# Behaviour of Uniform Drava River Sand in Drained Condition--A Critical State Approach
## 1 Introduction  
One of the most useful tools and theories for the modelling of soil behaviour is the critical state and steady state theory [1; 2; 3; 4; 5; 6; 7]. The critical state theory has been a subject of soil investigation during the last several decades and was started with the research done by [PERSON] [2]. As a theoretical framework, the critical state of soil was defined by [PERSON] and [PERSON] [5]. The critical state parameters have an important role in the geotechnical structure design, i.e., design of the stability of retaining walls, bearing capacity of spread foundation, etc. [8]. A soil, by definition, has reached its critical state when the shear strains (\(\gamma\)) or deviatoric strains (\(e_{q}\)) are developing without changes in mean effective stress (\(p^{\prime}\)), deviatoric stress (\(q\)) and specific volume (\(v\)). The critical state of a soil is such a state at which the plastic yielding can constantly develop without the change in deviatoric stress and specific volume at constant mean normal stress (\(p^{\prime}\)) [5; 6; 9]. Such yielding changes an initial soil fabric and structure, by destroying the initial contacts between the grains and rearranging them. Over the several past decades, there have been numerous research of triaxial tests on sand and sand-like materials. Extensive drained and undrained strength tests of uniform sands became an important research subject particularly after Niigata earthquake in 1964 [10; 11]. The results lead to the development of the advanced soil constitutive models and laboratory testing devices, as well as to the establishment of a worldwide database of different types of uniform sandy materials. Advanced drained and undrained triaxial tests and simple shear tests on uniform sands, which provided important insights into the critical state of sandy materials, have been performed on the Toyoura sand [12; 13; 14; 15; 16; 17; 18], Nevada sand [7; 19; 20], Ottawa sand [7; 21; 22; 23], Monterey sand, e.g., [24; 25; 22; 26] and Erksak sand, e.g., [9; 27; 28]. In addition to the fact that the above have established a database of the shear behaviour of uniform sands, they have also pointed out the difficulties and issues that may arise with the use of a triaxial device in laboratory research. [PERSON] et al. [29] gave an overview of the main factors (i.e., sample size, particle size, void ratio and initial state) that can affect the behaviour of sand and its critical state. In Eastern Croatia, which is a part of the European Pannonian Basin [30], uniform sands occur in the wider area of the City of Osijek. The City of Osijek is the largest economic centre of the Eastern Croatia and is the fourth largest city in Croatia, with a population of approximately 110,000. It is located on the right bank of the Drava River and has been constantly expanding in the last several years. The expansion of the city means that more and more geotechnical and structural work will take place on these uniform sandy deposits. Unfortunately, there is a lack of data on shear strength properties of this uniform sand. Several other cities and settlements are also situated close to the Drava River bank, on this type of sand. Cities such as Osijek are constantly widening with little or no knowledge of the soil material beneath. This type of sand has its use in constructions of sidewalks, as a fill material and a base for stone slab pavement or as a part of road construction [31; 32; 33]. The main aim of this study was to define critical state parameters of the uniform Drava River sand, by static drained triaxial tests. The sand was sampled in the area of Drava River bank, in the wider city centre of Osijek, from an excavation pit which is a part of Osijek Port Tranzit complex. Beside the critical state parameters, physical properties of the Drava River sand (i.e., specific gravity, grain size distribution, minimum and maximum void ratio) are also determined in this study.