Negative Pore Water Pressure Research Articles

Analytical solution for radial consolidation of combined electroosmosis-vacuum-surcharge preloading considering free strain and cyclic loading

In this study, electro-osmotic consolidation considering smear effect and free strain under cyclic loading was investigated. The analytical solution of radial consolidation of electroosmosis-vacuum-surcharge combined preloading is derived by using the Bessel function and eigenfunction methods. Subsequently, the effectiveness of the proposed method is validated through comparison with existing numerical solutions. Based on the derived solutions, the influence of the smear effect, applied voltage, vacuum pressure, and cyclic loading on soil consolidation characteristics was analyzed. The results showed that the smearing effect slows the rate of consolidation, but the final average consolidation and negative excess pore water pressure are enhanced. Compared with only cyclic loading, the combined effect of electroosmosis, vacuum, and surcharge preloading enables the soil to achieve higher strength and consolidation. When the effect of electroosmosis alone on reinforcing low-permeability soils is not significant, the combination of electroosmosis with vacuum preloading helps enhance the soil reinforcement effect.

Dynamic response of seabed in wind power of deep-shallow sea induced by internal solitary waves

With the development of offshore wind power projects worldwide, the stability of deep and shallow sea wind power sites has become a crucial concern. Internal solitary waves (ISWs) are nonlinear and large amplitude waves in the stratified ocean. Their strong vertical and horizontal motion and vorticity and turbulence caused by fragmentation have an important impact on the marine environment, seabed sediments, and marine engineering. This study focuses on the interaction between ISWs and the seabed of wind power sites in deep and shallow seas. Specifically, we investigate the interaction between ISWs and monopile foundations or floating fan plate anchor structures in the seabed. Through the simulation of CFD software and Comsol software, a law of seabed pore pressure variation during the effect of ISWs on the structure can be well demonstrated. Our results demonstrate that ISWs induce the accumulation of excess pore water pressure around the structures. The monopile foundation experiences negative excess pore water pressure at its bottom and the plate anchor at its top. The pore water pressure at the bottom of the monopile foundation initially decreases and then increases. In contrast, the pore water pressure at the right side of the monopile foundation increases, decreases, and then increases. This phenomenon promotes the settlement of the structure. At the bottom of the plate anchor, there is a sharp increase in positive excess pore water pressure by ISW. The pore water pressure above the plate anchor structure initially decreases and then increases, while below the plate anchor, it increases and then decreases. This phenomenon leads to the movement of the anchorage structure and instability of the surrounding soil. The influence of ISWs on the seabed bottom intensifies with the obstruction of the structure, resulting in significant positive pressure at the bottom. Between the two anchoring structures, there is increased seepage of pore water, making the seabed more prone to instability. Through the study of this article, we know that ISW has different effects on the force of monopile foundation and plate anchor structure, which provides a favorable basis for its design and maintenance.

Experimental investigation of dewatering silty tailings using electrokinetic method

Mining and using underground resources demand high water usage, producing significant waste with environmental risks. Methods like electrokinetics prove effective in accelerating dewatering and stabilizing structures. This research provides the results of experimental investigation on dewatering silty tailings obtained from Sungun Tailings Dam (East Azerbaijan, Iran) using the electrokinetic water recovery method. Previous studies primarily examined the electrokinetic process in steady-state flow and saturated soil, with limited exploration of unsaturated soil parameters. In this research, the electrokinetic process in steady-state flow was initially investigated, and the saturated electro-osmotic permeability was determined. Subsequently, experiments were conducted in non-steady-state flow and unsaturated conditions, measuring the influential parameters with soil moisture sensors and tensiometers. Results show that decreasing sample moisture through electro-osmotic flow increases negative pore water pressure. Tailings' electrical conductivity is more influenced by moisture content, with a steeper reduction slope concerning volumetric moisture reduction over time. pH assessments show soil acidity at anode side and alkalinity on the cathode side. Higher applied voltage increasing maximum power consumption. Importantly, the results caution against assuming that higher applied voltage improves the electro-osmotic process, as it may lead to issues such as deep sample cracking; void space creation, interrupted electrical flow, and energy loss.

