Development of Underground Space for Engineering Application

Tunnels traditionally regarded as resilient to seismic events have recently garnered significant attention from engineers owing to a rise in incidents of seismic damage. In this paper, the reflection characteristics of the elastic plane wave incident on the free surface are analyzed, and the matrix analysis method SWIM (Seismic Wave Input Method) for the calculation of equivalent nodal loads with artificial truncated boundary conditions for seismic wave oblique incidence is established by using coordinate transformation technology, according to the displacement velocity and stress characteristics of a plane wave. The results show that the oblique incidence method is more effective in reflecting the traveling wave effect, and the “rotational effect” induced by oblique incidence must be considered for P wave and SV wave incidence, including the associated stress and deformation. This effect exhibits markedly distinct rotational phenomenon. In particular, the P wave incidence should be focused on the vault and the inverted arch due to the expansion wave. With the increase of the oblique incidence angle, the structural stress and deformation are rotated to a certain extent, and the values are significantly increased. Simultaneously, the shear action of the SV wave may result in “ovaling” of the tunnel structure, thereby facilitating damage to the arch shoulder and the sidewall components. As the oblique incidence angle, the potentially damaging effects of the “rotational effect” to the vault and the inverted arch, but the numerical value does not change significantly. In addition, in comparison to a circular cross-section, the low-frequency amplification of seismic waves in the surrounding rock and the difference of frequency response function in different parts of the lining are more pronounced. In particular, the dominant frequency characteristics are significant at P wave incidence and the seismic wave signal attenuation tends to be obvious with increasing incidence angle. In contrast, SV waves exhibit more uniform characteristics. Full article

In urban shield tunneling, reducing the disturbance of underground construction to the surrounding environment is important for both tunnel engineers and researchers. Among other factors, the quality of synchronous grouting is one of the crucial factors affecting the safe construction of shields. In order to determine a reasonable grouting pressure and grout amount during shield construction, the relationships among synchronous grouting pressure, grout amount and shield chamber pressure are analyzed using field monitoring data. Based on the tunnel face pressure and the ultimate yield conditions of the soil at the gap edge, a method for calculating the grouting pressure considering the overburdening load of the tunnel was proposed. Then, by linking the grout amount and the grouting pressure, an accurate calculation method for the simultaneous grout amount in shield construction was proposed. These methods were then used in the construction of the Jurong shield tunnel. The results show that the adopted grouting pressure and grout amount calculated by the proposed method, which considered the change of the overburdening load of the tunnel, can well control the ground deformation caused by the shield construction and significantly reduce the uneven settlement of the surface buildings. The proposed methods in this paper may provide a reference for other shield construction projects. Full article

As a special type of clay, expansive clay is widely distributed in China. Its characteristics of swelling and softening when meeting water and shrinking and cracking when losing water bring many hidden dangers to engineering construction. Expansive clay is known as “engineering cancer”, and in-depth research on the unloading mechanical response characteristics and the unloading constitutive relationships of expansive clay is a prerequisite for conducting geotechnical engineering design and safety analysis in expansive-soil areas. In order to obtain the unloading mechanical response characteristics and the expression of the unloading tangent modulus of expansive clay, typical expansive clay in the Hefei area was taken as the research object, and triaxial unloading stress path tests were conducted. The stress–strain properties, microstructures, macro failure modes, and strength indexes of the expansive clay were analyzed under unloading stress paths. Through an applicability analysis of several classical soil strength criteria, an unloading constitutive model and the unloading tangent modulus expression of the expansive clay were constructed based on the Mohr–Coulomb (hereinafter referred to as “M-C”) criterion, the Drucker–Prager (hereinafter referred to as “D-P”) criterion, and the extended Spatial Mobilized Plane (hereinafter referred to as “SMP”) criterion theoretical frameworks. The following research results were obtained: (1) The stress–strain curves of the three stress paths of the expansive clay were hyperbolic. The expansive clay showed typical strain-hardening characteristics and belonged to work-hardening soil. (2) Under the unloading stress paths, the soil particles were involved in the unloading process of stress release, and the failure samples showed obvious stretching, curling, and slipping phenomena in their soil sheet elements. (3) Under both unloading stress paths, the strength of the expansive clay was significantly weakened and reduced. Under the lateral unloading paths, the cohesive force (c) of the expansive clay was reduced by 32.7% and the internal friction angle (φ) was increased by 19% compared with those under conventional loading, while under the axial unloading path, c was reduced by 63.5% and φ was reduced by 28.7%. (4) For typical expansive clay in Hefei, the conventional triaxial compression (hereinafter referred to as “CTC”) test, the reduced triaxial compression (hereinafter referred to as “RTC”) test, and the reduced triaxial extension (hereinafter referred to as “RTE”) test stress paths were suitable for characterization and deformation prediction using the M-C strength criterion, D-P strength criterion, and extended SMP strength criterion, respectively. (5) The derived unloading constitutive model and the unified tangent modulus formula of the expansive clay could accurately predict the deformation characteristics of the unloading stress path of the expansive clay. These research results will provide an important reference for future engineering construction in expansive-clay areas. Full article

In this paper, joint precast piles with a cross-section of 400 × 400 mm and a pin-joined connection were considered, and their interaction with the soil of Western Kazakhstan has been analyzed. The following methods were used: assessment of the bearing capacity using the static compression load test (SCLT by ASTM) method, interpretation of the field test data, and the dynamic loading test (DLT) method for driving precast concrete joint piles, including Pile Driving Analyzer (PDA by ASTM) and Control and Provisioning of Wireless Access Points (CAPWAP) methods. According to the results, the composite piles tested by the PDA (by ASTM) method differ by 15 percent compared to the static load method, while the difference between the dynamic DLT (by ASTM) method and the static load (by ASTM) method was only 7 percent. So, according to the results, the alternative dynamic method DLT (by ASTM) is very effective and more accurate compared to other existing methods. Full article