), is reported. The laboratory results have then been considered for modelling the embankment performance under transient seepage and following a set of possible hydrometric peaks. The outcome of the present contribution may provide meaningful geotechnical insights, for practitioners and researchers, in the flood risk assessment of river embankments
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