Mechanism of a rainfall-induced landslide in a large-scale flume experiment on a weathered granite sand

IntroductionsA large-scale flume experiment was performed to evaluate the mechanism of landslide occurrence due to rainfall using weathered granite sand. The dimensions of the flume were 9 m (length), 1 m (width), and 1 m (depth). The weathered granite sand from the actual landslide site at Da Nang City, Vietnam was used. The pore water pressure was measured by a pore-water pressure transducer at two depths (middle and bottom) to determine the process of rainwater infiltration into the soil. The surface deformation was measured with extensometers at three positions of the slope. The deformation of the entire slope was determined by the 160 cylindrical-shaped makers evenly spaced in the slope and three cameras.ResultsThe results showed that the rainfall infiltrated into the slope process, increasing from negative pore water pressure to approximately 0. The maximum shear strain contour has been plotted in total and in time increments. The shear band was detected from the time increments maximum shear strain contour. The localization in the shear band formed just before failure.ConclusionsTo the best of our knowledge, this is the largest scale laboratory test ever conducted to calculate the shear band. Moreover, it was found that the failure occurred when the sand was in an unsaturated phase. Failure does not seem to depend on the increase in pore water pressure but on the maximum shear strain. This feature can be used to explain the phenomenon of landslides that occur even when the groundwater level does not increase but large deformation occurs.

Influences of strain rate on mechanical behaviors of unsaturated and quasi-saturated loess under varying drainage conditions

Although time-dependent deformation of geomaterials underpins slope-failure prediction models, the influence of strain rate on shearing strength and deformation behavior of loess remains unclear. The consolidated undrained (CU) and drained (CD) triaxial testing elucidated the impact of strain rate (0.005–0.3 mm/min) on strength envelopes, deformation moduli, pore pressures, and dilatancy characteristics of unsaturated and quasi-saturated loess. Under drained conditions with a controlled matric suction of 50 kPa, increasing strain rates from 0.005 mm/min to 0.011 mm/min induced decreases in failure deviatoric stress (qf), initial deformation modulus (Ei), and cohesion (c), while friction angles remained unaffected. Specimens displayed initial contractive volumetric strains transitioning to dilation across varying confining pressures. Higher rates diminished contractive volumetric strains and drainage volumes, indicating reduced densification and strength in the shear zone. Under undrained conditions, both unsaturated and quasi-saturated (pore pressure coefficient B = 0.75) loess exhibited deteriorating mechanical properties with increasing rates from 0.03 mm/min to 0.3 mm/min. For unsaturated loess, reduced contractive volumetric strains at higher rates manifested relatively looser structures in the pre-peak stress phase. The strength decrement in quasi-saturated loess arose from elevated excess porewater pressures diminishing effective stresses. Negative porewater pressures emerged in quasi-saturated loess at lower confining pressures and strain rates. Compared to previous studies, the qf and Ei exhibited rate sensitivity below threshold values before attaining minima with marginal subsequent influence. The underlying mechanism mirrors the transition from creep to accelerated deformation phase of landslides.

Long-term “memory” of extraordinary climatic seasons in the hysteretic seepage of an unsaturated infinite slope

This paper presents a study of the hydraulic response of an infinite unsaturated slope exposed to a perturbation of the ordinary seasonal climatic cycle. The ground flow is modelled via a simplified one-dimensional finite difference scheme by decomposing the two-dimensional slope seepage into antisymmetric and symmetric parts. The numerical scheme incorporates two distinct hysteretic and non-hysteretic soil water retention laws, whose parameters have been selected after a preliminary sensitivity analysis. Results indicate that, in the hysteretic case, the “memory” of the perturbation takes a long time to fade, and the ordinary soil saturation cycle is only restored after several years of normal weather. Instead, in the non-hysteretic case, the recovery of the ordinary saturation regime is almost immediate after the perturbation. In contrast with the markedly different predictions of degree of saturation, both hysteretic and non-hysteretic slope models predict virtually identical evolutions of negative pore water pressures, with an almost immediate restoration of the ordinary cycle after the perturbation.

A Temperature-Controlled Apparatus for Gas Permeability under Low Gas Pressure

The measurement of soil gas permeability is influenced by the temperature and pressure fluctuation in the low gas pressure region. In order to investigate these influences, a soil temperature-controlled apparatus connected to a low-gas-pressure supply equipment is proposed in this study. The low constant gas pressure is supplied by two Mariotte bottles, by which the airflow rate is measured. Meanwhile, the soil specimen is controlled by a temperature-controlled apparatus. During the test, the negative pore water pressure and volume change of the soil specimen are measured. Through the temperature-controlled apparatus, it is observed that as the temperature increases from 25 °C to 60 °C, there is a corresponding increase in soil sample porosity by 5.4%, while the negative pressure of pore water decreases by 11.1%. This can be attributed to the reduction in the surface tension of contractile skin caused by elevated temperatures. Furthermore, due to variations in gas viscosity with temperature, there was a significant decrease in the gas flow rate by 50.5%. And, the relationship between permeability and volumetric gas content at different temperatures in low-pressure regions well confirms the existing power-law model. In addition, the existence of a temperature-independent critical negative pore water pressure is observed, beyond which the intrinsic permeability remains constant. At 36 kPa of negative pore water pressure, the intrinsic permeability at 60 °C exhibits an 81.8% reduction compared to that at 25 °C. This decline in intrinsic permeability can be attributed to a diminished pore connectivity, resulting from elevated temperatures.

