Springer Science and Business Media LLC

A groundwater resources assessment has been carried out for the Lake Nyasa Basin east Africa, with reference to sub catchments further to the whole basin wise analysis, including quantification of potential yields from the aquifers. Numerical groundwater models, MODFLOW-SURFACT coupled with Visual MODFLOW, were used to assess sub-basin groundwater sustainability (Via “Zone Budget” software package). The model has been calibrated to observed hydraulic head and processed baseflow estimate. It is concluded that the aquifer system is sustained by episodic recharge and the long-term gaining storage which represents the maximum extractable volume. Future predictions of groundwater usage indicate that by 2035 the percentage of annual safe yield extracted will increase to between 11.3 and 103%. Model result suggests that there is a need to revise the current estimate of sustainable yield based on future climate change conditions and projected population growth, which would decrease spring flows substantially and decrease hydraulic head basin-wide. It also suggests that by 2035 some sub catchments will be nearly at or exceeding the annual safe yield leaving no room for socio-economic development, or the need to reduce existing socio-economic demands to meet domestic demands. Besides to improving the natural replenishment capacity through artificial recharge technique, the other option is to increase the percentage of total recharge allocated to the annual safe yield from 10% of the total annual recharge to 20% in these catchments. This provides a basis for management of individual groundwater scheme in sustaining livelihood activities or implications of policies and to develop a plan for potential groundwater extraction scenarios pertaining to water use and allocation.

The current study examines the potential of lignosulfonate to enhance the engineering behavior of two locally available expansive soils. The expansive soils were collected from Vijayawada and Amaravathi, located in the Capital Region of Andhra Pradesh, India. The soils were treated with four different percentages (0.5, 1, 2, and 4) of lignosulfonate and were allowed to interact for 7 and 28 days. A series of laboratory tests such as unconfined compressive strength, cation exchange capacity and scanning electron microscopy were carried out on the soil specimens. The results indicated that lignosulfonate has significant influence on the strength behavior of expansive soils. The amount of fines content present in soils defines the optimum percentage of lignosulfonate. Lignosulfonate treatment resulted in reduced negative surface charge of soils and formation of Polymer chain microstructure along with flocculated or aggregated particle microstructure, which may attribute to the enhanced strength of the expansive soils.

Sincethe availability of natural aggregates is very sparse, recycled industrial and construction waste provides a sustainable alternative to ground improvement using vibro replacement method. Utilizing recycled building waste caters the requirement for its disposal and offers an effective remedy for the scarcity of natural resources. The aim of this study was to give a sustainable alternative for the natural aggregates as the material for stone column. A good stone column material should be hard, dense, chemically inert and must comply with the size requirement. The utilization of construction debris and spent railway ballast as column material has been the subject of numerous researches. This work focuses on finding the suitability of railway ballast and concrete debris as alternatives for stone column material. A detailed laboratory testing of these materials has been carried to judge their strength requirements as the material for both Ordinary Stone Columns (OSCs) and Geosynthetic Encased Stone Columns (GESCs). The improvement in capacity of both OSCs and GESCs is evaluated by performing California Bearing Ratio (CBR) test in laboratory by creating unit cell stone column models of different recycled aggregates and comparing their load settlement behavior with natural aggregates. Railway ballast, natural aggregates, concrete debris and virgin soil were found to show decreasing order in CBR test results. Loading required for causing settlement in both OSCs and GESCsshowed remarkable increase as compared to that of virgin clay and the maximum load settlement improvement was observed for railway ballast in both the types of stone columns. The CBR values for GESC made from railway ballast, natural aggregates and concrete debris were 54, 49 and 38% respectively. On the other hand, CBR for OSC made from railway ballast, concrete debris and natural aggregates were found to be 25.5, 20.4 and 24% respectively and CBR of virgin clay was found to be just 11%. The demonstrated application of sustainable sources in place of natural aggregates provides a crucial pathway for utilizing the recycled aggregates as stone column filler material. Up on encasing the OSC with geotextile the performance of stone columns has improved appreciably in terms of load capacity. Railway ballast and concrete debris can be adopted as an alternate for the natural stone column materials to improve the bearing capacity of site consisting mainly of soft clays.

In professional activities aimed at seismic site classification, geophysical methods based on measurements of surface waves are often used to measure the shear-wave velocity (Vs), with the MASW survey being one of the most common techniques employed for this purpose. An MASW survey is characterized by an in-field configuration that requires a relatively simple setup; however, several uncertainties that arise are related to the survey execution process. Thus, surface irregularities and/or obstacles on the ground surface in conjunction with possible human-related errors can result in alterations to the MASW survey execution. Therefore, it is necessary to possess a clear understanding of the variables that can potentially produce alterations in Vs profiles. The purpose of this study was to evaluate, based on a field measurement campaign, the effect of the repeatability of the sledgehammer trajectory prior to striking the plate and the effects of variations in the collinearity of the geophone arrays on the Vs profile in consideration of various forced alterations commonly encountered in practice. The repeatability of the active source trajectory plays a significant role in the quality and reliability of Vs measurements. Likewise, altering the collinearity of the geophone array leads to reductions in the amplitude at low frequencies, thereby hindering the interpretation of the test. The recorded effects become more relevant depending on the local conditions and whether the surveyed terrain exhibits possible heterogeneity.

