Soils and Foundations最新文献

The area of the former Texcoco Lake in Mexico is characterized by soft lacustrine clay strata with high water content and high compressibility. The construction of a new airport was planned in this area, which requires soil stabilization. One soil improvement option is the use of vacuum preloading systems that apply a vacuum to the soil through vertical drains. This study evaluates the improvement on hydromechanical properties resulting from the implementation of two vacuum techniques. In 2016, two test embankments with surcharge preloading and vertical drains were constructed to apply a vacuum using the drain-to-drain technique in one embankment and the airtight membrane technique in the other. The average vacuum pressures applied for six months in the test embankments were −58 kPa and −63 kPa with the drain-to-drain and airtight membrane techniques, respectively. The improvement on the properties varied between the two techniques. The airtight membrane technique reduced the water content and the void ratio up to 50 % and 46 %, respectively. While the drain-to-drain technique reduced the water content and the void ratio up to 15 % and 13 %, respectively. The degree of consolidation estimated using different observational methods at the center of both test embankments ranged from 86 % to 88 %.

This study analytically and numerically investigates the impact of constant and non-constant Poisson’s ratio on the mobilized maximum load in the reinforcements, T_max, of reinforced soil walls with vertical facing under working stress conditions. This assessment is carried out considering different controlling factors including reinforcement stiffness, wall height, backfill friction angle, and compaction-induced stress. The analytical procedure and the numerical model are validated against data from an instrumented, large-scale, geosynthetic-reinforced soil wall under working stress conditions. Considering the key factors evaluated in the current study, the results show that the impact of the reinforcement stiffness is dominant over the approach used to consider Poisson’s ratio. A maximum difference of about 20% was obtained between the values of T_max calculated using constant and variable Poisson’s ratios. This implies that, from a practical standpoint, it may be appropriate to adopt a simpler approach that utilizes a constant Poisson's ratio for the determination of T_max under operational conditions.

The proper assessment of soil thermal properties, such as thermal conductivity, assumes a particular relevance for the design of Ground Source Heat Pump systems, as it determines the heat transfer and the energy efficiency design. Multiple methods can be used for thermal conductivity estimation, however significant scatters in measurements are often reported when using different (or even the same) methods. This work presents a detailed study of the thermal conductivity and the thermal contact conductance of a reference sand tested in transient conditions, analyzing the effect of several factors, such as the heating time, degree of saturation, soil density, temperature and heat flux intensity, on thermal conductivity measurements for dry state or fully saturated conditions. To avoid measurement errors and heterogeneity effects, only three samples were prepared with different compaction ratios, and systematically tested in dry and fully saturated conditions, under different control variables (temperature, testing time, and injected heat flux). Two analytical methods based on the line source solution were used to estimate soil thermal conductivity and to assess the probe-to-soil thermal contact conductance. Significant relationships were obtained between thermal conductivity and soil state conditions and testing variables, highlighting that a heating time longer than the one usually recommended in the standards is clearly needed. Finally, this study uses measured temperature values to determine the probe-to-soil thermal contact conductance, indicating its relevance in soil thermal conductivity estimation.

Jet grouting piles were widely employed for ground reinforcement in building and infrastructure engineering due to the low cost and construction convenience. However, this foundation treatment method is not allowed to be used in high-speed railway involved constructions in China because of the concerning of the negative effect on the lateral displacement of the existing high-speed railway. To find a reasonable application distance of jet grouting piles away from existing high-speed railway bridge in deep soft soils with medium sensibility, a series of laboratory and in-situ tests on the influence of the jet grouting piling on the deformation of surrounding soils and adjacent high-speed railway bridge are carried out. The geological characteristics of the construction site and the mechanical properties of the soft soil are deeply investigated by utilizing field and laboratory tests. The piling induced lateral displacement of the surrounding soils is monitored as well as the displacement of an adjacent high-speed railway bridge. The monitoring data reveal that the influence area of the jet grouting piling is approximately 1.75 ∼ 1.85 times of the pile length in deep soft soils. The critical distance of the jet grouting piles from the existing high-speed bridge should be larger than 2 times of the pile length.

