Multi-stage Triaxial Compression Research Articles

Investigation of a Proposed Four Storey Building Sites Using Geophysical and Laboratory Engineering Testing Methods in Lagos, Nigeria

The spate of engineering structures collapse in Lagos metropolis with its attendant loss of lives and properties has assumed an alarming proportion in recent times. Efforts to mitigate such incidence has necessitated an integrated geophysical and geotechnical investigation of a proposed four storey building sites with a view to determine the suitability of the site for the proposed project. Resistivity investigation, un-drained multi-stage triaxial compression and oedometer consolidation tests were carried out to determine the engineering properties of the subsurface. The results revealed peaty clay to silty sand materials characterized by 35kN/m 2 75kN/m 2 cohesion values, (5°-13°) internal friction, 29.3% 64.5% natural water content and 1.652 – 1.972 Mg/m 3 bulk density. The allowable bearing capacity of 50 kN/m 2 , volume compressibility from 0.115 m 2 /MN to 0.666 m 2 /MN, initial void ratio and consolidation coefficient of 0.779 1.381 and 2.7 m 2 /year 8.3 m 2 /year respectively on the pressure range of 0 to 400 kN/m 2 and estimated settlement values of 114 to 273 mm were obtained for the site materials. These results are indicative of soft to stiff clays and presence of sands and silts in the essentially clayey deposit. The study area is thus underlain by extensive zone of ductile and low strength founding materials having medium to high compressibility and settlement value that exceeds the tolerable limit suitable for founding a four storey building and should therefore be avoided. These characteristics preclude the use of conventional shallow foundations, piles or vibro-replacement up

Large Scale Tests on Jointed and Bedded Rocks Under Multi-Stage Triaxial Compression and Direct Shear

The mechanical behavior of bedded and jointed rock was examined in the context of the design of slopes, tunnels and tunnel portals along a planned new rail line. To obtain representative properties for describing the mechanical behavior of this material, large scale triaxial tests were performed. Specimens with a size of 60 cm diameter and 120 cm height composed of sandstone and claystone beds were tested in triaxial compression using a multi-stage technique. The specimens showed a ductile behavior for the stress regime tested. The strength parameters were calculated according to the Mohr–Coulomb failure criterion. The axial and volumetric deformations were measured and the viscosity of the composite rock material was assessed by deformation rate alterations. For some specimens, direct shear tests were conducted in samples containing joints. The results of the tests show that the failure of the bedded specimens was given by the combined failure of both materials. This was confirmed by a numerical model including rock discontinuities.

Shear strength of microfine cement grouted sands

Unconsolidated–undrained (single and multi-stage) triaxial compression tests were conducted to evaluate the shear strength of microfine cement grouted sands. Microfine cements of three different types were obtained by pulverising ordinary cements produced in Greece. Multi-stage triaxial compression tests can be used dependably for determination of the shear strength parameters of cement grouted sands. It has been observed that the Mohr–Coulomb failure criterion represents adequately the behaviour of the grouted sands. Grouting with microfine cement suspensions improves the strength of sands significantly, and the improvement is primarily controlled by the water-to-cement (W/C) ratio of the suspensions. The positive effect of microfine cement grouting on the shear strength of sands is mainly the addition of cohesion, which is substantial even at a distance of 1·2 m from the injection point. Grouting with suspension, using W/C = 1 provides the sand with cohesion of about 2·6 MPa. The shear strength parameters vary with axial strain, and cohesion attains a maximum value well before failure.

Strength and deformation behavior of red sandstone under multi-stage triaxial compression

Based on multi-stage triaxial experimental results of red sandstone with circumferential deformation control, the influence of confining pressure on strength and deformation behavior of red sandstone under multi-stage triaxial compression is investigated. The results show that the confining pressure has an obvious effect on the deformation parameters of red sandstone under multi-stage triaxial compression. A multi-stage triaxial compression experiment with only one specimen can be used to confirm the peak strength of rock under different confining pressures. Under single-stage and multi-stage triaxial compression, the peak strength behavior of red sandstone agrees better with the nonlinear Hoek–Brown criterion than the linear Mohr–Coulomb criterion. However, the difference between single-stage and multi-stage triaxial strength changes with different post-peak deformation values, and the reason for the difference, is discussed. To predict single-stage triaxial strength using the obtained multi-stage triaxial strength with only one specimen, a new method is put forward to revise multi-stage triaxial strength of red sandstone, which testifies to being reasonable. The concluding remarks are very useful and significant for deep geotechnical and underground structural engineering.

