Unconfined compressive strength and failure behaviour of completely weathered granite from a fault zone

Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation.In this study,a series of unconfined compression tests were conducted to investigate the mechanical characteristics and failure behaviour of completely weathered granite(CWG)from a fault zone,considering with height-diameter(h/d)ratio,dry densities(ρd)and moisture contents(ω).Based on the experimental results,a regression mathematical model of unconfined compressive strength(UCS)for CWG was developed using the Multiple Nonlinear Regression method(MNLR).The research results indicated that the UCS of the specimen with a h/d ratio of 0.6 decreased with the increase ofω.When the h/d ratio increased to 1.0,the UCS increasedωwith up to 10.5%and then decreased.Increasingρd is conducive to the improvement of the UCS at anyω.The deformation and rupture process as well as final failure modes of the specimen are controlled by h/d ratio,ρd andω,and the h/d ratio is the dominant factor affecting the final failure mode,followed byωandρd.The specimens with different h/d ratio exhibited completely different fracture mode,i.e.,typical splitting failure(h/d=0.6)and shear failure(h/d=1.0).By comparing the experimental results,this regression model for predicting UCS is accurate and reliable,and the h/d ratio is the dominant factor affecting the UCS of CWG,followed byρd and thenω.These findings provide important references for maintenance of the tunnel crossing other fault fractured zones,especially at low confining pressure or unconfined condition.

Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays

Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of undisturbed natural marine clay obtained from the same depth at the same site were deliberately disturbed to different levels. Then, the specimens with different extents of sample disturbance were trimmed for both oedometer tests and unconfined compression tests. The degree of sample disturbance SD is obtained from the oedometer test data. The relationship between the unconfined compressive strength q u and SD is studied for investigating the effect of sample disturbance on q u. It is found that the value of q u decreases linearly with the increase in SD. Then, a simple method of correcting q u for sample disturbance is proposed. Its validity is also verified through analysis of the existing published data.

Testing and numerical simulation of a medium strength rock material under unconfined compression loading

This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength(UCS) is one of the most important parameters in characterising rock material behaviour. Hence the UCS is crucial in understanding the failure mechanism of fractured rocks. An effective approach to determine the UCS and to investigate the behaviours of rock materials under unconfined compression is essential in the majority of research fields of rock mechanics. The experimental configuration for the unconfined compression test, suggested by the protocols of the ASTM standard, has some limitations which affect the accuracy in determination of the real UCS. Among several alternative configurations proposed, the Mogi’s configuration seems to be the most appropriate one. Therefore, the ASTM and Mogi’s configurations were used to perform the tests on a medium strength rock material, i.e. Pietra Serena sandstone. The results using two configurations were discussed in terms of the differences. The tests were also replicated in LSDYNA using a finite element method(FEM) coupled smooth particle hydrodynamics(SPH) technique.This technique is employed in this study due to its capabilities to cope with large deformation issues related to the rocks. An advanced material model, called the Karagozian and Case Concrete(KCC) model,is implemented in the numerical simulations. The KCC model consists of three independent fixed failure surfaces and it can consider the damage accumulation based on the current state of stress among these failure surfaces. An equation-of-state(EOS) is used in conjunction with KCC material model for decoupling the volumetric and deviatoric responses. The numerical and experimental results were finally compared with the focus on the stress-strain diagram and the failure patterns. The comparison shows that the numerical results are in good agreement with the experimental results.

Improving the Unconfined Compressive Strength of Red Clay by Combining Biopolymers with Fibers

To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.

Comparison between Neuman(1975) and Jacob(1946) application for analysing pumping test data of unconfined aquifer

Pumping test of a water table aquifer is carried out to estimate the aquifer parameters, the obtained data were analysed through the solution of both Neuman(1975) and Jacob(1946) methods through AQTESOLV and Spreadsheet programs, the results of each methods are compared to evaluate the applicability and accuracy of the solution theoretically and practically. In the paper an example is presented, which is conducted for a constant rate pumping test from Ohio, in Fairborn(near Dayton), and it supplied by S.E. Norris(U.S. Geological Survey, Columbus, Ohio). The main objective of this study is to introduce both program and the way of the applications, and compare the results and the hand on of both programs in the field.

The Influence of Freeze-Thaw Cycles on Unconfined Compressive Strength of Lignin Fiber-Reinforced Loess

In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.

