Ilhan Chang

A New Alternative for Estimation of Geotechnical Engineering Parameters in Reclaimed Clays by Using Shear Wave Velocity

The consolidation behavior of reclaimed clay can be categorized as large strain deformation. Findings from previous studies indicate that the effective stress and the void ratio are important geotechnical engineering parameters for the characterization of large strain consolidation behavior. However, existing in situ consolidation characterization methods of reclaimed clay cannot adequately estimate changes of the effective stress and void ratio during a consolidation process. This paper suggests an alternative method for estimating the geotechnical engineering parameters of reclaimed clays using a shear wave. An in situ self-weight consolidation process of reclaimed clay is simulated in laboratory while shear wave velocity is continuously measured. Experimental results show that there are single trends in relationships among the shear wave velocity, effective stress, void ratio, and geotechnical engineering parameters for a normally consolidated clay (e.g., reclaimed clay). As a practical application, the in situ parameters and the expected settlement are predicted by incorporating the obtained relationships with the in situ shear wave velocity. The predicted values are in good accordance with the values measured in field. Therefore, the proposed method can be used effectively for geotechnical engineering parameter estimations of reclaimed clay during/after self-weight consolidation with the aid of in situ seismic exploration techniques.

Application of Microbial Biopolymers as an Alternative Construction Binder for Earth Buildings in Underdeveloped Countries

Earth buildings are still a common type of residence for one-third of the world’s population. However, these buildings are not durable or resistant against earthquakes and floods, and this amplifies their potential harm to humans. Earthen construction without soil binders (e.g., cement) is known to result in poor strength and durability performance of earth buildings. Failure to use construction binders is related to the imbalance in binder prices in different countries. In particular, the price of cement in Africa, Middle East, and Southwest Asia countries is extremely high relative to the global trend of consumer goods and accounts for the limited usage of cement in those regions. Moreover, environmental concerns regarding cement usage have recently risen due to high CO2 emissions. Meanwhile, biopolymers have been introduced as an alternative binder for soil strengthening. Previous studies and feasibility attempts in this area show that the mechanical properties (i.e., compressive strength) of biopolymer mixed soil blocks (i.e, both 1% xanthan gum and 1% gellan gum) satisfied the international criteria for binders used in earthen structures. Economic and market analyses have demonstrated that the biopolymer binder has high potential as a self-sufficient local construction binder for earth buildings where the usage of ordinary cement is restricted.

Characterization of Clay Sedimentation Using Piezoelectric Bender Elements

Sedimentation is one of the most basic processes in the formation of a soil structure in nature. Many studies have been performed to describe the characteristics of clay sedimentation, based on settlement and water content measurement. In addition, there have been some attempts in numerical modeling to describe soil structure formation as a whole. However, these effects still fall short in explaining the overall process of soil structure formation because some relevant properties are measured after a self-weight consolidation is completed. Furthermore some measurement techniques significantly alter soil structure. Thus, a non-destructive evaluation is necessary for the effective description of soil characteristics during the sedimentation process. In this study, a testing device is designed that continuously monitors the self-weight consolidation process of sedimentation with shear waves. Piezoelectric bender elements are installed into a testing cell to generate and receive shear waves in a small strain regime. Slurries are prepared with kaolinite-type clay and placed in the cell. Shear wave velocities are continuously measured as a function of time during the whole process of the self weight consolidation. The experimental results suggest that as clay sediment is subjected to a certain loading, the shear wave velocity increases as time increases, showing an abrupt change in log time. This abrupt change is relevant to the formation of a stable soil skeleton. It is concluded that the time-dependent variations in shear wave velocity reflect sedimentation and self weight consolidation behavior and the evolution of the effective stress increment.

Evolution of Joint Roughness Degradation from Cyclic Loading and Its Effect on the Elastic Wave Velocity

The application of stress to the rock joint has a significant impact on morphological and mechanical properties of the joint. In particular, the evolution of the joint condition is dramatic on the surface of the weathered rock whose material integrity is altered in a manner similar to the rock joint behavior from weathering effects (Resende et al. 2010). As indicated in Kabeya and Legge (1997), a significant change in the weathered rock joint surface can be induced by the modification of grain properties of the joint surface. The grain size distribution has been found to be strongly correlated with the shear behavior and the joint roughness coefficient (JRC). The open joint or gouge dominates in weathered joints of the rock mass structure, thereby providing access for weathering agents to increase the failure likelihood from a slickenside (Wooet al. 2010).This granular disintegration leads to surface flakes to transform the joint aperture into a wider opening. In the rock mass rating (RMR) system, the geomechanic classification method for rock masses is associated with the roughness of the rock joint surface as the discontinuity condition (Hoek 2007). Conventionally, the roughness of a rock joint surface is rated and quantified in term of the JRC, which ranges from 0 to 20 (Barton and Choubey 1977). However, the validity of techniques and the accuracy of measurement methods for identifying and classifying rock joint surfaces are generally questioned because of the subjectivity of JRC results. The undulation and unevenness of a rock joint surface are recognized by its peak-to-valley height (Hotar and Novotny 2005) to classify the rock joint surface profile. In particular, Mohd-Nordin et al. (2014) applied the JRC to naturally fractured rock surfaces using the scan line technique through the implementation of the peak-to-valley height. In this regard, the maximum peak-to-valley height (Pmax) can be used as a meaningful quantitative indicator of the degree of roughness of a rock joint surface. Previous studies have examined the propagation of elastic waves across multiple jointed rock masses by considering joint surface conditions (Mohd-Nordin et al. 2014; Huang et al. 2014a; Cha et al. 2009). One of the main findings is that the roughness and unevenness of a replicated natural rock joint surface have significant effects on the propagation of elastic waves. However, changes in & Ki-Il Song ksong@inha.ac.kr

