You will also need to decide whether you’ll be able to load the concrete directly into the trenches or whether a pump will be needed. The turnaround time, or distance to the tip, will dictate how many lorries are needed to maintain continuity on the dig. Otherwise, you’ll have to organise lorries to take it to a tip. If it’s staying on site you may need to hire in a dumper so that it can be stored in a suitable place where it won’t interfere with the build. The design office should be prepared to amend the design, if excavation shows variation in ground conditions from those predicted from the site soil survey and investigation.For even more advice, information and inspiration delivered straight to your door, subscribe to Homebuilding & Renovating magazine.īefore you fire up the digger you’ll need to decide what’s going to happen to the spoil. A fast-track programme for superstructure construction can be negated by slow foundation construction. Time is often of the essence for a client needing early return on capital investment. Speed and economy can conflict in foundation construction – an initial low-cost solution may increase the construction period. Consider TimeĪlternative safe designs should be checked for economy, speed and simplicity of construction. Cost Controlīefore finalizing the choice of foundation type, the preliminary costing of alternative superstructure designs should be made, to determine the economics of increasing superstructure costs in order to reduce foundation costs. If these are unacceptable then a revised allowable bearing pressure should be determined, and the foundation design amended to increase its area, or the foundations should be taken down to a deeper and stronger stratum. Settlement calculations should be carried out to check that the total and differential settlements are acceptable. The variation of vertical stress w.r.t depth is determined, to check for possible over-stressing of any underlying weak strata. The selection is usually based on economics, speed and buildability of construction. This determines the preliminary design of the types or combination of types of foundation. The foundation area required is determined from the characteristic (working) loads and estimated allowable pressure. The invert level (underside) of the foundation is determined by either the minimum depth below ground level unaffected by temperature, moisture content variation or erosion – this can be as low as 450 mm in granular soils but, depending on the site and ground conditions, can exceed 1 m – or by the depth of basement, boiler house, service ducts or similar. These values – or presumed bearing values (from any standards or codes) in the absence of a site investigation – are used to estimate the allowable bearing pressure. Estimate Allowable Bearing Pressure of Soil Using Ground Investigation Report.įrom a study of the site ground investigation (if available), the strength of the soil at various depths or strata below foundation level should be studied, to determine the safe bearing capacity at various levels. The loads should be classified into dead, imposed and wind loadings, giving the appropriate partial safety factors for these loads. On the building plan, the position of columns and loadbearing walls should be marked, and any other induced loadings and bending moments. Decide the Location of Columns & Foundation and Type of Loads Acting on Them.(e.x Deal load, Live load or Wind load) The following procedures should help to achieve this and an ‘educated’ client will recognize the importance of funding this work with a realistic fee. Good design must not only be safe but must aim to save construction costs, time and materials. Design Procedures for a Building Foundation (Step by Step) Design Procedure of foundation
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