Field Tests on Bearing Characteristics of Large-Diameter Combined Tip-and-Side Post Grouted Drilled Shafts

Zhitong Zhang,Guoliang Dai,Yu Zhu,Weiming Gong,Hao Huang,Xiaolin Cao

doi:10.3390/app112411883

Zhitong Zhang, Guoliang Dai + Show 4 more

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https://doi.org/10.3390/app112411883

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Abstract

This paper presents a field study on the axial behavior of four large-diameter drilled shafts embedded in coarse sand. The grouting and loading test procedures were reported. The bearing capacity of shafts (TS1 and TS2) and grouted drilled shafts (TS3 and TS4) were herein determined by the bi-directional static test and top-down load test, respectively. The enhancement mechanism of bearing characteristics of the grouted shafts was discussed in detail. The test results indicate that the bearing characteristics and load transfer mechanisms of the test shafts were significantly affected by the quantity of pressurized cement slurry and the mechanical properties of the soil surrounding the shafts. Furthermore, the tip resistance of shaft can be mobilized more rapidly and fully after grouting, the side and tip resistance are mobilized in a more synchronized and coordinated manner due to the pre-mobilization of the grouted cement. Additionally, the standard penetration test (SPT) prediction model was introduced to calculate and predict the SPT blow counts of soil after grouting. The results show that the post grouting has a more obvious improvement on the strength of cohesionless soil.

Highlights

Drilled shafts have a long history of use where soil strata immediately below the shallow ground are not strong enough to prevent bearing failures or excessive settlements.Drilled shafts develop loading resistance from a combination of tip and side resistances that are mobilized as the shafts are loaded
A significant portion of a drilled shaft’s tip resistance is unusable due to the vertical displacement required for mobilization [1,2,3]
Due to factors related to construction difficulties and higher costs, continuous attempts are being made to improve the performance of drilled shafts without increasing the diameter of the shafts [4,5]

Summary

Introduction

Drilled shafts have a long history of use where soil strata immediately below the shallow ground are not strong enough to prevent bearing failures or excessive settlements.Drilled shafts develop loading resistance from a combination of tip and side resistances that are mobilized as the shafts are loaded. A significant portion of a drilled shaft’s tip resistance is unusable due to the vertical displacement required for mobilization [1,2,3]. This leads to larger diameter and deeper shafts or more numbers of shafts to be utilized than would be needed if the shaft tip capacity were incorporated into the design. Post grouting techniques have gradually become a trend to be used as a method to improve shaft performance In this procedure, the compaction grout is pumped into the soil around the shaft; the mud around the shaft and the sediments at the tip of the shaft are penetrated, compacted and separated by the cement slurry. The mechanical properties of the soil around the shaft are improved and the bearing performance of the shaft is further enhanced [6,7,8,9,10]

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