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Consolidating dredged clay slurries using a combination of vacuum pressure and prefabricated horizontal drains (PHDs) is widely used in practice. This is a large strain problem, but there is no existing large strain theory for PHD induced consolidation. A method with explicit equations has been proposed to consider both mechanical and geometrical non-linearities in analyzing PHD induced consolidation. The method considers stepwise variation of properties using imaginary time concept. An imaginary time is determined by the condition of continuity of degree of consolidation before and after changing the properties. Then the method was applied to analyze a large scale model test of vacuum consolidation with PHD. Two analyses were conducted. One considered both the mechanical and geometrical non-linearity (large strain), and another only considered mechanical non-linearity (small strain). The results of large strain analysis agree with the measured settlement curve and excess pore pressures well. While the small strain analysis under-estimated the rate of consolidation significantly. The results from this study indicate that for analyzing PHD induced consolidation of clay slurries considering the effect of large strain is important, and the proposed method can be a useful design tool.

Prefabricated vertical drains (PVDs) and deep cement mixing (DCM) columns combined ground improvement with a vacuum pressure for embankment construction on soft clay deposits has advantages, such as limiting embankment load induced deformation of adjacent areas and reducing total ground improvement cost. However, for design this kind of soft ground improvement, there are no methods for estimating amount of ground deformations as well as maximum tensile stress in the DCM columns. A series finite element analyses (FEA) were carried out to investigate the performance of embankments on combined PVD together with a vacuum pressure and DCM column improved soft deposit. Based on the results of FEA, explicit method for calculating ground settlement under the center of embankments, graphic methods for predicting maximum tensile stress in the column and maximum lateral displacement under the toe of embankments have been established. It is suggested that these methods can be useful tools for design this kind of combined soft ground improvement, and a working example has been demonstrated.

In this study, a deep excavation in an under-consolidated deposit in Zhuhai, China, was reported and investigated via plane strain finite element analysis (FEA). First, the project was simulated via FEA (under-consolidated deposit), and a reasonable agreement between the lateral displacement of the measured and simulated retaining wall was obtained. Another FEA was then conducted under the assumption that the deposit was in a normally consolidated state. The numerical results indicate that the under-consolidated case resulted in a 25% increase in maximum lateral displacement of the contiguous pile-formed retaining wall, a 32% increase in bending moment in the wall, and approximately twice the maximum surface settlement behind the wall, when compared with those of the normally consolidated case. The main reasons for this are as follows: (1) the under-consolidated deposit was weaker, and (2) the ongoing consolidation of the under-consolidated deposit induced green-field settlement (approximately 4 mm) during the project period, thereby enhancing the bending deformation of the wall. Therefore, when designing deep excavation in an under-consolidated deposit, not only its weaker strength but also the negative effect of green-field settlement during the project period should be considered.

This study investigates the reduction of groundwater level in the soil deposit below the ground surface under vacuum consolidation. Theoretically, when the applied vacuum pressure is less than the air-entry value (AEV) of the soil deposit, the deposit will be in a saturated state and the groundwater level in the pre-fabricated vertical drains (PVDs) will not go below the ground surface during the vacuum consolidation process. In this case, the groundwater level is not a phreatic water level. If the applied vacuum pressure is larger than the AEV of the soil, part of the soil deposit can become unsaturated and the groundwater level in the PVDs can go below the ground surface. Further, the results of a large-scale vacuum consolidation model test using clay confirmed that during the consolidation process, the water level in the mini-PVD was always above the top surface of the model ground. Therefore, an attempt to measure the groundwater level in a vacuum consolidation area composed of clay deposits may not be worthwhile.

Prior investigations have revealed that the stress characteristics of columns at different locations beneath an embankment vary. A failed column releases stress and causes significant increases in the stresses within neighbouring columns, possibly leading to progressive failure of adjacent columns and global failure of the embankment. Prior studies have presented insights into the progressive failure of column-supported embankments. However, limited insight has been provided into the progressive failure mechanism of geosynthetic-reinforced and rigid column-supported embankments. In this technical note, the effects of geosynthetic reinforcement on progressive failure are numerically analysed. A comparison of the progressive failure of rigid columns with and without geosynthetic reinforcement is first conducted. The restraining effects of geosynthetics on progressive failure of the columns and the influence of geosynthetic tensile stiffness on embankment stability are analysed. The results reveal that progressive failure is primarily governed by the distribution of the bending moment and the axial force within the columns. To further investigate the contribution of geosynthetics to resisting progressive failure of rigid columns, the internal forces in the columns and tensile strains in the geosynthetics are discussed.

