Slope failures often occur during soil wetting, yet most analyses rely solely on drying soil-water characteristic curve (SWCC), leading to results that do not reflect field conditions. This study develops a mathematical model to estimate bimodal permeability functions under both soil drying and wetting, and to investigate the influence of hysteresis on the stability of dual-porosity soil slopes. Analyses were performed under three scenarios: using only the drying SWCC, using only the wetting SWCC, and using both the drying and wetting SWCCs. Rainfall patterns were chosen according to records of rainfall intensities in central Asia. Drying and wetting SWCCs were tested in the laboratory, while the shear strength of unsaturated soil was a function of matric suction linked to the SWCC. Comparing the results of analyses using the three scenarios indicates that ignoring hysteresis provides an 'overly conservative' factor of safety, with differences of up to 67%. Thus, using the relevant SWCC to model drying and wetting processes in slope stability analyses is important to avoid unsafe or excessively conservative designs.
This study examines the influence of geotextile size and depth of placement (0.25B and 0.5B from footing base, where B is footing width) on the swelling characteristics and bearing capacity of expansive clay for surface and embedded square footings. The geometry of the embedment for the embedded cases is represented by a ratio Df/B, where Df is the embedment depth. The value of (Df/B) is 0.5 and the value of B is set at 6 cm. The results of swelling pressure and expansion index tests revealed that the geotextile at shallow depth (0.25H where H is the thickness of the swelling soil) reduced the swelling pressure and expansion index by 41% and 40%, respectively. Placement at 0.75H, in comparison, was practically insignificant. The optimum reinforcement structural configuration was with a 12 & times; 12 cm geotextile reinforcement, with (b/B = 2.0) and (hr/B = 0.25), where b is geotextile sheet width and hr is geotextile depth under footing base.
This paper evaluates the displacement behaviour of spun piles under lateral load in uniform fill layer overlying soft soil through three-dimensional finite element method. The numerical model is initially verified through the field measurement from the lateral pile test by adopting the solid and embedded beam (spring) element model approach. The results showed that both approaches could accurately simulate lateral pile behaviour, with the solid element offering more detailed soil-structure interaction and the embedded beam model offering computational efficiency with adequate accuracy. The parametric study demonstrates that the upper fill layer above the pile fixity point plays a major role in controlling lateral displacement, while pile diameter and load eccentricity significantly influence spun pile performance, especially in more flexible, thinner-walled piles. Furthermore, a simplified method is proposed to estimate the fixity point of a laterally loaded pile and was validated using field observations from various pile case histories.
Active earth pressure theories often ignore matric suction in unsaturated backfills behind retaining walls, yet suction enhances soil arching and alters pressure distribution, especially in narrow spaces. This study extends unsaturated soil shear strength models to soil-structure interfaces, validates them with experimental data, then develops an improved horizontal slice method using arch-shaped elements and two suction profiles to account for infiltration. A semi-analytical solution for wall rotation about the base (RB) is obtained via the fourth-order Runge-Kutta method. The framework agrees well with numerical simulations, experiment data, and existing theories. Parametric studies show: suction reduces active pressure, producing S- or M-shaped profiles; its effect fades beyond a critical change rate; pressure depends on suction type and soil properties; and the critical aspect ratio varies with displacement mode, suction, and strength model. These findings underscore the importance of unsaturated soil mechanics in retaining wall design, particularly for narrow backfills.
As vital fill for tropical reef engineering, coral sand features distinctive mechanical properties under complex slope stress. Undrained cyclic torsional shear tests were performed to explore shear strain (gamma) and excess pore-water pressure (u(e)) of saturated coral sand subjected to varied initial static shear stress (tau(s)). Results show that total gamma includes cyclic fluctuating and residual parts: zero tau(s) yields fluctuating gamma, whereas tau(s) induces monotonic gamma growth dominated by residual strain. Defined R-CSR approximate to 0.33 marks equal contribution of two strain fractions; residual strain ratio depends on relative density (D-r), with fitted prediction formulas derived. Based on the 5% single-amplitude shear strain failure threshold, an evolution model linking residual strain to cycle ratio (N/N-f) is proposed. Rising static shear stress ratio (SSR) restrains u(e) buildup; D-r and and cyclic stress ratio barely affect failure u(e) . Modified hyperbolic formulations well reproduce ue ratio development against N/N-f.
The simultaneous movement of heat and water underground is a complex and complicated process playing a vital role in the performance, sustainability, and durability of shallow geothermal systems. An experimental investigation was carried out to assess the influence of water flow on the temperature distribution and effective thermal conductivity in a mixture of sand and kaolin with 0, 20, 40, 80, 90 and 100% sand content. The effective thermal conductivity (ke) was determined taking into account the contribution of heat conduction and convection under steady-state condition. The results show that water movement has an effect on the temperature distributions even at the mixtures with low sand content, the mixtures with low water velocity and the effect depends on initial temperature of the moving water and velocity. The ke increased because of the convective heat of the water, in particular, in mixtures with high velocity, in sand-kaolin mixtures with 80%, 90%, and 100% sand content where the velocity was in the range between 4.98 & times;10-5 and 6.18 & times;10-7 m/s. Analysis of data shows that a preliminary evaluation of the influence of water flow could be known by inspecting the Peclet number (Pe) using water velocity and mean pore size of the soil mixture..
