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Investigation of soil stabilize and strengthening by using biopolymer
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Cheng, Zhanbo (2022) Investigation of soil stabilize and strengthening by using biopolymer. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3877335~S15
Abstract
Civil engineering infrastructures are commonly constructed on weak soil (e.g., poor drainage and low bearing capacity) and there need various reinforcement methods to efficiently increase soil strength. Biopolymer, as an eco-friendly material, extracted from plants, metastatic products of microorganisms, or cell walls of algae easily, is abundant in nature. Moreover, it was successfully used in the fields of packaging, medical, food, and oil recovery processes before. In recent years, biopolymer has been attempted to enhance and improve soil strength in geotechnical engineering.
The aims of this thesis are to comprehensive reveal the physical and mechanical properties of biopolymer treated various soil types (e.g., clay, sand/sand-clay mixture, and natural soil) with considering various factors (e.g., biopolymer cross-linking, initial water content, long-term curing, mixing method). The objections of the current research can be concluded: 1) To investigate the soil consistency of various biopolymer treated clay (Chapter 3); 2) To illustrate the strengthening and durability of biopolymer treated soil (Chapter 4, 5, 6); 3) To reveal the influence of various factors on the strength of biopolymer treated soil (Chapters 4, 5, 6); 4) To propose the application fields and limitations of biopolymer treated soil (Chapters 3, 4, 7).
The first part of this research is to summarize and review the current literature on the compaction properties, Atterberg limits, shear strength behaviours, and unconfined compressive strength of biopolymer treated soil (Chapter 2). Throughout the literature view, the previous researches mainly consider the influence of soil type, biopolymer type and compaction energy on the compaction properties of biopolymer treated soil. However, it mainly focuses on the compaction properties of biopolymer treated sand. In section 3.2, taking the typical biopolymer, xanthan gum as an example, the maximum dry density and optimum moisture content of xanthan gum treated kaolinite are obtained at different xanthan gum concentrations from 0.2% to 5%. In addition, the soil consistency and undrained shear strength of of biopolymer treated soil mainly focuses on the xanthan gum treated different soil types under various pore fluids. For meeting this gap, in section 3.3-3.4, the soil consistency, undrained shear strength and shear viscosity of biopolymer treated clay are explored and predicted with considering eight biopolymer types under a wide range of biopolymer concentrations from 0.1% to 5% (Chapter 3).
In terms of the mechanical behaviours of biopolymer treated soil, although the thesis summaries the previous research on the unconfined compressive strength of biopolymer treated soil with considering biopolymer type, biopolymer concentration, soil type, curing time, curing temperature, rewetting-drying, freeze-thaw, most of research mainly focuses on single biopolymer treated one type of soil in the same paper. Moreover, there is limited research on illustrating the influence of initial water content and mixing method on the strength of biopolymer treated soil. In addition, there is no research to investigate the unconfined compressive strength of biopolymer treated soil with considering biopolymer cross-linking. Thus, the unconfined compressive of biopolymer treated clay are comprehensively explored by considering biopolymer type (e.g., xanthan gum (XG), sodium alginate (SA), locust bean gum (LBG), guar gum (GG), carrageenan kappa gum (KG), gellan gum (GE) and agar gum (AG), chitosan (CH)), biopolymer concentration (e.g., 0.5%-5%), initial mositrue content (e.g., 30%-60%), curing time (e.g., 0-70 days), durability (e.g., curing 378 days and rewetting-drying), biopolymer cross-linking (xanthan gum-agar gum, xanthan gum-carrageenan kappa gum and xanthan gum-locust bean gum) and mixing method (e.g., room temperature water-dry (RDM), room temperature water-wet (RWM), hot water-dry (HDM) and hot water-wet (HWM)) (Chapter 4). Subsequently, the unconfined compressive strength of biopolymer treated sand/sand-clay mixture is illustrated by considering biopolymer type (e.g., XG, SA, LBG, KG, GE and AG), biopolymer concentration (e.g., 1%, 2% and 3%), soil type (e.g., two comerical sand, kaolinite, each commercial sand-kaolinite with the ratio of 4-1, 1-1, 1-4) and curing time (e.g., 14-70 days) (Chapter 5). For revealing the performance of biopolymer treated natural soil, the unconfined compressive strength of biopolymer treated three types of natural soil is demonstrated by considering biopolymer type (e.g., XG, SA, LBG, KG, GE and AG), biopolymer concentration ((e.g., 1%, 2% and 3%)) and curing time (e.g., 0-365 days) (Chapter 6).
Although the shear behaviours of biopolymer-treated soil have been verified in previous direct shear tests, there has limited attempt to examine shear behaviours under different confining stress conditions. Moreover, the previous research mainly focuses on biopolymer treated sand. The effectiveness of biopolymer treatments in practical conditions has been limited analysis, especially for biopolymer treated clay. Therefore, in section 4.3, varying confining pressures (e.g., 30 kPa, 100 kPa, 200 kPa, 300 kPa and 400 kPa) representing construction depths are applied to investiage the shear behaviors of biopolymer treated kaolinite using a laboratory triaxial system by considering biopolymer type (e.g., carrageenan kappa gum, xanthan gum, agar gum, locust bean gum, sodium alginate, gellan gum, guar gum, chitosan, casein, sucralose, wine tannin, glycerine), biopolymer concentration (e.g., 1%, 2% and 5%) and water condition (e.g., hydrated and dehydrated conditions) (Chapter 4). In addition, the possible implementation and filed application, further research and limitation of biopolymer treated clay are comprehensive illustrated (Chapters 3, 4 and 7).