Semi-analytical solution of pore-water pressure in unsaturated ground and infinite slope considering highly nonlinear soil hydraulic properties

A multi-exponential function (ME) is proposed to depict the highly nonlinear soil water retention curve and hydraulic conductivity function. Then, semi-analytical solution of pore-water pressure in an unsaturated infinite slope at steady state is derived using ME to depict soil hydraulic properties. The solution is verified with experimental and numerical results. It is found that ME can better describe the highly nonlinear hydraulic properties of soil than the single exponential function (SE), which is commonly-used previously. At steady state, the adoption of SE results in overestimating negative pore-water pressure (PWP; i.e., matric suction) by about 25 kPa and slope’s factor of safety (FOS) by 100% under rainfall, but underestimating negative PWP by about 50 kPa under evaporation. The difference between PWP and FOS calculated by using SE and ME becomes more significant for soil with bimodal hydraulic conductivity function than that with unimodal one. This difference reduces at a larger slope angle and deeper depth. Moreover, this difference generally increases at a lower SME/SSE, where SME and SSE represent the suction at which the unsaturated hydraulic conductivity expressed by ME and SE equals the applied rainfall intensity or evaporation rate, respectively. When SME/SSE is greater than 0.1, the difference basically diminishes.

Analytical solution of electroosmotic-surcharge preloading coupled consolidation for unsaturated soil via Electric Prefabricated Vertical Drains (EVDs)

Electric prefabricated vertical drain made of new geosynthetic materials has the advantages of corrosion resistance, good water filtration, and unobstructed drainage. It has been used in unsaturated soils for embankment and slope stabilization as well as roadbed improvement. A theoretical model of the axisymmetric, free-strain consolidation for unsaturated soil under the coupled electrical-flow-mechanical fields considering radial-vertical flow is formulated, using the homogenization theory, method of separation of variables, and Bessel-Fourier series orthogonality. The relevant cases of saturated and unsaturated conditions are compared with the current analytical solution to examine the validity. The spatial and temporal distributions of excess pore-water and pore-air pressure are accurately reflected in the proposed solution, and its variation under electric fields is effectively displayed. The numerical calculations are also performed to investigate the effects of various important parameters, such as the single-layer unsaturated soil thickness, the effective voltage, and the radial water-to-electrical permeability ratio, on the excess pore-water pressure, excess pore-air pressure, and surface settlement. It is observed that the final negative pore-water pressure and the final settlement increase linearly as the effective voltage increases.

Partially drained uplift behaviour of plant roots in dilative soils

A large volume of research reporting the pull-out behaviour of root systems is available, but no study has considered the effects of soil drainage. This work implemented a modified three-dimensional embedded beam element model in a finite element platform that solved model equations by using a fully hydromechanically coupled algorithm. The model was validated against published centrifuge pull-out tests on root analogues, and the validated model was then applied to study parametrically the influence of the ratio of uplift rate to soil hydraulic conductivity on pull-out behaviour. The results demonstrated that the model can well capture the prepeak behaviour of the root systems up to the peak pull-out resistance. The generation of negative pore–water pressure ( p e x) owing to soil dilation upon root–soil interfacial shearing was the major reason for increased pull-out resistances under partially drained conditions. Compared with other root systems, root systems with smaller branch angles and deeper branch depths mobilised considerably more significant plastic deviatoric strains in the soil in their vicinity, generating more negative p e x. Hyperbolic dimensionless backbone curves were derived to explain the transitional pull-out behaviours of root systems of different geometries under drainage conditions that ranged from fully drained to undrained.