A large volume of groundwater is withdrawn annually in Tianjin Municipality, China, to meet agricultural, industrial, and municipal water uses. Groundwater overdraft in the urban districts and the Binhai New District in Tianjin Municipality has caused land subsidence. A series of field observation wells were installed to monitor the long-term groundwater level (GWL). The hydrostratigraphy of the aquifer system underlying Tianjin consists of four aquifer layers. The middle two aquifer layers are the main layers for groundwater withdrawal. The GWL of the top two aquifer layers responded rapidly to recharge from precipitation and seawater intrusion. The GWLs of the bottom two aquifer layers have been dropping steadily over the past 50 years. The aquifer sediments underlying Tianjin Municipality consist mainly of fine sand, silt, and clayey soil. The decline of the GWL has induced substantial land subsidence and led to overconsolidated compressible sediments.

Anionic polyacrylamide (APAM) and quicklime are used to improve vacuum preloading of waste slurry in Shanghai, China. To investigate the influence of these reagents on waste slurry sediment consolidation, tests on laboratory-scale models with and without the reagents were conducted and the results analyzed. Sediment settling was recorded and used to calculate the water content changes during vacuum consolidation. After vacuum consolidation, the water content of sediment samples collected at different distances from the drain at the center of the model were measured and pore properties were determined by mercury intrusion porosimetry. The tests with and without reagents indicated that anionic polyacrylamide (APAM) and quicklime can decrease the water content of waste slurry and change the slurry's properties. In addition, the results of the settlement analysis were used to investigate the characteristics of vacuum consolidation.

The hydraulic and swelling properties of a polymerized bentonite (PB), and the self-healing capacity of a geosynthetic clay liner (GCL) using the PB as the core material (PB-GCL) were investigated experimentally. Five different test liquids included of deionized water, NaCl solutions (0.1 M and 0.6 M) and CaCl2 solutions (0.1 M and 0.6 M) were used in this study. The PB exhibited a higher free swelling index (FSI) than that of the untreated bentonite (UB) for all test liquids. For permeability test, under a given void ratio (e), the value of k of the PB is much lower than that of the UB in NaCl and CaCl2 solutions. The PB-GCL specimens demonstrated a higher self-healing capacity than that of the corresponding GCL specimens using the UB (UB-GCL). Specifically, when using a 0.6 M CaCl2 solution for a 20-mm-diameter damage hole, the UB-GCL specimen provided a zero healing ratio (healed damage area/total damage area), but the PB-GCL specimen demonstrated an approximately 76% healing ratio. The results from this study indicate that the PB-GCL provided better barrier performance against cationic liquids with higher cation valence and concentrations compared to that of the UB-GCL.

A series of modified triaxial tests was conducted to investigate the deformation characteristics of mini-prefabricated vertical drain (PVD) unit cells. The factors considered are the (1) magnitudes of surcharge load (ps) and vacuum pressure (pvac); (2) pre-vacuum consolidation period (tva) before applying surcharge load; (3) surcharge loading rate (SLR); and (4) initial effective stress state in the specimens. Based on the test results, relationships between the coefficient of earth pressure (Kes) at the end of surcharge load application and the normalized horizontal and vertical specimen strains are established. Further, a method is proposed for estimating the value of Kes, and therefore the horizontal and vertical strains of the PVD improved soil layer subjected to combined vacuum pressure and surcharge load using loading conditions and basic soil properties. Finally, the proposed method was applied to a case history reported in the literature and good agreement between the field-measured and calculated lateral displacement and settlement was obtained, which suggesting that the proposed method can be a useful tool for designing preloading projects involving combined vacuum and surcharge loads.

A test embankment with a reinforced slope on column improved soft clay deposits was reported and simulated by the finite element analysis (FEA). Reasonable agreement between the field measured results and FEA results was obtained in terms of the surface settlements, lateral displacements, and excess pore water pressures. The field-measured maximum lateral displacement and numerically simulated stress state in the cement deep mixing (CDM) columns indicate the possibility of partial tensile failure/yielding of the column under the toe of the steep slope. These results suggest that to design an embankment with reinforced steep slopes on CDM column improved soft deposits, possible bending failure of the columns should be considered. The results of further numerical investigations indicate that (1) a combination of basal reinforcement and adding an additional row of CDM columns under the toe of the reinforced steep slope (enhancing the ground improvement), and (2) using a CDM column-slab system are possible effective methods for preventing the bending failure of CDM columns.