Hydrogeochemistry and Water Quality Evaluation along the Flow Path in the Unconfined Aquifer of the Düzce Plain, North-western Turkey

The Diizce Plain has a multi-aquifer system, which consists of a near surface unconfined aquifer, along with first and second deeper confined aquifers. Hydrochemical evolution and water quality are related to infiltration of the precipitation, recharge from the formations surrounding the plain, flow path of groundwater and the relationship between surface and groundwater. The groundwater in the unconfined aquifer flows towards the Efteni Lake and the Biiyiik Melen River. Surface waters are divided into two main hydrochemical facies in the study area： （a） Ca2＋-HCO3-; and （b） Ca2＋, Mg2＋-HCOc-, SO4^2-. The groundwater has generally three main hydrochemical facies： （a） Ca2＋-HCO3-; （b） Ca2＋, Mg2＋-HCO3-; and （c） Ca2＋, Mg2＋-HCO3-, Cl-. The hydrochemical facies ＂a＂ and ＂b＂ dominate within shallow depths in recharge areas under rapid flow conditions, while hydrochemical facies ＂c＂ characterizes shallow and mixed groundwater, which dominate intermediate or discharge areas （near Efteni Lake and Biiyiik Melen River） during low flow conditions and agricultural contamination. Calcium and bicarbonate ions, total hardness and electrical conductivity of total dissolved solids （EC-TDS） values increase along the groundwater flow path; but these parameters remain within the limits specified by the standards set for industrial and agricultural usages.

Estimating Unconfined Compressive Strength of Sedimentary Rocks in United Arab Emirates from Point Load Strength Index

In this paper, three rock types including Sandstone, Mudstone, and Crystalline Gypsum were part of a laboratory study conducted to develop a dataset for predicting the unconfined compressive strength of UAE intact sedimentary rock specimens. Four hundred nineteen rock samples from various areas along the coastal region of the UAE were collected and tested for the development of this dataset and evaluation of models. From the statistical analysis of the data, regression equations were established among rock parameters and correlations were expressed and compared by the ones proposed in literature.

Groundwater Flow Modeling for Qushtapa Plain Unconfined Aquifer in Southern Erbil Basin, Kurdistan Region, Iraq

Increasing population growth and water demand for various purposes such as irrigation, domestic and industrial production in many parts of the Kurdistan Region is causing deficit in fresh water and rising groundwater dependence. Drilling many deep wells in the area unsystematically and continuously increased pumping water from groundwater reservoirs results in lowering of water table. Therefore, it is essential to assess the management of water resources. The study focuses on the groundwater modeling for the Qushtapa District plain area in particular under steady state flow conditions. The aquifer was simulated under unconfined condition and is represented by a single layer of 100 m thickness. MODPATH was used to measure contamination track lines and travel times. This approach involved the introduction of particles at sources of contaminants in the wells and the recharge area, then the identification of the path lines and the determination of the special distribution of contaminants through steady state flow conditions. The simulation of the groundwater head shows that the groundwater head starts from the northeastern part of the plain and decreases towards Lesser Zab River in the south of the plain from 420 m to 140 m above sea level. The modeled layer was calibrated under steady state conditions using hydraulic parameters obtained from observation and pumping wells. The calibrated model is effective in producing steady-state groundwater head distribution and good compliance with observed data. The standard error was estimated as 4.88 m, the normalized root mean square error is 8.3% and the residual mean is 15.79 m. The results of the forward tracking show the source of potential pollutants from the recharge area after different travel time, the particles released at the northern boundary travels to the center and the western part toward the pollution sources. The results of the backward tracking show that the particles located in the extraction wells moved toward the recharge area in the north and northeastern part of the study area.

Winter Rain versus Snow in Headwater Catchments: Responses of an Unconfined Pumice Aquifer, South-Central Oregon, USA

