# Lateral Pressure of Poured Concrete: Arguments from Ultra-Deep Diaphragm Wall (120 m) Construction
###### Abstract  
Formwork lateral pressures are critical with respect to engineering safety, and laboratory tests are often limited by time, height, etc. Formwork lateral pressures are related to early concrete fluid behavior (e.g., thixotropy). In this paper, we propose the use of ultra-deep underground diaphragm walls instead of formwork for conventional lateral pressure testing. During the construction process, three measurement points were set up in an ultra-deep diaphragm wall at \(-40\) m, \(-80\) m and \(-100\) m. The concrete was divided into 22 casts, and the development of lateral pressure and the effect of time on lateral pressure were observed under each of the casts. We found that the characteristic height of all three measurement points was approximately 21 m. The average casting speed for this test was 16.846 m/h, with the fastest speed of 32.148 m/h. A time-dependent phenomenon of rapid rise and fall in lateral pressure with each casting was observed. This method provides a new way to conceptualize formwork lateral pressure, with the advantages of long testing time, high casting height and multiple tests, not only for formwork lateral pressure but also for early age thixotropy measurement of concrete. concrete; formwork pressure; lateral pressure; underground structure; monitoring technology +
Footnote †: journal: Applied  
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treating each of these factors as a factor (\(K\)). They assumed a bilinear distribution; however, this is not always the case due to the thixotropic behavior of concrete. The model also ignores concrete behavior and structural construction. Another model that can be used for the design of self-compacting concrete formwork was included in the DIN 18218 standard [14]. This model describes the pressure measurement of vertical formwork for freshly placed concrete of varying strength classes. It assumes the use of internal vibrators during the casting process for casting heights \(<\)10 m, so the applicability of this model is very limited. In summary, the prediction equation for formwork pressure is incomplete, especially at high casting rates [15; 16; 17]. In this case, the full hydrostatic pressure applied by the \"fluid\" concrete [18] was used to set the upper limit as a result of the limitations of common test methods. The lateral pressure of poured concrete is not only related to formwork safety but also closely related to early age properties of the concrete, such as thixotropy and setting time [4; 5]. Normal field testing of formwork pressure is usually performed by pouring experimental columns and/or walls, although this method is subject to several limitations. First, the size of the test is limited by cost and site constraints. Laboratory tests are usually below 2.5 m [19; 20; 21], and the height of columns and walls is usually between 5 m and 10 m. Second, due to the limited height, the casting time is very short, usually within a few minutes. Therefore, there is no time to study the thixotropy of the concrete during the pouring process. There are two types of filling processes: filling from the top of the formwork and filling from the bottom of the formwork. The advantages and disadvantages of these two methods are summarized in [22]. Most importantly, due to thixotropy, the concrete in the lower part of the formwork starts to build a structure that can withstand the pressure of the concrete above. This process is continuously interrupted when the formwork is filled from the bottom up, leading to increased horizontal pressure on the formwork walls. In the present study, lateral pressure tests were carried out during the construction of an ultra-deep underground diaphragm wall. The formwork pressure was obtained by monitoring the lateral pressure of the concrete during the placement of the diaphragm wall. Pressure gauges were mounted on reinforcement bars at the edges of the wall, which were close to the natural soil.