A modified method for predicting self-healing capacity of GCL with circular or slit damages has been presented. The usefulness of the method has been checked by applying it to two sets of self-healing capacity test data reported in the literature, and fair to good agreements between the measured and predicted self-healing ratios (healed area divided by the total damage area) were obtained. Further, the self-healing capacity of a handmade GCL using a newly developed polymerized bentonite (PB) as core material (PB-GCL) was investigated experimentally. The test results show that the PB-GCL has higher self-healing capacity than that of GCL using natural bentonite, and with deionized water, a circular damage hole up to 100 mm in diameter and with 0.6 M NaCl solution (simulating sea water), a hole up to 15 mm in diameter were self-healed. Finally, the method for predicting self-healing capacity of GCL was applied to the PB-GCL, and the results indicate that a key model parameter, a reference mass of bentonite entered a damage hole has to be modified from 3 g (for natural bentonite) to 5.5 g (for PB).

A simple method has been proposed for calculating the settlement-time curves of deposits improved by prefabricated vertical drains (PVDs). This method considers the vertical and radial horizontal drainage effects of a surface/bottom layer on the degree of consolidation of the PVD-improved deposit and the time-dependent loading. An approximate method with appropriately subdivided loading steps was developed to evaluate the consolidation of PVD-improved deposits induced by a time-dependent loading; the utility of the proposed method was verified by numerical investigations using finite element analyses. Finally, an experimental analysis of a test embankment was conducted on a PVD improved deposit in China to demonstrate the usefulness of the proposed settlement prediction method.

Rigid piles (e.g., concrete piles) have been widely used to improve soft clay for the rapid construction of embankments. In this study, a damage plasticity model that considers the brittle failure behavior of concrete and the frictional properties along cracks is proposed to study the progressive failure of rigid piles under an embankment load. The mechanical characteristics of piles in different locations have been analyzed. The results show that the essential failure mode for rigid piles is tensile failure, which is primarily governed by the distribution of the bending moment and the axial force within the piles. Pile rupture releases stress and causes a significant increase in the tensile stress within neighboring piles, possibly leading to the progressive failure of adjacent piles. Failure in the upper section of piles ultimately leads to the propagation of a slip surface and the global failure of the embankment. The parametric analysis indicates that increases in the pile stiffness and the embankment load result in a higher tensile stress within the piles and a change in the failure mechanism from shear failure to bending failure. In addition, a failure envelope is proposed to determine the failure mode of the piles.

A case history of embankment construction on soft clay deposit improved by a combination of deep cement mixing (DCM) columns and prefabricated vertical drain (PVDs) installation method was simulated and investigated by finite element analysis (FEA). The function of the DCM columns is to control the settlement and lateral displacement under the toe of the embankment, and the function of the PVDs is to accelerate consolidation rate for a zone under the central of the embankment. For this case, only the surface settlements were measured, and the simulations agree with the measured data well, while the results of FEA give relative large lateral displacements under the toe of the embankment with a value of about 370 mm. Further numerical investigation was carried out assuming part of the preloading load was vacuum pressure, with which to result in the similar final surface settlement. The numerical results indicate that with the vacuum pressure, the lateral displacement under the toe of the embankment as well as the maximum compressive stress in the columns can be reduced significantly. These results indicate that combination of DCM columns and PVDs installation with vacuum pressure as part of preloading pressure can be an effective and economic ground improvement method for embankment construction on soft clay deposit.

