Behavior of zeolite-cement grouted sand under triaxial compression test

Permeation grouting with cement agent is one of the most widely used methods in various geotechnical projects,such as increasing bearing capacity,controlling deformation,and reducing permeability of soils.Due to air pollution induced during cement production as well as its high energy consumption,the use of supplementary materials to replace in part cement can be attractive.Natural zeolite(NZ),as an environmentally friendly material,is an alternative to reduce cement consumption.In the present study,a series of consolidated undrained(CU) triaxial tests on loose sandy soil(with relative density D_r=30%)grouted with cementitious materials(zeolite and cement) having cement replacement with zeolite content(Z) of 0%,10%,30%,50%,70% and 90%,and water to cementitious material ratios(W/CM) of 3,5 and 7 has been conducted.The results indicated that the peak deviatoric stress(q_(max)) of the grouted specimens increased with Z up to 50%(Z_(50)) and then decreased.The strength of the grouted specimens reduced with increasing W/CM of the grouts from 3 to 7.In addition,by increasing the stress applied on the grouted specimens from yield stress(q_y) to the maximum stress(q_(max)),due to the bond breakage,the effect of cohesion(c') on the shear strength reduced gradually,while the effect of friction angle(φ')increased.Furthermore,in some grouted specimens,high confining pressure caused breakage of the cemented bonds and reduced their expected strength.     

Deformation and cyclic resistance of sand in large-strain undrained torsional shear tests with initial static shear stress

This paper presents the findings from an experimental study focusing on the undrained cyclic behavior of sand in the presence of initial static shear stress. A series of undrained cyclic torsional shear tests was performed on saturated air-pluviated Toyoura sand specimens up to single amplitude shear strain ($\gamma$_SA) exceeding 50%. Two types of cyclic loading conditions, namely, stress reversal (SR) and stress non-reversal (SNR), were employed by changing the amplitude of the combined initial static shear and cyclic shear stresses. The tests covered a broad range of initial states in terms of relative density (Dr = 20–74%) and the initial static shear stress ratio (α = 0–0.30). The following five distinct modes of deformation were identified from the tests based on the density state, the transient undrained peak shear stress, and the combined cyclic and static shear stresses: 1) static liquefaction, 2) cyclic liquefaction, 3) cyclic mobility, 4) shear deformation failure, and 5) limited deformation. Of these, cyclic liquefaction and static liquefaction are the most critical. They occur in very loose sand (D_r ≤ 24%) under SR and SNR, respectively, and are characterized by abrupt flow-type shear deformation. Cyclic mobility occurs under SR in loose to dense sand with D_r ≥ 24%. Contrarily, shear deformation failure typically occurs under SNR in sand with 24 < D_r < 65%, and limited deformation may take place in dense sand with D_r ≥ 65%. In this paper, a stress-void ratio-based predictive method is proposed to identify the likely mode of deformation/failure in sand under undrained shear loading with static shear. Furthermore, the cyclic resistance is evaluated at three different levels of $\gamma$_SA (i.e., small, $\gamma$_SA = 3%; moderate, $\gamma$_SA = 7.5%; and large, $\gamma$_SA = 20%). The results show that, independent of the density state, the cyclic resistance continuously decreases with an increase in α at the small $\gamma$_SA level, while it first decreases and then increases for both loose and dense sand at the moderate and large $\gamma$_SA levels.     

Optimizing the evolution of strength for lime-stabilized rammed soil

In the present study,unconfined compressive strength(q_u)values of two lime-treated soils(soil 1 and 2)with curing times of 28 d,90 d and 360 d were optimized.The influence of void/lime ratio was represented by the porosity/volumetric lime content ratio(η/L_(iv))as the main parameter.η/L_(iv) represents the volume of void influenced by compaction effort and lime volume.The evolution of qu was analyzed for each soil using the coefficient of determination as the optimization parameter.Aiming at providing adjustments to the mechanical resistance values,the η/L_(iv) parameter was modified to η/L_(iv)~C using the adjustment exponent C(to make q_u-η/L_(iv) variation rates compatible).The results show that with the decrease of η/L_(iv)~C.qu increases potentially and the optimized values of C were 0.14-0.18.The mechanical resistance data show similar trends between q_u and η/L_(iv)~C for the studied silty soil-ground lime mixtures,which were cured at ambient temperature(23±2)℃ with different curing times of 28—360 d.Finally,optimized equations were presented using the normalized strengths and the proposed optimization model,which show 6% error and 95% acceptability on average.     