Fracturing fluid contacting shale reservoirs triggers spontaneous imbibition and clay hydration, altering shale matrix structures and causing fracture generation or blockage, which hinders reservoir evaluation and production planning. Taking Sichuan Basin shale cores as research objects, this study conducted imbibition, clay hydration, pore testing and well soaking experiments to clarify matrix and fracture evolution during imbibition. The results indicate montmorillonite and illite water absorption and expansion dominate shale imbibition. Clay hydration deformation lags hydration stress, with dual effects on fracture extension. Montmorillonite's sustained hydration promotes fracture propagation. The optimal soaking time is 30 days for montmorillonite-rich Block B and 20 days for illite-rich Block A.
The award-winning New Bridgewater Bridge (NBB) Project represents Tasmania's largest-ever transport infrastructure undertaking. Its success hinges on the geotechnical design of large-diameter monopiles supporting 21 bridge piers and two abutment piers across the River Derwent. Ranging from 2.1 to 2.45 meters in diameter and socketed into variable rock, one pile reached 91.5 meters, potentially making it the deepest mono-bored pile in the Southern Hemisphere. The challenging geological environment, featuring estuarine muds and diverse rocks, demanded rigorous assessments of scour and seismic hazards, including liquefaction and lateral spreading. Advanced iterative design processes were utilized. Osterberg cell (O-cell) testing provided pivotal design validation, confirming that mobilized shaft skin friction and end bearing resistance exceeded assumptions. Surveys showed over 82% of the piles exhibited settlements matching predictions within +/- 1-4 mm under dead loads. This robust empirical validation proves the accuracy of the employed methodologies, offering significant insights for future deep foundation projects.
To investigate the influence of structural characteristics on the bearing capacity of strong-weak composite backfills, the strength and deformation-failure characteristics of homogeneous backfill (HB), horizontally layered-structured composite backfill (HLS), and vertically strip-structured composite backfill (VSS) were compared under the same overall cement-to-tailings ratio. Results show that VSS is less sensitive to differences in strong-weak media properties, has higher energy storage capacity, and exhibits staged failure, with damage initiating in weak strips and ultimately governed by strong strips, resulting in greater energy release. HLS exhibits lower overall strength and elastic modulus, with failure concentrated in the weak layer, which enhances the stability of critical roof and floor load-bearing regions. These findings provide a theoretical basis for selecting appropriate strong-weak composite backfill structures under differentiated engineering conditions.
This paper investigates shaft resistance mobilization of two large-diameter bored piles subjected to axial upward and downward static loading using Osterberg cell (O-cell) tests in soft clay for the Sei Alalak Bridge Project, South Kalimantan, Indonesia. A two-dimensional axisymmetric finite element model was developed to evaluate the pile response. Field and numerical axial load displacement curves show that the lower pile segment experienced larger displacement than the upper segment. Good agreement was also observed between field measurements and numerical predictions in terms of the equivalent top load settlement curve and shaft resistance displacement relationship. Numerical results further indicate that full skin friction and tip resistance were mobilized at pile displacements of approximately 0.5% to 0.75% and 10% of the pile diameter, respectively, confirming that shaft resistance requires much smaller displacement than tip resistance, and is mainly controlled by pile soil relative displacement and interface shear development.
Drilling vertical and deviated wells in the southern Iraqi oilfield encountered several challenges. One of the most prevalent issue is the mechanical pipe sticking, resulting from inadequate hole cleaning and borehole instability. This will result in an escalation of both expenses and non-productive time (NPT) related to well drilling. This study was motivated to overcome the issue of the mechanical pipe sticking by developing two separate models for the area of concern. To successfully remove the drill cuttings from the wellbore to the surface, a hole-cleaning model was firstly constructed using the Well Plan (TM) software. Thus, the required minimum flow rate and cutting bed height were determined. Then, to ensure stable and secure borehole conditions, a one-dimensional geomechanical model was established to identify a suitable drilling fluid density for different wellbore trajectories. The findings indicate that the drill string stuck at a depth of 2214 m (Tanuma formation) because the value of the minimum flow rate (732 gpm) exceeded the actual flow rate (629 gpm). Further, using low mud weights ranging from 10.46 to 10.80 ppg to drill intermediate and production borehole sections was the primary cause of the mechanical pipe sticking issue in this particular well. It is advisable to increase the mud weight range from 10.8 to 12.6 ppg for both borehole sections at an inclination angle of approximately <= 30 degrees and an azimuth of 140 degrees. Finally, this study proposes cost-effective approaches for organising nearby directional wellbores to boost drilling efficiency.
