Fall cone test on biopolymer-treated clay

Fall cone tests were conducted to evaluate the consistency variations of clay soils treated with six types of biopolymers, e.g. carrageenan kappa gum (KG), locust bean gum (BG), xanthan gum (XG), agar gum (AG), guar gum (GG) and sodium alginate (SA) at various concentrations (e.g. between 0.1% to 5% biopolymer to soil mass ratio). The dependences of shear viscosity on water content, and undrained shear strength on water content were established. The results indicated that KG and SA increased the liquid limit (LL) of treated soils after the biopolymer content exceeded a certain limit (e.g. 0.5%), BG and GG contributed to a peak point in LL at biopolymer concentration of 1% to 2%, while XG and AG almost did not change the LL at all. The plastic limit (PL) was about 25% to 50% of the LL, leading to a trend of plasticity index (PI) similar to liquid limit. In order to further simplify the testing procedure and get the Atterberg limits for biopolymer-treated soil, one-point method was adopted

Study on overlying strata movement and surface subsidence of coal workfaces with Karst aquifer water

The overlying strata layers of coal workfaces with karst aquifer water normally causes serious safety problems due to the precipitation, drainage and water inrush, such as a wide range and long term of surface subsidence. In this study, by taking 10,301 working faces of the Daojiao coal mine in Guizhou Province as the engineering background, the numerical model of water-bearing strata with fluid-solid coupling was established by using UDEC to illustrate the laws of overlying strata movement and surface subsidence. A theory model was proposed to calculate the surface settlement caused by the drainage of aquifer based on the principle of effective stress modified by the Biot coefficient αb. The results showed that the corresponding maximum value (0.72 m) and the range of the surface subsidence with the occurrence of karst aquifer water were larger than that of the overlying strata without karst aquifer water (e.g., the maximum value of surface subsidence with 0.1 m). Moreover, the surface subsidence caused by the drainage of aquifer accounted for 17.8% of the total surface subsidence caused by coal mining. According to the field monitoring of surface subsidence in 10,301 working faces, the maximum value was 0.74 m, which was highly consistent with the results of numerical simulation and theoretical analysis. It verified the accuracy and reliability of the numerical model and the theory model in this study

Study on mechanical characteristics and failure modes of coal−mudstone combined body with prefabricated crack

There are normally pre-existing cracks that can be observed in the coal seam and immediate roof that influences the stability of the rib spalling and the movement law of overlying strata. In this study, comprehensive research methods (e.g., theory analysis, experimental tests and numerical simulations) were adopted to reveal the mechanical characteristics, acoustic emission behaviors and failure modes of a coal−mudstone combined body with a single prefabricated non-penetrating crack. The results show that the influence of the crack angle on the elastic modulus of the coal−mudstone combined body samples was limited. With the increase in the crack angle, the unconfined compressive strength of samples decreased first and then increased in a V-shaped trend. In addition, the minimum unconfined compressive strength could be observed at a crack angle of 45°. Moreover, the number of acoustic emissions significantly increased with the process of continuous loading. In addition, the stress reduction zone could be observed in both ends of the prefabricated cracks at the initial stage of loading. The high- and low-stress zones were transformed with the process of continuous loading. Under an unconfined compression test, the failure models of the coal body part in the samples were mainly caused by shear failure, and only a few cracks occurred in the upper tip of the prefabricated cracks of the mudstone part. Therefore, airfoil cracks could be observed in the samples due to the strength difference of the coal mass and mudstone

Simulation study of the velocity profile and deflection rate of non-Newtonian fluids in the bend part of the pipe

As resource extraction moves deeper underground, backfill mining has received a lot of attention from the industry as a very promising mining method that can provide a safe workplace for workers. However, the safe and efficient transport of fill slurry through pipelines still needs more exploration, especially in the bend section. In order to investigate the flow characteristics and velocity evolution of the slurry in the bend section of the pipe, a three-dimensional (3D) pipe model was developed using the computational fluid dynamics software Fluent, and nine sets of two-factor, three-level simulations were performed. Furthermore, a single-factor analysis was presented to investigate the effects of the two main influencing factors on the shifting of the maximum velocity of the slurry towards the distal side in the bend section, respectively. Then, the response surface analysis method was applied to the two-factor analysis of the maximum velocity shift and the weights of the two influencing factors were specified