Ultrasonic P-Wave Reflection Monitoring of Soil Erosion for Erosion Function Apparatus

Erosion of soils in river, lake, and seabeds is an important component for scour estimation and design of underwater structures. This is because the scour can cause severe structural damage to underwater foundations or embankments. The erosion function apparatus (EFA) method is widely used to estimate the erosion rate of soils in the laboratory, where a soil protrusion of 1 mm thick is exposed to water flow and the time taken to erode this protrusion is measured. However, determining this erosion time is a difficult task because it is only visually inspected, and this can cause considerable measurement errors. Therefore, this study explored the feasibility of using an ultrasonic P-wave reflection monitoring method to more quantitatively assess the erosion rate that otherwise has been measured by visual inspection. The erosion rates were monitored using ultrasonic transducers mounted above a soil surface during the EFA testing on the prepared soil samples containing different clay fractions. Via the P-wave monitoring results, several important semi-quantitative observations were made: an increase in erosion resistance with an increase in the clay fraction, a discontinuous erosion behavior of fine-grained soils with sudden removal of soil lumps by water flows, a continuous erosive action of coarse-grained soils, and inherent heterogeneous erosion even at a specimen scale (i.e., the scale of milli-to-centimeter). While both the P-wave monitoring method and the visual inspection showed similar estimation on the erosion rate, the former was found to provide overall better quantitative assessment, particularly in conditions of very slow or rapid erosion and in the conditions with high turbidity water, unevenly eroded sample surfaces, or limited control on the soil protruding thickness.

Elastic Wave Behaviors of Beta-Glucan Biopolymer treated Residual Soil

Biopolymers, which are polymers produced by living organisms, have been generally used in various fields such as medical, food, cosmetic, and medicine according to their mechanical and beneficial health properties. Recently, the utilization of biopolymer has been slightly attempted for soil erosion control, aggregate stabilization, and drilling enhancement. However, the biological effect on the geotechnical behavior of soil has been poorly understood, although it is important for geotechnical engineering practice. In this study, an purified biopolymer (i.e., β-1,3/1,6-glucan) was used as an engineered soil additive to ordinary residual soil (i.e., a typical topsoil in Korea; hwangtoh). Micro (i.e., small strain) geotechnical properties of β-1,3/1,6-glucan treated Korean residual soil were measured via a non-destructive laboratory tests. In details, the elastic wave velocities of β-1,3/1,6-glucan treated soil was evaluated by using a piezoelectric sensor embedded oedometric cell. P- and S-wave velocities were measured simultaneously with axial loading. The results show shear modulus increases as the β-1,3/1,6-glucan content in soil increases. Meanwhile, β-1,3/1,6-glucan treatment has no effect on the compressional stiffness of soil.

Development and Geotechnical Engineering Properties of KLS-1 Lunar Simulant

AbstractLunar exploration, which slowed in the 21st century after the Apollo program, has seen more activity recently with the participation of Asian countries such as Japan, China, and India. Beca...

Geotechnical design parameter evaluation using the alluvial plain characteristics in southeastern Iraq

Geotechnical construction is responsible for the overall stability of superstructures, and if there are design errors, the structure will be exposed to potential problems. Geotechnical design starts with the correct interpretation of the target ground. Southeastern Iraq is mainly comprised of an alluvial plain with diverse geological features, and, therefore, geotechnical design requires a detailed interpretation and understanding of the area. This paper reports on laboratory and field tests and in-depth analyses conducted on these alluvial plains. The results reveal that the upper layer of this area is highly over-consolidated. This may have been caused by the removal of overburden pressure as a result of glaciation and desiccation. The highly over-consolidated soils caused considerable sample disturbance by swelling the bored sample; this provided less reliable results. However, the cone penetration test was regarded as the most appropriate field assessment method for deriving sensible geotechnical design parameters. Despite its limitations in clayey soils, the standard penetration test provided results that matched well with previous observations due to the high penetration resistance of the highly over-consolidated ground. Down-hole tests and plate load tests were considered less reliable methods due to their limited applicability in this area. This study considers geographical features, laboratory methods, and empirical correlations from in situ tests, and, therefore, provides a well-summarized guideline to evaluate special geotechnical characteristics of the alluvial plain in southeastern Iraq.

A Laboratory Procedure to Characterize Reclaimed Clay Deposits using Shear Waves

The utilization of reclamation methods to expand coastlands and create artificial islands is becoming more and more popular recently. Reclaimed clay, however, is generally weak, and thus effective prediction of its in-situ strength and consolidation status is of critical importance. In-situ reclaimed clay sequentially follows sedimentation and consolidation processes under self-weight. In the case of kaolinite clay, the free fall settling process is short; thus consolidation is a more dominant process for kaolinite-type reclaimed deposits. Conventionally, large tank sedimentation tests, settlement monitoring, and CPT test methods are widely used for characterization of reclaimed sites. However, these methods are often inefficient and disagree with the existing consolidation theories. The present study suggests a laboratory procedure to characterize reclaimed clays using shear waves. Because it is difficult to obtain undisturbed soil samples, small scale sedimentation tests are performed in the similar environmental conditions as in the field so as to reproduce the in-situ soil fabric in the laboratory. Consolidation tests are also performed to simulate the field consolidation process. During the consolidation test, shear wave velocities of soil are continuously measured. The experimental results show that for a given normally consolidated clay, the shear wave velocity is uniquely related to the effective stress and the void ratio. Based on the relationships, the shear wave velocity is used to estimate design parameters such as the degree of consolidation, and undrained shear strength. Finally, the in-situ consolidation state and shear strength are estimable by comparing the obtained relationships with the in-situ shear wave velocity.