<p>Compared to conventional cross-lot strutting systems, concrete ring-truss strutting systems (CR-TSS) offer significant advantages, including much larger unbraced open areas for efficient soil removal and disposal, shorter construction periods, and lower project costs. While several databases in literature had compiled numerous cases of deep excavations braced with cross-lot struts in soft clays worldwide, well-documented cases of CR-TSS-supported excavations remained scarce, despite their successful application in some projects of China. To better characterize the behaviors of deep excavations braced by CR-TSS, this paper presented a collection and analysis of 132 relevant case histories from China; all cases were constructed in soft clay and involved six types of earth retaining walls braced by CR-TSS in eight distinct configurations. It began with an extensive review of the design principles and construction practices associated with CR-TSS. Then, key design parameters—including final excavation depth (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${H}_{e}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <mi>e</mi> </msub> </math></EquationSource> </InlineEquation>), wall penetration ratio (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">${R}_{p}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation>), ring’s diameter (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$D$</EquationSource> <EquationSource Format="MATHML"><math> <mi>D</mi> </math></EquationSource> </InlineEquation>), ring’s cross-sectional area (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">${A}_{cs}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mrow> <mi mathvariant="italic">cs</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>), ring’s radial stiffness (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">${K}_{r}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>r</mi> </msub> </math></EquationSource> </InlineEquation>), ring’s axial rigidity (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">$\xi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>ξ</mi> </math></EquationSource> </InlineEquation>) and the stiffness of earth support system [<InlineEquation ID="IEq7"> <EquationSource Format="TEX">$EI/({\gamma }_{w}{h}^{4})$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mi>I</mi> <mo stretchy="false">/</mo> <mo stretchy="false">(</mo> <msub> <mi>γ</mi> <mi>w</mi> </msub> <msup> <mrow> <mi>h</mi> </mrow> <mn>4</mn> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>] were analyzed alongside the maximum lateral wall displacements (<InlineEquation ID="IEq8"> <EquationSource Format="TEX">${\delta }_{hm}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>). The analysis results indicated that continuous bored pile wall (CBPW) and diaphragm wall (DW) braced by CR-TSS featuring one or multiple individual non-concentric concrete rings in plane were the two most favorable earth retention systems; the excavations braced with CR-TSS outperformed those propped by internal cross-lot struts. Specifically, 75% of the normalized displacement values (<InlineEquation ID="IEq9"> <EquationSource Format="TEX">${\delta }_{hm}/{H}_{e}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> <mo stretchy="false">/</mo> <msub> <mi>H</mi> <mi>e</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>) in this database were less than 0.35%, which is substantially lower than the 0.55% reported for the excavations in soft clay braced by cross-lot struts. Overall, the performance of CR-TSS-braced excavations was influenced by both soil conditions and key design parameters. Excavations in very soft, unconsolidated muddy clay exhibited much poorer performance than those in normally consolidated clay; likewise, excavations retained by rock-socketed walls outperformed those retained by non-socketed walls. However, no clear correlation was found between excavation performance and either the CR-TSS configurations or the retaining wall types. The <InlineEquation ID="IEq10"> <EquationSource Format="TEX">${\delta }_{hm}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> magnitudes showed a positive correlation with both <InlineEquation ID="IEq11"> <EquationSource Format="TEX">${H}_{e}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <mi>e</mi> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq12"> <EquationSource Format="TEX">$D$</EquationSource> <EquationSource Format="MATHML"><math> <mi>D</mi> </math></EquationSource> </InlineEquation>, and a negative correlation with <InlineEquation ID="IEq13"> <EquationSource Format="TEX">${R}_{p}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq14"> <EquationSource Format="TEX">${A}_{cs}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mrow> <mi mathvariant="italic">cs</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq15"> <EquationSource Format="TEX">${K}_{r}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>r</mi> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq16"> <EquationSource Format="TEX">$\xi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>ξ</mi> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq17"> <EquationSource Format="TEX">$EI/({\gamma }_{w}{h}^{4})$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mi>I</mi> <mo stretchy="false">/</mo> <mo stretchy="false">(</mo> <msub> <mi>γ</mi> <mi>w</mi> </msub> <msup> <mrow> <mi>h</mi> </mrow> <mn>4</mn> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. Despite these relevancies, once an adequate value of <InlineEquation ID="IEq18"> <EquationSource Format="TEX">${R}_{p}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation> or <InlineEquation ID="IEq19"> <EquationSource Format="TEX">$EI/({\gamma }_{w}{h}^{4})$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mi>I</mi> <mo stretchy="false">/</mo> <mo stretchy="false">(</mo> <msub> <mi>γ</mi> <mi>w</mi> </msub> <msup> <mrow> <mi>h</mi> </mrow> <mn>4</mn> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> was designed, further increase yielded no significant reduction in <InlineEquation ID="IEq20"> <EquationSource Format="TEX">${\delta }_{hm}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>. Among all design factors, <InlineEquation ID="IEq21"> <EquationSource Format="TEX">$D$</EquationSource> <EquationSource Format="MATHML"><math> <mi>D</mi> </math></EquationSource> </InlineEquation> was identified as a most critical one; <InlineEquation ID="IEq22"> <EquationSource Format="TEX">$D=90 \text{m}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>D</mi> <mo>=</mo> <mn>90</mn> <mtext>m</mtext> </mrow> </math></EquationSource> </InlineEquation> was established as the threshold for effective deformation control in CR-TSS systems. Moreover, the study examined the factors responsible for both abnormally large (<InlineEquation ID="IEq23"> <EquationSource Format="TEX">${\delta }_{hm}/{H}_{e}>0.57\%$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> <mo stretchy="false">/</mo> <msub> <mi>H</mi> <mi>e</mi> </msub> <mo>></mo> <mn>0.57</mn> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation>) and relatively small (<InlineEquation ID="IEq24"> <EquationSource Format="TEX">${\delta }_{hm}/{H}_{e}<0.17\%$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">hm</mi> </mrow> </msub> <mo stretchy="false">/</mo> <msub> <mi>H</mi> <mi>e</mi> </msub> <mo><</mo> <mn>0.17</mn> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation>) displacements observed in specific cases. The findings underscore that excavation performance is governed by the synergistic effect of multiple factors, not by any single factor along; inadequate consideration of any key aspect can consequently lead to excessive deformation.</p>

