İzmit körfezi alüvyonlarının birincil ve ikincil konsolidasyon özellikleri

Abstract

Suya doygun kohezyonlu zeminlerde toplam oturmanın, ani oturma ihmal edilirse, iki bileşeni vardır. Bunlar, birincil ve ikincil konsolidasyon oturmalarıdır. Bir inşaat yapılmadan evvel zeminde meydana gelebilecek konsolidasyon oturmalarını tahmin edebilmek için ve zamanında tedbir alabilmek için çeşitli arazi ve laboratuar deneyleri yapılır ve oluşabilecek oturma miktarları hesaplanır. Genellikle ikincil konsolidasyondan dolayı oluşabilecek oturmalar göz önüne alınmaz. Bu çalışmada, İzmit Körfezi Alüvyonları baz alınarak birincil konsolidasyon oturma miktarlarını bulabilmek için laboratuar ve arazi deneyleri yapılarak, bunların arasındaki farklılık ve muhtemel nedenleri vurgulanmış, aynı zeminde oluşan ikincil konsolidasyon oturma değerlerinin bulunabilmesi için çalışmalar yapılıp, ikincil oturmanında bazı zeminlerde önemli bir bileşen olup olamayacağı üzerinde durulmuştur.

In this thesis, laboratory and in-situ tests have been carried out on Izmit Bay alluviums and also this thesis concentrate on the differences between laboratory and in-situ values. In addition, secondary consolidation properties of this soil have been determined through laboratory tests. In these tests, conventional consolidation test equipments have been used. Chapter 1 of this thesis is the introduction to the subject and also brief information about the objectives of this study are given in this chapter. In Chapter 2, general knowledge that are related to subject and give the idea to follow for reaching the objectives of this thesis are given. To reach knowledge, the science literature especially periodicals such as ASCE, Geotechnique, Canadian Geotechnical Journal have been used widely. In this Chapter, also, wide knowledge about the methods that were used in this study are given with figures and tables when they were necessary. Chapter 3 deals with laboratory studies. In this Chapter, not only the results obtained from these studies but also information about equipments that were used and methods that were followed in these studies are given. In Chapter 4, outcomes of the in-situ tests, information about using tools for tests are shown. Chapter 5 gives the comparison between laboratory and in-situ values with tables. Finally, in Outcome and Proposals part, overall results that obtained from all studies in this thesis and in accordance with these results, advised proposal are provided. In saturated cohesive soils, if the immediate settlement is ignored, total settlement has only two dimensions. In other words, it consists of two parts. These dimensions or parts are; 1. Primary consolidation 2. Secondary consolidation In order to estimate hugeness of the consolidation settlement, laboratory or in-situ tests are carried out. For a lot of types of the soil, secondary consolidation values are so small. Thus, secondary consolidation for these types of soils can be ignored. In this thesis, a study were carried out on Izmit Bay alluviums and to obtain primary and secondary consolidation values of this soil, laboratory and in-situ tests were carried out and focused on the differences between laboratory and in-situ values and probable causes of this incidence. Xlll Alluviums form soil structure around the İzmit Bay. On the this soil structure, in recent years, important investments are constructed. Because, these constructions especially in terms of the engineering, have brought important and huge amount additional loads to soil, knowing the consolidation properties of this soil structure has become so vital. It is so clear that there can be some settlement problems due to these constructions and their additional loads. A good example of this is that in İzmit integrate environment project that is the biggest integrate environment project of Turkey, because of the soil structure, some settlement problems emerged. This project contains rehabilitation of the Sari and Kiraz streams construction of the remnant plant and installation of the collectors. At the installation stage of the collectors, settlement problems emerged so, pile foundations were used. In addition, it was investigated that "Is the secondary important for Izmit Bay alluviums?". In order to determine the primary consolidation properties of this soil, firstly, in-situ test has been carried out. For this aim, a test embankment has been constructed along the river shore. Test embankment was the 3m height and density of the test fill was 20 KN/m^ so it has brought additional 60 KN/m^ pressure on the soil. In order to observe the settlements, 9 plates have been placed in the different part of the embankment. During 60 days, values that were obtained from dials, were taken and through them, tço values of every plates were calculated with Taylor method. From these values, average tço value of these plates has found as 1 1 days. Final settlements that were obtained from plates were in the range of 0.405-0. 506m. According to these values, average final settlement was found as 0.464 m. Beside, for each plate, primary and secondary settlement values were determined and from them, ss/Sp ratios (secondary settlement value/primary settlement value) for every plates were calculated. As a result of this, ss/sp values found in the range of 10.6- 19.5%. It can be said that average ss/Sp ratio of this soil is 14.7%. In addition to test embankment, other some test were carried out to determine other properties of the soil. Especially to find out the soil profile and the properties of the layers in the soil profiles, CPT and boreholls were used. For these aims, two boreholls and the five CPTs were done. As a result of these tests, soil profile and layers in were determined as follow. There are embankment soil between the (+3.00) and (-2.00)m, loose sand between (-2.00) and (-5.00)m, soft-medium stiff silty clay between (-5.00) and (-32.0)m, sand between (-32.00) and (-33.00)m and sandy stiff clay under the (-33.00)m. Main investigation area of this thesis is the soft-medium stiff silty clay that is between (-5.00) and (-32.00)m in the soil profile. These altitudes that are given as above are based on that level of the underground water is (±0.00). Also, cv value of this clay layer was calculated as 1.625 cm^/sec. After in-situ tests, laboratory tests were carried out to compare values that were found from