Unconfined Compressive Strength Qu Research Articles

Experimental study on the thixotropic strength of the marine soft clay from the Yangtze River estuary

Soft clay in the offshore area of the Yangtze River estuary has been investigated considering its basic physical properties. Forty-five unconfined compressive strength tests were conducted on the remolded marine soft clay to investigate the impacts of curing time T, water content w, plasticity index IP, and clay particle content ρc on the thixotropic static shear strength ratio As of the marine soft clay from the Yangtze River estuary. Results show that the stress–strain curves were primarily strain hardening and strain softening curve types. Unconfined compressive strength qu increased with an increase in T. All specimens with different basic physical properties were capable of thixotropic strength recovery. When T = 0–28 days, As increased rapidly, while for T > 28 days, As of most specimens increased slightly or tended to stabilize. The impacts of w, IP and ρc on As do not follow a consistent pattern, but there is a strong correlation between As and w/wL (wL is the liquid-limit water content). For w/wL < 0.75, As increased with increasing w/wL, whereas for w/wL ≥0.75, As decreased with increasing w/wL. We proposed a simple and widely applicable power function prediction model for the As of the soft clay from the Yangtze River estuary.

Assessing the Scale Effect on Bearing Capacity of Undrained Subsoil: Implications for Seismic Resilience of Shallow Foundations.

This research investigates the influence of the scale effect on the bearing capacity of fine-grained subsoil under undrained conditions. The analyses were conducted based on laboratory tests of silty clay. Uniformly compacted samples were subjected to an unconfined compression test. The research was performed on cylindrical specimens. Three different variants of the diameter D (38 mm, 70 mm, 100 mm) and the corresponding height H = 2D were analyzed. Based on the tests results, the unconfined compression strength qu was determined, and from this, the undrained shear strength cu was calculated. The obtained results showed a clear decrease in cu with increasing sample size. However, in the existing reference documents, there are no specific guidelines for calculations of bearing capacity with consideration of sample size effect on the soil shear strength. Therefore, this study utilized the laboratory soil test data to calculate the bearing capacity of undrained subsoil, taking into account the seismic impacts, with a particular focus on spread foundations.

Selection of single machine learning model for designing compressive strength of stabilized soil containing lime, cement and bitumen

The unconfined compressive strength (Qu) is one of the most important criteria of stabilized soil to design in order to evaluate the effective of soft soil improvement. The unconfined compressive strength of stabilized soil is strongly affected by numerous factors such as the soil properties, the binder content, etc. Machine Learning (ML) approach can take into account these factors to predict the unconfined compressive strength (Qu) with high performance and reliability. The aim of this paper is to select a single ML model to design Qu of stabilized soil containing some chemical stabilizer agents such as lime, cement and bitumen. In order to build the single ML model, a database is created based on the literature investigation. The database contains 200 data samples, 12 input variables (Liquid limit, Plastic limit, Plasticity index, Linear shrinkage, Clay content, Sand content, Gravel content, Optimum water content, Density of stabilized soil, Lime content, Cement content, Bitumen content) and the output variable Qu. The performance and reliability of ML model are evaluated by the popular validation technique Monte Carlo simulation with aided of three criteria metrics including coefficient of determination R2, Root Mean Square Error (RMSE) and Mean Square Error (MAE). ML model based on Gradient Boosting algorithm is selected as highest performance and highest reliability ML model for designing Qu of stabilized soil. Explanation of feature effects on the unconfined compressive strength Qu of stabilized soil is carried out by Permutation importance, Partial Dependence Plot (PDP 2D) in two dimensions and SHapley Additive exPlanations (SHAP) local value. The ML model proposed in this investigation is single and useful for professional engineers with using the mapping Maximal dry density-Linear shrinkage created by PDP 2D.