The objectives of this study were to understand the characteristics of heavy metal pollution caused by mining activities on the two sides of the Shun&rsquo, an river and the response of soil microorganisms to the habitats by different contamination levels and vegetation. This paper selected soil samples from the banks of the Shun&rsquo, an River near the Shizishan mining area, which is at the left of the river, in Tongling, Anhui Province, China. Using Illumina MiSeq 2500 technology, we analyzed the relationship between environmental factors and microbial communities. As the distance from the mining area increased, the heavy metal comprehensive pollution and potential risk value decreased. Additionally, the pollution severity and risk value of the left bank, where the mining area lies, were generally higher than those of the right bank. Because the symmetric sampling points on both banks of the river had similar planting types, their environmental factors and microbial community structure were similar and clustered. However, under different vegetation, the paddy soils tended to have a higher nutrient content and community richness and diversity than the vegetable fields or the abandoned land. It was found that soil microbial communities in this area were mostly affected by pH and Nemerow pollution index (PN). The pH significantly affected the abundance and structure of most microorganisms. In addition, Proteobacteria, Acidobacteria, and Bacteroidetes had significant tolerance to Zn, Pb, and Cd. By exploring the potential use of these tolerant microorganisms, we seek to provide strains and the theoretical basis for the bioremediation of areas contaminated by heavy metal.

The unsaturated permeability (kuns) is one of the key parameters in geotechnical and geo-environmental engineering involving unsaturated soils. To measured kuns in a matrix suction range of few Pa to thousands of kPa is time consuming and sometimes not practical. Thus, various methods for predicting the values of kuns were established, and their performances are quite different. The performance of two commonly used methods, i.e. Mualem’s method adopting Van Genuchten’s soil water characteristic curve (SWCC) (designated as MVG), and Fredlund et al.’s method (designated as FXM), have been evaluated comparing the predicted values with the measured data, which are test data from this study and the data from literature. The analysis results indicate that MVG method yielded a better prediction.

This note presents an investigation on the lateral continuous wear caused weight loss of disc cutter in soft ground condition with quartz sand. The energy consumed during the wearing process is evaluated by analysing the friction process. The contact pressure on cutter ring is analysed by the cavity expansion theory. A regressed equation is proposed to convert the consumed energy into the weight loss of a disc cutter. A new model to predict the lateral continuous wear of cutter rings is then proposed. The model is validated using the field observed data from tunnel constructed in Shenzhen, China.

This paper presents the field measurements and analysis of a preloading project with the installation of prefabricated vertical drains (PVDs) in Wenzhou, China. At the site, PVDs were installed to a depth of 22 m from the ground surface with a spacing of 1.5 m in a triangular pattern. The preloading fill thickness was 6 m with a unit weight of approximately 18 kN/m3. After a total elapsed time of 310 days, approximately 3 m thick fill was removed. The measured preloading settlement was approximately 1.5 m. The measurements and analytical results indicated that the soil layer with PVD improvement reached almost 100% primary consolidation when part of the fill was removed. After partial unloading, the PVD-improved zone was in an over-consolidated state. After the runway was opened for traffic, a settlement increment of approximately 7 mm was monitored over a period of 11 months. Analysis indicated that the settlement was mainly due to the consolidation of soil layers below the PVD-improved zone and post-surcharge secondary consolidation of the PVD-improved zone. The values of the parameters related to PVD improvement were back-estimated from the field measurements. These findings can be used to guide the design of PVDs improvement along the east coast of China.

A modified method for estimating permeability of clayey deposits in the horizontal direction (kh) based on piezocone sounding (uCPT) results is proposed. Most of the currently available methods relate the value of kh with the Δu/[Formula: see text] ratio (Δu is the measured excess pore pressure from uCPT at the shoulder of the cone and [Formula: see text] is the initial vertical effective stress at the measurement location). However, it has been understood that the effect of the overconsolidation ratio (OCR) on the Δu/[Formula: see text] ratio is more significant than that on the value of kh. As a result, for an overconsolidated deposit, there is no suitable method for estimating the value of kh based on uCPT results. Based on the results of laboratory model uCPT, an empirical equation for considering the effect of the OCR on Δu/[Formula: see text] and then kh corresponding to the yield vertical effective stress ([Formula: see text]) and initial vertical effective stress ([Formula: see text]) for OCR > 1.0 is established. The modified method for kh corresponding to [Formula: see text] requires two parameters: OCR and a model parameter (α). In addition, for kh corresponding to [Formula: see text], two more soil parameters are needed: the swelling index (Cs) and the initial void ratio (e0). The methods for estimating these parameters are also proposed. Finally, the modified method is applied to three field case histories to show its usefulness.

