Application of Deep Vertical Vibratory Compaction Using Resonance Amplification

K. Rainer Massarsch

ABSTRACT: The mechanism which governs the compaction of granular soils is reviewed. Two different effects are identified: densification (volume change) and an increase in horizontal stress. The ground vibration velocity, which is directly related to shear strain, is a crucial parameter of soil densification. The implementation of deep vertical vibratory compaction (DVVC) is described. The compaction effect in granular soils depends primarily on shear strain amplitude and number of vibration cycles. Vibration amplification occurs at the resonance frequency of the vibrator-probe-soil system. Resonance can be achieved by changing the operating frequency of the vibrator. Resonance compaction (DVVCr), which utilizes the vibration amplification effect, is discussed. The shape and mass of the compaction probe are important parameters for enhancing the compaction effect. An important aspect of DVVCr is the monitoring and process control system (MPCS), which assists the machine operator in executing the compaction process. Resonance compaction has the advantage that the treatment process can be carried out at a significantly lower frequency than conventional vibratory driving, resulting in lower energy consumption.

KEYWORDS: Vibratory compaction, Granular soil, Resonance.

Hydraulic Conductivity Behavior of Soilcrete Specimens Created from Dredging Sand, Cement, and Bentonite

Hoang-Hung Tran-Nguyen, Bich Thi Luong, Phong Duy Nguyen, and Khanh Duy Tuan Nguyen

ABSTRACT: Dredging sand is an inexpensive material utilized to rise elevations of highway embankments and earth levee bodies in the Southern Vietnam. However, the high permeability of the dredging sand can cause failures due to seepage flows during annual flood seasons. The dredging sand mixing cement with or without bentonite is expected to be suitable low permeability as an impermeable material. However, hydraulic conductivity of soilcrete and bentonite specimens created from dredging sand taken in the Mekong delta has limit research data. This study aims at better understanding of the hydraulic conductivity of the dredging sand samples taken in Dong Thap province mixed with cement and bentonite. The effects of the hydraulic conductivity of soilcrete and bentonite soilcrete specimens on time, cement contents, bentonite contents, cement types, and hydraulic gradients were investigated. The tests followed the ASTM D5084 standard using the both falling head-constant tailwater and falling head-rising tailwater methods. The results indicate that: (1) the hydraulic conductivity of the soilcrete and bentonite specimens decreased with increasing in testing duration and cement contents; (2) the hydraulic conductivity of the soilcrete specimens was lower 104 to 105 times than that of the compacted sand; (3) the hydraulic conductivity of the bentonite soilcrete specimens was lower 10 times than those of the soilcrete specimens; (4) the PCS cement can induce the long-term reduction of soilcrete permeability; (5) the effect of hydraulic gradients on soilcrete hydraulic conductivity was ignorable; (6) the soilcrete hydraulic conductivity varies from 10-9 to 10-10 m/s.

KEYWORDS: Hydraulic conductivity, Permeability, Soilcrete, Dredging sand, Hydraulic gradient.

Experimental and Numerical Analysis of Unsaturated Soil Slope Stability with Rainfall and Jute Fibre Reinforcement Condition

Saurabh Kumar and La Bahadur Roy

ABSTRACT: Rainfall has become a main trigger of slope failure for embankments in most coastal areas. The common slope stability analysis is incapable of accurately forecasting slides where suction pressures play a critical role. This realization is used for elaborate stability analyses, which include mesh and suction to better predict rainfall-induced slides at effective slopes. Jute fibre is one of the reinforced materials which is utilized to improve soil strength. Accordingly, the present study explores to study the effects of slope inclination on soil stability and the collected soil samples using jute fibre in artificial rainfalls. Therefore, this article presented various assessments for soil sample testing. Different tests like sieve analysis, permeability test, direct shear test (DST), liquid limit, plasticity limit, and numerical modelling were conducted in the laboratory. Geo-studio 2021 is the software utilized for numerical and experimental modelling. The findings of the research revealed that the failure is caused by a soil suction loss when the inclination of the slope is higher than the soil friction angle. Subsequently, when the inclination of the slope is lower than the soil’s friction angle, the collapse is caused at the slope’s toe due to the improvement of the positive water pressure. Furthermore, when the slope angle increases, slopes are becoming increasingly vulnerable to rapid collapse under rainfall. Consequently, the article studies the jute fibre which is combined with soil to improve its soil performance while using two rows, three rows, and four rows of jute. This estimation results that the jute fibre performs better than the without using jute fibre under different rainfall conditions. According to the findings, the random distribution of jute fibres had a favourable influence on both strength measurements and safety aspects. Utilizing the factor of safety and matric suction, the performance of jute fibre is superior to those without using jute fibres. Consequently, the proposed work improves the stabilization of soil, and factor of safety with jute fibre in rainfall conditions.

Keywords: Soil samples, Slope stability, Reinforced material, Jute fibre, Sieve analysis, Factor of safety, Matric suction, Deformation.

Undrained Shear Strength of Soft Soil in Some Areas of Vietnam’s North Central Region

Nguyen Thi Nu, Bui Truong Son, Nguyen Thanh Duong, Do Minh Ngoc, and Vu Dinh Tho

ABSTRACT: The paper aims to investigate the undrained shear properties of soft soil distributed in some areas of Vietnam’s North Central region. To study the undrained shear strength properties of soft soil, different test methods in the laboratory and in – situ at different sites were carried out. In the laboratory tests, the undrained shear strength of soft soil was determined by an undrained unconsolidated compressive test, unconfined compressive test, and consolidated undrained compression test. For the in-situ test, vane shear tests were performed at different depths in the borehole. The experimental results showed that there were various characteristics of undrained shear strength of soft soil in the study area. The undrained shear strength of soft soil depended on many factors, such as liquid limit, dry unit weight, void ratio, and plasticity index. The research results also showed that the correlations between the undrained shear strength of soft soil and physical properties have high determination coefficients.

KEYWORDS: Undrained shear strength, Qu test, UU test, CU test, Field vane shear test, Soft soil.

The Application of Rice Husk Ash and Lime as a Stabilizer for Constriction Purposes

Abdullah All Noman, M. Raton, and Koshnur Rahman

ABSTRACT: The objective of this study is to improve the engineering properties, strength, and CBR value of sandy, fine-grained soil. All types of earthen structures rest directly on the soil. The CBR value refers to the strength of the subgrade soil, which greatly affects the durability and cost of pavement. By properly treating the subgrade soil, its properties and strength can be improved to protect it from post-construction damage. Stabilization of soil is an effective technique for improving soil properties and the performance of the pavement system. With the same intention, an attempt was made to modify the engineering properties of soils collected from Mirpur-12, Dhaka, Bangladesh, by using rice husk ash and lime. The soil samples were mixed with rice husk ash in varying proportions of 4%, 8%, 12%, 16%, 20%, 24%, and 28% by weight, as well as 2%, 4%, 6%, 8%, 10%, 12%, 14%, and 16% lime content. Increases in stabilizer contents directly increase liquid and plastic limits. However, as the proportion of rice husk ash and lime increases, the plasticity index gradually decreases. The reduction in dry density was from 1.61 gm/cc to 1.38 gm/cc, and the increase in optimum moisture content was from 16% to 20.9% for the addition of 28% rice husk ash with the soils. In addition, the same reduction and increase were also observed for the lime stabilizer. Based on both the California bearing ratio and the unconfined compressive strength test, it is recommended to use 8% lime and 20% rice husk ash to stabilize this soil for sub-base materials.

KEYWORDS: Stabilizer, CBR, Unconfined compressive strength, Lime, Rice husk ash.