Study on failure characteristics and control technology of roadway surrounding rock under repeated mining in close-distance coal seam

In this study, taking the Sheng’an coal mine as an engineering background, the failure characteristics of the surrounding rock of a roadway under repeated mining in a close-distance coal seam is comprehensively illustrated through field measurements (e.g., drilling imaging), theory analysis and numerical simulation (finite difference method (FDM)). The results show that although the return airway 10905 remains intact, the apparent failure of the roadway’s roof and the coal pillar can be observed. In addition, the expression of floor failure depth caused by upper coal seam mining is obtained through elastic-plastic theory. Meanwhile, the deformation of the surrounding rock of the roadway increases with the increase of repeated mining times, especially for the horizontal displacement of the roadway on the coal pillar side. Moreover, the cracks’ evolution of surrounding rock in the roadway can be observed as asymmetric characteristics. Finally, the stability control technology of “asymmetric anchor net cable + I-steel” is proposed to prevent potential mining disasters, and the feasibility of this support scheme is verified by numerical simulation and field practices. It can meet the requirement of safe mining and provide guidelines to effectively solve the failure of a roadway in close-distance coal seam mining

Quasi-3D slope stability analysis of waste dump based on double wedge failure

The double wedges sliding along the weak layer of the foundation can be observed on the slope of the waste dump and the sliding body is divided into the active wedge and passive wedge by the weak foundation and the failure surfaces of the waste dump. Because the conventional limit equilibrium slice method cannot reflect the polygonal slip surface of the slope of the waste dump with weak foundation, this study proposed a double wedge calculation method for the slope of the waste dump with weak foundation. The limit equilibrium analysis is performed on double wedges by considering the direction and values of the interaction force between double wedges to obtain the safety factor of the slope of the waste dump. Meanwhile, the quasi-3D double wedges stability analysis method of the waste dump slope with weak foundation is proposed by considering the influence of the geometry and sliding direction of the slope surface on the slope stability. The safety factor of the inverted dump slope is 0.82, the volume of the sliding body is 6.43 million m3, and the main sliding direction is 20° south by east. The shear strain rate cloud diagram of the section is ‘y’ type distribution, and the sliding body is divided into two independent blocks. The safety factor of the sliding body section obtained by the double wedge method is between 0.76 and 0.92, and the closer to the boundary of the sliding body, the greater the safety factor of the section. The quasi-three-dimensional safety factor obtained by theoretical analysis is 0.817. The results show that the calculation results of quasi-3D double wedge are basically consistent with the calculation results of strength reduction method, while the proposed method is simpler. It can be used as a quick method to evaluate slope stability in engineering practice

Investigation of soil stabilize and strengthening by using biopolymer

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

Soil consistency and interparticle characteristics of various biopolymer types stabilization of clay

An environmentally friendly improvement method with using biopolymer stabilization of soil has been currently paid more attention for geotechnical engineering practices. And the existing concerns focused on the performance of biopolymers treated clay due to the occurrence of electrical interaction. Therefore, the effect of biopolymer types and water content on the behaviors of biopolymer-clay mixture should be firstly explored in terms of biopolymer applications. In this study, fall cone tests were conducted to evaluate the consistency variations of eight types of biopolymers treated clay, e.g., carrageenan kappa gum (KG), locust bean gum (LBG), xanthan gum (XG), agar gum (AG), guar gum (GG), sodium alginate (SA), gellan gum (GE) and chitosan (CH) at various biopolymer concentrations (e.g., between 0.1% to 5% biopolymer to soil mass ratio). The results indicated that neutral biopolymers (e.g., LBG and GG) significantly caused the increase of liquid limit and undrained shear strength regardless of biopolymer concentration. And the liquid limit and undrained shear strength of negative charged biopolymers (e.g., KG, SA, GE and XG) treated clay decreased firstly following increased, while AG and CH had limit effect on soil consistency. In addition, the trend of plasticity index was similar to liquid limit altering the USCS classification of biopolymer treated clay as silt or clay. Moreover, empirical equations determining undrained shear strength and shear viscosity of biopolymer-treated clay were also established