The breakage of cutter ring during shield tunnelling is studied in this paper. The field observation reveals that the major reason for the cutter ring breakage is attributed to the unbalanced forces between two sides of the cutter ring during cutting process. Based on the three-dimensional (3D) circular cutting analysis, a semi-theoretical equation for the inner side force acting on the cutter ring is derived, by assuming that the cutting groove in the rock sample is caused by shearing failure. Numerical simulations are performed to determine the effect of angular velocity and further verify the proposed equation for the inner side force. Based on the proposed equation, the following influential factors for the magnitude of inner side force can be identified: i) circular cutting radius, ii) penetrating depth, and iii) angular velocity. The contribution to the inner side force from the above factors is discussed then. Finally, the relationship between cutter ring breakage and inner side force is analysed, which indicates that the inner side force has a significant effect on the breakage of the cutter ring.

The zero load readings of cone resistance (qc) and sleeve friction (fs) measured by a piezocone (uCPT) shift with the ambient temperature. A method of correcting the effect of temperature on uCPT measurements in seabed sediments has been proposed for the case where there is no temperature sensor in the uCPT probe. This method is based on the assumption that the “actual” profile of fs of soft shallow seabed sediments linearly increases with depth, and a rate of increase of α = 0.2 kPa/m was obtained using measured ground temperatures and fs values in seabed sediments in Isahaya Bay, Japan. An “actual” fs profile can then be constructed using the measured fs value at the shallow surface and the value of α. Using the differences between the measured and the estimated “actual” fs profiles, the ground temperature profile can be obtained, and then the effect of temperature on the uCPT measurements can be corrected. The proposed method was used for temperature corrections on uCPT measurements in Isahaya ...

The behaviour of two sections of a test embankment constructed in Ballina, Australia, was predicted by finite element analyses before (Class-A) and after (Class-C) knowing the field-measured data. By comparing the predictions with the field data, it is concluded that simple models such as modified Cam clay, with reliable values of model parameters, can produce reasonable results for the performance of embankments on clayey deposit improved through prefabricated vertical drains for a relatively short time period. The Class-A prediction is judged as reasonably good, and the Class-C prediction gives satisfactory simulations of the field performance.

A method for predicting drying-wetting and scanning soil-water characteristic curves (SWCCs) of a soil has been proposed, which mainly uses Fredlund and Xing’s SWCC function with the fitting parameters evaluated from the saturated permeability (ks), grain size distribution curve and plastic index (PI) of a soil. The usefulness of the method has been checked by applying it to three sets of test data from this study and seven sets of test data from the literature. Fair and acceptable predictions were obtained. It is suggested that the method can be used to approximately predict SWCCs of a soil in case there is no test data available.

Consolidation deformation induced by low frequency cyclic loads was investigated by finite element analysis (FEA) and some available test data. Both one-dimensional (1D) consolidation and the consolidation of a prefabricated vertical drain (PVD) unit cell were considered. With theoretical reasoning and using the results of FEA, it has been established that the amount and the rate of consolidation deformation induced by a continuous cyclic load with a maximum load increment of q, can be calculated using the consolidation result of a static load with a magnitude of q/2. Providing the compression increment (ΔS) near the drainage boundary where the effective stress increment is larger than q/2 is taking into account. The magnitude of ΔS is cyclic load frequency dependent and a method for evaluating it has been proposed. Further, it has been proposed that during the cyclic loading period, the creep deformation induced by sustained static load on a soil layer should be included into the total deformation. The proposed method was applied to two 1D and one PVD unit cell laboratory tests of cyclic load induced consolidations. Good agreement between the measured and the calculated settlement – time curves was obtained.

The mechanism of bending failure and the magnitude of the bending moment in a column formed by cement deep mixing (CDM) under an embankment load were investigated by a series of three-dimensional (3D) finite element analyses. Based on the numerical results, a design method to consider the bending failure of the CDM column has been established. The usefulness of the proposed methods was verified using the results of two centrifuge model tests of the embankments on the CDM column improved soft model ground model reported in the literature, and the columns had tensile cracks or showed complete failure.

The electroosmosis method is regarded especially suitable for the disposal of dredged clay sediment, but its excessive power consumption and electrode corrosion has limited its widespread applicati...

