EPB TBM'lerde kullanılan köpüklerin özelliklerinin killi bir zeminin şartlandırılmasına etkileri
Effects of properties of foams used with EPB TBMs on conditioning of a clayey soil
Yazar: ORHAN FARUK ÇINAR
Danışman: PROF. HANİFİ ÇOPUR
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Maden Mühendisliği Ana Bilim Dalı / Maden Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Maden Mühendisliği ve Madencilik = Mining Engineering and Mining

Özet:
Tez çalışmasının temel amacı köpük karakteristikleri (köpük kimyasalı yoğunluğu, köpük yarı-ömrü, köpük plastikleşme etkisi) ile şartlandırma karakteristiği (optimum FIR, penetrasyon, güç tüketimi, yapışma, kesme dayanımı) arasındaki ilişkileri-trendleri incelemektir. Ayrıca, şartlandırma deney sonuçları arasındaki ilişkiler-trendler de incelenmiştir. Deneylerde üç baz köpük, iki aşınma önleyici ve bir anti-kil (yapışma önleyici) köpük kimyasalı kullanılmıştır. 
Deneylerde kullanılan köpük kimyasallarının özellikleri köpük kimyasalı yoğunluğu, köpük yarı-ömrü deneyleri ve köpüğün plastikleşme etkisi (standart kum-köpük karışımında yayılma tablası) deneyi ile ölçülmüştür. Zemin numunesinin karakteristiklerini belirlemek amacıyla doğal nem içeriği, Atterberg kıvam limitleri (likit ve plastik limitler) ve boyut dağılım deneyleri (elek analizi ve hidrometre) yapılmıştır. Zemin+köpük karışımının karaktersitiklerini belirlemek için güç ve yapışma ölçümlü mikser deneyi, konik penetrometre deneyi ve cep tipi kanatlı kesme (vane shear) deneyi yapılmıştır. Zemin+köpük karışımının karaktersitiklerini ve köpüğün plastikleşme etkisini belirlemek için kullanılan köpükler sabit köpük konsantrasyonunda (Cf = %3), sabit köpük genleşme oranında (FER = 15) ve sabit su içeriğinde (Wn = % 67) üretilerek, köpük enjeksiyon oranı %0 ile %40 arasında değiştirilmiştir. 
Bu çalışma sonucunda köpük yarı-ömrü arttıkça, yapışma ve kesme dayanımının arttığı görülmüştür. Bu durum kil numunelerde daha düşük yarı-ömürlü (dolayısı ile genellikle daha ucuz) köpük kimyasallarının tercih edilmesi gerektiğini göstermektedir. Ancak, yarı-ömrün çok düşük olması da köpüğün işlevini tam olarak yerine getirememesi riski oluşturabilecektir. Şartlandırma deneylerinin kendi aralarındaki ilişkilere bakıldığında ise yapışma ölçümlü karıştırma deney sonuçları kullanılarak zemin + köpük karışımının kesme dayanımının tahmin edilebileceği görülmüştür.

Abstract:
EPB TBMs (Earth Pressure Balance Tunnel Boring Machines) are a type of tunnel boring machine used in soft ground conditions where the tunnel face is unstable. The significance of EPB TBMs lies in their ability to maintain balanced pressure between the excavated material and the support (thrust) provided by the machine. This helps prevent ground settlement and potential collapse of the tunnel, making them ideal for urban tunneling projects where disturbances to the surface need to be minimized. EPB TBMs are commonly used in subway construction, sewer projects, and other underground infrastructure developments. 
EPB TBMs require usually that the soil being excavated should be conditioned by injecting foams to the excavation chamber, screw conveyor and excavation face. Foams consist of usually a surfactant, water and air; sometimes different polimers and fine materials. Soil conditioning plays a crucial role in ensuring the safety, stability, and efficiency of construction projects in various ground conditions. Conditioning the soil can make it easier to excavate, reducing the resistance faced by excavation equipment. By adding certain materials to the soil, the ground stability can be improved, reducing the risk of face collapses and/or surface settlements during excavation. Conditioning can help control water content in the soil, preventing excessive water ingress into the excavation area, which can cause complications during construction. In tunneling projects, conditioned soil can provide better support for tunnel walls, reducing the need for additional support structures or reinforcements. 
Literature survey indicates that the effect of foam characteristic properties on soil conditioning have not been studied in detail. The main objective of this study is to investigate the effects of foam properties on conditioning of a clayey sample taken from the Mahmutbey-Bahçeşehir-Esenyurt Metro Project tunnels. Soil Samples (the S1 rear tunnel). 