Performance of Deep Excavations Supported by Concrete Ring-Truss Strutting Systems in Soft Clay: A Chinese Database

期刊论文
发表日期：

2026年1月12日

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Yong Tan,
Ye Lu

摘要

Compared to conventional cross-lot strutting systems, concrete ring-truss strutting systems (CR-TSS) offer significant advantages, including much larger unbraced open areas for efficient soil removal and disposal, shorter construction periods, and lower project costs. While several databases in literature had compiled numerous cases of deep excavations braced with cross-lot struts in soft clays worldwide, well-documented cases of CR-TSS-supported excavations remained scarce, despite their successful application in some projects of China. To better characterize the behaviors of deep excavations braced by CR-TSS, this paper presented a collection and analysis of 132 relevant case histories from China; all cases were constructed in soft clay and involved six types of earth retaining walls braced by CR-TSS in eight distinct configurations. It began with an extensive review of the design principles and construction practices associated with CR-TSS. Then, key design parameters—including final excavation depth ( ${H}_{e}$ $H_{e}$ ), wall penetration ratio ( ${R}_{p}$ $R_{p}$ ), ring’s diameter ( $D$ $D$ ), ring’s cross-sectional area ( ${A}_{cs}$ $A_{cs}$ ), ring’s radial stiffness ( ${K}_{r}$ $K_{r}$ ), ring’s axial rigidity ( $\xi$ $ξ$ ) and the stiffness of earth support system [ $EI/({\gamma }_{w}{h}^{4})$ $E I / (γ_{w} h^{4})$ ] were analyzed alongside the maximum lateral wall displacements ( ${\delta }_{hm}$ $δ_{hm}$ ). The analysis results indicated that continuous bored pile wall (CBPW) and diaphragm wall (DW) braced by CR-TSS featuring one or multiple individual non-concentric concrete rings in plane were the two most favorable earth retention systems; the excavations braced with CR-TSS outperformed those propped by internal cross-lot struts. Specifically, 75% of the normalized displacement values ( ${\delta }_{hm}/{H}_{e}$ $δ_{hm} / H_{e}$ ) in this database were less than 0.35%, which is substantially lower than the 0.55% reported for the excavations in soft clay braced by cross-lot struts. Overall, the performance of CR-TSS-braced excavations was influenced by both soil conditions and key design parameters. Excavations in very soft, unconsolidated muddy clay exhibited much poorer performance than those in normally consolidated clay; likewise, excavations retained by rock-socketed walls outperformed those retained by non-socketed walls. However, no clear correlation was found between excavation performance and either the CR-TSS configurations or the retaining wall types. The ${\delta }_{hm}$ $δ_{hm}$ magnitudes showed a positive correlation with both ${H}_{e}$ $H_{e}$ and $D$ $D$ , and a negative correlation with ${R}_{p}$ $R_{p}$ , ${A}_{cs}$ $A_{cs}$ , ${K}_{r}$ $K_{r}$ , $\xi$ $ξ$ and $EI/({\gamma }_{w}{h}^{4})$ $E I / (γ_{w} h^{4})$ . Despite these relevancies, once an adequate value of ${R}_{p}$ $R_{p}$ or $EI/({\gamma }_{w}{h}^{4})$ $E I / (γ_{w} h^{4})$ was designed, further increase yielded no significant reduction in ${\delta }_{hm}$ $δ_{hm}$ . Among all design factors, $D$ $D$ was identified as a most critical one; $D=90 \text{m}$ $D = 90 m$ was established as the threshold for effective deformation control in CR-TSS systems. Moreover, the study examined the factors responsible for both abnormally large ( ${\delta }_{hm}/{H}_{e}>0.57\%$ $δ_{hm} / H_{e} > 0.57 %$ ) and relatively small ( ${\delta }_{hm}/{H}_{e}<0.17\%$ $δ_{hm} / H_{e} < 0.17 %$ ) displacements observed in specific cases. The findings underscore that excavation performance is governed by the synergistic effect of multiple factors, not by any single factor along; inadequate consideration of any key aspect can consequently lead to excessive deformation.