Winter precipitation in two headwaters catchments (elevation ~1600 m) in the rain shadow of the Cascades volcanic arc in south-central Oregon normally falls as snow. However, in water year 2015, winter precipitation fell mainly as rain. An eight year study of the unconfined pumice aquifer allowed inter-annual comparison of groundwater recharge during the freshet and discharge during the growing season. During these water years precipitation ranged from 67% (WY2014) to 132% (WY2017) of the 30 year average, and included the rain dominated winter of WY2015 when precipitation during the water year was 98% of the 30 year average. Change in storage in the pumice aquifer was estimated from thickness of the pumice deposit and depth to water table from the ground surface. Measurements were made where 1) the pumice aquifer was exposed at the surface;2) where the aquifer was partially eroded and overlain by either alluvium or lacustrine glassy silt to fine sand;3) fens where the partially eroded aquifer was overlain by peat;and 4) monitoring wells drilled through the pumice aquifer into bedrock. In all settings, groundwater storage in the pumice aquifer following the rain-dominated winter of WY2015 was similar or less than storage following the drought of WY2014 when winter precipitation fell as snow. Storage at the end of WY2014 and WY2015 was the least observed in the eight year study. Winter-time rain during WY2015 produced runoff rather than storage in snow pack. Runoff conveyed from the catchments by flow in stream reaches normally dry from late summer through the winter months. Rain-dominated winter precipitation stresses the perched pumice aquifer. Winter storms starting as rain and turning late to snow and ground-freezing temperatures lead to runoff during the next rain-dominated precipitation event. These patterns produced stream flow in channels that are commonly dry during the winter, reduced near-surface groundwater storage in the pumice aquifer, muted springtime freshet, and stressing of groundwater-dependent ecosystems, forage in meadows, and forest health.

Ground Rupturing Due to Entrapped Air/Gas in the Unconfined Zone

The sudden and large oscillation of pressure of compressed air/gas entrapped in porous medium due to the changes in the actual pore-fluid pressure, during recharge of water following intense rainfall after a prolonged period of dryness such that the rainfall intensity exceeding infiltration capacity, leads to the generation of hydo-tremors. These hydro-tremors cause ground rupturing, subsidence, developments of cracks in the building, etc. A theoretical model has been presented to estimate the successive values of compressed air/gas pressures due to the successive development of actual pore-fluid pressures and effective stresses during recharge of water of the unconfined zone during the onset of the summer monsoon of 2008 in the northern parts of India.

Experimental Study on Dispersion of Unconfined Aquifer in a Site of Jilin City

Dispersion parameter is an important parameter for the establishment of groundwater solute transport model.The dispersion test uses sodium chloride as a tracer,which was conducted in a site in Jilin City.The standard curve comparison method was used to solve the dispersion parameters of the aquifer under the natural flow field.The test results show that under the natural flow field,the longitudinal dispersion of unconfined aquifer in Jilin City is 0.400m,and the transverse dispersion is 1.933×10-5~6.557×10-3m;while the longitudinal dispersion coefficient is 0.246m2/d,the transverse dispersion coefficient is 1.191×10-5~4.039×10-3m2/d.The above results can provide an important parameter basis for the establishment of groundwater solute transport model,the accurate prediction of temporal and spatial variation of pollutant concentration in groundwater and the formulation of groundwater pollution prevention and control scheme.

Performance evaluation of laterite soil embankment stabilized with bottom ash,coir fiber,and lime

In tropical regions,heavy rainfall induces erosion and shallow landslides on road embankments.Cement-based stabilization methods,common in these regions,contribute to climate change due to their high carbon footprint.This study explored the potential application of coir fiber-reinforced laterite soil-bottom ash mixtures as embankment materials in the tropics.The objective is to enhance engineered embankment slopes'erosion resistance and stability while offering reuse options for industrial byproducts.This study examined various mix designs for unconfined compressive strength(UCS)and permeability,utilizing 30%bottom ash(BA)and 1%coir fiber(CF)with varying sizes ranging from 10 to 40 mm,6%lime,and laterite soil(LS),followed by microstructural analyses.The results demonstrate that the compressive strength increases as the CF length increases to 25 mm.In contrast,permeability increases continuously with increasing CF length.Lime-treated mixtures exhibit superior short-and long-term strength and reduce permeability owing to the formation of cementitious materials,as confirmed by microstructural analyses.A lab-scale slope box was constructed to evaluate the surface erosion of the stabilized laterite soil embankment.Based on the rainfall simulation results,the LS-BA-CF mixtures show better resistance to erosion and deformation compared to untreated LS,especially when lime is added to the top layer.This study provides insights into a sustainable and cost-effective approach for slope stabilization using BA and CF,offering a promising solution for tropical regions susceptible to surface erosion and landslides.