Based on the double nonlinear consolidation constitutive associated with the compression and permeability coefficients, presented by Mesri and Rokhsar (1974), this paper derives an approximate closed-form solution for the one-dimensional nonlinear consolidation of the arbitrary layered soils incorporating the continuous drainage boundary condition. The approximate closed-form solution is obtained by the homogenization of the boundary conditions and eigenfunction method. A model test is conducted to justify the rationality of the approximation and the continuous drainage condition utilized in this study. The calculated results are also compared with those acquired from the simplified analytical solution and the finite difference method. A parametric study is conducted to investigate the influence of various parameters on the consolidation process. The most significant finding is that the influence of $N_{\text{q}}$ appears to be completely different for the cases when $C_{\text{c}}/C_{\text{k}}>1$ and $C_{\text{c}}/C_{\text{k}}<1$. When $C_{\text{c}}/C_{\text{k}}>1$, the increase of $N_{\text{q}}$ shows an adverse influence on the consolidation, whereas the influence becomes positive when $C_{\text{c}}/C_{\text{k}}<1$. The approximate solution derived herein offers a rigorous analytical approach for the double nonlinear consolidation problems of arbitrary layered soils, providing an effective benchmark for comparison and verification of future sophisticated numerical approaches.

The pile bearing capacity varies even within the same site. This study aims to gain a better understanding of the effect of pile penetration techniques on the variability of bearing capacity. The study uses data from 83 jack-in test piles to explore the variations in penetration resistance at the pile head, base, and shaft. The semivariance increases with an increase of the horizontal distance, so we focus on the semivariance between 5 m range, whose error was defined as the error due to piling workmanship. The analysis shows that the errors follow a lognormal probability distribution, and the coefficient of variation (COV) in penetration resistance at the heads and bases is about 10%, while the COV in extracted resistance varies widely, with a range of 5–25%. Little difference in the variations due to piling workmanship was observed among different penetration motions, speeds, and soil types.

To utilize industrial by-products in construction projects, soil stabilization using paper sludge ash-based stabilizers (PSASs) has recently been developed. PSASs can be manufactured by insolubilizing the heavy metals in original paper sludge (PS) ash, which is a waste product emitted from paper mills. This study assessed the durability of clays treated with PSASs in wet-dry or dry-wet environments through various evaluation tests. Initially, the particle size distributions (PSDs) in the clays that had undergone various pretreatments were assessed. Then, unconfined compression tests were performed on the treated clays that had undergone dry and wet curing cycles using demolded specimens. Finally, cone index tests were carried out on the treated clays that had undergone dry and wet curing cycles while the samples were constrained in molds. Based on the test results, the durability assessment of the clays treated with PSASs was discussed, considering the specifics of each evaluation test and contrasting the findings with those obtained for clays treated with cement. The generated PSDs were found to contain more fine particles as the time spent washing the samples prior to sieving was increased. The findings indicated that PSAS-treated clays will eventually become muddy, even though it is unlikely that these treated clays will ever be subjected to washing with water while being stirred after construction. The unconfined compression test results also demonstrated that, after several dry-wet cycles, the strength of the PSAS-treated specimens had decreased. It was revealed that clays treated with PSASs might be less resistant to dry-wet curing cycles than those treated with cement. However, PSAS-treated samples using unconfined compression test specimens are still being investigated and are a topic of debate because the strength development mechanisms of PSASs and cement are not similar. To address this issue, a series of cone index tests were conducted on samples treated with PSASs to examine the change in strength caused by the dry-wet curing process. The results of the cone index tests were different from those of the unconfined compression tests. The cone index test results revealed that the samples must be constrained during the assessment tests in order to assess the durability of PSAS-treated soils subjected to dry-wet curing. In addition, it was proposed in this study that the idea of maturity would be applicable to PSAS-treated soils with a range of curing temperatures and curing times as long as the soils were constrained during the assessment tests.

