PECULIARITY OF THE FOUNDATIONS DEEPENING IN RENOVATED BUILDINGS USING EXCAVATION / KAI KURIOS REKONSTRUOJAMŲ PASTATŲ PAMATŲ PAGILINIMO IŠKASOMIS PROBLEMOS IR JŲ SPRENDIMO METODAI
Authors: Medzvieckas Jurgis , Sližytė Danutė 
Published: October 2012

Deepening foundations is often necessary for renovating old buildings. The process is required for several reasons: first, basement rooms are adapted for activity, since the space of basement rooms is not sufficient, and therefore heightening rooms is essential; second, when the walls of the building are cracked, strengthening foundations is needed; third, renovating buildings increases a load onto foundations. Taking into account the above introduced reasons, an appropriate method for changing the construction of foundations must be chosen. Experience shows that, in most cases, ground resistance under building reconstruction is sufficient and foundations may carry a greater load. Before renovation, the exploitation degree of ground strength must be assessed, which may be expressed as a ratio between foundation pressure and ground resistance. Experience also indicates that, in many cases, the strength of the ground is used irrationally. The foundations of the previously built buildings have a low exploitation degree of strength due to the fact that for designing foundations very simple rules have been used. The other reason is that the ground under foundations takes new characteristics due consolidation over a long period of time. In a compacted soil layer, the angle of shear resistance in sands and cohesion in clays increase. Depending on the maintenance period and soils of base building, ground resistance increases from 1.1 to 1.5 times. Building walls frequently have cracks, as a result of unequal settlements of foundations. In this instance, it is necessary to look for ways to increase the bearing capacity of foundations. Therefore, changing the construction of foundations is required. Foundation basics are often deepened using excavations to adapt the basement rooms for activity and strengthen foundations. The use of this method looks at solving the following questions: excavation depth and width; the distance between simultaneously conducted excavations; the influence of different settlements on building structures; methods for reducing the effects of different settlements. Excavations change the distribution of the pressure under foundations, and therefore excavation depth and width must be calculated considering an increase in pressure under the process of reconstructing foundations. Settlements are inevitable when foundations are deepened. Installing stiffness bands in walls is recommended for reducing the effects from different settlements. Stiffness bands are very effective means of reducing the action of different settlements inevitable when making changes in the con-struction of foundations. Another effective way is the use of jet grouting that accelerates the process of deepening foundation basics. The solid of cemented soil is formed under foundations, and therefore this is a safer and more rapid way than conducting excavations and filling them with concrete. The use of jet grouting reduces uneven settlements. Santrauka Renovuojant senus pastatus, labai dažnai tenka gilinti pamatus. Tai daroma dėl kelių priežasčių: pirma, kai norima rūsio patalpas pritaikyti veiklai. Kadangi rūsio patalpų aukštis būna per mažas, tenka aukštinti patalpas; antra, kai pastato sienos dėl nuosėdžių yra supleišėjusios ir būtina stiprinti pamatus; trečia, dėl padidėjusių apkrovų, renovuojant pastatus. Atsižvelgiant į šias priežastis, pasirenkamas būdas, kuriuo keičiama pamato konstrukcija. Dažnai taikomas pamatų pado gilinimo iškasomis būdas. Šiuo atveju būtina spręsti tokius klausimus: iškasų gylį ir plotį; atstumą tarp vienu metu daromų iškasų; papildomų pamatų nuosėdžių dydį ir poveikį pastato konstrukcijoms; būdus, mažinančius nevienodų nuosėdžių pasekmes. Iškasa keičia slėgio pasiskirstymą po pamatu, todėl iškasos gylis ir plotis turi būti apskaičiuotas įvertinant slėgio didėjimą po renovuojamu pamatu. Gilinant pamatus neišvengiami papildomi pamatų nuosėdžiai. Spartinant pamato pado gilinimo procesą iškasomis efektyvu daryti injekcijas. Taikant srautinį injektavimą, po pamatu suformuojamas sucementuoto grunto masyvas. Pamatai gilinami iškasomis ar injektuojant atskirais ruožais, todėl galimi nevienodi nuosėdžiai. Mažinant nevienodų nuosėdžių poveikį, būtini tam tikri konstrukciniai sprendimai.