The paper presents the compressive strength of mortar samples when replacing natural sand by bottom ash of An Khanh and Cao Ngan thermal power plants (TPPs) in Thai Nguyen province. Experimental research is the main method applied in this research. Research results show that replacing natural sand by bottom ash in the two TPPs, the compressive strength of samples reached the required mortar’s strength. The compressive strength of the mortar sample replaced all-natural sand, particularly for masonry mortar and plastering mortar, is 10.9 MPa and 16.4 MPa respectively for An Khánh TTP, and 12.7 MPa and 12.6 MPa for Cao Ngan TTP, while the compressive strength of the motar used all natural sand, reached 13.2 MPa and 8.6 MPa.

Liquefaction of sand is not a rare geological phenomenon. When it happens, it causes great damage to people. However, 1 District, Ho Chi Minh city where despite being a leading economic and political zone of Ho Chi Minh city, where many buildings with different loads and metro lines have been and will be rebuilt, but liquefaction potential has not been assessed. This paper presents a study on liquefaction potential of sand belonging to the Pleistocene sand lithological complex of marine origin on amSQ13 in 1 District, Ho Chi Minh based on standard penetration test (SPT) with different peak ground acceleration scenarios. Research results show that, when the peak ground acceleration amax = 0.0848 g, few points in this area occur liquefaction. However, when peak ground acceleration increased, specifically amax = 0.1 g and amax= 0.15 g, there were 8% and 68% of the survey points in the area where liquefaction occurred, respectively. The study also shows that, with a depth of about 20m, liquefaction in 1 District is still possible with amax = 0.1 g and amax = 0.15 g. The research results contribute to additional references for researchers and urban spatial planning in this area.

Breakwater is an important construction in Chan May port. The construction of breakwaters faces many difficulties due to the soft soil layer with a thickness of more than ten meters and located under the sea level. Breakwater is unstable as well as high of settlement. Therefore, the soft soil under the breakwater was replaced by fine rock. The results show that it is feasible to replace soft soil by fine rock when constructing breakwater in the sea. This is the basis for the design of soft ground treatment for breakwaters in Vietnam.

Base on proposed formulation and testing results, method of determination of initial excess pore water pressure, which is used in filtration consolidation and other geotechnical problems in case of plane and spatial problems. Unlike supposition in initial time t = 0, σ = uwo, i.e. accepting a value of coefficient of initial pore water pressure β=1, by the laboratory testing results in triaxial cell, value of coefficient of initial pore water pressure of weak saturated clayey soils in HoChi Minh City and Mekong delta is lower 1. Output computation and research results show, that initial excess pore water pressure depends on water saturation, value of compression stress and groundwater level. Using the suggested formula allows determining coefficient of initial excess pore water pressure and applies to estimate initial settlement, distribution initial pore water pressure in consolidation and long term settlement.

Earth pressure on buried pipes structure depends not only on soil type, shape and dimension of structure but also on depth, shape and dimension of excavated holes and other factors such as structure load, underground water level. Based on the selected and modified computational scheme with self-established program, the earth pressure on pipe structures according to the construction condition is evaluated and analysed. It is recommended to choose the buried depth for structure in “cut and cover” excavation method so that the influence of earth pressure is reasonably steady from the buried point downward. The replacement of backfill material to cohesive material partially can help to reduce significantly the earth pressure on the buried structure. In addition, evaluation of the the degree of approaching to limit state in surroundings in bored tunnelling excavation allows for analysing the stability in various geological conditions according to the appearance of plastic zone. The research results are useful for calculating and arranging underground structures reasonably in actual condition