The relation between the state indices and the characteristic features of undrained behaviour of silty sand

The characteristic features of a series of isotropically and K₀-consolidated undrained triaxial compression behaviour of a silty sand were investigated for a range of initial void ratio ($e)$ and mean effective confining stress ($p^{\prime }$). The silty sand used in this study contained about 10% natural fines. The critical state line (CSL) of K₀-consolidated specimens, K₀U was slightly lower than the CSL for isotropically consolidated specimens, CIU. The respective CSLs for K₀U and CIU were used to define state indices, such as state parameter ($\psi )$, state index ($I_s$), state pressure index ($I_p$) and modified state parameter (${\psi }_m$), within critical state soil mechanics (CSSM) framework. It was found that each state index exhibit a unique relation with liquefaction potential, irrespective of consolidation type, however different relationships were observed between state indices and the stress ratio at the triggering of liquefaction, ${\eta }_{\mathit{IS}}$ or the liquefaction resistance, $q_{\mathit{IS}}$. The correlation of characteristic features of undrained shearing (i.e., liquefaction potential, ${\eta }_{\mathit{IS}}$ and $q_{\mathit{IS}}$) and drained shearing (maximum rate of volume change, ${\left(d{\epsilon }_v/d{\epsilon }_a\right)}_{\mathit{m}\mathit{a}\mathit{x}}$) with state indices were compared statistically in terms of root mean square deviations (RMSD). All characteristic features of undrained shearing generally showed the best correlation with $I_p$ in term of RMSDs, however $\psi$ showed comparatively wider scatter for the specimens showing flow and limited flow behaviour.     

On the influence of grain shape on the cumulative deformations in sand under drained high-cyclic loading

The cumulative response of three granular materials with significantly different grain shape and surface characteristics (glass beads, natural sand with subrounded grains and crushed sand with very angular particles) but identical grain size distribution curve has been studied in drained cyclic triaxial tests. For each material, several tests with 100,000 cycles and different amplitudes, densities, average mean pressures and average stress ratios have been performed. In case of glass beads and natural sand, an approximately square relationship between the residual strain accumulation rates and stress or strain amplitude was found (${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$ ～ ${\left({\epsilon }^{\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}}\right)}^2$), while an almost proportional dependence was measured for the crushed sand (${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$ ～ ${\epsilon }^{\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}}$). The largest differences in the cumulative response of the three tested materials were observed regarding the pressure-dependence of ${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$. For glass beads and (less pronounced) for natural sand, the residual strain accumulation rates decreased with average mean pressure, while the opposite tendency was obtained for the crushed sand. At small pressures, the residual strains were much larger for the glass beads than for the natural sand and particularly the crushed sand, while these differences in the accumulated strains almost diminished at larger pressures. Independent of the shape and the surface characteristics of the particles, it was confirmed that the average stress ratio is the governing parameter of the cyclic flow rule. Finally, the parameters of the high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) were analyzed considering the grain shape parameters (aspect ratio, circularity) obtained from an automated grain shape analysis.     

The PenetraCone,a new robust field measurement device for determining the penetrability of cementitious grouts

One of the most crucial parameters for successful grouting is to ensure that the grout can penetrate the necessary apertures. For the most commonly used grout, cementitious grout, the available methods for determining the ability to penetrate apertures involves several measurements with different meshes or similar, which need to be evaluated. However, during the grouting process in the field there is rarely any time for evaluation and the most commonly used field method today stipulates a mesh width through which a certain volume need to pass. This implies that only an indirect measurement of the penetrability is performed. In order to perform direct and fast field measurements of the penetrability, a new, robust measuring device has been developed at Chalmers University of Technology in Gothenburg, Sweden. The device is named PenetraCone and the measuring part consists of a gap that is formed between two conical cylinders. The penetrability characteristics are measured by decreasing this gap as grout flows through. The gap is measured using a dial indicator gauge. Initial tests with the PenetraCone show that two characteristic gaps or widths can be evaluated. The width as the grout flow goes from continuous flow to dripping is termed b_filter and when the flow stops completely it is termed b_stop. The parameter b_filter is related to the commencement of clogging or filtration of the cementitious grout. This means that for apertures larger than b_filter the cement passes unrestricted but for narrower apertures filtration will commence. This filtration process will occur in apertures down to b_stop, which indicates the smallest aperture that the cement can pass through and for apertures below b_stop the cement will not penetrate at all. The device is easy to use and the tests show that consistent values are obtained. The accuracy seems good enough for use as a control of the penetrability of cementitious grouts in the field. For use in production, the PenetraCone should be placed on the grouting rig, after the mixer, so that direct measurements can be performed on the grout that will actually be used for grouting. By relating the measured parameters to the penetrability requirements, quick decisions regarding the quality of the grout can be made directly on the grouting rig.     

