Reinforced jet-grouted piles. Part 1: analysis and design

Abstract

This two-part set of papers reports some recent experiences in the design of jet-grouted piles (under predominantly lateral load) when their intended use is primarily structural, as is certainly the case when reinforcing steel is present. Although unusual, a number of such design solutions have been documented – several of them recent and applied to major structures. In the absence of specialist rules for the design of jet-grouted piles with steel reinforcement, codes of practice for reinforced concrete (RC) are usually adopted and applied as discussed in this paper. However, certain important differences between concrete and jet-grouted soil (fully discussed in the companion paper) must be clearly understood and allowed for by designers with the result that analysis and design from first principles should be undertaken instead of relying automatically on RC codes of practice. This use of first principles must be combined with a refined construction method to improve the accuracy of construction if the designer is to utilise the potential benefits of the system.

Mechanical properties of soilcrete mixtures modified with metakaolin

“…The absolute values for the average compressive strength measured for all different soilcrete samples (between 17 and 57 MPa in range) were significantly higher than those reported in similar studies found in the literature (between 1 and 15 MPa) not only in soil-based structural members but also in grouting applications and repair mortars [6,7,18,21,22,[33][34][35]. Even though a list of crucial design parameters such as the soil's origin and physicochemical properties, the selected binder synthesis, the chosen W/B ratio, the potential use of special additives (i.e.…”

“…A natural clay ground soil (CGS) was selected for this study since it corresponds to a typical worst case scenario of a low plasticity stiff soil that is difficult to be eroded during jet-grouting [6,7]. Natural clay ground soil was dried at 105°C for 5 days in an electrical laboratory oven and then sieved in order to pass a 2 mm sieve.…”

“…This method has been employed for the construction of structural elements such as piles [6,7]. These elements are constructed of mixed soil and grout (soilcrete) introduced by drilling and injecting grout at very high pressures (jet-grouting) into the soil with surplus grout rising to the surface and filling the annulus left between the soil and the drilling rods during extraction.…”

“…With the introduction of steel reinforcement into these piles the latter elements were allowed to obtain lateral strength and stiffness enabling them to undertake loads acting both parallel and normal to their axis and therefore can be used to form retaining walls. This type of structural elements has been used in several important (high profile) projects such as for the upgrading of quay walls of the Southampton Port [6,7].…”

“…This appears at first to be a reasonable option, and seems to provide a sensible approximation, with the grout mimicking concrete in appearance, role and even properties. However, in spite the similarities, it is important that engineers be also aware of the differences between reinforced soilcrete (RS) and reinforced concrete (RC), particularly as regards material characteristics and construction tolerances [6,7]. Such differences are not accounted for in current codes of practice for RC and therefore designers must use these codes with caution when applying them to RS members during structural analysis and design.…”