| Geotechnical investigation is required for the determination of ground parameter for safe and economic design of the foundations of civil engineering.If proper study of the properties of underlying soil is not taken into account,it may cause damage to the structures.Compression indexes(C_c)and secondary compression index(C_s)are soil parameters that is required for the calculation of foundation settlement.Compression index is required for computation of the settlements of structures founded on soils strata.It can be obtained by performing laboratory tests on undisturbed soil samples using the consolidometer test.Compression index(C_s)is the slope of semi logarithmic curve between void ratio and effective stress,which is obtained from consolidation test data,conducted in laboratory.Consolidation test is a conventional test,which is assumed to simulate the compression of the foundation soil when subjected to structural loads.However,the determination of compression index from consolidation tests is expensive,cumbersome and time consuming since it takes almost two weeks to complete a typical consolidation test including sampling of undisturbed soil samples from the field.A lot of maturity and skills are required on the part of engineer in interpreting the results of the laboratory tests for application to the conditions in the field.Because of these factors,several attempts have been made in the past to predict the compression index using index properties which are relatively easier to determine and take lesser time to obtain in the laboratory.Index properties of soil such as Atterburg’s Limits and moisture content are basic properties of soils;therefore,it is possible to use these index properties to predict the compression index of the soil.Empirical models relating various index properties to the compression index have been presented by many researchers.These equations were obtained by research conducted on soils from the country of origin of the researchers,in most cases and when used in other countries,these equations either overestimate or underestimate the value of C_c.This paper aim to verify the already available empirical correlations by comparing the actual value of compression index obtained from laboratory data with those obtained from the available empirical formulae,or propose a new correlation based on the laboratory tests data,if needed.In this way,lengthy consolidation tests are avoided when determining C_c.In this research for verification of the correlations already developed;firstly the soil samples were classified as per Unified Soil Classification System.Sieve analysis was performed and Liquid Limit,Plastic Limit and Moisture contents and other parameters were found in laboratory,according to their designations.Consolidation tests were performed for different soil samples obtained from different sites in Bannu.Undisturbed soil samples were obtained from the depth of more than one meter manually.The soil samples were kept in water during application of load.The tests data were plotted,such as the graph between effective pressure and void ratio is plotted.The slope of straight line portion is found which is the Compression Index(C_c)of the soil sample.The compression indexes of these soil samples were also found from the famous correlations such as that of Skempton(1944),Nishida(1956)Hough(1957),and Nagaraj and Murty(1985)and some others;by putting the parameters(such as liquid limit,plastic limit,initial void ratio,specific gravity,natural moisture content etc whichever is required)in their proposed empirical equations.The values of compression index from consolidation tests and that obtained from the correlations were compared.In collaboration to lab work;various geotechnical reports were consulted to grasp more and more data.The research is mostly consists of data which has been taken in the period between 2007 and 2020.The main source of data is the Department of Civil Engineering,University of Engineering and Technology Benno Campus.Some data is acquired from other government and non government organizations and some other private construction firms.From the analysis of data finally it is seen that the values of compression index from the correlation of Nishida(1956)are similar up to two digits after decimal with the actual values of C_c.So it can be concluded that the most suitable correlation for finding the value of compression index for the soil of Benno city,is that developed by Nishida(1956).And some modifications are needed to be made in the correlation by A Singh and S Noor(2012).(This research was initially supposed to be done on soil in Inner Mongolia Autonomous region in the People’s Republic of China,but due to the current situation created by the novel corona virus,and the restrictions over international flights into China,the research is done on the soil of Benno;a southern city of Khyber Pakhtoon-Khwah province in Pakistan)... |