Behavior of Partially Saturated Cohesive Soil under Strip Footing

In this paper, a shallow foundation (strip footing), 1 m in width is assumed to be constructed on fully saturated and partially saturated Iraqi soils, and analyzed by finite element method. A procedure is proposed to define the H – modulus function from the soil water characteristic curve which is measured by the filter paper method. Fitting methods are applied through the program (SoilVision). Then, the soil water characteristic curve is converted to relation correlating the void ratio and matric suction. The slope of the latter relation can be used to define the H – modulus function. The finite element programs SIGMA/W and SEEP/W are then used in the analysis. Eight nodded isoparametric quadrilateral elements are used for modeling both the soil skeleton and pore water pressure. A parametric study was carried out and different parameters were changed to study their effects on the behavior of partially saturated soil. These parameters include the degree of saturation of the soil (S) and depth of water table. The study reveals that when the soil becomes partially saturated by dropping water table at different depths with different degrees of saturation, the bearing capacity of shallow foundation increases about (4 – 7) times higher than the bearing capacity of the same soil under saturated conditions. This result is attributed to matric suction value (i.e negative pore water pressure). The behavior of soil in partially saturated condition is likethat of fully saturated condition but with smaller values of displacement. It is found that the settlement is reduced when the water table drops to a depth of 2 m (i.e. twice the foundation width) by about (92 %).

Fluid–Solid Coupling Numerical Analysis of Pore Water Pressure and Settlement in Vacuum-Preloaded Soft Foundation Based on FLAC3D

There are few calculation methods for the design and construction of vacuum preloading to strengthen soft foundations. Based on the FLAC3D, a calculation model was established for the vacuum preloading project of the Beijing–Shanghai high-speed railway. Through calculation and comparison of measured values, the following results were obtained: (1) The top surface of the reinforcement area and the sand drain can be regarded as the load boundary, which can be realized by assigning the node pore water pressure. (2) After 30 days of vacuum action, the settlement rate at each depth decreased significantly and the deformation gradually became stable. It is reasonable to design the vacuum preloading time as 2–4 months. (3) The negative pore water pressure has different transmission times and uneven distribution, which makes the consolidation time and degree of soil on the same level uneven. After 30 days of vacuum action, this uneven phenomenon will be transformed into a uniform phenomenon. (4) The change time of pore water pressure under vacuum preloading is about 30 days. After that, the pore water pressure at different depths will tend to have different constant values. The influence depth of vacuum preloading can reach 16 m. These works can make up for the deficiency of vacuum preloading calculation methods.

Effects of plant-biochar interaction on the performance of a landfill cover system: field monitoring and numerical modelling

Biochar has been used as a sustainable amendment to moderate the risks of climate change to plant and soil management. A 3-year field monitoring was conducted at Shenzhen Xiaping landfill to evaluate the performance of a three-layer landfill cover using plant and biochar. Coarse-grained completely decomposed granites (CDG) amended with peanut shell biochar at 0%, 5% and 10% (m3/m3) were used for the top layers of three grass plots (10 m×5 m each), respectively. Coarse recycled concrete and fine-grained CDG were used for the middle and bottom layers of all plots. Numerical simulation was conducted to back analyse the monitored results. The results show that the grassed cover with biochar can retain over four times higher negative pore-water pressure than that without biochar. During the monitoring, over 62% of total rainfall was evapotranspirated from biochar amended covers, which was 10% larger than the cover without biochar. With biochar amendments, the infiltration amount was reduced by 13%, but water storage was improved by up to 15%. The measured and computed percolation of the grassed covers with 0%, 5% and 10% biochar meet the recommended criterion by USEPA. It is recommended that 5% biochar content is sufficient to minimise water percolation.

Experimental study of ultra-high backpressure influence on the monotonic mechanical characteristic of silty sand

In this paper, a series of monotonic triaxial tests were carried out at a relatively wide range of backpressure conditions (from 100 kPa to 29 MPa) to investigate its influence on the shear properties of silt sand.Backpressure effect on the shear strength, excess pore pressure, and volumetric strain behavior were analyzed,and the underlying influencing mechanism was preliminarily discussed. According to test results, the application of higher backpressure conditions on quasi-saturated samples resulted in a significant buildup of negative excess pore water pressure, which led to an increase in shear strength. The trend became less pronounced after the backpressure exceeded 5 MPa. Nevertheless, within this range, the shear strength increased by approximately 40 kPa for every 100 kPa increase in backpressure. Furthermore, the consolidated-drained (CD) test results revealed that the value of backpressure (at least within 29 MPa) had no detectable influence on the shear properties of saturated samples. It was indirectly proved that the undrained shear strength was influenced by the change of effective stress caused by excess pore water pressure in the shear dilation stage of quasi-saturated samples. The applicability of the effective stress principle to predict soil strength even in ultra-high backpressure conditions was confirmed.