The main innovation and contribution of this research are highlighted as follows.
(1) The previous research mainly focused on the soil consistency of XG treated various soil types under different pore fluids without considering the influence of various biopolymer types and concentrations. Therefore, in this study, it can be found that the plastic limit of biopolymer treated clay increases with the increase of biopolymer concentration regardless of biopolymer type, and the trend of the plasticity index is consistent with the liquid limit. In addition, the liquid limit of biopolymer treated clay can be divided into three conditions depending on biopolymer types. The liquid limit of KG, SA and GE treated clay decreases firstly at low concentration (e.g., 0.2%), and then continuously increasesing with the increase of biopolymer concentration. Moreover, the liquid limit of XG, LBG and GG treated clay has a peak point of 0.5%, 1% and 1%, respectively, and the liquid limit tends to keep constant after 3% concentration. Meanwhile, the liquid limit of AG and CH treated clay tends to remain constant. Moreover, m value of 0.323 can be used to estimate the liquid limit of biopolymer treated clay by one fall cone test with cone penetration falling between 15 and 25 mm. Meanwhile, two empirical equations are proposed to predict the undrained shear strength and shear viscosity of biopolymer treated clay.
(2) The previous researches mainly illustrated the uncondined compressive strength of single biopolymer treated one soil type with limited biopolymer concentrations (e.g., < 2%) and curing time (e.g., less 28 days), and there are limited references on researching the influence of rewetting-drying, initial water content, mixing method and biopolymer cross-linking on the mechanical behaviours of biopolymer treated soil, espcically for clay and clay-sand mixture. Therefore, in this study, it can be illustrated that the biopolymer can significantly increase the mechanical properties of soil. Especially for after even curing 378 days, the unconfined compressive strength of biopolymer treated soil can be still more 7 times than that of untreated soil. In addition, the unconfined compressive strength of biopolymer treated clay after rewetting-drying cycles is also more 2 times than that of the highest unconfined compressive strength of untreated clay, while the untreated clay samples are broken after one rewetting-drying cycle due to the weak connection of soil particles. Through performing single control variable method on each factor, it can be obtained that there is the optimum biopolymer type (e.g., XG, SA and LBG), optimum biopolymer concentration (e.g., 1%-2%), optimum curing time (e.g., 14-35 days), optimum biopolymer cross-link (e.g., XG-KG) to obtain the better reinforcement effect. The optimum soil type, optimum initial water content and optimum mixing method depends on curing time, biopolymer type and concentration. For example, the optimum initial water of 0.5%, 1%, 2% and 3% XG treated clay is 40%, 45%, 50% and 60%, respectively, while the optimum intial water of SA treated clay is 50% or 55% depending on SA concentration. The maximum unconfined compressive strength of XG, SA and KG treated clay is obtained in the hot water-dry mixing method, while the optimum mixing method of AG, GE and LBG (thermal gelation biopolymers) treated clay is the hot water-wet mixing method. At 1% XG concentration, the highest UCS is obtained in the S1C1-1 regardless of curing time, and the highest UCS is observed in pure sand for less than 42 days at 2% XG concentration, while the UCS of 3% XG treated pure clay can be observed as the highest value at curing 70 days. Overall, the clay content plays a vital role in the strength of biopolymer treated sand-clay mixture, especially for high biopolymer concentration.
(3) The shear beviours of biopolymer treated soil in previous work are illustrated through direct shear tests, and there are limited refereces concerning the mechanical proeperties of biopolymer treated clay by considering different confining stress conditions, especially for clay. Therefore, in this study, it can be revealed that biopolymer significantly increases the peak deviatoric stress for strengthening and stabilising clay at hydraulic conditions. SA, AG, GE and guar gum (GG) are the most effective biopolymer to increase soil cohesion among twelve biopolymers treated clay. Subsequently, KG, Glycerine (GL) and casine (CA) have a similar effect on enhancing soil cohesion. With the increase of biopolymer concentration, the increment of cohesion decreases and there exists the optimum biopolymer concentration (e.g., 1-2%) to obtain the better shear behavious of biopolymer treated soil. On the other hand, the internal friction angle of biopolymer treated clay varies with the increase of biopolymer concentration depending on biopolymer type. At hydrated condition, there is an optimum curing time to obtain the maximum shear strength of biopolymer treated clay (e.g., 42 days for XG treated clay). With the continuous increase of curing time, the shear strength decreases, while the shear strength of biopolymer treated clay is still significantly larger than that of untreated clay, and the strength decrement ratio of biopolymer treated clay is smaller than untreated clay.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TP Chemical technology |
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Library of Congress Subject Headings (LCSH): | Soil mechanics, Soil conditioners, Biopolymers | ||||
Official Date: | October 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Geng, Xueyu | ||||
Sponsors: | China Scholarship Council ; University of Warwick. School of Engineering | ||||
Extent: | xiii, 215 pages : illustrations, charts, map | ||||
Language: | eng |
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