In order to determine the characteristic properties of the soil, natural moisture content, grain size distribution (sieve analysis and hydrometer tests) and Atterberg consistency limits (plastic and liquid limits) tests are performed. 
Six different foam chemicals (three base foam chemicals, two anti-wear foam chemicals and one anti-clay foam chemical) are used in this study. Foam chemicals are numbered from 1 to 6. Foam 1 and Foam 2 are from the first company (Foam 1 of base foam chemical and Foam 2 of anti-wear foam). Foam 3 and Foam 4 are from the second company (Foam 3 of base foam and Foam 4 of anti-wear foam). Foam 5 and Foam 6 are from the third company (Foam 5 of base foam and Foam 6 of anti-clay foam). A laboratory scale foam generator found in the Mining Engineering Department of Istanbul Technical University is used for generating the required foam.
In order to determine the characteristics of the foam chemicals, foam half-life, density of foam chemical (in liquid form) and DIN flow table (with standard sand+foam mixture to determine the plasticization effects of foams) experiments are performed at constant foam concentration ratio of Cf=%3 and foam expansion ratio of FER=15; foam injection ratio of FIR is varied up to 20% (in 5% increments) in the flow table experiments by using standard sand sample after adding 3% water). 
To determine the properties of the clay + foam mixture, i.e. the optimum conditioning parameters, mixing with power and sticking measurements, cone penetrometer and pocket type vane shear tests are performed at constant foam concentration ratio of Cf=%3 and foam expansion ratio of FER=15; foam injection ratio FIR is varied as 20%, 30% and 40%. 
The relationships or trends among the foam properties, between the foam properties and the conditioning parameters (i.e. foam injection ratio FIR, power consumption and sticking amount measurements in mixing tests, cone penetration, and vane shear strength) and among the characteristics of soil+foam mixture are investigated.
The tests on the clay sample indicate that it consists of 85% clay and silt and 15% fine sand. It is identified as high plasticity clay according to the Unified Soil Classification and having medium clogging potential according to a commonly used clogging chart. The clogging chart indicates that the clay sample requires additional 20% water to its natural water content of 32% to give it the required consistency. However, the early soil conditioning tests indicated that 35% water had to be added to the naturel water content of 32% summing up 67% total water content, which is kept constant during all soil conditioning tests.
Densities of the foam chemicals (in liquid form) vary between 1.001 and 1.032 g/cm3. The half-life values vary between 311 and 441 seconds. Flow table (plasticization eff ect of the foam) tests indicate that the sand+foam mixture is very soft (running) and the flow diameter decreas with increasing FIR, which is unexpectedly opposed to the findings found in literature. Therefore, it is recommended additional studies with lower water contents and higher FIR rates.
The soil conditioning tests (of soil + foam mixtures) indicate that the optimum FIR values for all foams are obtained only in the cone penetrometer test. The optimum FIR values are obtained at 30~40% for all foams by the cone penetration tests. The optimum FIR values can not be obtained or obtained for only one or two foams in the other soil conditioning tests. Therefore, when the relationships or trends are analyzed, the conditioning parameters obtained at 40% FIR are used (although they are not optimum for the other soil + foam characterization (conditioning) tests other than cone penetrometer test).
No significant trend or relationship is observed among the foam characteristics, which indicates that each foam characterization test reflect different characteristics of foams.
When the trends or relationships between foam characteristics and conditioning parameters (at 40% FIR) are analyzed, it is seen that only the half-life shows a clear trend with both sticking amount and vane shear strength. As the foam half-life increases, sticking amount and vane shear strength increase. Accordingly, it can be concluded that having a low foam half-life provides an advantage in terms of excavation performance, but it should be noted that at very low half-life values, the foam may not fulfill the expected function. Density of foam chemical and flow diameter (at 15% FIR) do not show any relationship with the conditioning parameters obtained at 40% FIR.
The general trends expected in the field of soil conditioning science are observed among the soil + foam interaction test results. The most striking of these trends is the low-scatter (highly correlated) linear relationship between the amount of sticking and vane shear strength. Accordingly, it can be concluded that it would be possible to predict the shear strength of the soil + foam mixture using the mixer test results with sticking measurements.
This work needs to be further studied with additional experiments, particularly by determining optimum FIR values; thus, identified trends can be transformed into statistical relationships.