Case Study and Risk Assessment of Water Inrush Disaster in Qingdao Metro Line 4

Water inrush is one of the most frequent and catastrophic hazards in tunnel engineering, and poses serious threats to the safety of engineering and personnel. This paper presents a case study of a water inrush and ground collapse in the Qingdao Metro Line 4, which caused a cave-in with the diameter and depth of about 30 m and 6 m, respectively. Based on the field data and numerical modelling, the causes of the disaster were analyzed. A numerical model was used to analyze the changes of surface settlement, vault settlement and water pressure during the tunnel excavation. The results of the study indicate that the cause of this disaster was the failure of the tunnel vault surrounding rock caused by the weakening of the tunnel surrounding rock and water pressure, which in turn triggered the water inrush in the tunnel and caused a large volume of surface collapse. As the tunnel was excavated from the slightly weathered area to the strongly weathered area, the vault settlement increased, and the influence zone expanded towards the surface due to the continuous decrease in the strength of the surrounding rock. In particular, a negative pore water pressure zone was formed in a certain area around the tunnel during the water inrush. The negative pressure zone caused the surrounding groundwater to converge here, leading to an increase in the amount of water inflow, which also increased the scope and scale of the impact of this disaster. A risk assessment method for water inrush in tunnels is proposed. According to the geological and engineering characteristics of Qingdao area, the evaluation index system of tunnel water inrush risk was established. An RBF neural network was improved by gray correlation analysis and a PAM clustering algorithm to establish the tunnel water inrush risk assessment model. Comparing the evaluation data with the actual data, the prediction data of a traditional RBF neural network and a BP neural network, the accuracy and reliability of the model were verified. This study has value in reducing the occurrence of water inrush in a composite formation tunnel.

Numerical Simulation of Embankment Settlement in Vacuum Preloading Systems

In Indonesia, the construction of the road has challenges because the road was built on soft clay soil. The vacuum preloading method was used to improve the shear strength and compressibility properties of soft soil in this project. Moreover, what needs to be a concern for practitioners is the issue of increasing simulation accuracy in predicting soil settlement in a vacuum preloading system. The research objective of this study was to determine changes in soil settlement behavior that occurred from the vacuum preloading system using a numerical simulations Geostudio with the 2D Multi Drain-Plane Strain approach and the settlement result of the simulation will be compare with instrumentation data. In this study the vacuum pressure distribution is modeled using water total head negative pore water pressure and the pressure value used following vacuum gauge data in the field with distribution approach is 100% at the surface of the sand platform, 85% to a depth of 5 m, then 60% to the end of the PVD. Based on the simulations, the conlusion is the vacuum pressure applied along the vertical drainage is not modeled constant, but changes with depth, the value of 60% at the bottom of the vertical drainage is quite representative of the conditions in the field and the settlement from the simulation is quite good at approaching the field observation with a prediction of the settlement due to vacuum preloading of ±0.93 m, when compared to the field observation data there is a difference of about 1.6%.

Pore pressure response during tube sampling in gold tailings

Capturing the in-situ state of mine tailings is important in determining its behaviour under loading for evaluating the risk of failure of tailings dams. Obtaining a high-quality undisturbed sample through tube sampling is thus of great value to the responsible engineer. However, the sampling process itself disturbs the soil and changes its state. Since soil behaviour is driven by effective stress, one method to evaluate the disturbance induced during tube sampling is to monitor the soil’s positive and negative pore water pressure response during the process. A laboratory study was conducted where tailings samples were prepared at a controlled void ratio and subsequently saturated with water. Tube samplers of different diameters were driven into the material and extracted by means of an electric actuator during which internal sample pore pressures were monitored using tensiometers. The material experienced significant instantaneous contractive and dilative tendencies during insertion. Instantaneous negative responses during extraction of the tube samplers were also measured. It was found that the largest tube sampler (100mm diameter) performed best in the study.

