Jurgis Medzvieckas

Superiority of artificial neural networks over statistical methods in prediction of the optimal length of rock bolts

Abstract Rock bolting is one of the most important support systems used for rock structures. Rock bolts are widely used in underground excavations as they are suitable for a wide range of geological conditions and allow using progressive design methods; besides, they help economising in the use of materials and manpower. Thus, to provide the most effective support at minimum cost by means of rock bolting, it is essential to optimise the elements contributing to bolt design, including their length, as well as bolt density and tension during installation. This paper considers the length of bolts for optimisation of the design phase, which is one of the most important parameters impacting the entire design procedure. Presenting and comparing results of some statistical models, neural network modeling is introduced as powerful means in prediction of the optimal length of rock bolts. Subsequent to training and testing of a large number of 1-layer and 2-layer backpropagation neural networks, it was reported tha...

Multicriteria Evaluation of Building Foundation Alternatives

In real conditions, decision makers usually deal with multiple objectives and should make a decision in a state of certainty or uncertainty. The selection of the best constructions for a building from a number of alternatives is of great importance for owners, contractors, and stakeholders. Dozens of multicriteria/multi-attribute decision-making MCDM/MADM models developed for evaluating the performance of the available alternatives can be used for selecting the most suitable alternative from a given finite set of options based on a set of attributes. A guide to systematic selection among the available alternatives of building structures is the integrated methodology, thoroughly analyzed in the article. The article presents a MCDM model for selecting the type of foundation for a single-storey dwelling house based on the WASPAS-G Weighted Aggregated Sum Product Assessment method and Analytic Hierarchy Process AHP approach. The aggregate criteria weights are determined by using the AHP and experts judgement methods.

Evaluating Elastic-Plastic Behaviour of Rock Materials Using Hoek–Brown Failure Criterion

Abstract As a matter of fact, the failure criteria only predict failures initiation in materials. And, in order to predict post-yield behaviour of materials, a much complicated formulation for stress-strain relationship is required, which we know as plasticity theory. For instance, these formulations are developed based on Mohr-Coulomb criterion for soils and Drucker-Prager criterion for concrete. According to a majority of rock mechanics researchers, the empirical and experimental Hoek-Brown failure criterion is one of the well-progressed and suitable criteria, which can efficiently predict the rock failure initiation under different stress states for various types of intact rocks and rock masses. In this article, according to the suggestion by Heok explained in his paper of 1997, this rugged mentioned criterion is considered as a yield criterion and the elastic-perfect plastic behaviour of rock masses is determined using calculating material constitutive matrixs arrays in terms of Hoek-Browns materia...

Kai kurios rekonstruojamų pastatų pamatų pagilinimo iškasomis problemos ir jų sprendimo metodai

Santrauka Renovuojant senus pastatus, labai dažnai tenka gilinti pamatus. Tai daroma dėl kelių priežascių: pirma, kai norima rūsio patalpas pritaikyti veiklai. Kadangi rūsio patalpų aukstis būna per mažas, tenka aukstinti patalpas; antra, kai pastato sienos dėl nuosėdžių yra supleisėjusios ir būtina stiprinti pamatus; trecia, dėl padidėjusių apkrovų, renovuojant pastatus. Atsižvelgiant į sias priežastis, pasirenkamas būdas, kuriuo keiciama pamato konstrukcija. Dažnai taikomas pamatų pado gilinimo iskasomis būdas. Siuo atveju būtina spresti tokius klausimus: iskasų gylį ir plotį; atstumą tarp vienu metu daromų iskasų; papildomų pamatų nuosėdžių dydį ir poveikį pastato konstrukcijoms; būdus, mažinancius nevienodų nuosėdžių pasekmes. Iskasa keicia slėgio pasiskirstymą po pamatu, todėl iskasos gylis ir plotis turi būti apskaiciuotas įvertinant slėgio didėjimą po renovuojamu pamatu. Gilinant pamatus neisvengiami papildomi pamatų nuosėdžiai. Spartinant pamato pado gilinimo procesą iskasomis efektyvu daryti inje...