A rock bolt is one of 3 major support members, including shotcrete, steel rib, playing an important role in stabilizing the underground space with its various functions. Currently, studies at home and abroad tend to focus on the development of new rock bolt methods. For most of the studies on the reinforcing effects, a numerical analysis has been adopted; however the experimental analysis is insufficient. Therefore this study tried to create a model ground of the jointed rock mass in a cantilever shape and to carry out a large scale model test. Subsequently, it sought to inversely derive the modulus of the elasticity of the model ground with a deflection formula of the cantilever and proposed the reinforcing effects of the rock bolt using the equation.

One of the methods that can stabilize clean sand type (SP) is blending the waste crushed glass and cement with these sands. In this paper, the laboratory tests are conducted on combination of clean sand, crushed glass, and cement in different condition for soil stabilization. Blends were stabilized by cement with 3, 5 and 10 weight percent of specimens. Different compounds of crushed glass used in this paper consists of 100% SP (poor graded sand) and ratio of glass to sand is in sequence, 10/90, 30/70 and 50/50 (G/S). A series of drained triaxial, direct shear, unconfined compressive strength and standard proctor tests on various combinations of glass and stabilizing sands with cement. The results show that increasing the percentage of crushed glass will reduce the amount wopt samples in connection increases γd,max. It can also unconfined compressive strength (qu). Relative density and strength parameters c and ϕ significantly increase. The minimum value of crushed glass which is improved the sandy soil properties is 10%. Also, by adding 10, 30 and 50% crushed glass to sandy soil which had stabilized 10% cement, the samples shear strength will be increased to 70, 98 and 244%, respectively. Therefore, adding crushed glass to the soil will correct unsuitable soil parameters with respect to ease of implementation, very easy access and reduce operational costs associated with its use in construction work.

Việc đưa các cột cát vào trong đất sét sẽ tăng cường khả năng chịu tải của đất, tăng tốc độ lún, ngăn chặn hiện tượng chảy lỏng trong các loại đất cát lỏng lẻo và cung cấp kháng cự bên chống lại sự chuyển động ngang. Nghiên cứu này nhằm điều tra tác động của các cột nổi trong đất sét có trầm tích bùn thông qua việc phát triển các mô hình thí nghiệm quy mô nhỏ trong phòng thí nghiệm. Tác động của các cột cát đối với các loại đất có độ bền cắt khác nhau, tỉ lệ chiều cao/đường kính (L/D) của các cột đã được nghiên cứu. Tác động của nhóm cũng được kiểm tra bằng cách thay đổi khoảng cách giữa các cột. Kết quả thí nghiệm được so sánh với kết quả phân tích số. Một lưới tam giác 15 nút đã được tạo ra bằng cách sử dụng công cụ phần tử hữu hạn PLAXIS 2D. Phân tích phần tử hữu hạn được thực hiện sử dụng tiêu chí Coulomb của Mohr, xem xét phân tích không thoát nước cho đất sét mềm và phân tích thoát nước cho các cột cát. Kết luận cho thấy các cột cát có thể tăng đáng kể khả năng chịu tải tối đa của các loại đất mềm. Kết quả chỉ ra rằng chiều dài quan trọng cho cột nổi dao động từ 4 đến 5.5 lần đường kính của cột, quá ngưỡng này sẽ xảy ra hiện tượng phình ra và khả năng chịu tải giảm. Tác động của nhóm cũng được điều tra và quan sát rằng với khoảng cách lớn giữa các cột cát, hiệu quả nhóm giảm. Khả năng chịu tải trục của các cột cát giảm khi khoảng cách giữa các cột gia tăng.

In this study, various rock and cementitious rock-like material specimens with same ratio of length to diameter and different sizes were tested under various deformation controlled loading rate (mm/min) and load controlled rate (kN/s) conditions. According to the results obtained from 93 specimens of 5 different types of rock material and 2 different rock-like materials (cement paste and a concrete mix including sand) tested in this study, uniaxial compressive strength (UCS) values were found to significantly decrease with an increase in the specimen size under the condition of a load controlled rate (kN/s) selection. To practically remove the size effect on UCS values, the uniaxial compression test is suggested to perform selecting the loading rate as strain controlled (s−1) and proportional to diameters of specimens with different sizes and same geometry. In addition to the UCS values, Modulus of elasticity values, stress and strain graph shapes and deformation characteristics were found to significantly change with the change of the specimen size and loading rate. According to the results, both modulus of elasticity values and brittleness were found to notably increase as a result of increase in loading rate values.