Experimental Investigation into Multistage versus Conventional Triaxial Compression Tests for a <i>C</i>-Phi Soil

The procedure for conventional triaxial compression (CTC) test requires three separate soil specimens to be examined to failure under different confining pressures so that Mohr-Coulomb (or stress path) failure envelope can be determined and soil shear strength parameters can be obtained. An alternative procedure is the multi-stage triaxial (MST) compression test, which requires only one soil specimen to be tested at three stages of shearing with different confining pressures. There are several advantages for using MST over CTC, which apart from fewer soil specimens, include less laboratory time consumption and reduced effects of heterogeneity among the specimens tested. However, it has been argued in the literature that the advantages of using MST may be compromised by its inability to obtain reliable soil behavior or accurate shear strength parameters. In this paper, the accuracy of MST compared to CTC is investigated for a c-phi soil, and a simple procedure that can be adopted to rectify the MST results is proposed.

Effect of chemical additives on the strength of sandstone

Chemical alteration of the strength of sandstone has been investigated to establish the fundamental knowledge for chemically assisted fracturing. If the rock strength can be chemically lowered, this technology would be useful to raise the fracturing efficiency. The purpose of the present study is to evaluate the effect of chemical solutions on the strength. To evaluate experimentally the effect, Brazilian tests and multi-stage triaxial compression tests have been performed on Gosford sandstone saturated with solutions of dodecyltrimethyl ammonium bromide (DTAB), polyethylene oxide (PEO) and aluminium chloride (AlCl 3 ). The tensile strength varied with the concentration of chemical additives, became the lowest at certain concentrations which are consistent with the zero zeta-potential concentrations. AE activity is the most active in dry specimen, and the least AE activity is found in the specimen saturated with chemical solution. The uniaxial and triaxial strengths did not vary significantly with concentration of the chemical solutions. In case of compression test where failure mode is dominated by shear failure, there is little effect of chemical solutions on the compressive strength.

Influence of stope geometry and blasting patterns on recorded overbreak

Chemical alteration of the strength of sandstone has been investigated to establish the fundamental knowledge for chemically assisted fracturing. If the rock strength can be chemically lowered, this technology would be useful to raise the fracturing efficiency. The purpose of the present study is to evaluate the effect of chemical solutions on the strength. To evaluate experimentally the effect, Brazilian tests and multi-stage triaxial compression tests have been performed on Gosford sandstone saturated with solutions of dodecyltrimethyl ammonium bromide (DTAB), polyethylene oxide (PEO) and aluminium chloride (AlCl 3 ). The tensile strength varied with the concentration of chemical additives, became the lowest at certain concentrations which are consistent with the zero zeta-potential concentrations. AE activity is the most active in dry specimen, and the least AE activity is found in the specimen saturated with chemical solution. The uniaxial and triaxial strengths did not vary significantly with concentration of the chemical solutions. In case of compression test where failure mode is dominated by shear failure, there is little effect of chemical solutions on the compressive strength.

Results and interpretation of multistage triaxial compression tests : Soranzo, M Proc Symposium on Advanced Triaxial Testing of Soil and Rock, Louisville, 19–20 June 1986P353–362. Publ Philadelphia: ASTM, 1988 (ASTM Special Technical Publication 977)

Results and interpretation of multistage triaxial compression tests : Soranzo, M Proc Symposium on Advanced Triaxial Testing of Soil and Rock, Louisville, 19–20 June 1986P353–362. Publ Philadelphia: ASTM, 1988 (ASTM Special Technical Publication 977)