in-situ tests with others that were obtained from laboratory studies and to observe whether there were differences between these values. For this, consolidation tests have been carried out on 7 specimens that were taken from same place in-situ. In these tests, classical consolidation equipments were used. Properties of the ring that were used in tests as below; A= 45.59 cm2 (Area of the ring) H0= 23 mm (initial height of the specimen) D = 7.5 cm (Diameter of the ring) XIV In addition to consolidation tests, also Atterberg limits tests were done. Through these tests, liquidity limit, plastic limit and natural water content of this soil were found as below;. wL=73%. w"=61%. wp=41% One of the seven tests was used to determine coefficients of soil such as pre- consolidation pressure of the soil, initial porosity etc. and number of this test is 3. In this test, specimen was loaded from 25 KN/m2 to 200 KN/m2 firstly and after that it was unloaded to initial load (25 KN/m2) and finally it was loaded to 1000 KN/m2. Observed values of this test was pointed in the e-logav plane and in accordance with the Casagrande method, pre-consolidation pressure was found as 77 KN/m2. Related to this value, OCR was found as 1 that implies that this soil is normally consolidated. In addition, e0 was found as 1.84. Other 6 tests were used to investigate long-term behavior of the soil. In this tests, specimens were observed during 60 days that is the same time for in-situ tests. Daily load increment was done and under some final loads, specimens were observed. To explain consolidation behavior of the soil under different final load, final loads of the tests were differentiated. These tests and their final loads are;. 3 tests under 100 KN/m2 final load. 2 tests under 50 KN/m2 final load. 1 tests under 200 KN/m2 final load Through Taylor method, teo values of every tests were determined and they were found in the range of 3.5-4 hours. Average tgo values was calculated as 4 hours. For same tests, Ss/Sp values for every tests were determined in the range of 8.5-17.7%. Also s9/Sp values were classified in terms of their final loads. As a result of this classification, Ss/Sp values were found as below;. 13.3% for 50-100 KN/m2. 8% for 25-50 KN/m2 With same tests, Cv values were determined in the range of 0.54-0.82 (10"4 cm2/sec). In addition, secondary compression index were found in the range of 0.5-2.5%. From these values, modified secondary compression were calculated. These values varied between 0.2-1.0%. Also these values were ranked in accordance with their final loads and modified secondary compression indexes were found as below;. 0.67% for 50-100 KN/m2 2. 0.30% for 25-50 KN/m With calculations, secondary compression index / compression index ratios were found for all tests. These values were between 4.1-4.8. They were pointed in the plane of Ca and Cc. In these values, most convenient line was drawn and tangent of this line gave the Ca / Cc value for this soil as 0.044(4.4%). XV Also according to Boussinesq-Steinbrenner aback, pressure coming from geological load to medium point of the clay layer was found as 31.2 KN./m2. According to this pressure and mv value of the clay layer that was determined from consolidation test, value of the settlement in the medium point of clay layer was calculated as 0.47m. When coming to comparison of the laboratory and in-situ values, firstly great amount differences between Cy values of the laboratory and in-situ seemed. Cv in-situ values were in the range of the 19817-30093 times greater than the Cy laboratory values. It can be said that Cv in-situ values were 25000 times greater than the c\. laboratory values in average. In the comparison of t9o values of laboratory and in-situ, it can be shown that in-situ values are 66 times greater than laboratory values. In addition to these comparisons, average secondary settlement value/primary settlement for laboratory and in-situ also compared. As a result of this comparison, it seemed that in-situ value is about 1.10 times greater than the laboratory value. In this comparison, using average secondary settlement value for laboratory is the average of the tests of 1,5 and 7. Because, these tests were done under 50-100 KN/m2 and this load is the closest value to in-situ value. In terms of the final settlement values, in-situ values are 0.98 times greater than the laboratory values and it implies that about there is no differences between laboratory and in-situ values for final settlement. Outcomes of all these studies and assessments about them can be ranked as below; 1.Difference between Cy values of in-situ and laboratory was found as well as 25000 times. Probable reason for this incidence is that great amount differences can be seen especially in saturated alluvial originated heterogeneous silty and sandy clays that seemed in the literature survey stage. In addition, specimens that are taken from in- situ, can not represent whole heterogeneous structure of the soil and temperature, other factors such as disturbances, transportation's of specimens from in-situ to laboratory play big role for this result. Especially for these types of soils that have heterogeneous structure, to determine relation between settlement-time, instead of the laboratory tests, using in-situ tests are more reliable. 2. As a result of the long-term consolidation test that were carried out on specimens, modified secondary compression index of the soil was found as 0.67. If this value is compared values that were obtained from literature survey, it can be seen that this value is close to medium value. Thus, secondary compression for this soil can not be ignored. Secondary settlement is about 14% of the primary settlement that is presented before. 3. When final settlement values are compared, it can be seen that there is no important differences between laboratory and in-situ values. Final settlement value obtained from laboratory is a little bit greater than other value that obtained from in- situ. Thus, it can be said that laboratory and in-situ values have same reliability in terms of the final settlement values. XVI 4. In the comparison of the t9o values of the in-situ and laboratory, there is a difference between them as 66 times. Reasons for this difference are same with first one. Main factor is differences between thickness' of laboratory specimen and layer in-situ.