Designing Aquifer Model for the Banks of the Serayu River, Sokawera, Somagede, Banyumas, Indonesia by Means of 1D-Electrical Resistivity Data

A geoelectric survey using the 1D-electrical resistivity method was applied to design a groundwater aquifer model for the banks of the Serayu River in Sokawera Village, Somagede District, Banyumas Regency, Indonesia. The aim of this research was to identify the characteristics of aquifers in the research area based on resistivity log data. Acquisition, modeling, and interpretation of resistivity data were carried out and the results were lithological logs at seven sounding points. Correlation between the lithological logs resulted in a hydrostratigraphic model. This model is composed of several hydrological units, i.e. shallow aquifer, aquitard, and deep aquifer. The shallow aquifers are composed of sandy clay (10.81-18.21 Wm) and clayey sand (3.04-7.43 Wm) with a depth of groundwater from the water table to 27.51 m. The deep aquifers are composed of sandstone with variation of porosity (2.24-12.04 Wm) at a depth of more than 54.98 m. Based on this model, potential shallow aquifers were estimated to be at sounding points Sch-5, Sch-6, and Sch-7. This hydrostratigraphic model shows that the two types of aquifers are separated by an aquitard layer, allowing groundwater infiltration from the shallow aquifer to the deep aquifer and vice versa. Moreover, the Serayu riverbanks in this research area are estimated to be a groundwater discharge area.

Coupling cyclic and water retention response of a clayey sand subjected to traffic and environmental cycles

Compacted soils used as formation layers of railways and roads continuously undergo water content and suction changes due to seasonal variations. Such variations together with the impact of cyclic traffic-induced loads can alter the hydro-mechanical behaviour of the soil, which in turn affects the performance of the superstructure. This study investigates the impact of hydraulic cycles on the coupled water retention and cyclic response of a compacted soil. Suction-monitored cyclic triaxial tests were performed on a compacted clayey sand. The cyclic response of the soil obtained after applying drying and wetting paths was different to that obtained immediately after compaction. The results showed that both suction and degree of saturation are required to interpret the cyclic behaviour. A new approach was developed using (i) a hysteretic water retention model to predict suction variations during cyclic loading and (ii) Bishop's stress together with a bonding parameter to predict accumulated permanent strain and resilient modulus. The proposed formulations were able to predict the water retention behaviour, accumulated permanent strains and resilient modulus well, indicating the potential capability of using the fundamentals of unsaturated soils for predicting the effects of drying and wetting cycles on the coupled soil water retention and cyclic response.

Shear Strength of Unsaturated Soils with Different Plasticity

A series of shear box tests were conducted on four different types of soils in this study. The first set , (clay1) is the host clay, Middle Delta Nile clay “MDNC” which was obtained from Mid Delta Nile zone, Qalyubiyya Governorate, Egypt. The second set, (clay2) consists of the host clay MDNC but mixed with 40% sand. The third set of tests (clay3) was carried out on natural low plastic clay samples brought from El-Tal El-Kbeer area in Ismailia Governorate. The fourth set (clayey sand -SC) consists of 25% of the host clay MDNC mixed with 75% sand. The purpose is to predict the unsaturated shear strength for various soil types. The results illustrate that for clay1, clay2, and clay3, the relationships between the unsaturated shear strength and matric suction are approximated to two linear failure envelopes intersected at matric suction equals to plastic limit. Each segment has an angle of internal friction due to matric suction  b ranging from 1.80 o to 2.90o for the first zone and  b ranging from 0.28 o to 0.20o for the second zone. Meanwhile, for SC soil it appears to have one linear failure envelope for all saturation levels with angle of internal friction due to matric suction;  b=1.19 o.. Design- Expert® software applied the least square method (LSM) to fit a mathematical model for the experimental data. The Response Surface Methodology (RSM) of the program is used to predict the required model. The paper proposed two general equations to calculate the shear strength of unsaturated clays and one equation for granular soils, which are presented at the end of the paper with their coefficients.

2-D Electrical Resistivity Imaging Survey for Lithological Assessment at Igwete Primary School, Amai, South-South Nigeria

Electrical Resistivity Imaging (ERI) is a useful near-surface imaging technique, which mainly include data acquisition, numerical modelling and tomographic inversion. Within the study area, only one – dimensional (1-D) Electrical Resistivity survey has been carried out for Geophysical investigations. Therefore, 2-D ERI survey was carried out at the Igwete Primary School, Amai to provide electrical picture of the subsurface from which discrete bodies and lithology are better revealed vertically and in lateral extent. The 2-D ERT survey data were acquired using the Petrozenith Earth Resistivity meter while employing the Wenner electrode array. The 2-D apparent resistivity data were inverted to obtain true resistivities of the subsurface using res2dinv software running on personal computer. The subsurface resistivity models were displayed as pseudo sections and inverted resistivity section in the form of colour shaded contour maps. The inverse resistivity model images indicate that at a lateral extent in the range (15.00-21.00) m and (33.00-39.00) m, anomalies suspected to be gravel mixed with sand is in place with resistivities of about (254.00-948.00) Ωm. From the geologic section we can infer that a geological formation is observed at a lateral position of (27.00-32.00) m of resistivity in the range (90.00-93.00) Ωm. This structure is inferred to be a clay pocket. The sandy nature of the formation requires that underground water development be sought for at (9.00-15.00) m over a depth (2.30-8.00) m in the sandy environment. Results of 2D resistivity imaging has helped to delineate the lithology which comprise mainly of; sand, sandy clay, clayey sand depositional environment. The resistivity of these lithology falls in the range (90.00-93.00) Ωm with depth to formation of about (2.30-6.00) m.

Two-Scale Investigation of the Retention Behavior of a Well-Graded Mixed Soil

The hydraulic characterization of mixed compacted soils is helpful for the design of earthworks subjected to drying–wetting cycles. When the mixed soil is well-graded and made of both coarse and fine fractions, its matric suction may also be due to the short-range adsorption phenomena, as for the soil investigated in this research work. A silty–clayey sand was created by a mixing procedure and experimentally investigated at two different scales. Physical modeling of an infiltration process was performed, allowing an inverse numerical analysis to infer the water retention and the hydraulic conductivity functions of the soil, whereas element testing on soil specimens allowed direct determination of the same equations. In the article, problems related to the employed suction measurement techniques have been pointed out and discussed. By this two-scale combined strategy, features of the soil hydraulic behavior, such as the wetting collapse, the shrinkage during drying, and the loop of hysteresis, were also determined.