INFLUENCE OF SEEPAGE FACE OBLIQUITY ON DISCHARGE OF GROUNDWATER AND ITS POLLUTANT INTO LAKE FROM A TYPICAL UNCONFINED AQUIFER

Lab experiment and mathematical simulation Modular three dimensional finite difference groundwater （MODFLOW） were performed in a soil tank to simulate the hydrogeochemical interaction between lake and typical unconfined aquifer. Results show that the velocity decreases exponentially with the transect distance on seepage face. The maximal velocity occurs at the top point of seepage face. The obliquity of seepage face has a great influence on the maximum and distribution of seepage velocity. With the increase of the obliquity of seepage face, the maximal velocity decreases quickly and the velocity distribution becomes much more even. Most of groundwater flow and pollutant flux discharges through a narrow portion near the top of seepage face. The flow and mass concentrated in the narrow portion increase with the decrease of the obliquity of seepage face. These will benefit to design a reasonable and economical scenario to manage lakeshore and to control the pollution of lake water near lakeshore.

Unconfined compressive strength prediction of soils stabilized using artificial neural networks and support vector machines

This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models.The soils used in this study are stabilized using various combinations of cement,lime,and rice husk ash.To predict the results of unconfined compressive strength tests conducted on soils,a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement,lime,and rice husk ash is used.Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement,lime,and rice husk ash under different conditions.The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering.This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks.The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models.Moreover,based on sensitivity analysis results,it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.

Modeling of unconfined compressive strength of soil-RAP blend stabilized with Portland cement using multivariate adaptive regression spline

The recycled layer in full-depth reclamation (FDR) method is a mixture of coarse aggregates and reclaimed asphalt pavement (RAP) which is stabilized by a stabilizer agent. For design and quality control of the final product in FDR method, the unconfined compressive strength of stabilized material should be known. This paper aims to develop a mathematical model for predicting the unconfined compressive strength (UCS) of soil-RAP blend stabilized with Portland cement based on multivariate adaptive regression spline (MARS). To this end, two different aggregate materials were mixed with different percentages of RAP and then stabilized by different percentages of Portland cement. For training and testing of MARS model, total of 64 experimental UCS data were employed. Predictors or independent variables in the developed model are percentage of RAP, percentage of cement, optimum moisture content, percent passing of #200 sieve, and curing time. The results demonstrate that MARS has a great ability for prediction of the UCS in case of soil-RAP blend stabilized with Portland cement (R2 is more than 0.97). Sensitivity analysis of the proposed model showed that the cement, optimum moisture content, and percent passing of #200 sieve are the most influential parameters on the UCS of FDR layer.

EXPERIMENTAL STUDY OF AIRFLOW INDUCED BY PUMPING TESTS IN UNCONFINED AQUIFER WITH LOW-PERMEABILITY CAP

The airflow in unsaturated soils is an issue of great importance in various fields such as in agricultural, nuclear, environmental engineering. However, up to now, little attention was paid to the generation of the airflow induced by a pumping test in an unconfined aquifer with a low-permeability cap and its influence on the pumping test. In this paper, pumping tests were carried out experimentally in the aquifer with a low-permeability cap in order to study the influence of the airflow induced by the pumping on the drawdown of the tests. It is shown that： （1） there is an airflow with negative pressure generated by the pumping tests, （2） the Negative air Pressure （NP） is increased with the pumping rate but decreased with the radial distance, and （3） the NP also changes with the initial water table. The results provide a good basis for further theoretical study of the airflow induced by pumping.

Investigation of a practical load model for a natural gas explosion in an unconfined space

Natural gas is extensively used as a clean energy source in cities and industries;consequently,there are associ-ated risks of accidental explosions.To reduce the hazards associated with natural gas explosions,it is important to study the inherent laws of natural gas blast loads in unconfined spaces and establish load models.Using ex-periments on natural gas explosions in unconfined spaces,this study demonstrates the influence of natural gas concentrations,propagation distances,and gas volumes upon explosion loads.A new load model was proposed for the overpressure-time history curves of natural-gas explosions in an unconfined space.A comparison with the empirical model indicated that the predictive effect was superior to that of previous models,such as the TNT equivalent model and the TNO multi-energy model.

MANAGEMENT MODEL OF UNCONFINED AQUIFER SYSTEM WITH SMALL THICKNESS WITH RESPECT TO DRAWDOWN BASED ON TWO-LEVEL RESPONSE MATRIX

In the management of unconfined aquifer systems, if the thickness of the aquifer is very small and the drawdown is relatively big, errors may arise when the superposition principle is adopted. directly. In allusion to this limitation, a new management model for the management of unconfined aquifer systems called two-level response matrix method is put forward. This method is applied in groundwater resources management in Shenyang city. The managing results show that this method can, in some degree, increase the efficiency of management and decrease the risk of management.