The K 0 -consolidated soil elements beneath structures like quay walls, bridge abutments, cut and cover tunnels and similar structures may be subjected to static shear involving the rotation of the principal stress prior to cyclic loading, which results in the presence of initial shear stress. A hollow cylindrical apparatus was employed and a series of drained cyclic tests was conducted to examine the effects of the initial shear stress induced by drained static shear prior to the application of cyclic loading. Both the initial vertical stress and the initial torsional shear stress were considered in the drained cyclic deformation behavior. The experimental observations indicate that the initial vertical stress accelerates the accumulation of vertical permanent strain during the first 100 cycles only when the initial vertical stress exceeds the value corresponding to the K 0 -consolidated stress state. The average growth rate of strain increases due to the presence of the initial torsional shear stress. A Critical Static Shear Line (CSSL), initiating from the K 0 -consolidated stress state in the ( σ z − σ θ ) − 2 σ zθ plane, divides the volume change responses into contraction and dilation in subsequent cyclic loading. To account for the combined effects of the initial vertical stress and the initial torsional shear stress on the deformation behavior, a modified model is proposed to predict the vertical permanent strain.

Methods for estimating the overconsolidation ratio (OCR) of soil deposits from piezocone sounding results have been investigated. Three existing methods have been briefly reviewed and a new method has been proposed. The proposed method can be applied to both normally consolidated/overconsolidated and underconsolidated deposits. Furthermore, existing methods have been modified so that they can be applied to underconsolidated deposits. Then, all the methods have been applied to 12 case histories collected from 6 different countries. The estimated values of OCR have been compared with the measured data. It has been shown that if the parameters (soil properties and empirical parameters) can be determined appropriately, then all the methods can achieve a reasonable prediction. It has also been shown that the proposed method exhibits a relatively better performance and results in less scattered data than the other methods.

This paper presents a case study of ground collapse (30 m wide and 16 m deep) during tunnelling under a water channel in the city of Hangzhou, China. The ground collapse damaged the constructed tunnel locally, and remedial measures had to be taken to resume the tunnelling works. In this paper, a forensic geotechnical and geological study was undertaken in which the geological condition at the collapsed site was reviewed, the causes for the collapse were investigated, and the development of the soil failure mechanism was evaluated. Remediation measures undertaken at the project site are also discussed. During this forensic investigation study, the strata over the tunnel was found to be of low strength and furthermore erodible to groundwater seepage. Groundwater seepage was detected, which was attributed to be the triggering force that contributed to the collapse. Tunnelling construction using explosives for blasting rocks was attributed to be one of the causes of the failure. A four-step rapid remediation measure was proposed on site, which included filling of the collapsed crater, reinforcement of collapsed debris in the tunnel, grouting and dewatering, and removal of debris and tunnelling. Tunnelling was resumed soon thereafter. The field monitoring data validated effectiveness of the proposed rapid remediation.

This paper investigated the effect of non-uniform consolidation within a prefabricated vertical drain (PVD) unit cell on the average degree of consolidation through laboratory model tests and finite-element analysis. By considering the permeability (k) changing with the void ratio (e), the results of the finite-element analysis showed that the effect of non-uniform consolidation has a considerable effect on the average degree of consolidation of a PVD unit cell. Further laboratory model tests of a PVD unit cell were conducted, and analyses of the model test results confirmed the effect of non-uniform consolidation. Finally, a method of considering the effect of non-uniform consolidation for the analysis of PVD-induced consolidation was established with an equivalent ‘smear’ effect concept.

The Saga Plain in Japan contains a 10–30 m thick Holocene clayey soil deposit with a natural water content generally more than 100% and a liquidity index (I L ) larger than 1.0. Most of this is a marine deposit known as the Ariake clay formation. Using salinity in the pore water of this deposit as an index, the mechanism of post-depositional salinity leaching from the Ariake clay formation has been investigated. This has been achieved using current measurements of the salinity distribution in the deposit and the groundwater flow velocity in an underlying Pleistocene gravelly sand layer, together with advection–diffusion analyses. It is suggested that diffusion together with possible rainfall percolation and/or upward seepage flow from the Pleistocene gravelly sand layer was the main mechanism causing salinity leaching. Detailed analysis of the test results from four boreholes indicates that for the locations where the activity of the clay minerals was less than 1.25, salinity leaching probably accounts for the observed low undrained shear strength (

A failed embankment on a cement deep mixing (CDM)-formed column–improved soft clay deposit in Saga, Japan, has been reported and analyzed. Based on the results of the field investigation an...

