EVALUATION OF GROUTING AS A MEASURE FOR CONTROLLING GULLY EROSION IN NANKA SANDS GEOLOGIC UNIT IN ANAMBRA STATE. NIGERIA

SOURCE:

Faculty: Environmental Sciences
Department: Environmental Management

CONTRIBUTORS:

Onuoha, D. C.
Onwuka, S. U.

ABSTRACT:

Sequel to the persistence of the problem of gully erosion in Anambra State despite all control efforts, the untimely failure of most of the control measures put in place and the unfair consideration of geology as a very critical factor of gullying in Anambra State; this study was conceived with the aim of evaluating grouting as an effective measure for controlling gully erosion in Nanka Sands geologic unit in Anambra State with a view to identifying the best chemical(s) to be adopted for the grouting/stabilization of the Nanka Sands formation. The study adopted a laboratory and field survey design, judgementally selecting to sample Nanka sand underlain part of Anambra State as it has been proven by literature to be the geologic unit that is mostly troubled by gully within the state. Four chemicals (AlFeSiO4, NaSiO4, CaOH, and CaCl¬) were purposively adopted for the grouting experiment considering their availability, gumming ability, cost and complimentary role they may play to the elemental composition of the soils. Six hypotheses were postulated and tested using appropriate statistical tools; while hypotheses 1 and 2 were tested with one way ANOVA, 3 was tested with paired sample T-Test while 4, 5 and 6 were tested using one sample T-Test. The entire parameters were subjected to univariate analysis to determination of the overall best among the grouting chemicals. The hypotheses tests results shows that: There is no significant difference in the chemical composition of the soils of the gully erosion sites in the study area; There is no significant difference in the physical characteristics of the soils of the gully erosion sites in the study area; There is significant difference between the pre-grouting porosity and permeability and the post grouting porosity and permeability of the soils of the study area; There is significant difference between the pre-grouting and the post grouting erodibilities of the samples collected; There is significant difference between the water samples collected before and after grouting; the grouting chemicals impacts the water significantly. The study found NaSiO4 to be the best amongst the four grouting chemicals used. Inline with these findings, the study concluded that chemical grouting increases soil resistance, reduces erodibility and should be encouraged in the study area to better manage gully erosion problems. The study recommended that chemical grouting be adopted as a gully control measure in the State, timely information of the development of new gullies be given, quick response to gully development alerts and immediate commencement of an advancement in the research to model the stabilization of the Nanka Sand geologic unit. The study also developed a project management framework for execution of grouting as a gully erosion control measure in Anambra State.