Parametric Analysis of Factors that Affects the Rainfall Induced Slope Stability

Slope failures are one of the most vital problems in geotechnical engineering applications which may cause damage both in human life and financial. Slope failures are frequently observed especially in regions where rainfall is high. The most important factor affecting slope stabilities is rainfall infiltration. It is known that infilled soils are generally unsaturated soil. Therefore, the analysis of infill slopes should be performed within the scope of unsaturated soil mechanics. Rainfall infiltration causes the groundwater level to rise, which reduces the shear strength of the soil causing slope instability. In this study, the effect of rainfall intensity, rainfall duration, soil permeability, groundwater level, cohesion of soil, internal friction angle of the soil, and slope angle of the slope on the slope stability were analyzed parametrically by using GEOSTUDIO software. The infiltration analyses were performed using Seep/w module and factor of safety number of unsaturated soil slope were determined using Morgenstern method of Slope/w module of GEOSTUDIO software. Furthermore, different factor of safety numbers was found for each analysis along with the interpretation of the parameters effecting the slope stability. The results obtained in the present investigation showed that the rainfall intensity affects the stability of the slope. It was determined that there existed a non-linear relationship between rainfall intensity and safety number. As the rainfall intensity increases, the negative pore water pressure in the soil decreases nonlinearly, and the factor of safety number of the slope similarly decreases by 10% relative to the initial condition. When the rainfall duration change was taken into account, it was found that short time-heavy rainfalls affected the slope stability more than long time-low density rainfalls. Moreover, slope angle significantly influenced slope stability. It was observed that when the slope angle increased from 40° to 50°, factor of safety number decreased by 18.34%.

Drained Shear Strength Parameters Of Saprock From A Weathering Profile Over Porphyritic Biotite Granite At Km 31 Of The Kuala Lumpur - Karak Highway, Peninsular Malaysia

Three broad zones can be differentiated at the weathering profile; an upper, 9.4 m thick, pedological soil (zone I), an intermediate, 31.7 m thick, saprock (zone II) and the bottom bedrock (zone III). The saprock (zone II) comprises gravelly silty sands that distinctly preserve the minerals, textures and structures of the original bedrock and can be separated into sub-zones II A, II B, II C and II D based on differences in preservation of relict structures and content of litho-relicts (core-boulders). To characterize the drained strength of saprock, samples were collected from sub-zones II B, II C and II D, and their physical and soil index properties determined before consolidated, drained triaxial tests were carried out on remolded specimens. Three individual specimens from each sub-zone were consolidated for 24 hours and compressed at a rate of 0.152 mm/min under confining pressures of 138 kPa, 207 kPa and 276 kPa. The tests yielded effective cohesions (c’) of 30.6 kPa, 9.5 kPa, and 20.2 kPa, and friction angles of 33.2o, 31.4o and 34.4o, for the samples from sub-zones II B, II C and II D, respectively. Regression analyses show effective cohesions (c’) to increase with increasing moisture contents retained at 4.19 pF (1,500 kPa) suction; a feature indicating the influence of negative pore water pressures (matric suction). Regression analyses also show effective friction angles to increase with increasing sand, and sand and gravel, contents; a feature indicating increased inter-locking and resistance to displacement of coarse particles during shear. It is concluded that the saprock is characterized by an average effective cohesion of 14.5 kPa, and friction angle of 34.3o; these parameters influenced by the moisture content retained at 1,500 kPa suction, and the sand and gravel contents.

Suction dynamics‐induced bubbly sand under groundwater table fluctuations

ABSTRACTBubbly sand is found in intertidal zones and has been considered to be closely related to swash and tides. Unlike bubble structures that arise from in situ methane gas production and bubble growth in river and marine sediments due to organic matter decomposition, the formation mechanism and conditions of bubbly sand remain unresolved. The present study aims to resolve them on the basis of a conceptual model and controlled laboratory experiments. The study demonstrates that bubbly sand is a consequence of the cyclic expansion of sand under groundwater table fluctuations. The varying intensity of dynamics of suction, which is sand moisture tension defined by negative pore water pressure relative to atmospheric pressure, controls the manifestation of a full spectrum of sand behaviour relevant to the formation of bubbly sand. Namely, with increasing intensity of suction dynamics under larger groundwater table fluctuations, the sand behaviour varies from enhanced cyclic contraction, to weak contraction, loosening and expansion resulting in bubbly sand. The suction dynamics‐induced cyclic expansion of sand occurs under conditions where the maximum suction developed exceeds the air‐entry suction of sand such that the degree of saturation becomes lower than 60%, while the groundwater tables cyclically rise to and fall from the sediment surface. Accordingly, the sand porosity changes remarkably from dense to super‐loose states of bubbly sand. These findings account for previously unanswered questions with respect to bubbly sand, both qualitatively and quantitatively, and will lead to a renewed understanding of the geological record and morphological features at waterfronts that are subject to groundwater table fluctuations.