The hydraulic behavior of a polymerized bentonite (PB) and the self-healing capacity of a geosynthetic clay liner (GCL) using the PB as core material (PB-GCL) in corrosive solutions (pH ranging from 1 to 13) were investigated through a series of laboratory tests [i.e., free swelling index, swelling pressure, permeability (k) (consolidation), and leakage rate tests]. The test results indicate that the PB had a higher swelling capacity than that of the corresponding untreated bentonite (UB). Particularly, for pH greater than 12.5 solutions, PB had a higher free swelling index (FSI), higher swelling pressure, and lower k value than that of the PB with deionized water. PB-GCL with a damage hole had lower permittivity for the damage hole (ψhole) and a higher self-healing capacity than that of the GCL using UB as the core (UB-GCL). Based on the test results, it is suggested that PB-GCL can be used as an effective barrier material to contain acidic and alkaline liquids.

A series of laboratory model tests of combined vacuum consolidation and compaction were conducted on two clayey sands and two silty sands (intermediate soils). From the test results, it was shown that, after vacuum consolidation, the compaction had induced further reduction of air void and increased the efficiency of vacuum consolidation in successive cycle. The air-entry values (AEVs) of the four soils tested were less than 40 kPa. Then, considering the field achievable vacuum pressure, it is suggested that practically the technique can be applied for soils with AEVs less than about 80 kPa. The ratios of void ratio reduction show that the combined technique is much more effective than one-dimensional consolidation by the same magnitude of surcharge load with vacuum pressure or vacuum consolidation alone. According to the ratios of void ratio reduction, the effectiveness of the vacuum consolidation–compaction technique reduces with increase of clay content of the soil. It is suggested that for treating an intermediate soil with clay content more than 40%, vacuum consolidation alone might be more effective.

The effect of initial water content (w0) and pore water chemistry on the intrinsic compression curve of clays was investigated experimentally. The test results indicate that w0 had a considerable effect on the intrinsic compression curve of a clay, and the degree of the effect is a function of pore water chemistry. The fundamental mechanism of the effect of w0 and pore water chemistry on the intrinsic compression curve is through its influence on the microstructure of clays. For relatively stable flocculated microstructures, the effect of w0 will disappear under a small value of effective vertical consolidation stress, σ′v, for example, σ′v 1,000 kPa. Furthermore, it has been shown that when σ′v is larger than the remolded yield stress, almost all the test data follow the intrinsic compression line (ICL) proposed by Burland. Finally, based on the test data, a new equation for estimating void ratio () under σ′v = 100 kPa on ICL from the void ratio (el) corresponding to the liquid limit water content has been proposed.\ud \ud

The effect of pore water chemistry on anisotropic behavior of consolidation and shear strength of reconstituted Ariake clay has been investigated experimentally. Two types of chemicals added into the pore water of the soil for enhancing flocculation microstructure of soil particles are sodium chloride (salt) (NaCl), and calcium chloride (CaCl2); and two dispersants added are sodium triphosphate (Na5P3O10) and sodium hexametaphosphate (Na6P6O18), respectively. The concentrations of these chemicals in pore water were 2–3%. Degrees of anisotropy of the coefficient of consolidation and undrained shear strength decreased with adding NaCl and CaCl2, but increased with adding the dispersants. Degree of anisotropy also increased with one-dimensional (1D) deformation and the samples with dispersive additives had higher increase rate. It has been confirmed qualitatively by scanning electron microscopy (SEM) images that adding dispersive chemicals promoted the formation of dispersive microstructure and increased the degree of anisotropy, and the chemicals enhancing flocculent microstructure had an inverse effect. The possible application of the findings to underground construction has been discussed also.

Self-healing ratio of geosynthetic clay liner (GCL) with a damage hole has been investigated and a prediction method has been proposed. Laboratory leakage rate/self-healing capacity tests of GCLs with a damage hole were conducted and the test results indicate that the amount of bentonite entered the damage hole and its water content are a function of the type of liquid used, diameter of the damage hole and overburden pressure on the GCL sample. The proposed prediction method uses basic physical properties of a GCL, and the liquid limit of the bentonite in the GCL with the corresponding liquid. Good agreement has been obtained between the predicted and laboratory measured self-healing ratio (healed area divided by the total damage area). It is suggested that the method can be used to evaluate the suitability of a GCL to a particular site.