Field experiment of cement-modified loess

The construction of a compacted and stabilized layer with local soil from the excavation, mixed with Portland cement, is a soil improvement technique widely applied in foundation works in collapsible loess ground in Bulgaria. Commonly, the role of that cement-modified layer is to replace a part of the collapsible ground, to increase the bearing capacity of the soil base, and/or to be an engineering barrier against migration of harmful substances in the geoenvironment. A multi-barrier near-surface short-lived low- and intermediate-level radioactive waste repository is under construction in Bulgaria. A cement-modified soil layer beneath the disposal cells is going to be built by in-situ compacted mixture of local loess and Portland cement. The cement-modified layer (indicated as loess-cement cushion) is not a continuation of the foundation, but it is a part of the soil base and performs two main functions: to be an engineering barrier against eventual migration of radionuclides in the geoenvironment and to increase the bearing capacity to restrict deferential settlement of the soil base. The present paper describes a field experiment aiming to verify the strength and deformation characteristics of a selected optimum loess–cement mixture by implementation of in-situ cement-modified loess ground. After 28-day curing at in-situ conditions, the loess-cement did not exhibit any fissuring or other disturbances. The allowable bearing capacity qa of the cement-modified loess ground exceeded 900 kN/m2, and it possessed the following strength and deformation characteristics: deformation (plate) modulus EPLT = 500 MPa; coefficient of sub-grade reaction ks = 2158 МPa/m, and unconfined compressive strength qu = 2.00 MPa.

Characteristics of Clay Soft Soil in the Mekong Delta of Vietnam and Improvement Result with Cement

The results of research on the characteristics of soft clay soils distributed in some provinces of the Mekong Delta show that most of the soils are contaminated with easily soluble salts, containing organic matter, pH < 7. Sandy clay, clay in An Giang, and clay mud in Tien Giang are less acidic, not salty, and contamination of salts in the form of sulfate- chloride. Clay mud in Hau Giang is less acidic, less salt, and contamination of salts in the form of chloride-sulfate. Clay mud in Bac Lieu and Ca Mau are lots of salty soil, contaminated with chloride of salts. Peat soil in Kien Giang is strongly acidic, not salty, contaminated with sulfate -chloride. All of them have a large compression coefficient, small load capacity, therefore they should be reinforced when construction works. Unconfined compressive strength of reinforced soils with cement showed that sandy clay in An Giang is the best, and then is soft clay in An Giang and clay mud in Tien Giang, Hau Giang, Bạc Lieu, and Ca Mau. Peat soil in Kien Giang has a low strength at different contents and days of age (with a concents 400 kg/m3 at 91 days has unconfined compressive strength qu = 201 kPa), only 12.8 to 23.0% compared to the soil elsewhere. The curing time process samples show that the compressive strength of the peat soil mixed cement is increased initially, then they were decreased over a period of 28 days.

Utilization of biomass-based by-product lignin to suppress moisture loss-induced shrinkage of silty soil

The global stockpiles of by-product lignin are increasing rapidly with the growing demand on wood-based industry and biomass energy, creating a potential threat to environmental safety without proper disposal. The presented study aimed to evaluate the feasibility of utilizing biomass-based by-product lignin to suppress the shrinkage of silt expected as filling material in engineering construction. A series of laboratory experiments were conducted to investigate the variations in geometry size, mass loss Δm, moisture content w, and unconfined compressive strength qu of the treated samples exposed to the artificial dry condition. The effects of additive dosage and curing time on shrinkage behaviors of lignin treated silt were analyzed. The roles of matric suction on qu and soil microstructure were discussed to understand the mechanism leading to the soil shrinkage. The test results demonstrated that the addition of lignin effectively suppressed shrinkage of compacted silt subjected to dry curing. Both linear shrinkage rate es and volumetric shrinkage rate ev increased with an increase in lignin dosage, indicating excessive addition of lignin produced a negative impact on the shrinkage resistance. The values of es and ev of lignin treated samples were controlled within 1.0% and 3.0%, respectively. As compared to quicklime, lignin exhibited slightly inferior performance of suppressing shrinkage, while it promoted the water-holding capacity of the treated silt. The matric suction resulted from moisture loss was beneficial for strength improvement and also accelerated the process of soil shrinkage. The shrinkage characteristics of lignin treated silt mainly depended on the combined functions of lignin cementation and matric suction. Additional research is recommended to quantitatively evaluate the matric suction variation of lignin treated soils in dry environment. The outcomes of this study are invaluable in facilitating sustainable soil treatment in engineering construction and providing a viable answer to the cleaner production of biomass-based business.