Compressibility of biocemented loose sands under constant rate of strain,loading, and pseudo K0-triaxial conditions

The compressibility behavior of loose sands treated with Microbially Induced Carbonate Precipitation (MICP) is presented in this paper. The paper discusses the strain rate effects and evolution of at-rest earth pressure coefficient and elastic shear modulus during $K_0$-loading. The soil samples were prepared in a triaxial cell in which a biological solution containing the ureolytic bacteria Sporosarcina pasteurii was injected and held under a small back pressure. Cementation treatments were injected following an alternated top and bottom sequence. The constant rate of strain, constant rate of loading, and pseudo $K_0$-triaxial tests were performed at different strain and stress rates. On-specimen internal instrumentation consisting of a submersible load cell, three Hall Effect transducers, and vertical Bender Elements were used to control radial strains during $K_0$-loading and measure small-strain shear modulus changes. Based on shear wave velocity measurements, the MICP-treated sand was lightly cemented and displayed soil-like behavior. The experimental results demonstrated a significant reduction in soil compressibility after MICP treatment. The material response was remarkably similar for every tested strain rate. The very small values of axial strains measured for the biotreated samples in relation to untreated control specimens for vertical effective stress levels below 200 kPa is evidence of the suitability of this treatment and shows its potential for use in field applications at relatively shallow depths.     

New mixture design approach to paper sludge ash-based stabilizers for treatment of potential irrigation earth dam materials with high water contents

In those cases where construction-generated soils with high water contents are used as filling or embankment materials, it is sometimes difficult to satisfy the specified compaction degrees. Recently, soil stabilization using a paper sludge ash-based stabilizer (PSAS) has been developed. Paper sludge (PS) ash is waste generated by the incineration of PS discharged from paper mills. It has been found that PS ash can absorb and retain excess water; and therefore, PS ash can simultaneously improve the stability of muds when it is mixed with them. However, the current mixture design approach for PSAS-treated soils is only applicable to muds with water contents exceeding the liquid limits and cannot be applied to construction-generated soils in which the coarse fraction is dominant. Therefore, this study evaluated the effects of a PSAS on the compaction and mechanical characteristics of coarse-grained soils to use them as materials for irrigation earth dams. A series of compaction tests were conducted on two types of soil samples treated with a PSAS to investigate its effects on the compaction characteristics. The compaction characteristics obtained from the tests were assessed considering the water absorption and retention performance of the PSAS. It was found that the modified optimum water content w*_opt of the treated samples, which was evaluated using the amount of water unabsorbed and unretained by the PSAS, was almost equal to the w_opt of the untreated samples. Consequently, a new mixture design approach was proposed based on the compaction characteristics. The calculated results successfully demonstrated that, if the compaction curve of an untreated sample and the water absorption and retention ratio, W_ab, of the PSAS corresponding to a certain curing period are obtained, the range in the PSAS addition amount, A_PS^1m3, required to attain the targeted compaction degree, (D_c)_target, for the curing period can be estimated without conducting compaction tests on the treated samples. Finally, the strength characteristics of the treated samples prescribed by the proposed mixture design method were investigated by conducting CBR tests and $\overline{\text{CU}}$TC tests. Based on the test results, discussions were made on the contribution of the proposed mixture design to the strength development of the treated samples and on the development mechanism.     

An example of estimating rock mass deformation around an underground opening using numerical modeling

In rock engineering, rock strength is regarded as an important rock mass parameter and it is widely estimated using the uniaxial compressive strength (UCS) test. A UCS test in laboratory requires sampling and preparation of core samples, which necessitates time consuming and expensive studies. Furthermore, preparation of cores is almost impossible for a weak rock material taken from foliated, laminated or thinly bedded rock masses of low Rock Quality Designation (RQD) values (0–20%). In this case, determination of UCS by laboratory test may be impossible in compliance with ISRM or ASTM standards. To overcome this difficulty, indirect tests, such as Point Load Index (PLI), Schmidt Hammer (SH) Rebound Number tests are often employed to predict the UCS. However, indirect tests are likely to yield UCS values with large standard deviations depending on the geological origin of the rock mass.The Block Punch Index (BPI) has recently been developed to overcome the drawbacks of UCS and indirect tests and to minimize the errors arisen from the structural deficiencies and large standard deviations. In this study, determination of rock mass behavior in laminated–foliated Bornova Melange (yellowish-brown flysch and grayish-black flysch) and well-jointed Yamanlar Volcanics–Altindag Formation, where the second phase of the Izmir Metro tunnels was excavated is aimed. The BPI ratings were directly used in RMR calculations and indirectly used to estimate the UCS values of rock materials. Then, the obtained results were input into numerical models along with the rock mass strength (UCS_RM) and deformation modulus of rock mass (E_RM). The results obtained from the numerical models agreed with that obtained results from inner tunnel convergence and ground settlement measurements.