The utilization of waste materials in soil improvement is the potential for the reduction of the negative effect on the environment and the construction cost as well. One of the waste materials is rice husk ash (RHA), which is an agricultural-by product and can be utilized for soil improvement. This paper aims to present a comprehensive review of the numerous investigations on rice husk ash and its utilization in soil improvement. Based on the literature review, there are some findings as follows: (i) burning rice husk ash in incinerator under a controlled temperature of 500÷8000C and time of 1÷4 hours will produce RHA with high pozzolanic activity; (ii) the RHA can be considered as a stabilizer for different types of soil, and it can be used in combination with different chemical binders and waste materials for soil improvement; (iii) from the view of engineering purposes, the RHA from about 3 to 20%, the lime from 2 to 9%, the cement from 2 to 15% were mostly suggested to improve the soil for pavement, road (base and sub-base layers), and building houses in rural areas. However, the research on the utilization of RHA in soft ground improvement by deep mixing method using lime and cement is still limited, and it is therefore recommended for further research. In addition, the experimental field research on the utilization of RHA for soil improvement in engineering practice needs to be conducted.

Using photo data of unmanned aerial vehicle (UAV) for building 3D models has been widely used in recent years. However, building a 3D model for deep open - pit coal mines with the mean height difference between surface and bottom of mines to over 500 m, there has not been researched mentioned. The paper deals with the assessment possibility of developing 3D models for deep open - pit mines from UAV image data. To accomplish this goal, DJI's Inspire 2 flying device is used to take the photo at Coc Sau coal mine. The flying area is 4 km2, the flight altitude compared to the takeoff point on the mine surface is 250 m, the overlaying coverage is both horizontal and vertical is 70%. The average errors of the horizontal and height elements of the reference points photo correlates are 0.011 m, 0.017 m, 0.016 m, 0.049 m, and 0.051 m. The maximum error on the X-axis is - 0,025 m, and the Y-axis is 0.028 m, the maximum horizontal error is 0.034 m, the maximum error on the Z-axis is 0.095 m, and the position error is 0.095 m. These results show that the 3D model established from photographic data by Inspire 2 device has satisfied the requirements of the accuracy of establishing the mining terrain map 1: 1000 scale.

Ground granulated blast furnace slag (GGBFS) is the by-products from pig iron plants which can cause a serious problem for land, soil, and water. Thus, the study for reusing GGBFS is very nessesary. This paper presents the utilisation of GGBFS for soft soil improvement by cement deep mixing method. Portland cement was replaced by GGBFS from 0 to 100% and a total of 33 specimens were used to determine the unconfined compressive strength and deformation modulus of treated soil. The experimental results showed that replacement of GGBFS from 0 to 60% cement could increase the unconfined compressive strength and deformation modulus of treated soil. The optimum GGBFS content was found to be 30% of cement content. In general, the utilisation of GGBFS for soil improvement could increase the properies of soft soil and soil treated with cement. The result of this study will be basic for utilisation of GGBFS in ground improvement by cement deep mixing method.

Due to the effects of dynamic pressure, the stress distribution of rock mass is very complex. The reason for this could be a risk of stability loss for an auxiliary tunnel system constructed within the study area. In this article by using Flac3D software the author simulated two adjacent working faces with the thickness of 5 m natural coal pillar. Three factors: the upper working face excavation process, auxiliary tunnel mining process, and the location of lower working face, affected by deformation, stress distribution, safety of lower floor area and surrounding rock mass of tunnel. The research results show that during the excavation, the mechanical behavior of the rock mass surrounding the auxiliary tunnel showed displacements, volatility, and phase characteristic. The displacement on the auxiliary tunnel boundary in both excavation and working face cases showed that the roof and the left side wall displacement was greater than the right side wall and the bottom. Therefore, the distance between the auxiliary tunnel and the empty mining space needs to be computed to meet technical and economic requirements.

Tunneling in urban areas is growing in response to the increased needs for efficient transportation. Many urban tunnels are constructed in soft ground at shallow depths. Metro tunnels are usually constructed as twin-parallel tunnels and their adjacent constructions may lead to surface deformation, affecting the surface environment and the safety of the tunnels. Shield tunnelling is a commonly used as construction technique because it is very effective in reducing ground deformations and thus damage to urban infrastructure. The paper presents a 3D simulation of shield tunneling machines via the finite element code Abaqus and analysis model of ground surface settlements induced by a construction of twin-parallel tunnels. The results show that ground surface settlements induced by a construction of the left tunnel causes surface settlements of about 22÷24 mm and after the construction of both tunnels, it will cause ground subsidence has the greatest value of 33÷35 mm.