Influence of statistical sample size on evaluation of overall strength of cement-treated soil column

The quality of cement-treated soil columns is normally assured based on the unconfined compressive strength qu of core samples. qu of core samples varies spatially and the statistical parameters of qu (i.e., mean µqu, variance [Formula: see text], and autocorrelation distance θqu) are adopted in quality assurance procedures. The statistical parameters of qu evaluated from the core sample strengths have a statistical uncertainty depending on the statistical sample size. The present study investigates the influence of the statistical sample size on the evaluation of overall strength of a cement-treated soil column. A probabilistic framework in which a Bayesian inference analysis and a finite element method analysis are incorporated is used to calculate the overall strength while simultaneously considering the statistical uncertainty and spatial variability of core strength. The probabilistic framework is briefly described, and a parametric analysis is performed to investigate the influence of the statistical sample size on the evaluation of the overall strength of a full-scale column. The numerical results show that the sample size and spatial correlation influence the variability of the overall strength, and the influence can be reasonably described using an equivalent number of independent data.

Mechanical and electrical properties of coarse-grained soil affected by cyclic freeze-thaw in high cold regions

To evaluate the geotechnical properties of coarse-grained soil affected by cyclic freeze-thaw, the electrical resistivity and mechanical tests are conducted. The soil specimens are prepared under different water contents, dry densities and exposed to 0-20 freeze-thaw cycles. As a result, the stress-strain behavior of the specimen (w =14.0% and ρd=1.90 g/cm3) changes from strain-hardening into strain-softening due to the freeze-thaw effect. The electrical resistivity of test specimen increases with the freeze-thaw cycles change, but the mechanical parameters (the unconfined compressive strength qu and the deformation modulus E) and brittleness index decrease considerably at the same conditions. All of them tend to be stable after 7−9 cycles. Moreover, both the dry density and the water content have reciprocal effects on the freeze-thaw actions. The failure and pore characteristics of specimens affected by freeze-thaw cycles are discussed by using the image analysis method. Then, an exponential function equation is developed to assess the electrical resistivity of specimens affected by the cyclic freeze-thaw. Linear relations between the mechanical parameters and the electrical resistivity of specimens are established to evaluate the geotechnical properties of the soil exposed to freeze-thaw actions through the corresponding electrical resistivity.

Investigation of Performance of Soil-Cement Pile in Support of Foundation Systems for High-Rise Buildings

This paper presents the experimental study of Soil-Cement Pile (SCpile) by wet mixing method in sandy soils, with the typical project at An Trung Complex apartment, Da Nang city, Vietnam. With the characteristic of soil layers is sandy soil, the strength of laboratory stabilized soils with the amount of cement from 150¸300 kg/m3 was determined. Simultaneously, the authors also performed the experiments of 20 test piles collected from the site which has cement content about 280 kg/m3 and the unconfined compressive strength qu= (4.5-6.0) MPa. After that, a full-scale model static axial compressive load tests of two single piles and a group of four piles with diameter 800 mm and 12 m length were also conducted. The experiment results show that the bearing capacity of every single pile is 1.200 kN with settlement 6.93 mm and the group of four CSpiles is 3.200 kN with settlement 5.03 mm. The results presented in the paper illustrate that SCpile is the suitable solution for foundation construction process with low cost and saving time for high rise buildings. The result shows a capable application of soil cement piles for support of high-rise buildings.

