مقاله انگلیسی رایگان در مورد ظرفیت باربری پی های کم عمق در شن از N و φ – اسپرینگر 2017

Over the past two to three decades, in situ tests have gained preference over laboratory tests for delineation of site stratigraphy and estimation of geotechnical design parameters. This has occurred for several reasons. Firstly, in situ tests can be performed relatively faster than costly laboratory tests. Secondly, the quality of disturbed or undisturbed (UD) soil samples, extracted from the field and brought to the laboratory for testing, depends on the tools employed in their retrieval and the expertise of the people chosen for logging the samples. Among the various in situ tests, the Standard Penetration Test (SPT) is widely used in India and in many countries around the world for site exploration and ground characterization. The SPT is a relatively crude test, whose essence is to drive a standard split-spoon sampler, 45 cm into the soil, by the blows of a 63.5 kg hammer falling from a height of 75 cm [1]. The 45-cm penetration is divided into three separate advances of 15 cm each. The standard penetration resistance, N, is obtained by adding the number of blows required for the penetration of the sampler through the final 30 cm into the soil, after discarding the blow count for the initial 15 cm seating drive. The greater the N value, the stronger and stiffer the soil is expected to be. Most soil investigation agencies in India prefer to carry out SPT in sandy soils instead of extracting UD samples for laboratory testing. The most important shear strength parameter that controls the bearing capacity of shallow foundations in sand is the angle of shearing resistance, /, which can be estimated either directly from laboratory direct shear and drained triaxial compression test results [2–5], or indirectly from correlation with N [6]. Correlations of the net safe bearing capacity, qns, and the net safe settlement pressure, qnssp, with N are widely used in the design of shallow foundations in sand [7–9]. Indian standard code IS:6403 [6] specifies a chart between N and / for different categories of soil compactness (Fig. 1), and recommends the calculation of qns using the value of / obtained from the chart. However, there exists some confusion among geotechnical engineers and consultants on whether to estimate qns directly from N [7] or indirectly from / [6] for shallow foundations in sand. Also, no investigation has been reported so far in the literature to address this issue. This work attempts to fill the above gap in the literature through an analytical parametric study performed to compare qns estimated directly from N using the empirical equations proposed by the researcher [7], against that computed from / (obtained based on N) as per IS:6403 [6], for strip, square, circular footings and raft foundations in sand. Similarly, qnssp determined from IS:8009 (Part 1) [8], based on N, is compared with that obtained from the wellknown semi-empirical approach of [9].