The water permeability of conditioned soils is one of the most essential properties for Earth Pressure Balance (EPB) tunnelling in coarse-grained soils. Permeability tests are conducted to study the influence of water heads on the permeability of foam-conditioned sands. The initial permeability coefficient of foam-conditioned sands increases with the water head, while the stable permeability coefficient and the initial stable period duration decrease. Meanwhile, a novel analytical model is proposed to estimate the initial permeability coefficient. In this model, the effect of the water head on the initial permeability coefficient is incorporated by calculating void ratios of the foam and effective diameters of foam bubbles under different water pressures. Experimental results are in close agreement with analytical solutions, indicating the excellent performance of the proposed calculation method. In addition, the physical mechanisms of how the water head affects the permeability of foam-conditioned sands are discussed from the contraction and evolution of foam bubbles.

Pumice sand of volcanic origin contains a high fraction of non-plastic fines (>40 % for Satozuka pumice sand in Sapporo, Japan). Suffusion in such soil can wash away a portion of the fine particles and alter the soil microstructure. The moisture content and degree of compaction can affect the suffusion characteristics of soil deposits, however their effect has not yet been evaluated. Future construction sites in growing Sapporo City, consisting of pumice sand, will require a high degree of compaction (over 90 % and preferably over 95 %) as this sand is prone to suffusion in spite of its dense state. The aim of this study is to assess the impact of suffusion on densely compacted pumice sand with a high proportion of fines, based on its mechanical properties, with an emphasis on shear strength and dilatancy. Firstly, the suffusion characteristics of Satozuka pumice sand were evaluated. Subsequently, undrained triaxial tests ($\overline{CU}$ tests) under monotonic loading were conducted on high-density specimens, with suffusion and without suffusion, to study the impact of suffusion. It is seen in the results that the hydraulic conductivity, shear strength, stress paths, and dilatancy are all noticeably affected by suffusion. The specimens with suffusion exhibit an increase in residual shear strength and maximum deviator stress under shearing and experience an earlier occurrence of phase transformation from contraction to dilation during shearing. This tendency implies that suffusion has no significant negative impact on the deterioration of earth fill made from pumice sand and non-plastic fines, and that it persists at degrees of compaction between 80 % and 100 %.

The liquefaction resistance of partially saturated soil was experimentally investigated for one clean sand and one silty sand collected from a site in Christchurch, in an area severely affected by liquefaction in the 2010–2011 Canterbury earthquakes. A series of cyclic undrained tests were performed on fully and partially saturated sand and silty sand specimens, in conjunction with evaluation of saturation conditions in situ based on comprehensive field measurements of P-wave velocity (V_p) in Christchurch deposits. The Skempton’s B-value and P-wave velocity were comparatively used as measures for partial saturation in the laboratory. B-value - V_p relationships from the test results indicate that V_p steadily increases with the B-value until a threshold B-value is reached beyond which V_p remains unchanged at values indicating full saturation, i.e. V_p ;≥ ;1600 ;m/s. In general, the liquefaction resistance of tested sand and silty sand increases with a decrease in the B-value or V_p, i.e. with a reduction in the degree of saturation. Furthermore, test results suggest existence of threshold B-values and V_p for tested soils beyond which no significant increase in the liquefaction resistance was observed. This threshold B-values and V_p were found to be dependent on soil type and applied confining stress. The effects of partial saturation on liquefaction strength are different for the sand and silty sand when using V_p as a measure for the degree of saturation. While a gradual rate of increase in liquefaction strength with decreasing V_p is observed for the tested sand, the liquefaction strength of silty sand shows similar gradual increase with a decrease in V_p up to about 800 ;m/s, which is then followed by an abrupt increase in the liquefaction strength for V_p ;< ;800 ;m/s. Generally good agreement between liquefaction strength of tested soils and published data was observed, with a clear distinctive feature in the behaviour of the silty sand as compared to clean sands.