Compression and strength behavior of cement–lime–polymer-solidified dredged material at high water content

ABSTRACTThe potential use and engineering properties of cement-solidified clay with superabsorbent polymer (SAP), which is implemented as raw material for backfill or reclamation, are investigated. SAP is added, as water-reducing agent, into the cement mixing method to improve the effectiveness of cementation for high-water content-dredged material in China. Test results show that the vertical yield stress () and unconfined compression strength qu significantly increase with SAP content, cement and lime content, and curing time, which are attributed to greater degree of cementation bonding. By contrast, the influence of SAP on the compressibility of cement-treated clay at postyield state is negligible. The clay–water/cement ratio hypothesis was used successfully to analyze the strength development of cement–lime–polymer-solidified Kemen clay at various SAP contents. For given clay–water/cement ratio, the strength of the cement-solidified clay increases with an increasing SAP content. Hence, to increase cementation efficiency and improve the economic impact, SAP can be used to enhance the strength of cement-solidified clay at notably high water content.

Compressibility and strength behavior of marine soils solidified with MgO—A green and low carbon binder

ABSTRACTAlthough extensive research has been conducted on the soil solidification with traditional binders such as lime and cement, there has been less emphasis on the mechanical behavior of marine soils solidified with a novel type of binder MgO. The experimental tests were performed to investigate the strength and compressibility behavior of MgO-solidified soils, taking into consideration curing time and MgO content. The results show that the yielding stress tends to increase with curing time and MgO content, but drops as the initial void ratio e0 and void ratio ey at increase. The incorporation of MgO leads to an important reduction in compression index Cc and recompression index Cr. The unconfined test analysis indicates that an increasing trend can be observed for unconfined compressive strength qu and deformation modulus E50 when evaluating the effect of curing time and MgO content, accompanied by a decrease in failure strain εf and a slight drop of qu at 28 days. The improvement of mechanical performance is attributed to the hydration process of MgO with water, producing an alkaline environment and precipitation of Mg(OH)2. Based on the confined and unconfined compression test results, an effort is made to establish the correlations between characteristic parameters, including Cc vs. e0, vs. e0, vs. ey, qu vs. εf, and qu vs. E50.

Parameters Controlling Tensile and Compressive Strength of Artificially Cemented Sand

The enhancement of local soils with cement for the construction of stabilized pavement bases, canal lining, and support layer for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, as well as the need of a spoil area. The present research aims to quantify the influence of the amount of cement, the porosity, and the voids/cement ratio in the assessment of unconfined compressive strength qu and splitting tensile strength qt of an artificially cemented sand, as well as in the evaluation of qt /qu relationship. A program of splitting tensile tests and unconfined compression tests considering three distinct voids ratio and seven cement contents, varying from 1 to 12%, was carried out in the present study. The results show that a power function adapts well qt and qu values with increasing cement content and with reducing porosity of the compacted mixture. The voids/cement ratio is demonstrated to be an appropriate parameter to assess both qt and qu of the sand-cement mixture studied. Finally, the qt /qu relationship is unique for the sand-cement studied, being independent of the voids/cement ratio. DOI: 10.1061/ASCEGT.1943-5606.0000278 CE Database subject headings: Tensile strength; Compressive strength; Soil cement; Compacted soils. Author keywords: Tensile strength; Compressive strength; Soil cement; Compacted soils.

Dynamic Properties of Weathered Sedimentary Soft Rocks

ABSTRACT The mechanical properties, in particular, the dynamic deformation properties of sedimentary soft rocks which were artificially weathered through dry-wet and freeze-thaw sequence are determined by cyclic triaxial tests and ultrasonic pulse tests in the laboratory. First, the relations among unconfined compressive strength qu, Young’s modulus E by uniaxial compression tests, and shear wave velocity Vs by ultrasonic pulse tests are investigated, and it is shown that probable values of qu and E of weathered soft rocks can be estimated from Vs. Also, it is concluded from cyclic triaxial tests that (1) the greater the extent of weathering, the larger becomes the dependency on confining pressure of shear modulus Go at very small strain, (2) relations between shear modulus ratio G/Go and shear strain amplitude γ depend on the extent of weathering, namely the degree of degradation of G/Go with γ of heavily weathered specimens is smaller than that of fresh samples. However, if γ is normalized with respect to the reference strain γr, G/Go versus γ/γr relations are uniquely expressed irrespective of the degree of weathering, (3) moreover, material damping h versus γ/γr relations are also uniquely defined, (4) relations between Vs and γr are given as linear on log-log scaled paper, and the larger the shear wave velocity γr. the smaller becomes the reference strain γr. While this relation slightly depends on kind of materials and magnitude of confining pressure, the probable values of γr which have a significant influence on the strain dependency of G and h may be estimated from Vs.

On the Characteristics of Hard Clay in Yabakei Formation

The authors tested characteristics of brown and white hard clay developed in state of vein in tuff brecciaand tufferous andesite in Yabakei district, Oita Prefecture. The brown hard clay is natural unit weight γt=1.89 g/cm3, moisture content ω=34.9%, velocity of elastic wave Vp=2.2 km/sec, Vs= 0.8 km/sec, and unconfinedcompressive strength qu=14.5 kg/cm2, and it has characteristics similar to tertiary muddy soft rocks.But hair cracks are caused to dry it. The dried brown hard clay break down small pieces, 2 or 3 mm in dia., in a moment as it is soaked in water, and it occurs high expansive pressure.The hard clay is consisted of montmorillonite, halloysite, feldspar and other clay minerals according to Xrayanalysis. It is considered that the hard clay is consisted of bad crystalline clay minerals, thinking of otheranalyses with X-ray analysis.The authors consider that the hard clay is producted by hydrothermal alternation under 50°C.

On the Mechanism of Squeezing-Swelling Rock Pressure of Mudstone on Tunnel Support in Relation to the Case History of Noshiro Tunnel

This paper discusses the mechanism of squeezing-swelling rock pressure of mudstone and presents the quantitative data of rock pressure measured during tunnel construction in the field together with the associated measnrements of physical and mechanical properties of the rocks.Wire-strain-gauges were used to determine the axial force N, bending moment M and the shearing force Q and the resultants of external forces P and S due to rock pressure were calculated at selected points using the method originally proposed by Prof. Murayama14), thus the pressure distribution concentric with the tunnel axis being obtained (Fig. 14).Three of the tunnels of the main irrigation water line for Noshiro Reclamation Project in Akita Prefecture provide the data for this paper. These three tunnels No.3, No.4 & No.6 were all constracted in massive, occasionally faulted tertiary mudstone named as Fujikotogawa Formation.The phenomena encountered during the construction of the tunnel No.4 were very different from those of the tunnels No.3 and No.6.In the case of the tunnel No.4, the heavy rock pressure caused an excessive deformation of the first placed light steel supports, resulting in the necessity to change to the heavier supports with invert struts.However, in the case of the tunnels No.3 and No.6, the rock pressure was considerably smaller in spite of the fact that the mudstone encountered in these tunnels was apparently similar to those of the tunnel No.4.To investigate the reason for this and to assist in the deeper understanding of the mechanism of squeezing and swelling rock pressure, tests were made to determine the unconfined compressive strength qu of the rocks, the swelling characteristics of the artificial mudstone or remoulded mudstone**, clay mineral identification and the pF water content relationships of the rock powder (Fig.10, 15, 16, 11, 19).As shown in Fig.11, expansive clay minerals (montmorillonite) were contained in the mudstone of the three tnnnels but as shown in Fig. 10 the strength qu, of the rocks sampled from the tunnel No.4 was approximately one half to one third (or even less) of those sampled from the tunnel No.3 and No.6 and nearly equal to or less than two times the initial vertical stress induced by the weight of the rock itself at the side wall, indicating that the mudstone around the tunnel No.4 was broken and plastic zone of failure was formed (Fig.4), whereas the mudstone of the tunnels No.3 and No.6 underwent little breakage by the stress of the same magnitude.On top of this, the swelling capacity of the remoulded mudstone sampled from the former tunnel was conspicuous (Fig.15) and much larger than that of the latters, indicating that the strength parameters and the unconfined compressive strength qu of the mass of broken rocks of tunnel No.4 reduced considerably in the course of time, resulting in the much increase of σi as is clear from Eq. 14 and Fig. 8.These facts not only explain the reasons of the difference of the rock pressure phenomena but also the mechanism of the squeezing-swelling rock pressure of mudstone.